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-rw-r--r--compiler/rustc_ast/src/ast_traits.rs33
-rw-r--r--compiler/rustc_ast/src/attr/mod.rs3
-rw-r--r--compiler/rustc_ast/src/lib.rs2
-rw-r--r--compiler/rustc_ast/src/mut_visit.rs2
-rw-r--r--compiler/rustc_ast/src/tokenstream.rs33
-rw-r--r--compiler/rustc_borrowck/src/lib.rs9
-rw-r--r--compiler/rustc_borrowck/src/polonius/loan_invalidations.rs6
-rw-r--r--compiler/rustc_borrowck/src/type_check/mod.rs87
-rw-r--r--compiler/rustc_builtin_macros/src/cfg_eval.rs2
-rw-r--r--compiler/rustc_codegen_cranelift/src/base.rs5
-rw-r--r--compiler/rustc_codegen_cranelift/src/constant.rs1
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/analyze.rs1
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/block.rs7
-rw-r--r--compiler/rustc_const_eval/src/check_consts/check.rs15
-rw-r--r--compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs1
-rw-r--r--compiler/rustc_const_eval/src/interpret/eval_context.rs157
-rw-r--r--compiler/rustc_const_eval/src/interpret/machine.rs14
-rw-r--r--compiler/rustc_const_eval/src/interpret/mod.rs2
-rw-r--r--compiler/rustc_const_eval/src/interpret/step.rs2
-rw-r--r--compiler/rustc_const_eval/src/interpret/terminator.rs154
-rw-r--r--compiler/rustc_errors/src/diagnostic_impls.rs14
-rw-r--r--compiler/rustc_expand/src/config.rs29
-rw-r--r--compiler/rustc_expand/src/mbe/metavar_expr.rs74
-rw-r--r--compiler/rustc_expand/src/mbe/transcribe.rs32
-rw-r--r--compiler/rustc_hir_analysis/src/check/compare_impl_item.rs1
-rw-r--r--compiler/rustc_hir_analysis/src/check/intrinsic.rs18
-rw-r--r--compiler/rustc_hir_analysis/src/check/wfcheck.rs114
-rw-r--r--compiler/rustc_hir_analysis/src/coherence/orphan.rs15
-rw-r--r--compiler/rustc_hir_analysis/src/collect.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs1
-rw-r--r--compiler/rustc_hir_analysis/src/lib.rs1
-rw-r--r--compiler/rustc_hir_typeck/messages.ftl5
-rw-r--r--compiler/rustc_hir_typeck/src/cast.rs148
-rw-r--r--compiler/rustc_hir_typeck/src/closure.rs102
-rw-r--r--compiler/rustc_hir_typeck/src/coercion.rs9
-rw-r--r--compiler/rustc_hir_typeck/src/demand.rs1
-rw-r--r--compiler/rustc_hir_typeck/src/errors.rs11
-rw-r--r--compiler/rustc_hir_typeck/src/expr_use_visitor.rs4
-rw-r--r--compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs1
-rw-r--r--compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs2
-rw-r--r--compiler/rustc_hir_typeck/src/method/probe.rs3
-rw-r--r--compiler/rustc_hir_typeck/src/pat.rs1
-rw-r--r--compiler/rustc_infer/src/infer/context.rs4
-rw-r--r--compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs4
-rw-r--r--compiler/rustc_infer/src/infer/mod.rs16
-rw-r--r--compiler/rustc_infer/src/traits/util.rs349
-rw-r--r--compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs4
-rw-r--r--compiler/rustc_lint/src/unused.rs4
-rw-r--r--compiler/rustc_lint_defs/src/builtin.rs54
-rw-r--r--compiler/rustc_middle/src/hir/map/mod.rs34
-rw-r--r--compiler/rustc_middle/src/mir/pretty.rs17
-rw-r--r--compiler/rustc_middle/src/mir/syntax.rs31
-rw-r--r--compiler/rustc_middle/src/mir/terminator.rs13
-rw-r--r--compiler/rustc_middle/src/mir/visit.rs11
-rw-r--r--compiler/rustc_middle/src/traits/mod.rs1
-rw-r--r--compiler/rustc_middle/src/traits/util.rs62
-rw-r--r--compiler/rustc_middle/src/ty/adt.rs4
-rw-r--r--compiler/rustc_middle/src/ty/context.rs55
-rw-r--r--compiler/rustc_middle/src/ty/elaborate_impl.rs84
-rw-r--r--compiler/rustc_middle/src/ty/generics.rs2
-rw-r--r--compiler/rustc_middle/src/ty/mod.rs1
-rw-r--r--compiler/rustc_middle/src/ty/predicate.rs18
-rw-r--r--compiler/rustc_middle/src/ty/print/pretty.rs15
-rw-r--r--compiler/rustc_middle/src/ty/sty.rs8
-rw-r--r--compiler/rustc_middle/src/ty/trait_def.rs7
-rw-r--r--compiler/rustc_mir_build/src/build/expr/stmt.rs39
-rw-r--r--compiler/rustc_mir_build/src/build/scope.rs86
-rw-r--r--compiler/rustc_mir_build/src/lints.rs16
-rw-r--r--compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs1
-rw-r--r--compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs2
-rw-r--r--compiler/rustc_mir_dataflow/src/move_paths/builder.rs6
-rw-r--r--compiler/rustc_mir_dataflow/src/value_analysis.rs3
-rw-r--r--compiler/rustc_mir_transform/src/coroutine.rs5
-rw-r--r--compiler/rustc_mir_transform/src/cost_checker.rs7
-rw-r--r--compiler/rustc_mir_transform/src/coverage/graph.rs9
-rw-r--r--compiler/rustc_mir_transform/src/coverage/mod.rs80
-rw-r--r--compiler/rustc_mir_transform/src/coverage/spans.rs7
-rw-r--r--compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs44
-rw-r--r--compiler/rustc_mir_transform/src/dest_prop.rs6
-rw-r--r--compiler/rustc_mir_transform/src/gvn.rs14
-rw-r--r--compiler/rustc_mir_transform/src/inline.rs9
-rw-r--r--compiler/rustc_mir_transform/src/jump_threading.rs1
-rw-r--r--compiler/rustc_mir_transform/src/known_panics_lint.rs1
-rw-r--r--compiler/rustc_mir_transform/src/mentioned_items.rs2
-rw-r--r--compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs1
-rw-r--r--compiler/rustc_mir_transform/src/validate.rs77
-rw-r--r--compiler/rustc_monomorphize/src/collector.rs3
-rw-r--r--compiler/rustc_next_trait_solver/src/coherence.rs469
-rw-r--r--compiler/rustc_next_trait_solver/src/delegate.rs15
-rw-r--r--compiler/rustc_next_trait_solver/src/lib.rs1
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs3
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs4
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs4
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/trait_goals.rs7
-rw-r--r--compiler/rustc_parse/src/parser/attr.rs6
-rw-r--r--compiler/rustc_parse/src/parser/attr_wrapper.rs53
-rw-r--r--compiler/rustc_parse/src/parser/mod.rs17
-rw-r--r--compiler/rustc_resolve/src/build_reduced_graph.rs10
-rw-r--r--compiler/rustc_resolve/src/def_collector.rs23
-rw-r--r--compiler/rustc_resolve/src/diagnostics.rs6
-rw-r--r--compiler/rustc_resolve/src/late.rs2
-rw-r--r--compiler/rustc_resolve/src/late/diagnostics.rs44
-rw-r--r--compiler/rustc_resolve/src/lib.rs23
-rw-r--r--compiler/rustc_resolve/src/macros.rs9
-rw-r--r--compiler/rustc_smir/src/rustc_smir/convert/mir.rs1
-rw-r--r--compiler/rustc_trait_selection/src/infer.rs11
-rw-r--r--compiler/rustc_trait_selection/src/lib.rs1
-rw-r--r--compiler/rustc_trait_selection/src/solve/delegate.rs18
-rw-r--r--compiler/rustc_trait_selection/src/traits/coherence.rs450
-rw-r--r--compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs11
-rw-r--r--compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs4
-rw-r--r--compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs2
-rw-r--r--compiler/rustc_trait_selection/src/traits/object_safety.rs2
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/mod.rs4
-rw-r--r--compiler/rustc_ty_utils/src/opaque_types.rs6
-rw-r--r--compiler/rustc_ty_utils/src/sig_types.rs2
-rw-r--r--compiler/rustc_type_ir/src/binder.rs6
-rw-r--r--compiler/rustc_type_ir/src/elaborate.rs305
-rw-r--r--compiler/rustc_type_ir/src/infer_ctxt.rs7
-rw-r--r--compiler/rustc_type_ir/src/inherent.rs41
-rw-r--r--compiler/rustc_type_ir/src/interner.rs19
-rw-r--r--compiler/rustc_type_ir/src/lib.rs1
-rw-r--r--library/alloc/src/boxed.rs6
-rw-r--r--library/alloc/src/collections/btree/map/tests.rs18
-rw-r--r--library/alloc/src/collections/btree/set/tests.rs6
-rw-r--r--library/alloc/src/collections/linked_list.rs20
-rw-r--r--library/alloc/src/collections/vec_deque/mod.rs30
-rw-r--r--library/alloc/src/collections/vec_deque/spec_extend.rs13
-rw-r--r--library/alloc/src/fmt.rs4
-rw-r--r--library/alloc/src/lib.rs2
-rw-r--r--library/alloc/src/macros.rs12
-rw-r--r--library/alloc/src/sync.rs8
-rw-r--r--library/alloc/src/vec/mod.rs20
-rw-r--r--library/alloc/tests/fmt.rs10
-rw-r--r--library/core/src/any.rs2
-rw-r--r--library/core/src/ffi/mod.rs414
-rw-r--r--library/core/src/ffi/va_list.rs301
-rw-r--r--library/core/src/iter/traits/collect.rs122
-rw-r--r--library/core/src/mem/mod.rs14
-rw-r--r--library/core/src/num/f16.rs15
-rw-r--r--library/core/tests/fmt/builders.rs6
-rw-r--r--library/std/build.rs4
-rw-r--r--library/std/src/os/fd/owned.rs5
-rw-r--r--library/std/src/path.rs13
-rw-r--r--library/std/src/path/tests.rs35
-rw-r--r--library/std/src/sync/once_lock.rs19
-rw-r--r--src/bootstrap/Cargo.lock1
-rw-r--r--src/bootstrap/Cargo.toml1
-rw-r--r--src/bootstrap/src/core/build_steps/clean.rs2
-rw-r--r--src/bootstrap/src/core/build_steps/compile.rs30
-rw-r--r--src/bootstrap/src/core/build_steps/dist.rs265
-rw-r--r--src/bootstrap/src/core/build_steps/doc.rs38
-rw-r--r--src/bootstrap/src/core/build_steps/format.rs38
-rw-r--r--src/bootstrap/src/core/build_steps/install.rs6
-rw-r--r--src/bootstrap/src/core/build_steps/llvm.rs20
-rw-r--r--src/bootstrap/src/core/build_steps/perf.rs2
-rw-r--r--src/bootstrap/src/core/build_steps/run.rs19
-rw-r--r--src/bootstrap/src/core/build_steps/suggest.rs12
-rw-r--r--src/bootstrap/src/core/build_steps/synthetic_targets.rs6
-rw-r--r--src/bootstrap/src/core/build_steps/test.rs120
-rw-r--r--src/bootstrap/src/core/build_steps/tool.rs17
-rw-r--r--src/bootstrap/src/core/build_steps/vendor.rs6
-rw-r--r--src/bootstrap/src/core/builder.rs26
-rw-r--r--src/bootstrap/src/core/download.rs4
-rw-r--r--src/bootstrap/src/core/metadata.rs6
-rw-r--r--src/bootstrap/src/core/sanity.rs9
-rw-r--r--src/bootstrap/src/lib.rs71
-rw-r--r--src/bootstrap/src/utils/cache.rs7
-rw-r--r--src/bootstrap/src/utils/cc_detect.rs6
-rw-r--r--src/bootstrap/src/utils/exec.rs29
-rw-r--r--src/bootstrap/src/utils/helpers.rs10
-rw-r--r--src/bootstrap/src/utils/tarball.rs2
-rw-r--r--src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md2
-rw-r--r--src/librustdoc/clean/mod.rs3
m---------src/tools/cargo0
-rw-r--r--src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs3
-rw-r--r--src/tools/clippy/clippy_utils/src/ty.rs2
-rw-r--r--src/tools/clippy/tests/ui/or_fun_call.fixed2
-rw-r--r--src/tools/clippy/tests/ui/or_fun_call.stderr8
-rw-r--r--src/tools/miri/rust-version2
-rw-r--r--src/tools/miri/src/machine.rs2
-rw-r--r--src/tools/miri/src/shims/panic.rs6
-rw-r--r--src/tools/miri/tests/fail/tail_calls/cc-mismatch.rs10
-rw-r--r--src/tools/miri/tests/fail/tail_calls/cc-mismatch.stderr25
-rw-r--r--src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.rs17
-rw-r--r--src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.stderr17
-rw-r--r--src/tools/miri/tests/pass/intptrcast.rs4
-rw-r--r--src/tools/miri/tests/pass/packed_struct.rs2
-rw-r--r--src/tools/miri/tests/pass/shims/fs.rs4
-rw-r--r--src/tools/miri/tests/pass/shims/io.rs2
-rw-r--r--src/tools/miri/tests/pass/tail_call.rs39
-rw-r--r--src/tools/miri/tests/pass/vecdeque.rs4
-rw-r--r--src/tools/run-make-support/src/diff/mod.rs34
-rw-r--r--src/tools/run-make-support/src/fs_wrapper.rs20
-rw-r--r--src/tools/run-make-support/src/lib.rs19
-rw-r--r--src/tools/run-make-support/src/rustc.rs15
-rw-r--r--src/tools/rust-analyzer/crates/stdx/src/anymap.rs71
-rw-r--r--src/tools/tidy/src/allowed_run_make_makefiles.txt15
-rw-r--r--src/tools/tidy/src/pal.rs2
-rw-r--r--src/tools/tidy/src/style.rs3
-rw-r--r--tests/coverage-run-rustdoc/doctest.coverage8
-rw-r--r--tests/coverage/async.cov-map41
-rw-r--r--tests/coverage/async.coverage20
-rw-r--r--tests/coverage/async.rs10
-rw-r--r--tests/coverage/attr/nested.cov-map8
-rw-r--r--tests/coverage/attr/nested.coverage5
-rw-r--r--tests/coverage/attr/nested.rs5
-rw-r--r--tests/coverage/attr/off-on-sandwich.cov-map21
-rw-r--r--tests/coverage/attr/off-on-sandwich.coverage21
-rw-r--r--tests/coverage/attr/off-on-sandwich.rs5
-rw-r--r--tests/coverage/closure_macro.cov-map5
-rw-r--r--tests/coverage/closure_macro_async.cov-map5
-rw-r--r--tests/coverage/holes.cov-map47
-rw-r--r--tests/coverage/holes.coverage68
-rw-r--r--tests/coverage/holes.rs67
-rw-r--r--tests/coverage/no_cov_crate.cov-map14
-rw-r--r--tests/coverage/no_cov_crate.coverage20
-rw-r--r--tests/crashes/125099.rs24
-rw-r--r--tests/crashes/127332.rs9
-rw-r--r--tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-abort.diff108
-rw-r--r--tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-unwind.diff109
-rw-r--r--tests/mir-opt/tail_call_drops.f.built.after.panic-abort.mir118
-rw-r--r--tests/mir-opt/tail_call_drops.f.built.after.panic-unwind.mir118
-rw-r--r--tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-abort.diff184
-rw-r--r--tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-unwind.diff184
-rw-r--r--tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-abort.mir202
-rw-r--r--tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-unwind.mir202
-rw-r--r--tests/mir-opt/tail_call_drops.rs41
-rw-r--r--tests/pretty/issue-4264.pp21
-rw-r--r--tests/run-make/emit-path-unhashed/Makefile37
-rw-r--r--tests/run-make/emit-path-unhashed/rmake.rs34
-rw-r--r--tests/run-make/emit-shared-files/Makefile46
-rw-r--r--tests/run-make/emit-shared-files/rmake.rs102
-rw-r--r--tests/run-make/intrinsic-unreachable/Makefile12
-rw-r--r--tests/run-make/intrinsic-unreachable/rmake.rs20
-rw-r--r--tests/run-make/issue-37839/Makefile7
-rw-r--r--tests/run-make/llvm-ident/rmake.rs22
-rw-r--r--tests/run-make/output-type-permutations/rmake.rs5
-rw-r--r--tests/run-make/pass-linker-flags-flavor/Makefile11
-rw-r--r--tests/run-make/pass-linker-flags-flavor/rmake.rs84
-rw-r--r--tests/run-make/pass-linker-flags-from-dep/Makefile12
-rw-r--r--tests/run-make/pass-linker-flags-from-dep/rmake.rs43
-rw-r--r--tests/run-make/pass-linker-flags/Makefile5
-rw-r--r--tests/run-make/pass-linker-flags/rmake.rs28
-rw-r--r--tests/run-make/proc-macro-three-crates/a.rs (renamed from tests/run-make/issue-37839/a.rs)0
-rw-r--r--tests/run-make/proc-macro-three-crates/b.rs (renamed from tests/run-make/issue-37839/b.rs)0
-rw-r--r--tests/run-make/proc-macro-three-crates/c.rs (renamed from tests/run-make/issue-37839/c.rs)0
-rw-r--r--tests/run-make/proc-macro-three-crates/rmake.rs20
-rw-r--r--tests/run-make/sepcomp-cci-copies/Makefile12
-rw-r--r--tests/run-make/sepcomp-cci-copies/rmake.rs17
-rw-r--r--tests/run-make/sepcomp-inlining/Makefile15
-rw-r--r--tests/run-make/sepcomp-inlining/rmake.rs23
-rw-r--r--tests/run-make/sepcomp-separate/Makefile9
-rw-r--r--tests/run-make/sepcomp-separate/rmake.rs15
-rw-r--r--tests/run-make/target-cpu-native/Makefile20
-rw-r--r--tests/run-make/target-cpu-native/rmake.rs14
-rw-r--r--tests/run-make/target-specs/Makefile12
-rw-r--r--tests/run-make/target-specs/rmake.rs71
-rw-r--r--tests/run-make/target-without-atomic-cas/Makefile5
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-rw-r--r--tests/run-make/track-path-dep-info/Makefile13
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-rw-r--r--tests/run-make/track-pgo-dep-info/Makefile25
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-rw-r--r--tests/rustdoc-json/trait_alias.rs18
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-rw-r--r--tests/ui/async-await/async-closures/signature-inference-from-two-part-bound.rs27
-rw-r--r--tests/ui/cast/cast-rfc0401-vtable-kinds.rs18
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-rw-r--r--tests/ui/cast/ptr-to-trait-obj-ok.rs17
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-rw-r--r--tests/ui/deriving/deriving-in-fn.rs2
-rw-r--r--tests/ui/explicit-tail-calls/constck.rs22
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-rw-r--r--tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.rs14
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-rw-r--r--tests/ui/fmt/struct-field-as-captured-argument.fixed14
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-rw-r--r--tests/ui/fmt/struct-field-as-captured-argument.stderr70
-rw-r--r--tests/ui/generic-associated-types/assume-gat-normalization-for-nested-goals.next.stderr2
-rw-r--r--tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.current.stderr173
-rw-r--r--tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.rs51
-rw-r--r--tests/ui/impl-trait/nested_impl_trait.rs4
-rw-r--r--tests/ui/impl-trait/nested_impl_trait.stderr4
-rw-r--r--tests/ui/intrinsics/not-overridden.rs2
-rw-r--r--tests/ui/intrinsics/safe-intrinsic-mismatch.effects.stderr52
-rw-r--r--tests/ui/intrinsics/safe-intrinsic-mismatch.rs7
-rw-r--r--tests/ui/intrinsics/safe-intrinsic-mismatch.stock.stderr (renamed from tests/ui/intrinsics/safe-intrinsic-mismatch.stderr)12
-rw-r--r--tests/ui/issues/issue-20676.rs2
-rw-r--r--tests/ui/lint/lint-unconditional-recursion-tail-calls.rs24
-rw-r--r--tests/ui/lint/lint-unconditional-recursion-tail-calls.stderr18
-rw-r--r--tests/ui/macros/macro-metavar-expr-concat/allowed-operations.rs12
-rw-r--r--tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.rs6
-rw-r--r--tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.stderr6
-rw-r--r--tests/ui/macros/macro-metavar-expr-concat/syntax-errors.rs78
-rw-r--r--tests/ui/macros/macro-metavar-expr-concat/syntax-errors.stderr107
-rw-r--r--tests/ui/macros/macro-metavar-expr-concat/unicode-expansion.rs14
-rw-r--r--tests/ui/macros/out-of-scope-calls-false-positives.rs10
-rw-r--r--tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr2
-rw-r--r--tests/ui/mir/alignment/misaligned-constant-gvn.rs8
-rw-r--r--tests/ui/mismatched_types/cast-rfc0401.rs2
-rw-r--r--tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2015.stderr (renamed from tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.stderr)20
-rw-r--r--tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2024.stderr116
-rw-r--r--tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.rs46
-rw-r--r--tests/ui/parser/bad-let-else-statement.rs16
-rw-r--r--tests/ui/parser/bad-let-else-statement.stderr15
-rw-r--r--tests/ui/resolve/field-and-method-in-self-not-available-in-assoc-fn.stderr4
-rw-r--r--tests/ui/resolve/issue-2356.stderr4
-rw-r--r--tests/ui/resolve/issue-60057.stderr2
-rw-r--r--tests/ui/resolve/typo-suggestion-for-variable-with-name-similar-to-struct-field.stderr4
-rw-r--r--tests/ui/resolve/unresolved_static_type_field.stderr2
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs42
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr24
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.nn.stderr12
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.ny.stderr12
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.rs3
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yn.stderr12
-rw-r--r--tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yy.stderr12
-rw-r--r--tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.fixed4
-rw-r--r--tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.rs4
-rw-r--r--tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.stderr10
-rw-r--r--tests/ui/traits/next-solver/auto-with-drop_tracking_mir.fail.stderr4
-rw-r--r--tests/ui/traits/next-solver/typeck/receiver-self-ty-check-eq.rs23
-rw-r--r--tests/ui/traits/upcast_soundness_bug.rs8
-rw-r--r--tests/ui/traits/upcast_soundness_bug.stderr13
-rw-r--r--tests/ui/type-alias-impl-trait/method_resolution3.current.stderr2
-rw-r--r--tests/ui/type-alias-impl-trait/method_resolution3.next.stderr18
-rw-r--r--tests/ui/type-alias-impl-trait/method_resolution3.rs6
-rw-r--r--tests/ui/type-alias-impl-trait/method_resolution4.current.stderr2
-rw-r--r--tests/ui/type-alias-impl-trait/method_resolution4.next.stderr18
-rw-r--r--tests/ui/type-alias-impl-trait/method_resolution4.rs6
-rw-r--r--tests/ui/typeck/ice-with-expr-not-struct-127332.rs15
-rw-r--r--tests/ui/typeck/ice-with-expr-not-struct-127332.stderr9
357 files changed, 7495 insertions, 3179 deletions
diff --git a/compiler/rustc_ast/src/ast_traits.rs b/compiler/rustc_ast/src/ast_traits.rs
index 2cf811e9122..7754ca0a0f5 100644
--- a/compiler/rustc_ast/src/ast_traits.rs
+++ b/compiler/rustc_ast/src/ast_traits.rs
@@ -10,8 +10,6 @@ use crate::{AssocItem, Expr, ForeignItem, Item, NodeId};
 use crate::{AttrItem, AttrKind, Block, Pat, Path, Ty, Visibility};
 use crate::{AttrVec, Attribute, Stmt, StmtKind};
 
-use rustc_span::Span;
-
 use std::fmt;
 use std::marker::PhantomData;
 
@@ -91,37 +89,6 @@ impl<T: AstDeref<Target: HasNodeId>> HasNodeId for T {
     }
 }
 
-/// A trait for AST nodes having a span.
-pub trait HasSpan {
-    fn span(&self) -> Span;
-}
-
-macro_rules! impl_has_span {
-    ($($T:ty),+ $(,)?) => {
-        $(
-            impl HasSpan for $T {
-                fn span(&self) -> Span {
-                    self.span
-                }
-            }
-        )+
-    };
-}
-
-impl_has_span!(AssocItem, Block, Expr, ForeignItem, Item, Pat, Path, Stmt, Ty, Visibility);
-
-impl<T: AstDeref<Target: HasSpan>> HasSpan for T {
-    fn span(&self) -> Span {
-        self.ast_deref().span()
-    }
-}
-
-impl HasSpan for AttrItem {
-    fn span(&self) -> Span {
-        self.span()
-    }
-}
-
 /// A trait for AST nodes having (or not having) collected tokens.
 pub trait HasTokens {
     fn tokens(&self) -> Option<&LazyAttrTokenStream>;
diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index 65f1b5dbaf5..088ae9ba441 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -202,7 +202,8 @@ impl Attribute {
         }
     }
 
-    pub fn tokens(&self) -> TokenStream {
+    // Named `get_tokens` to distinguish it from the `<Attribute as HasTokens>::tokens` method.
+    pub fn get_tokens(&self) -> TokenStream {
         match &self.kind {
             AttrKind::Normal(normal) => TokenStream::new(
                 normal
diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index 7ca950e50e6..846a108091f 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -44,7 +44,7 @@ pub mod tokenstream;
 pub mod visit;
 
 pub use self::ast::*;
-pub use self::ast_traits::{AstDeref, AstNodeWrapper, HasAttrs, HasNodeId, HasSpan, HasTokens};
+pub use self::ast_traits::{AstDeref, AstNodeWrapper, HasAttrs, HasNodeId, HasTokens};
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index f816375b912..cbf21317f1a 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -704,7 +704,7 @@ fn visit_attr_tt<T: MutVisitor>(tt: &mut AttrTokenTree, vis: &mut T) {
             visit_attr_tts(tts, vis);
             visit_delim_span(dspan, vis);
         }
-        AttrTokenTree::Attributes(AttributesData { attrs, tokens }) => {
+        AttrTokenTree::AttrsTarget(AttrsTarget { attrs, tokens }) => {
             visit_attrs(attrs, vis);
             visit_lazy_tts_opt_mut(Some(tokens), vis);
         }
diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index 655c18e4559..ee068f19332 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -14,7 +14,7 @@
 //! ownership of the original.
 
 use crate::ast::{AttrStyle, StmtKind};
-use crate::ast_traits::{HasAttrs, HasSpan, HasTokens};
+use crate::ast_traits::{HasAttrs, HasTokens};
 use crate::token::{self, Delimiter, Nonterminal, Token, TokenKind};
 use crate::AttrVec;
 
@@ -170,8 +170,8 @@ pub enum AttrTokenTree {
     Delimited(DelimSpan, DelimSpacing, Delimiter, AttrTokenStream),
     /// Stores the attributes for an attribute target,
     /// along with the tokens for that attribute target.
-    /// See `AttributesData` for more information
-    Attributes(AttributesData),
+    /// See `AttrsTarget` for more information
+    AttrsTarget(AttrsTarget),
 }
 
 impl AttrTokenStream {
@@ -180,7 +180,7 @@ impl AttrTokenStream {
     }
 
     /// Converts this `AttrTokenStream` to a plain `Vec<TokenTree>`.
-    /// During conversion, `AttrTokenTree::Attributes` get 'flattened'
+    /// During conversion, `AttrTokenTree::AttrsTarget` get 'flattened'
     /// back to a `TokenStream` of the form `outer_attr attr_target`.
     /// If there are inner attributes, they are inserted into the proper
     /// place in the attribute target tokens.
@@ -199,13 +199,13 @@ impl AttrTokenStream {
                         TokenStream::new(stream.to_token_trees()),
                     ))
                 }
-                AttrTokenTree::Attributes(data) => {
-                    let idx = data
+                AttrTokenTree::AttrsTarget(target) => {
+                    let idx = target
                         .attrs
                         .partition_point(|attr| matches!(attr.style, crate::AttrStyle::Outer));
-                    let (outer_attrs, inner_attrs) = data.attrs.split_at(idx);
+                    let (outer_attrs, inner_attrs) = target.attrs.split_at(idx);
 
-                    let mut target_tokens = data.tokens.to_attr_token_stream().to_token_trees();
+                    let mut target_tokens = target.tokens.to_attr_token_stream().to_token_trees();
                     if !inner_attrs.is_empty() {
                         let mut found = false;
                         // Check the last two trees (to account for a trailing semi)
@@ -227,7 +227,7 @@ impl AttrTokenStream {
 
                                 let mut stream = TokenStream::default();
                                 for inner_attr in inner_attrs {
-                                    stream.push_stream(inner_attr.tokens());
+                                    stream.push_stream(inner_attr.get_tokens());
                                 }
                                 stream.push_stream(delim_tokens.clone());
                                 *tree = TokenTree::Delimited(*span, *spacing, *delim, stream);
@@ -242,7 +242,7 @@ impl AttrTokenStream {
                         );
                     }
                     for attr in outer_attrs {
-                        res.extend(attr.tokens().0.iter().cloned());
+                        res.extend(attr.get_tokens().0.iter().cloned());
                     }
                     res.extend(target_tokens);
                 }
@@ -262,7 +262,7 @@ impl AttrTokenStream {
 /// have an `attrs` field containing the `#[cfg(FALSE)]` attr,
 /// and a `tokens` field storing the (unparsed) tokens `struct Foo {}`
 #[derive(Clone, Debug, Encodable, Decodable)]
-pub struct AttributesData {
+pub struct AttrsTarget {
     /// Attributes, both outer and inner.
     /// These are stored in the original order that they were parsed in.
     pub attrs: AttrVec,
@@ -436,17 +436,17 @@ impl TokenStream {
         TokenStream::new(vec![TokenTree::token_alone(kind, span)])
     }
 
-    pub fn from_ast(node: &(impl HasAttrs + HasSpan + HasTokens + fmt::Debug)) -> TokenStream {
+    pub fn from_ast(node: &(impl HasAttrs + HasTokens + fmt::Debug)) -> TokenStream {
         let Some(tokens) = node.tokens() else {
-            panic!("missing tokens for node at {:?}: {:?}", node.span(), node);
+            panic!("missing tokens for node: {:?}", node);
         };
         let attrs = node.attrs();
         let attr_stream = if attrs.is_empty() {
             tokens.to_attr_token_stream()
         } else {
-            let attr_data =
-                AttributesData { attrs: attrs.iter().cloned().collect(), tokens: tokens.clone() };
-            AttrTokenStream::new(vec![AttrTokenTree::Attributes(attr_data)])
+            let target =
+                AttrsTarget { attrs: attrs.iter().cloned().collect(), tokens: tokens.clone() };
+            AttrTokenStream::new(vec![AttrTokenTree::AttrsTarget(target)])
         };
         TokenStream::new(attr_stream.to_token_trees())
     }
@@ -765,6 +765,7 @@ mod size_asserts {
     static_assert_size!(AttrTokenStream, 8);
     static_assert_size!(AttrTokenTree, 32);
     static_assert_size!(LazyAttrTokenStream, 8);
+    static_assert_size!(Option<LazyAttrTokenStream>, 8); // must be small, used in many AST nodes
     static_assert_size!(TokenStream, 8);
     static_assert_size!(TokenTree, 32);
     // tidy-alphabetical-end
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 36ba1d81be6..d258c68b959 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -727,6 +727,12 @@ impl<'a, 'mir, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'mir, 'tcx, R>
                 }
                 self.mutate_place(loc, (*destination, span), Deep, flow_state);
             }
+            TerminatorKind::TailCall { func, args, fn_span: _ } => {
+                self.consume_operand(loc, (func, span), flow_state);
+                for arg in args {
+                    self.consume_operand(loc, (&arg.node, arg.span), flow_state);
+                }
+            }
             TerminatorKind::Assert { cond, expected: _, msg, target: _, unwind: _ } => {
                 self.consume_operand(loc, (cond, span), flow_state);
                 if let AssertKind::BoundsCheck { len, index } = &**msg {
@@ -813,9 +819,8 @@ impl<'a, 'mir, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'mir, 'tcx, R>
 
             TerminatorKind::UnwindResume
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::CoroutineDrop => {
-                // Returning from the function implicitly kills storage for all locals and statics.
-                // Often, the storage will already have been killed by an explicit
                 // StorageDead, but we don't always emit those (notably on unwind paths),
                 // so this "extra check" serves as a kind of backup.
                 let borrow_set = self.borrow_set.clone();
diff --git a/compiler/rustc_borrowck/src/polonius/loan_invalidations.rs b/compiler/rustc_borrowck/src/polonius/loan_invalidations.rs
index 6979910a02d..30dfc4c21b0 100644
--- a/compiler/rustc_borrowck/src/polonius/loan_invalidations.rs
+++ b/compiler/rustc_borrowck/src/polonius/loan_invalidations.rs
@@ -125,6 +125,12 @@ impl<'cx, 'tcx> Visitor<'tcx> for LoanInvalidationsGenerator<'cx, 'tcx> {
                 }
                 self.mutate_place(location, *destination, Deep);
             }
+            TerminatorKind::TailCall { func, args, .. } => {
+                self.consume_operand(location, func);
+                for arg in args {
+                    self.consume_operand(location, &arg.node);
+                }
+            }
             TerminatorKind::Assert { cond, expected: _, msg, target: _, unwind: _ } => {
                 self.consume_operand(location, cond);
                 use rustc_middle::mir::AssertKind;
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index aa25e3adf28..db4b5209145 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -38,6 +38,7 @@ use rustc_span::def_id::CRATE_DEF_ID;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
+use rustc_span::DUMMY_SP;
 use rustc_target::abi::{FieldIdx, FIRST_VARIANT};
 use rustc_trait_selection::traits::query::type_op::custom::scrape_region_constraints;
 use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
@@ -49,6 +50,7 @@ use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::MoveData;
 use rustc_mir_dataflow::ResultsCursor;
 
+use crate::renumber::RegionCtxt;
 use crate::session_diagnostics::{MoveUnsized, SimdIntrinsicArgConst};
 use crate::{
     borrow_set::BorrowSet,
@@ -1352,7 +1354,14 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
                 // FIXME: check the values
             }
-            TerminatorKind::Call { func, args, destination, call_source, target, .. } => {
+            TerminatorKind::Call { func, args, .. }
+            | TerminatorKind::TailCall { func, args, .. } => {
+                let call_source = match term.kind {
+                    TerminatorKind::Call { call_source, .. } => call_source,
+                    TerminatorKind::TailCall { .. } => CallSource::Normal,
+                    _ => unreachable!(),
+                };
+
                 self.check_operand(func, term_location);
                 for arg in args {
                     self.check_operand(&arg.node, term_location);
@@ -1425,7 +1434,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     );
                 }
 
-                self.check_call_dest(body, term, &sig, *destination, *target, term_location);
+                if let TerminatorKind::Call { destination, target, .. } = term.kind {
+                    self.check_call_dest(body, term, &sig, destination, target, term_location);
+                }
 
                 // The ordinary liveness rules will ensure that all
                 // regions in the type of the callee are live here. We
@@ -1443,7 +1454,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         .add_location(region_vid, term_location);
                 }
 
-                self.check_call_inputs(body, term, func, &sig, args, term_location, *call_source);
+                self.check_call_inputs(body, term, func, &sig, args, term_location, call_source);
             }
             TerminatorKind::Assert { cond, msg, .. } => {
                 self.check_operand(cond, term_location);
@@ -1675,6 +1686,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     span_mirbug!(self, block_data, "return on cleanup block")
                 }
             }
+            TerminatorKind::TailCall { .. } => {
+                if is_cleanup {
+                    span_mirbug!(self, block_data, "tailcall on cleanup block")
+                }
+            }
             TerminatorKind::CoroutineDrop { .. } => {
                 if is_cleanup {
                     span_mirbug!(self, block_data, "coroutine_drop in cleanup block")
@@ -2319,7 +2335,57 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         let cast_ty_from = CastTy::from_ty(ty_from);
                         let cast_ty_to = CastTy::from_ty(*ty);
                         match (cast_ty_from, cast_ty_to) {
-                            (Some(CastTy::Ptr(_)), Some(CastTy::Ptr(_))) => (),
+                            (Some(CastTy::Ptr(src)), Some(CastTy::Ptr(dst))) => {
+                                let mut normalize = |t| self.normalize(t, location);
+                                let src_tail =
+                                    tcx.struct_tail_with_normalize(src.ty, &mut normalize, || ());
+                                let dst_tail =
+                                    tcx.struct_tail_with_normalize(dst.ty, &mut normalize, || ());
+
+                                // This checks (lifetime part of) vtable validity for pointer casts,
+                                // which is irrelevant when there are aren't principal traits on both sides (aka only auto traits).
+                                //
+                                // Note that other checks (such as denying `dyn Send` -> `dyn Debug`) are in `rustc_hir_typeck`.
+                                if let ty::Dynamic(src_tty, ..) = src_tail.kind()
+                                    && let ty::Dynamic(dst_tty, ..) = dst_tail.kind()
+                                    && src_tty.principal().is_some()
+                                    && dst_tty.principal().is_some()
+                                {
+                                    // Remove auto traits.
+                                    // Auto trait checks are handled in `rustc_hir_typeck` as FCW.
+                                    let src_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                                        tcx.mk_poly_existential_predicates(
+                                            &src_tty.without_auto_traits().collect::<Vec<_>>(),
+                                        ),
+                                        tcx.lifetimes.re_static,
+                                        ty::Dyn,
+                                    ));
+                                    let dst_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                                        tcx.mk_poly_existential_predicates(
+                                            &dst_tty.without_auto_traits().collect::<Vec<_>>(),
+                                        ),
+                                        tcx.lifetimes.re_static,
+                                        ty::Dyn,
+                                    ));
+
+                                    // Replace trait object lifetimes with fresh vars, to allow casts like
+                                    // `*mut dyn FnOnce() + 'a` -> `*mut dyn FnOnce() + 'static`,
+                                    let src_obj =
+                                        freshen_single_trait_object_lifetime(self.infcx, src_obj);
+                                    let dst_obj =
+                                        freshen_single_trait_object_lifetime(self.infcx, dst_obj);
+
+                                    debug!(?src_tty, ?dst_tty, ?src_obj, ?dst_obj);
+
+                                    self.eq_types(
+                                        src_obj,
+                                        dst_obj,
+                                        location.to_locations(),
+                                        ConstraintCategory::Cast { unsize_to: None },
+                                    )
+                                    .unwrap();
+                                }
+                            }
                             _ => {
                                 span_mirbug!(
                                     self,
@@ -2842,3 +2908,16 @@ impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {
         Ok(output)
     }
 }
+
+fn freshen_single_trait_object_lifetime<'tcx>(
+    infcx: &BorrowckInferCtxt<'tcx>,
+    ty: Ty<'tcx>,
+) -> Ty<'tcx> {
+    let &ty::Dynamic(tty, _, dyn_kind @ ty::Dyn) = ty.kind() else { bug!("expected trait object") };
+
+    let fresh = infcx
+        .next_region_var(rustc_infer::infer::RegionVariableOrigin::MiscVariable(DUMMY_SP), || {
+            RegionCtxt::Unknown
+        });
+    infcx.tcx.mk_ty_from_kind(ty::Dynamic(tty, fresh, dyn_kind))
+}
diff --git a/compiler/rustc_builtin_macros/src/cfg_eval.rs b/compiler/rustc_builtin_macros/src/cfg_eval.rs
index 884cebf1939..b09975c0ba7 100644
--- a/compiler/rustc_builtin_macros/src/cfg_eval.rs
+++ b/compiler/rustc_builtin_macros/src/cfg_eval.rs
@@ -193,7 +193,7 @@ impl CfgEval<'_> {
 
         // Re-parse the tokens, setting the `capture_cfg` flag to save extra information
         // to the captured `AttrTokenStream` (specifically, we capture
-        // `AttrTokenTree::AttributesData` for all occurrences of `#[cfg]` and `#[cfg_attr]`)
+        // `AttrTokenTree::AttrsTarget` for all occurrences of `#[cfg]` and `#[cfg_attr]`)
         let mut parser = Parser::new(&self.0.sess.psess, orig_tokens, None);
         parser.capture_cfg = true;
         match parse_annotatable_with(&mut parser) {
diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
index c5b4277015a..5adbbb09ac8 100644
--- a/compiler/rustc_codegen_cranelift/src/base.rs
+++ b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -491,6 +491,11 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                     )
                 });
             }
+            // FIXME(explicit_tail_calls): add support for tail calls to the cranelift backend, once cranelift supports tail calls
+            TerminatorKind::TailCall { fn_span, .. } => span_bug!(
+                *fn_span,
+                "tail calls are not yet supported in `rustc_codegen_cranelift` backend"
+            ),
             TerminatorKind::InlineAsm {
                 template,
                 operands,
diff --git a/compiler/rustc_codegen_cranelift/src/constant.rs b/compiler/rustc_codegen_cranelift/src/constant.rs
index 9f7b95261d5..fd34ed88c0b 100644
--- a/compiler/rustc_codegen_cranelift/src/constant.rs
+++ b/compiler/rustc_codegen_cranelift/src/constant.rs
@@ -567,6 +567,7 @@ pub(crate) fn mir_operand_get_const_val<'tcx>(
                     {
                         return None;
                     }
+                    TerminatorKind::TailCall { .. } => return None,
                     TerminatorKind::Call { .. } => {}
                 }
             }
diff --git a/compiler/rustc_codegen_ssa/src/mir/analyze.rs b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
index 0577ba32ffd..ac2b6ca4e95 100644
--- a/compiler/rustc_codegen_ssa/src/mir/analyze.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
@@ -281,6 +281,7 @@ pub fn cleanup_kinds(mir: &mir::Body<'_>) -> IndexVec<mir::BasicBlock, CleanupKi
                 | TerminatorKind::UnwindResume
                 | TerminatorKind::UnwindTerminate(_)
                 | TerminatorKind::Return
+                | TerminatorKind::TailCall { .. }
                 | TerminatorKind::CoroutineDrop
                 | TerminatorKind::Unreachable
                 | TerminatorKind::SwitchInt { .. }
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 4adb95f85d6..6a5525dc2b3 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -1389,6 +1389,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 fn_span,
                 mergeable_succ(),
             ),
+            mir::TerminatorKind::TailCall { .. } => {
+                // FIXME(explicit_tail_calls): implement tail calls in ssa backend
+                span_bug!(
+                    terminator.source_info.span,
+                    "`TailCall` terminator is not yet supported by `rustc_codegen_ssa`"
+                )
+            }
             mir::TerminatorKind::CoroutineDrop | mir::TerminatorKind::Yield { .. } => {
                 bug!("coroutine ops in codegen")
             }
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 0d8a17775dd..412effba32d 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -135,6 +135,8 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
         ccx: &'mir ConstCx<'mir, 'tcx>,
         tainted_by_errors: Option<ErrorGuaranteed>,
     ) -> ConstQualifs {
+        // FIXME(explicit_tail_calls): uhhhh I think we can return without return now, does it change anything
+
         // Find the `Return` terminator if one exists.
         //
         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
@@ -711,7 +713,14 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
         self.super_terminator(terminator, location);
 
         match &terminator.kind {
-            TerminatorKind::Call { func, args, fn_span, call_source, .. } => {
+            TerminatorKind::Call { func, args, fn_span, .. }
+            | TerminatorKind::TailCall { func, args, fn_span, .. } => {
+                let call_source = match terminator.kind {
+                    TerminatorKind::Call { call_source, .. } => call_source,
+                    TerminatorKind::TailCall { .. } => CallSource::Normal,
+                    _ => unreachable!(),
+                };
+
                 let ConstCx { tcx, body, param_env, .. } = *self.ccx;
                 let caller = self.def_id();
 
@@ -783,7 +792,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                             callee,
                             args: fn_args,
                             span: *fn_span,
-                            call_source: *call_source,
+                            call_source,
                             feature: Some(if tcx.features().const_trait_impl {
                                 sym::effects
                             } else {
@@ -830,7 +839,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                         callee,
                         args: fn_args,
                         span: *fn_span,
-                        call_source: *call_source,
+                        call_source,
                         feature: None,
                     });
                     return;
diff --git a/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs b/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs
index f0763f1e490..f5e745454ab 100644
--- a/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs
+++ b/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs
@@ -108,6 +108,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
 
             mir::TerminatorKind::UnwindTerminate(_)
             | mir::TerminatorKind::Call { .. }
+            | mir::TerminatorKind::TailCall { .. }
             | mir::TerminatorKind::Assert { .. }
             | mir::TerminatorKind::FalseEdge { .. }
             | mir::TerminatorKind::FalseUnwind { .. }
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index 830c4bd3e26..6d3e5ea1031 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -26,8 +26,8 @@ use rustc_target::abi::{call::FnAbi, Align, HasDataLayout, Size, TargetDataLayou
 use super::{
     err_inval, throw_inval, throw_ub, throw_ub_custom, throw_unsup, GlobalId, Immediate,
     InterpErrorInfo, InterpResult, MPlaceTy, Machine, MemPlace, MemPlaceMeta, Memory, MemoryKind,
-    OpTy, Operand, Place, PlaceTy, Pointer, PointerArithmetic, Projectable, Provenance, Scalar,
-    StackPopJump,
+    OpTy, Operand, Place, PlaceTy, Pointer, PointerArithmetic, Projectable, Provenance,
+    ReturnAction, Scalar,
 };
 use crate::errors;
 use crate::util;
@@ -159,6 +159,19 @@ pub enum StackPopCleanup {
     Root { cleanup: bool },
 }
 
+/// Return type of [`InterpCx::pop_stack_frame`].
+pub struct StackPopInfo<'tcx, Prov: Provenance> {
+    /// Additional information about the action to be performed when returning from the popped
+    /// stack frame.
+    pub return_action: ReturnAction,
+
+    /// [`return_to_block`](Frame::return_to_block) of the popped stack frame.
+    pub return_to_block: StackPopCleanup,
+
+    /// [`return_place`](Frame::return_place) of the popped stack frame.
+    pub return_place: MPlaceTy<'tcx, Prov>,
+}
+
 /// State of a local variable including a memoized layout
 #[derive(Clone)]
 pub struct LocalState<'tcx, Prov: Provenance = CtfeProvenance> {
@@ -803,14 +816,31 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         return_to_block: StackPopCleanup,
     ) -> InterpResult<'tcx> {
         trace!("body: {:#?}", body);
+
+        // First push a stack frame so we have access to the local args
+        self.push_new_stack_frame(instance, body, return_to_block, return_place.clone())?;
+
+        self.after_stack_frame_push(instance, body)?;
+
+        Ok(())
+    }
+
+    /// Creates a new stack frame, initializes it and pushes it onto the stack.
+    /// A private helper for [`push_stack_frame`](InterpCx::push_stack_frame).
+    fn push_new_stack_frame(
+        &mut self,
+        instance: ty::Instance<'tcx>,
+        body: &'tcx mir::Body<'tcx>,
+        return_to_block: StackPopCleanup,
+        return_place: MPlaceTy<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx> {
         let dead_local = LocalState { value: LocalValue::Dead, layout: Cell::new(None) };
         let locals = IndexVec::from_elem(dead_local, &body.local_decls);
-        // First push a stack frame so we have access to the local args
         let pre_frame = Frame {
             body,
             loc: Right(body.span), // Span used for errors caused during preamble.
             return_to_block,
-            return_place: return_place.clone(),
+            return_place,
             locals,
             instance,
             tracing_span: SpanGuard::new(),
@@ -819,6 +849,15 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         let frame = M::init_frame(self, pre_frame)?;
         self.stack_mut().push(frame);
 
+        Ok(())
+    }
+
+    /// A private helper for [`push_stack_frame`](InterpCx::push_stack_frame).
+    fn after_stack_frame_push(
+        &mut self,
+        instance: ty::Instance<'tcx>,
+        body: &'tcx mir::Body<'tcx>,
+    ) -> InterpResult<'tcx> {
         // Make sure all the constants required by this frame evaluate successfully (post-monomorphization check).
         for &const_ in &body.required_consts {
             let c =
@@ -839,6 +878,61 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         Ok(())
     }
 
+    /// Pops a stack frame from the stack and returns some information about it.
+    ///
+    /// This also deallocates locals, if necessary.
+    ///
+    /// [`M::before_stack_pop`] should be called before calling this function.
+    /// [`M::after_stack_pop`] is called by this function automatically.
+    ///
+    /// [`M::before_stack_pop`]: Machine::before_stack_pop
+    /// [`M::after_stack_pop`]: Machine::after_stack_pop
+    pub fn pop_stack_frame(
+        &mut self,
+        unwinding: bool,
+    ) -> InterpResult<'tcx, StackPopInfo<'tcx, M::Provenance>> {
+        let cleanup = self.cleanup_current_frame_locals()?;
+
+        let frame =
+            self.stack_mut().pop().expect("tried to pop a stack frame, but there were none");
+
+        let return_to_block = frame.return_to_block;
+        let return_place = frame.return_place.clone();
+
+        let return_action;
+        if cleanup {
+            return_action = M::after_stack_pop(self, frame, unwinding)?;
+            assert_ne!(return_action, ReturnAction::NoCleanup);
+        } else {
+            return_action = ReturnAction::NoCleanup;
+        };
+
+        Ok(StackPopInfo { return_action, return_to_block, return_place })
+    }
+
+    /// A private helper for [`pop_stack_frame`](InterpCx::pop_stack_frame).
+    /// Returns `true` if cleanup has been done, `false` otherwise.
+    fn cleanup_current_frame_locals(&mut self) -> InterpResult<'tcx, bool> {
+        // Cleanup: deallocate locals.
+        // Usually we want to clean up (deallocate locals), but in a few rare cases we don't.
+        // We do this while the frame is still on the stack, so errors point to the callee.
+        let return_to_block = self.frame().return_to_block;
+        let cleanup = match return_to_block {
+            StackPopCleanup::Goto { .. } => true,
+            StackPopCleanup::Root { cleanup, .. } => cleanup,
+        };
+
+        if cleanup {
+            // We need to take the locals out, since we need to mutate while iterating.
+            let locals = mem::take(&mut self.frame_mut().locals);
+            for local in &locals {
+                self.deallocate_local(local.value)?;
+            }
+        }
+
+        Ok(cleanup)
+    }
+
     /// Jump to the given block.
     #[inline]
     pub fn go_to_block(&mut self, target: mir::BasicBlock) {
@@ -886,7 +980,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     }
 
     /// Pops the current frame from the stack, deallocating the
-    /// memory for allocated locals.
+    /// memory for allocated locals, and jumps to an appropriate place.
     ///
     /// If `unwinding` is `false`, then we are performing a normal return
     /// from a function. In this case, we jump back into the frame of the caller,
@@ -899,7 +993,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// The cleanup block ends with a special `Resume` terminator, which will
     /// cause us to continue unwinding.
     #[instrument(skip(self), level = "debug")]
-    pub(super) fn pop_stack_frame(&mut self, unwinding: bool) -> InterpResult<'tcx> {
+    pub(super) fn return_from_current_stack_frame(
+        &mut self,
+        unwinding: bool,
+    ) -> InterpResult<'tcx> {
         info!(
             "popping stack frame ({})",
             if unwinding { "during unwinding" } else { "returning from function" }
@@ -947,45 +1044,31 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             Ok(())
         };
 
-        // Cleanup: deallocate locals.
-        // Usually we want to clean up (deallocate locals), but in a few rare cases we don't.
-        // We do this while the frame is still on the stack, so errors point to the callee.
-        let return_to_block = self.frame().return_to_block;
-        let cleanup = match return_to_block {
-            StackPopCleanup::Goto { .. } => true,
-            StackPopCleanup::Root { cleanup, .. } => cleanup,
-        };
-        if cleanup {
-            // We need to take the locals out, since we need to mutate while iterating.
-            let locals = mem::take(&mut self.frame_mut().locals);
-            for local in &locals {
-                self.deallocate_local(local.value)?;
-            }
-        }
-
         // All right, now it is time to actually pop the frame.
-        // Note that its locals are gone already, but that's fine.
-        let frame =
-            self.stack_mut().pop().expect("tried to pop a stack frame, but there were none");
+        let stack_pop_info = self.pop_stack_frame(unwinding)?;
+
         // Report error from return value copy, if any.
         copy_ret_result?;
 
-        // If we are not doing cleanup, also skip everything else.
-        if !cleanup {
-            assert!(self.stack().is_empty(), "only the topmost frame should ever be leaked");
-            assert!(!unwinding, "tried to skip cleanup during unwinding");
-            // Skip machine hook.
-            return Ok(());
-        }
-        if M::after_stack_pop(self, frame, unwinding)? == StackPopJump::NoJump {
-            // The hook already did everything.
-            return Ok(());
+        match stack_pop_info.return_action {
+            ReturnAction::Normal => {}
+            ReturnAction::NoJump => {
+                // The hook already did everything.
+                return Ok(());
+            }
+            ReturnAction::NoCleanup => {
+                // If we are not doing cleanup, also skip everything else.
+                assert!(self.stack().is_empty(), "only the topmost frame should ever be leaked");
+                assert!(!unwinding, "tried to skip cleanup during unwinding");
+                // Skip machine hook.
+                return Ok(());
+            }
         }
 
         // Normal return, figure out where to jump.
         if unwinding {
             // Follow the unwind edge.
-            let unwind = match return_to_block {
+            let unwind = match stack_pop_info.return_to_block {
                 StackPopCleanup::Goto { unwind, .. } => unwind,
                 StackPopCleanup::Root { .. } => {
                     panic!("encountered StackPopCleanup::Root when unwinding!")
@@ -995,7 +1078,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             self.unwind_to_block(unwind)
         } else {
             // Follow the normal return edge.
-            match return_to_block {
+            match stack_pop_info.return_to_block {
                 StackPopCleanup::Goto { ret, .. } => self.return_to_block(ret),
                 StackPopCleanup::Root { .. } => {
                     assert!(
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index e91ab7c1791..7f2e9ce06a5 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -23,10 +23,11 @@ use super::{
     MemoryKind, Misalignment, OpTy, PlaceTy, Pointer, Provenance,
 };
 
-/// Data returned by Machine::stack_pop,
-/// to provide further control over the popping of the stack frame
+/// Data returned by [`Machine::after_stack_pop`], and consumed by
+/// [`InterpCx::return_from_current_stack_frame`] to determine what actions should be done when
+/// returning from a stack frame.
 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
-pub enum StackPopJump {
+pub enum ReturnAction {
     /// Indicates that no special handling should be
     /// done - we'll either return normally or unwind
     /// based on the terminator for the function
@@ -36,6 +37,9 @@ pub enum StackPopJump {
     /// Indicates that we should *not* jump to the return/unwind address, as the callback already
     /// took care of everything.
     NoJump,
+
+    /// Returned by [`InterpCx::pop_stack_frame`] when no cleanup should be done.
+    NoCleanup,
 }
 
 /// Whether this kind of memory is allowed to leak
@@ -522,10 +526,10 @@ pub trait Machine<'tcx>: Sized {
         _ecx: &mut InterpCx<'tcx, Self>,
         _frame: Frame<'tcx, Self::Provenance, Self::FrameExtra>,
         unwinding: bool,
-    ) -> InterpResult<'tcx, StackPopJump> {
+    ) -> InterpResult<'tcx, ReturnAction> {
         // By default, we do not support unwinding from panics
         assert!(!unwinding);
-        Ok(StackPopJump::Normal)
+        Ok(ReturnAction::Normal)
     }
 
     /// Called immediately after actual memory was allocated for a local
diff --git a/compiler/rustc_const_eval/src/interpret/mod.rs b/compiler/rustc_const_eval/src/interpret/mod.rs
index 7d7b421f869..f703c6fbe3e 100644
--- a/compiler/rustc_const_eval/src/interpret/mod.rs
+++ b/compiler/rustc_const_eval/src/interpret/mod.rs
@@ -26,7 +26,7 @@ pub use self::intern::{
     intern_const_alloc_for_constprop, intern_const_alloc_recursive, HasStaticRootDefId, InternKind,
     InternResult,
 };
-pub use self::machine::{compile_time_machine, AllocMap, Machine, MayLeak, StackPopJump};
+pub use self::machine::{compile_time_machine, AllocMap, Machine, MayLeak, ReturnAction};
 pub use self::memory::{AllocKind, AllocRef, AllocRefMut, FnVal, Memory, MemoryKind};
 pub use self::operand::{ImmTy, Immediate, OpTy, Readable};
 pub use self::place::{MPlaceTy, MemPlaceMeta, PlaceTy, Writeable};
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 1baf62baa81..b3124dfdfbc 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -32,7 +32,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             // We are unwinding and this fn has no cleanup code.
             // Just go on unwinding.
             trace!("unwinding: skipping frame");
-            self.pop_stack_frame(/* unwinding */ true)?;
+            self.return_from_current_stack_frame(/* unwinding */ true)?;
             return Ok(true);
         };
         let basic_block = &self.body().basic_blocks[loc.block];
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs
index 68acddf63d8..25f6bd64055 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -4,9 +4,8 @@ use either::Either;
 use rustc_middle::ty::TyCtxt;
 use tracing::trace;
 
-use rustc_middle::span_bug;
 use rustc_middle::{
-    mir,
+    bug, mir, span_bug,
     ty::{
         self,
         layout::{FnAbiOf, IntegerExt, LayoutOf, TyAndLayout},
@@ -26,7 +25,10 @@ use super::{
     InterpResult, MPlaceTy, Machine, OpTy, PlaceTy, Projectable, Provenance, Scalar,
     StackPopCleanup,
 };
-use crate::fluent_generated as fluent;
+use crate::{
+    fluent_generated as fluent,
+    interpret::{eval_context::StackPopInfo, ReturnAction},
+};
 
 /// An argment passed to a function.
 #[derive(Clone, Debug)]
@@ -47,6 +49,15 @@ impl<'tcx, Prov: Provenance> FnArg<'tcx, Prov> {
     }
 }
 
+struct EvaluatedCalleeAndArgs<'tcx, M: Machine<'tcx>> {
+    callee: FnVal<'tcx, M::ExtraFnVal>,
+    args: Vec<FnArg<'tcx, M::Provenance>>,
+    fn_sig: ty::FnSig<'tcx>,
+    fn_abi: &'tcx FnAbi<'tcx, Ty<'tcx>>,
+    /// True if the function is marked as `#[track_caller]` ([`ty::InstanceKind::requires_caller_location`])
+    with_caller_location: bool,
+}
+
 impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// Make a copy of the given fn_arg. Any `InPlace` are degenerated to copies, no protection of the
     /// original memory occurs.
@@ -84,7 +95,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         use rustc_middle::mir::TerminatorKind::*;
         match terminator.kind {
             Return => {
-                self.pop_stack_frame(/* unwinding */ false)?
+                self.return_from_current_stack_frame(/* unwinding */ false)?
             }
 
             Goto { target } => self.go_to_block(target),
@@ -124,40 +135,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             } => {
                 let old_stack = self.frame_idx();
                 let old_loc = self.frame().loc;
-                let func = self.eval_operand(func, None)?;
-                let args = self.eval_fn_call_arguments(args)?;
-
-                let fn_sig_binder = func.layout.ty.fn_sig(*self.tcx);
-                let fn_sig =
-                    self.tcx.normalize_erasing_late_bound_regions(self.param_env, fn_sig_binder);
-                let extra_args = &args[fn_sig.inputs().len()..];
-                let extra_args =
-                    self.tcx.mk_type_list_from_iter(extra_args.iter().map(|arg| arg.layout().ty));
-
-                let (fn_val, fn_abi, with_caller_location) = match *func.layout.ty.kind() {
-                    ty::FnPtr(_sig) => {
-                        let fn_ptr = self.read_pointer(&func)?;
-                        let fn_val = self.get_ptr_fn(fn_ptr)?;
-                        (fn_val, self.fn_abi_of_fn_ptr(fn_sig_binder, extra_args)?, false)
-                    }
-                    ty::FnDef(def_id, args) => {
-                        let instance = self.resolve(def_id, args)?;
-                        (
-                            FnVal::Instance(instance),
-                            self.fn_abi_of_instance(instance, extra_args)?,
-                            instance.def.requires_caller_location(*self.tcx),
-                        )
-                    }
-                    _ => span_bug!(
-                        terminator.source_info.span,
-                        "invalid callee of type {}",
-                        func.layout.ty
-                    ),
-                };
+
+                let EvaluatedCalleeAndArgs { callee, args, fn_sig, fn_abi, with_caller_location } =
+                    self.eval_callee_and_args(terminator, func, args)?;
 
                 let destination = self.force_allocation(&self.eval_place(destination)?)?;
                 self.eval_fn_call(
-                    fn_val,
+                    callee,
                     (fn_sig.abi, fn_abi),
                     &args,
                     with_caller_location,
@@ -172,6 +156,22 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 }
             }
 
+            TailCall { ref func, ref args, fn_span: _ } => {
+                let old_frame_idx = self.frame_idx();
+
+                let EvaluatedCalleeAndArgs { callee, args, fn_sig, fn_abi, with_caller_location } =
+                    self.eval_callee_and_args(terminator, func, args)?;
+
+                self.eval_fn_tail_call(callee, (fn_sig.abi, fn_abi), &args, with_caller_location)?;
+
+                if self.frame_idx() != old_frame_idx {
+                    span_bug!(
+                        terminator.source_info.span,
+                        "evaluating this tail call pushed a new stack frame"
+                    );
+                }
+            }
+
             Drop { place, target, unwind, replace: _ } => {
                 let place = self.eval_place(place)?;
                 let instance = Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
@@ -209,7 +209,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 trace!("unwinding: resuming from cleanup");
                 // By definition, a Resume terminator means
                 // that we're unwinding
-                self.pop_stack_frame(/* unwinding */ true)?;
+                self.return_from_current_stack_frame(/* unwinding */ true)?;
                 return Ok(());
             }
 
@@ -514,6 +514,45 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         Ok(())
     }
 
+    /// Shared part of `Call` and `TailCall` implementation — finding and evaluating all the
+    /// necessary information about callee and arguments to make a call.
+    fn eval_callee_and_args(
+        &self,
+        terminator: &mir::Terminator<'tcx>,
+        func: &mir::Operand<'tcx>,
+        args: &[Spanned<mir::Operand<'tcx>>],
+    ) -> InterpResult<'tcx, EvaluatedCalleeAndArgs<'tcx, M>> {
+        let func = self.eval_operand(func, None)?;
+        let args = self.eval_fn_call_arguments(args)?;
+
+        let fn_sig_binder = func.layout.ty.fn_sig(*self.tcx);
+        let fn_sig = self.tcx.normalize_erasing_late_bound_regions(self.param_env, fn_sig_binder);
+        let extra_args = &args[fn_sig.inputs().len()..];
+        let extra_args =
+            self.tcx.mk_type_list_from_iter(extra_args.iter().map(|arg| arg.layout().ty));
+
+        let (callee, fn_abi, with_caller_location) = match *func.layout.ty.kind() {
+            ty::FnPtr(_sig) => {
+                let fn_ptr = self.read_pointer(&func)?;
+                let fn_val = self.get_ptr_fn(fn_ptr)?;
+                (fn_val, self.fn_abi_of_fn_ptr(fn_sig_binder, extra_args)?, false)
+            }
+            ty::FnDef(def_id, args) => {
+                let instance = self.resolve(def_id, args)?;
+                (
+                    FnVal::Instance(instance),
+                    self.fn_abi_of_instance(instance, extra_args)?,
+                    instance.def.requires_caller_location(*self.tcx),
+                )
+            }
+            _ => {
+                span_bug!(terminator.source_info.span, "invalid callee of type {}", func.layout.ty)
+            }
+        };
+
+        Ok(EvaluatedCalleeAndArgs { callee, args, fn_sig, fn_abi, with_caller_location })
+    }
+
     /// Call this function -- pushing the stack frame and initializing the arguments.
     ///
     /// `caller_fn_abi` is used to determine if all the arguments are passed the proper way.
@@ -924,6 +963,49 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         }
     }
 
+    pub(crate) fn eval_fn_tail_call(
+        &mut self,
+        fn_val: FnVal<'tcx, M::ExtraFnVal>,
+        (caller_abi, caller_fn_abi): (Abi, &FnAbi<'tcx, Ty<'tcx>>),
+        args: &[FnArg<'tcx, M::Provenance>],
+        with_caller_location: bool,
+    ) -> InterpResult<'tcx> {
+        trace!("eval_fn_call: {:#?}", fn_val);
+
+        // This is the "canonical" implementation of tails calls,
+        // a pop of the current stack frame, followed by a normal call
+        // which pushes a new stack frame, with the return address from
+        // the popped stack frame.
+        //
+        // Note that we are using `pop_stack_frame` and not `return_from_current_stack_frame`,
+        // as the latter "executes" the goto to the return block, but we don't want to,
+        // only the tail called function should return to the current return block.
+        M::before_stack_pop(self, self.frame())?;
+
+        let StackPopInfo { return_action, return_to_block, return_place } =
+            self.pop_stack_frame(false)?;
+
+        assert_eq!(return_action, ReturnAction::Normal);
+
+        let StackPopCleanup::Goto { ret, unwind } = return_to_block else {
+            bug!("can't tailcall as root");
+        };
+
+        // FIXME(explicit_tail_calls):
+        //   we should check if both caller&callee can/n't unwind,
+        //   see <https://github.com/rust-lang/rust/pull/113128#issuecomment-1614979803>
+
+        self.eval_fn_call(
+            fn_val,
+            (caller_abi, caller_fn_abi),
+            args,
+            with_caller_location,
+            &return_place,
+            ret,
+            unwind,
+        )
+    }
+
     fn check_fn_target_features(&self, instance: ty::Instance<'tcx>) -> InterpResult<'tcx, ()> {
         // Calling functions with `#[target_feature]` is not unsafe on WASM, see #84988
         let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index 0af80bc5c67..e6ca1bf7bc4 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -298,15 +298,21 @@ impl IntoDiagArg for hir::def::Namespace {
 }
 
 #[derive(Clone)]
-pub struct DiagSymbolList(Vec<Symbol>);
+pub struct DiagSymbolList<S = Symbol>(Vec<S>);
 
-impl From<Vec<Symbol>> for DiagSymbolList {
-    fn from(v: Vec<Symbol>) -> Self {
+impl<S> From<Vec<S>> for DiagSymbolList<S> {
+    fn from(v: Vec<S>) -> Self {
         DiagSymbolList(v)
     }
 }
 
-impl IntoDiagArg for DiagSymbolList {
+impl<S> FromIterator<S> for DiagSymbolList<S> {
+    fn from_iter<T: IntoIterator<Item = S>>(iter: T) -> Self {
+        iter.into_iter().collect::<Vec<_>>().into()
+    }
+}
+
+impl<S: std::fmt::Display> IntoDiagArg for DiagSymbolList<S> {
     fn into_diag_arg(self) -> DiagArgValue {
         DiagArgValue::StrListSepByAnd(
             self.0.into_iter().map(|sym| Cow::Owned(format!("`{sym}`"))).collect(),
diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index 56cbb54fcec..40e16b45115 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -172,7 +172,7 @@ impl<'a> StripUnconfigured<'a> {
     fn configure_tokens(&self, stream: &AttrTokenStream) -> AttrTokenStream {
         fn can_skip(stream: &AttrTokenStream) -> bool {
             stream.0.iter().all(|tree| match tree {
-                AttrTokenTree::Attributes(_) => false,
+                AttrTokenTree::AttrsTarget(_) => false,
                 AttrTokenTree::Token(..) => true,
                 AttrTokenTree::Delimited(.., inner) => can_skip(inner),
             })
@@ -185,22 +185,22 @@ impl<'a> StripUnconfigured<'a> {
         let trees: Vec<_> = stream
             .0
             .iter()
-            .flat_map(|tree| match tree.clone() {
-                AttrTokenTree::Attributes(mut data) => {
-                    data.attrs.flat_map_in_place(|attr| self.process_cfg_attr(&attr));
+            .filter_map(|tree| match tree.clone() {
+                AttrTokenTree::AttrsTarget(mut target) => {
+                    target.attrs.flat_map_in_place(|attr| self.process_cfg_attr(&attr));
 
-                    if self.in_cfg(&data.attrs) {
-                        data.tokens = LazyAttrTokenStream::new(
-                            self.configure_tokens(&data.tokens.to_attr_token_stream()),
+                    if self.in_cfg(&target.attrs) {
+                        target.tokens = LazyAttrTokenStream::new(
+                            self.configure_tokens(&target.tokens.to_attr_token_stream()),
                         );
-                        Some(AttrTokenTree::Attributes(data)).into_iter()
+                        Some(AttrTokenTree::AttrsTarget(target))
                     } else {
-                        None.into_iter()
+                        None
                     }
                 }
                 AttrTokenTree::Delimited(sp, spacing, delim, mut inner) => {
                     inner = self.configure_tokens(&inner);
-                    Some(AttrTokenTree::Delimited(sp, spacing, delim, inner)).into_iter()
+                    Some(AttrTokenTree::Delimited(sp, spacing, delim, inner))
                 }
                 AttrTokenTree::Token(
                     Token {
@@ -220,9 +220,7 @@ impl<'a> StripUnconfigured<'a> {
                 ) => {
                     panic!("Should be `AttrTokenTree::Delimited`, not delim tokens: {:?}", tree);
                 }
-                AttrTokenTree::Token(token, spacing) => {
-                    Some(AttrTokenTree::Token(token, spacing)).into_iter()
-                }
+                AttrTokenTree::Token(token, spacing) => Some(AttrTokenTree::Token(token, spacing)),
             })
             .collect();
         AttrTokenStream::new(trees)
@@ -294,7 +292,7 @@ impl<'a> StripUnconfigured<'a> {
         attr: &Attribute,
         (item, item_span): (ast::AttrItem, Span),
     ) -> Attribute {
-        let orig_tokens = attr.tokens();
+        let orig_tokens = attr.get_tokens();
 
         // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
         // and producing an attribute of the form `#[attr]`. We
@@ -310,12 +308,11 @@ impl<'a> StripUnconfigured<'a> {
         else {
             panic!("Bad tokens for attribute {attr:?}");
         };
-        let pound_span = pound_token.span;
 
         // We don't really have a good span to use for the synthesized `[]`
         // in `#[attr]`, so just use the span of the `#` token.
         let bracket_group = AttrTokenTree::Delimited(
-            DelimSpan::from_single(pound_span),
+            DelimSpan::from_single(pound_token.span),
             DelimSpacing::new(Spacing::JointHidden, Spacing::Alone),
             Delimiter::Bracket,
             item.tokens
diff --git a/compiler/rustc_expand/src/mbe/metavar_expr.rs b/compiler/rustc_expand/src/mbe/metavar_expr.rs
index 25958e03028..dbbd948fd70 100644
--- a/compiler/rustc_expand/src/mbe/metavar_expr.rs
+++ b/compiler/rustc_expand/src/mbe/metavar_expr.rs
@@ -1,4 +1,4 @@
-use rustc_ast::token::{self, Delimiter, IdentIsRaw};
+use rustc_ast::token::{self, Delimiter, IdentIsRaw, Lit, Token, TokenKind};
 use rustc_ast::tokenstream::{RefTokenTreeCursor, TokenStream, TokenTree};
 use rustc_ast::{LitIntType, LitKind};
 use rustc_ast_pretty::pprust;
@@ -6,9 +6,10 @@ use rustc_errors::{Applicability, PResult};
 use rustc_macros::{Decodable, Encodable};
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::Ident;
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 
 pub(crate) const RAW_IDENT_ERR: &str = "`${concat(..)}` currently does not support raw identifiers";
+pub(crate) const UNSUPPORTED_CONCAT_ELEM_ERR: &str = "expected identifier or string literal";
 
 /// A meta-variable expression, for expansions based on properties of meta-variables.
 #[derive(Debug, PartialEq, Encodable, Decodable)]
@@ -51,11 +52,26 @@ impl MetaVarExpr {
                 let mut result = Vec::new();
                 loop {
                     let is_var = try_eat_dollar(&mut iter);
-                    let element_ident = parse_ident(&mut iter, psess, outer_span)?;
+                    let token = parse_token(&mut iter, psess, outer_span)?;
                     let element = if is_var {
-                        MetaVarExprConcatElem::Var(element_ident)
+                        MetaVarExprConcatElem::Var(parse_ident_from_token(psess, token)?)
+                    } else if let TokenKind::Literal(Lit {
+                        kind: token::LitKind::Str,
+                        symbol,
+                        suffix: None,
+                    }) = token.kind
+                    {
+                        MetaVarExprConcatElem::Literal(symbol)
                     } else {
-                        MetaVarExprConcatElem::Ident(element_ident)
+                        match parse_ident_from_token(psess, token) {
+                            Err(err) => {
+                                err.cancel();
+                                return Err(psess
+                                    .dcx()
+                                    .struct_span_err(token.span, UNSUPPORTED_CONCAT_ELEM_ERR));
+                            }
+                            Ok(elem) => MetaVarExprConcatElem::Ident(elem),
+                        }
                     };
                     result.push(element);
                     if iter.look_ahead(0).is_none() {
@@ -105,11 +121,13 @@ impl MetaVarExpr {
 
 #[derive(Debug, Decodable, Encodable, PartialEq)]
 pub(crate) enum MetaVarExprConcatElem {
-    /// There is NO preceding dollar sign, which means that this identifier should be interpreted
-    /// as a literal.
+    /// Identifier WITHOUT a preceding dollar sign, which means that this identifier should be
+    /// interpreted as a literal.
     Ident(Ident),
-    /// There is a preceding dollar sign, which means that this identifier should be expanded
-    /// and interpreted as a variable.
+    /// For example, a number or a string.
+    Literal(Symbol),
+    /// Identifier WITH a preceding dollar sign, which means that this identifier should be
+    /// expanded and interpreted as a variable.
     Var(Ident),
 }
 
@@ -158,7 +176,7 @@ fn parse_depth<'psess>(
     span: Span,
 ) -> PResult<'psess, usize> {
     let Some(tt) = iter.next() else { return Ok(0) };
-    let TokenTree::Token(token::Token { kind: token::TokenKind::Literal(lit), .. }, _) = tt else {
+    let TokenTree::Token(Token { kind: TokenKind::Literal(lit), .. }, _) = tt else {
         return Err(psess
             .dcx()
             .struct_span_err(span, "meta-variable expression depth must be a literal"));
@@ -180,12 +198,14 @@ fn parse_ident<'psess>(
     psess: &'psess ParseSess,
     fallback_span: Span,
 ) -> PResult<'psess, Ident> {
-    let Some(tt) = iter.next() else {
-        return Err(psess.dcx().struct_span_err(fallback_span, "expected identifier"));
-    };
-    let TokenTree::Token(token, _) = tt else {
-        return Err(psess.dcx().struct_span_err(tt.span(), "expected identifier"));
-    };
+    let token = parse_token(iter, psess, fallback_span)?;
+    parse_ident_from_token(psess, token)
+}
+
+fn parse_ident_from_token<'psess>(
+    psess: &'psess ParseSess,
+    token: &Token,
+) -> PResult<'psess, Ident> {
     if let Some((elem, is_raw)) = token.ident() {
         if let IdentIsRaw::Yes = is_raw {
             return Err(psess.dcx().struct_span_err(elem.span, RAW_IDENT_ERR));
@@ -205,10 +225,24 @@ fn parse_ident<'psess>(
     Err(err)
 }
 
+fn parse_token<'psess, 't>(
+    iter: &mut RefTokenTreeCursor<'t>,
+    psess: &'psess ParseSess,
+    fallback_span: Span,
+) -> PResult<'psess, &'t Token> {
+    let Some(tt) = iter.next() else {
+        return Err(psess.dcx().struct_span_err(fallback_span, UNSUPPORTED_CONCAT_ELEM_ERR));
+    };
+    let TokenTree::Token(token, _) = tt else {
+        return Err(psess.dcx().struct_span_err(tt.span(), UNSUPPORTED_CONCAT_ELEM_ERR));
+    };
+    Ok(token)
+}
+
 /// Tries to move the iterator forward returning `true` if there is a comma. If not, then the
 /// iterator is not modified and the result is `false`.
 fn try_eat_comma(iter: &mut RefTokenTreeCursor<'_>) -> bool {
-    if let Some(TokenTree::Token(token::Token { kind: token::Comma, .. }, _)) = iter.look_ahead(0) {
+    if let Some(TokenTree::Token(Token { kind: token::Comma, .. }, _)) = iter.look_ahead(0) {
         let _ = iter.next();
         return true;
     }
@@ -218,8 +252,7 @@ fn try_eat_comma(iter: &mut RefTokenTreeCursor<'_>) -> bool {
 /// Tries to move the iterator forward returning `true` if there is a dollar sign. If not, then the
 /// iterator is not modified and the result is `false`.
 fn try_eat_dollar(iter: &mut RefTokenTreeCursor<'_>) -> bool {
-    if let Some(TokenTree::Token(token::Token { kind: token::Dollar, .. }, _)) = iter.look_ahead(0)
-    {
+    if let Some(TokenTree::Token(Token { kind: token::Dollar, .. }, _)) = iter.look_ahead(0) {
         let _ = iter.next();
         return true;
     }
@@ -232,8 +265,7 @@ fn eat_dollar<'psess>(
     psess: &'psess ParseSess,
     span: Span,
 ) -> PResult<'psess, ()> {
-    if let Some(TokenTree::Token(token::Token { kind: token::Dollar, .. }, _)) = iter.look_ahead(0)
-    {
+    if let Some(TokenTree::Token(Token { kind: token::Dollar, .. }, _)) = iter.look_ahead(0) {
         let _ = iter.next();
         return Ok(());
     }
diff --git a/compiler/rustc_expand/src/mbe/transcribe.rs b/compiler/rustc_expand/src/mbe/transcribe.rs
index f935f1b77e0..9b4dc13c703 100644
--- a/compiler/rustc_expand/src/mbe/transcribe.rs
+++ b/compiler/rustc_expand/src/mbe/transcribe.rs
@@ -11,11 +11,13 @@ use rustc_ast::token::{self, Delimiter, Token, TokenKind};
 use rustc_ast::tokenstream::{DelimSpacing, DelimSpan, Spacing, TokenStream, TokenTree};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{pluralize, Diag, DiagCtxtHandle, PResult};
+use rustc_parse::lexer::nfc_normalize;
 use rustc_parse::parser::ParseNtResult;
 use rustc_session::parse::ParseSess;
+use rustc_session::parse::SymbolGallery;
 use rustc_span::hygiene::{LocalExpnId, Transparency};
 use rustc_span::symbol::{sym, Ident, MacroRulesNormalizedIdent};
-use rustc_span::{with_metavar_spans, Span, Symbol, SyntaxContext};
+use rustc_span::{with_metavar_spans, Span, SyntaxContext};
 use smallvec::{smallvec, SmallVec};
 use std::mem;
 
@@ -312,7 +314,16 @@ pub(super) fn transcribe<'a>(
 
             // Replace meta-variable expressions with the result of their expansion.
             mbe::TokenTree::MetaVarExpr(sp, expr) => {
-                transcribe_metavar_expr(dcx, expr, interp, &mut marker, &repeats, &mut result, sp)?;
+                transcribe_metavar_expr(
+                    dcx,
+                    expr,
+                    interp,
+                    &mut marker,
+                    &repeats,
+                    &mut result,
+                    sp,
+                    &psess.symbol_gallery,
+                )?;
             }
 
             // If we are entering a new delimiter, we push its contents to the `stack` to be
@@ -669,6 +680,7 @@ fn transcribe_metavar_expr<'a>(
     repeats: &[(usize, usize)],
     result: &mut Vec<TokenTree>,
     sp: &DelimSpan,
+    symbol_gallery: &SymbolGallery,
 ) -> PResult<'a, ()> {
     let mut visited_span = || {
         let mut span = sp.entire();
@@ -680,16 +692,26 @@ fn transcribe_metavar_expr<'a>(
             let mut concatenated = String::new();
             for element in elements.into_iter() {
                 let string = match element {
-                    MetaVarExprConcatElem::Ident(ident) => ident.to_string(),
-                    MetaVarExprConcatElem::Var(ident) => extract_ident(dcx, *ident, interp)?,
+                    MetaVarExprConcatElem::Ident(elem) => elem.to_string(),
+                    MetaVarExprConcatElem::Literal(elem) => elem.as_str().into(),
+                    MetaVarExprConcatElem::Var(elem) => extract_ident(dcx, *elem, interp)?,
                 };
                 concatenated.push_str(&string);
             }
+            let symbol = nfc_normalize(&concatenated);
+            let concatenated_span = visited_span();
+            if !rustc_lexer::is_ident(symbol.as_str()) {
+                return Err(dcx.struct_span_err(
+                    concatenated_span,
+                    "`${concat(..)}` is not generating a valid identifier",
+                ));
+            }
+            symbol_gallery.insert(symbol, concatenated_span);
             // The current implementation marks the span as coming from the macro regardless of
             // contexts of the concatenated identifiers but this behavior may change in the
             // future.
             result.push(TokenTree::Token(
-                Token::from_ast_ident(Ident::new(Symbol::intern(&concatenated), visited_span())),
+                Token::from_ast_ident(Ident::new(symbol, concatenated_span)),
                 Spacing::Alone,
             ));
         }
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 0dbe64c3ea7..8a1ee9374c3 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -21,6 +21,7 @@ use rustc_middle::ty::{
 use rustc_middle::ty::{GenericParamDefKind, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_span::Span;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index f21aeb4c0b9..6282499883b 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -26,15 +26,12 @@ fn equate_intrinsic_type<'tcx>(
     n_cts: usize,
     sig: ty::PolyFnSig<'tcx>,
 ) {
-    let (own_counts, span) = match tcx.hir_node_by_def_id(def_id) {
+    let (generics, span) = match tcx.hir_node_by_def_id(def_id) {
         hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. })
         | hir::Node::ForeignItem(hir::ForeignItem {
             kind: hir::ForeignItemKind::Fn(.., generics, _),
             ..
-        }) => {
-            let own_counts = tcx.generics_of(def_id).own_counts();
-            (own_counts, generics.span)
-        }
+        }) => (tcx.generics_of(def_id), generics.span),
         _ => {
             struct_span_code_err!(tcx.dcx(), span, E0622, "intrinsic must be a function")
                 .with_span_label(span, "expected a function")
@@ -42,6 +39,7 @@ fn equate_intrinsic_type<'tcx>(
             return;
         }
     };
+    let own_counts = generics.own_counts();
 
     let gen_count_ok = |found: usize, expected: usize, descr: &str| -> bool {
         if found != expected {
@@ -57,9 +55,17 @@ fn equate_intrinsic_type<'tcx>(
         }
     };
 
+    // the host effect param should be invisible as it shouldn't matter
+    // whether effects is enabled for the intrinsic provider crate.
+    let consts_count = if generics.host_effect_index.is_some() {
+        own_counts.consts - 1
+    } else {
+        own_counts.consts
+    };
+
     if gen_count_ok(own_counts.lifetimes, n_lts, "lifetime")
         && gen_count_ok(own_counts.types, n_tps, "type")
-        && gen_count_ok(own_counts.consts, n_cts, "const")
+        && gen_count_ok(consts_count, n_cts, "const")
     {
         let _ = check_function_signature(
             tcx,
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 2230528a5ae..a0eede31eb0 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -39,6 +39,7 @@ use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _
 use rustc_trait_selection::traits::{
     self, FulfillmentError, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
 };
+use rustc_type_ir::solve::NoSolution;
 use rustc_type_ir::TypeFlags;
 
 use std::cell::LazyCell;
@@ -477,7 +478,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
                             param_env,
                             item_def_id,
                             tcx.explicit_item_bounds(item_def_id)
-                                .instantiate_identity_iter_copied()
+                                .iter_identity_copied()
                                 .collect::<Vec<_>>(),
                             &FxIndexSet::default(),
                             gat_def_id,
@@ -1204,17 +1205,16 @@ fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: ty::AssocIt
     let bounds = wfcx.tcx().explicit_item_bounds(item.def_id);
 
     debug!("check_associated_type_bounds: bounds={:?}", bounds);
-    let wf_obligations =
-        bounds.instantiate_identity_iter_copied().flat_map(|(bound, bound_span)| {
-            let normalized_bound = wfcx.normalize(span, None, bound);
-            traits::wf::clause_obligations(
-                wfcx.infcx,
-                wfcx.param_env,
-                wfcx.body_def_id,
-                normalized_bound,
-                bound_span,
-            )
-        });
+    let wf_obligations = bounds.iter_identity_copied().flat_map(|(bound, bound_span)| {
+        let normalized_bound = wfcx.normalize(span, None, bound);
+        traits::wf::clause_obligations(
+            wfcx.infcx,
+            wfcx.param_env,
+            wfcx.body_def_id,
+            normalized_bound,
+            bound_span,
+        )
+    });
 
     wfcx.register_obligations(wf_obligations);
 }
@@ -1712,13 +1712,12 @@ fn receiver_is_valid<'tcx>(
     let cause =
         ObligationCause::new(span, wfcx.body_def_id, traits::ObligationCauseCode::MethodReceiver);
 
-    let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty);
-
-    // `self: Self` is always valid.
-    if can_eq_self(receiver_ty) {
-        if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, receiver_ty) {
-            infcx.err_ctxt().report_mismatched_types(&cause, self_ty, receiver_ty, err).emit();
-        }
+    // Special case `receiver == self_ty`, which doesn't necessarily require the `Receiver` lang item.
+    if let Ok(()) = wfcx.infcx.commit_if_ok(|_| {
+        let ocx = ObligationCtxt::new(wfcx.infcx);
+        ocx.eq(&cause, wfcx.param_env, self_ty, receiver_ty)?;
+        if ocx.select_all_or_error().is_empty() { Ok(()) } else { Err(NoSolution) }
+    }) {
         return true;
     }
 
@@ -1729,58 +1728,51 @@ fn receiver_is_valid<'tcx>(
         autoderef = autoderef.include_raw_pointers();
     }
 
-    // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
-    autoderef.next();
-
     let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, Some(span));
 
     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
-    loop {
-        if let Some((potential_self_ty, _)) = autoderef.next() {
-            debug!(
-                "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
-                potential_self_ty, self_ty
-            );
-
-            if can_eq_self(potential_self_ty) {
-                wfcx.register_obligations(autoderef.into_obligations());
+    while let Some((potential_self_ty, _)) = autoderef.next() {
+        debug!(
+            "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
+            potential_self_ty, self_ty
+        );
 
-                if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty) {
-                    infcx
-                        .err_ctxt()
-                        .report_mismatched_types(&cause, self_ty, potential_self_ty, err)
-                        .emit();
-                }
+        // Check if the self type unifies. If it does, then commit the result
+        // since it may have region side-effects.
+        if let Ok(()) = wfcx.infcx.commit_if_ok(|_| {
+            let ocx = ObligationCtxt::new(wfcx.infcx);
+            ocx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty)?;
+            if ocx.select_all_or_error().is_empty() { Ok(()) } else { Err(NoSolution) }
+        }) {
+            wfcx.register_obligations(autoderef.into_obligations());
+            return true;
+        }
 
+        // Without `feature(arbitrary_self_types)`, we require that each step in the
+        // deref chain implement `receiver`.
+        if !arbitrary_self_types_enabled {
+            if !receiver_is_implemented(
+                wfcx,
+                receiver_trait_def_id,
+                cause.clone(),
+                potential_self_ty,
+            ) {
+                // We cannot proceed.
                 break;
-            } else {
-                // Without `feature(arbitrary_self_types)`, we require that each step in the
-                // deref chain implement `receiver`
-                if !arbitrary_self_types_enabled
-                    && !receiver_is_implemented(
-                        wfcx,
-                        receiver_trait_def_id,
-                        cause.clone(),
-                        potential_self_ty,
-                    )
-                {
-                    return false;
-                }
             }
-        } else {
-            debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
-            return false;
-        }
-    }
 
-    // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
-    if !arbitrary_self_types_enabled
-        && !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty)
-    {
-        return false;
+            // Register the bound, in case it has any region side-effects.
+            wfcx.register_bound(
+                cause.clone(),
+                wfcx.param_env,
+                potential_self_ty,
+                receiver_trait_def_id,
+            );
+        }
     }
 
-    true
+    debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
+    false
 }
 
 fn receiver_is_implemented<'tcx>(
diff --git a/compiler/rustc_hir_analysis/src/coherence/orphan.rs b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
index 5cb91603fd0..16f72f38d60 100644
--- a/compiler/rustc_hir_analysis/src/coherence/orphan.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
@@ -286,7 +286,7 @@ fn orphan_check<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_def_id: LocalDefId,
     mode: OrphanCheckMode,
-) -> Result<(), OrphanCheckErr<'tcx, FxIndexSet<DefId>>> {
+) -> Result<(), OrphanCheckErr<TyCtxt<'tcx>, FxIndexSet<DefId>>> {
     // We only accept this routine to be invoked on implementations
     // of a trait, not inherent implementations.
     let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
@@ -326,17 +326,16 @@ fn orphan_check<'tcx>(
             ty
         };
 
-        Ok(ty)
+        Ok::<_, !>(ty)
     };
 
-    let Ok(result) = traits::orphan_check_trait_ref::<!>(
+    let result = traits::orphan_check_trait_ref(
         &infcx,
         trait_ref,
         traits::InCrate::Local { mode },
         lazily_normalize_ty,
-    ) else {
-        unreachable!()
-    };
+    )
+    .into_ok();
 
     // (2)  Try to map the remaining inference vars back to generic params.
     result.map_err(|err| match err {
@@ -369,7 +368,7 @@ fn emit_orphan_check_error<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_ref: ty::TraitRef<'tcx>,
     impl_def_id: LocalDefId,
-    err: traits::OrphanCheckErr<'tcx, FxIndexSet<DefId>>,
+    err: traits::OrphanCheckErr<TyCtxt<'tcx>, FxIndexSet<DefId>>,
 ) -> ErrorGuaranteed {
     match err {
         traits::OrphanCheckErr::NonLocalInputType(tys) => {
@@ -482,7 +481,7 @@ fn emit_orphan_check_error<'tcx>(
 
 fn lint_uncovered_ty_params<'tcx>(
     tcx: TyCtxt<'tcx>,
-    UncoveredTyParams { uncovered, local_ty }: UncoveredTyParams<'tcx, FxIndexSet<DefId>>,
+    UncoveredTyParams { uncovered, local_ty }: UncoveredTyParams<TyCtxt<'tcx>, FxIndexSet<DefId>>,
     impl_def_id: LocalDefId,
 ) {
     let hir_id = tcx.local_def_id_to_hir_id(impl_def_id);
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 41fbef48940..843e4d41e00 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -1201,6 +1201,7 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
 
     let is_marker = tcx.has_attr(def_id, sym::marker);
     let rustc_coinductive = tcx.has_attr(def_id, sym::rustc_coinductive);
+    let is_fundamental = tcx.has_attr(def_id, sym::fundamental);
 
     // FIXME: We could probably do way better attribute validation here.
     let mut skip_array_during_method_dispatch = false;
@@ -1352,6 +1353,7 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
         has_auto_impl: is_auto,
         is_marker,
         is_coinductive: rustc_coinductive || is_auto,
+        is_fundamental,
         skip_array_during_method_dispatch,
         skip_boxed_slice_during_method_dispatch,
         specialization_kind,
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 2a68d3915bb..02db0352daa 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -49,6 +49,7 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{sym, Span, DUMMY_SP};
 use rustc_target::spec::abi;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::wf::object_region_bounds;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 44f1830a3b1..2f6b0a582e5 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -71,6 +71,7 @@ This API is completely unstable and subject to change.
 #![feature(rustdoc_internals)]
 #![feature(slice_partition_dedup)]
 #![feature(try_blocks)]
+#![feature(unwrap_infallible)]
 // tidy-alphabetical-end
 
 #[macro_use]
diff --git a/compiler/rustc_hir_typeck/messages.ftl b/compiler/rustc_hir_typeck/messages.ftl
index 3c5070bd006..239b0c44690 100644
--- a/compiler/rustc_hir_typeck/messages.ftl
+++ b/compiler/rustc_hir_typeck/messages.ftl
@@ -138,6 +138,11 @@ hir_typeck_option_result_asref = use `{$def_path}::as_ref` to convert `{$expecte
 hir_typeck_option_result_cloned = use `{$def_path}::cloned` to clone the value inside the `{$def_path}`
 hir_typeck_option_result_copied = use `{$def_path}::copied` to copy the value inside the `{$def_path}`
 
+hir_typeck_ptr_cast_add_auto_to_object = adding {$traits_len ->
+    [1] an auto trait {$traits}
+    *[other] auto traits {$traits}
+} to a trait object in a pointer cast may cause UB later on
+
 hir_typeck_remove_semi_for_coerce = you might have meant to return the `match` expression
 hir_typeck_remove_semi_for_coerce_expr = this could be implicitly returned but it is a statement, not a tail expression
 hir_typeck_remove_semi_for_coerce_ret = the `match` arms can conform to this return type
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index 53e44d6bcae..341d533492d 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -32,9 +32,9 @@ use super::FnCtxt;
 
 use crate::errors;
 use crate::type_error_struct;
-use hir::ExprKind;
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{codes::*, Applicability, Diag, ErrorGuaranteed};
-use rustc_hir as hir;
+use rustc_hir::{self as hir, ExprKind};
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::bug;
 use rustc_middle::mir::Mutability;
@@ -44,7 +44,7 @@ use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::{self, Ty, TypeAndMut, TypeVisitableExt, VariantDef};
 use rustc_session::lint;
-use rustc_span::def_id::{DefId, LOCAL_CRATE};
+use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_span::DUMMY_SP;
@@ -73,7 +73,7 @@ enum PointerKind<'tcx> {
     /// No metadata attached, ie pointer to sized type or foreign type
     Thin,
     /// A trait object
-    VTable(Option<DefId>),
+    VTable(&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>),
     /// Slice
     Length,
     /// The unsize info of this projection or opaque type
@@ -101,7 +101,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         Ok(match *t.kind() {
             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
-            ty::Dynamic(tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())),
+            ty::Dynamic(tty, _, ty::Dyn) => Some(PointerKind::VTable(tty)),
             ty::Adt(def, args) if def.is_struct() => match def.non_enum_variant().tail_opt() {
                 None => Some(PointerKind::Thin),
                 Some(f) => {
@@ -755,7 +755,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                 Err(CastError::IllegalCast)
             }
 
-            // ptr -> *
+            // ptr -> ptr
             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 
             // ptr-addr-cast
@@ -799,40 +799,126 @@ impl<'a, 'tcx> CastCheck<'tcx> {
     fn check_ptr_ptr_cast(
         &self,
         fcx: &FnCtxt<'a, 'tcx>,
-        m_expr: ty::TypeAndMut<'tcx>,
-        m_cast: ty::TypeAndMut<'tcx>,
+        m_src: ty::TypeAndMut<'tcx>,
+        m_dst: ty::TypeAndMut<'tcx>,
     ) -> Result<CastKind, CastError> {
-        debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
+        debug!("check_ptr_ptr_cast m_src={m_src:?} m_dst={m_dst:?}");
         // ptr-ptr cast. vtables must match.
 
-        let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
-        let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
+        let src_kind = fcx.tcx.erase_regions(fcx.pointer_kind(m_src.ty, self.span)?);
+        let dst_kind = fcx.tcx.erase_regions(fcx.pointer_kind(m_dst.ty, self.span)?);
 
-        let Some(cast_kind) = cast_kind else {
+        match (src_kind, dst_kind) {
             // We can't cast if target pointer kind is unknown
-            return Err(CastError::UnknownCastPtrKind);
-        };
+            (_, None) => Err(CastError::UnknownCastPtrKind),
+            // Cast to thin pointer is OK
+            (_, Some(PointerKind::Thin)) => Ok(CastKind::PtrPtrCast),
 
-        // Cast to thin pointer is OK
-        if cast_kind == PointerKind::Thin {
-            return Ok(CastKind::PtrPtrCast);
-        }
-
-        let Some(expr_kind) = expr_kind else {
             // We can't cast to fat pointer if source pointer kind is unknown
-            return Err(CastError::UnknownExprPtrKind);
-        };
+            (None, _) => Err(CastError::UnknownExprPtrKind),
+
+            // thin -> fat? report invalid cast (don't complain about vtable kinds)
+            (Some(PointerKind::Thin), _) => Err(CastError::SizedUnsizedCast),
+
+            // trait object -> trait object? need to do additional checks
+            (Some(PointerKind::VTable(src_tty)), Some(PointerKind::VTable(dst_tty))) => {
+                match (src_tty.principal(), dst_tty.principal()) {
+                    // A<dyn Src<...> + SrcAuto> -> B<dyn Dst<...> + DstAuto>. need to make sure
+                    // - `Src` and `Dst` traits are the same
+                    // - traits have the same generic arguments
+                    // - `SrcAuto` is a superset of `DstAuto`
+                    (Some(src_principal), Some(dst_principal)) => {
+                        let tcx = fcx.tcx;
+
+                        // Check that the traits are actually the same.
+                        // The `dyn Src = dyn Dst` check below would suffice,
+                        // but this may produce a better diagnostic.
+                        //
+                        // Note that trait upcasting goes through a different mechanism (`coerce_unsized`)
+                        // and is unaffected by this check.
+                        if src_principal.def_id() != dst_principal.def_id() {
+                            return Err(CastError::DifferingKinds);
+                        }
 
-        // thin -> fat? report invalid cast (don't complain about vtable kinds)
-        if expr_kind == PointerKind::Thin {
-            return Err(CastError::SizedUnsizedCast);
-        }
+                        // We need to reconstruct trait object types.
+                        // `m_src` and `m_dst` won't work for us here because they will potentially
+                        // contain wrappers, which we do not care about.
+                        //
+                        // e.g. we want to allow `dyn T -> (dyn T,)`, etc.
+                        //
+                        // We also need to skip auto traits to emit an FCW and not an error.
+                        let src_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                            tcx.mk_poly_existential_predicates(
+                                &src_tty.without_auto_traits().collect::<Vec<_>>(),
+                            ),
+                            tcx.lifetimes.re_erased,
+                            ty::Dyn,
+                        ));
+                        let dst_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                            tcx.mk_poly_existential_predicates(
+                                &dst_tty.without_auto_traits().collect::<Vec<_>>(),
+                            ),
+                            tcx.lifetimes.re_erased,
+                            ty::Dyn,
+                        ));
 
-        // vtable kinds must match
-        if fcx.tcx.erase_regions(cast_kind) == fcx.tcx.erase_regions(expr_kind) {
-            Ok(CastKind::PtrPtrCast)
-        } else {
-            Err(CastError::DifferingKinds)
+                        // `dyn Src = dyn Dst`, this checks for matching traits/generics
+                        fcx.demand_eqtype(self.span, src_obj, dst_obj);
+
+                        // Check that `SrcAuto` (+auto traits implied by `Src`) is a superset of `DstAuto`.
+                        // Emit an FCW otherwise.
+                        let src_auto: FxHashSet<_> = src_tty
+                            .auto_traits()
+                            .chain(
+                                tcx.supertrait_def_ids(src_principal.def_id())
+                                    .filter(|def_id| tcx.trait_is_auto(*def_id)),
+                            )
+                            .collect();
+
+                        let added = dst_tty
+                            .auto_traits()
+                            .filter(|trait_did| !src_auto.contains(trait_did))
+                            .collect::<Vec<_>>();
+
+                        if !added.is_empty() {
+                            tcx.emit_node_span_lint(
+                                lint::builtin::PTR_CAST_ADD_AUTO_TO_OBJECT,
+                                self.expr.hir_id,
+                                self.span,
+                                errors::PtrCastAddAutoToObject {
+                                    traits_len: added.len(),
+                                    traits: {
+                                        let mut traits: Vec<_> = added
+                                            .into_iter()
+                                            .map(|trait_did| tcx.def_path_str(trait_did))
+                                            .collect();
+
+                                        traits.sort();
+                                        traits.into()
+                                    },
+                                },
+                            )
+                        }
+
+                        Ok(CastKind::PtrPtrCast)
+                    }
+
+                    // dyn Auto -> dyn Auto'? ok.
+                    (None, None) => Ok(CastKind::PtrPtrCast),
+
+                    // dyn Trait -> dyn Auto? should be ok, but we used to not allow it.
+                    // FIXME: allow this
+                    (Some(_), None) => Err(CastError::DifferingKinds),
+
+                    // dyn Auto -> dyn Trait? not ok.
+                    (None, Some(_)) => Err(CastError::DifferingKinds),
+                }
+            }
+
+            // fat -> fat? metadata kinds must match
+            (Some(src_kind), Some(dst_kind)) if src_kind == dst_kind => Ok(CastKind::PtrPtrCast),
+
+            (_, _) => Err(CastError::DifferingKinds),
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index ac7ed3e26f9..53cf121dfeb 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -424,9 +424,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if let Some(trait_def_id) = trait_def_id {
                 let found_kind = match closure_kind {
                     hir::ClosureKind::Closure => self.tcx.fn_trait_kind_from_def_id(trait_def_id),
-                    hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) => {
-                        self.tcx.async_fn_trait_kind_from_def_id(trait_def_id)
-                    }
+                    hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) => self
+                        .tcx
+                        .async_fn_trait_kind_from_def_id(trait_def_id)
+                        .or_else(|| self.tcx.fn_trait_kind_from_def_id(trait_def_id)),
                     _ => None,
                 };
 
@@ -470,14 +471,37 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // for closures and async closures, respectively.
         match closure_kind {
             hir::ClosureKind::Closure
-                if self.tcx.fn_trait_kind_from_def_id(trait_def_id).is_some() => {}
+                if self.tcx.fn_trait_kind_from_def_id(trait_def_id).is_some() =>
+            {
+                self.extract_sig_from_projection(cause_span, projection)
+            }
+            hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async)
+                if self.tcx.async_fn_trait_kind_from_def_id(trait_def_id).is_some() =>
+            {
+                self.extract_sig_from_projection(cause_span, projection)
+            }
+            // It's possible we've passed the closure to a (somewhat out-of-fashion)
+            // `F: FnOnce() -> Fut, Fut: Future<Output = T>` style bound. Let's still
+            // guide inference here, since it's beneficial for the user.
             hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async)
-                if self.tcx.async_fn_trait_kind_from_def_id(trait_def_id).is_some() => {}
-            _ => return None,
+                if self.tcx.fn_trait_kind_from_def_id(trait_def_id).is_some() =>
+            {
+                self.extract_sig_from_projection_and_future_bound(cause_span, projection)
+            }
+            _ => None,
         }
+    }
+
+    /// Given an `FnOnce::Output` or `AsyncFn::Output` projection, extract the args
+    /// and return type to infer a [`ty::PolyFnSig`] for the closure.
+    fn extract_sig_from_projection(
+        &self,
+        cause_span: Option<Span>,
+        projection: ty::PolyProjectionPredicate<'tcx>,
+    ) -> Option<ExpectedSig<'tcx>> {
+        let projection = self.resolve_vars_if_possible(projection);
 
         let arg_param_ty = projection.skip_binder().projection_term.args.type_at(1);
-        let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty);
         debug!(?arg_param_ty);
 
         let ty::Tuple(input_tys) = *arg_param_ty.kind() else {
@@ -486,7 +510,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Since this is a return parameter type it is safe to unwrap.
         let ret_param_ty = projection.skip_binder().term.expect_type();
-        let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty);
         debug!(?ret_param_ty);
 
         let sig = projection.rebind(self.tcx.mk_fn_sig(
@@ -500,6 +523,69 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         Some(ExpectedSig { cause_span, sig })
     }
 
+    /// When an async closure is passed to a function that has a "two-part" `Fn`
+    /// and `Future` trait bound, like:
+    ///
+    /// ```rust
+    /// use std::future::Future;
+    ///
+    /// fn not_exactly_an_async_closure<F, Fut>(_f: F)
+    /// where
+    ///     F: FnOnce(String, u32) -> Fut,
+    ///     Fut: Future<Output = i32>,
+    /// {}
+    /// ```
+    ///
+    /// The we want to be able to extract the signature to guide inference in the async
+    /// closure. We will have two projection predicates registered in this case. First,
+    /// we identify the `FnOnce<Args, Output = ?Fut>` bound, and if the output type is
+    /// an inference variable `?Fut`, we check if that is bounded by a `Future<Output = Ty>`
+    /// projection.
+    fn extract_sig_from_projection_and_future_bound(
+        &self,
+        cause_span: Option<Span>,
+        projection: ty::PolyProjectionPredicate<'tcx>,
+    ) -> Option<ExpectedSig<'tcx>> {
+        let projection = self.resolve_vars_if_possible(projection);
+
+        let arg_param_ty = projection.skip_binder().projection_term.args.type_at(1);
+        debug!(?arg_param_ty);
+
+        let ty::Tuple(input_tys) = *arg_param_ty.kind() else {
+            return None;
+        };
+
+        // If the return type is a type variable, look for bounds on it.
+        // We could theoretically support other kinds of return types here,
+        // but none of them would be useful, since async closures return
+        // concrete anonymous future types, and their futures are not coerced
+        // into any other type within the body of the async closure.
+        let ty::Infer(ty::TyVar(return_vid)) = *projection.skip_binder().term.expect_type().kind()
+        else {
+            return None;
+        };
+
+        // FIXME: We may want to elaborate here, though I assume this will be exceedingly rare.
+        for bound in self.obligations_for_self_ty(return_vid) {
+            if let Some(ret_projection) = bound.predicate.as_projection_clause()
+                && let Some(ret_projection) = ret_projection.no_bound_vars()
+                && self.tcx.is_lang_item(ret_projection.def_id(), LangItem::FutureOutput)
+            {
+                let sig = projection.rebind(self.tcx.mk_fn_sig(
+                    input_tys,
+                    ret_projection.term.expect_type(),
+                    false,
+                    hir::Safety::Safe,
+                    Abi::Rust,
+                ));
+
+                return Some(ExpectedSig { cause_span, sig });
+            }
+        }
+
+        None
+    }
+
     fn sig_of_closure(
         &self,
         expr_def_id: LocalDefId,
diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs
index f72e8a4afde..4f0a089ee95 100644
--- a/compiler/rustc_hir_typeck/src/coercion.rs
+++ b/compiler/rustc_hir_typeck/src/coercion.rs
@@ -1752,10 +1752,8 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
             fcx.probe(|_| {
                 let ocx = ObligationCtxt::new(fcx);
                 ocx.register_obligations(
-                    fcx.tcx
-                        .item_super_predicates(rpit_def_id)
-                        .instantiate_identity_iter()
-                        .filter_map(|clause| {
+                    fcx.tcx.item_super_predicates(rpit_def_id).iter_identity().filter_map(
+                        |clause| {
                             let predicate = clause
                                 .kind()
                                 .map_bound(|clause| match clause {
@@ -1776,7 +1774,8 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                                 fcx.param_env,
                                 predicate,
                             ))
-                        }),
+                        },
+                    ),
                 );
                 ocx.select_where_possible().is_empty()
             })
diff --git a/compiler/rustc_hir_typeck/src/demand.rs b/compiler/rustc_hir_typeck/src/demand.rs
index ad9c1e28211..4f1c2fdd922 100644
--- a/compiler/rustc_hir_typeck/src/demand.rs
+++ b/compiler/rustc_hir_typeck/src/demand.rs
@@ -13,6 +13,7 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, AssocItem, Ty, TypeFoldable, TypeVisitableExt};
 use rustc_span::symbol::sym;
 use rustc_span::{Span, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::ObligationCause;
 
 use super::method::probe;
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index f1ed2ade3d4..8b5b0a9b92f 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -4,8 +4,8 @@ use std::borrow::Cow;
 
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    codes::*, Applicability, Diag, DiagArgValue, EmissionGuarantee, IntoDiagArg, MultiSpan,
-    SubdiagMessageOp, Subdiagnostic,
+    codes::*, Applicability, Diag, DiagArgValue, DiagSymbolList, EmissionGuarantee, IntoDiagArg,
+    MultiSpan, SubdiagMessageOp, Subdiagnostic,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{self, Ty};
@@ -253,6 +253,13 @@ pub struct LossyProvenanceInt2Ptr<'tcx> {
     pub sugg: LossyProvenanceInt2PtrSuggestion,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(hir_typeck_ptr_cast_add_auto_to_object)]
+pub struct PtrCastAddAutoToObject {
+    pub traits_len: usize,
+    pub traits: DiagSymbolList<String>,
+}
+
 #[derive(Subdiagnostic)]
 #[multipart_suggestion(hir_typeck_suggestion, applicability = "has-placeholders")]
 pub struct LossyProvenanceInt2PtrSuggestion {
diff --git a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
index c8ab0429ffc..193dbbbcdf4 100644
--- a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
+++ b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
@@ -734,7 +734,9 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 // struct; however, when EUV is run during typeck, it
                 // may not. This will generate an error earlier in typeck,
                 // so we can just ignore it.
-                span_bug!(with_expr.span, "with expression doesn't evaluate to a struct");
+                if self.cx.tainted_by_errors().is_ok() {
+                    span_bug!(with_expr.span, "with expression doesn't evaluate to a struct");
+                }
             }
         }
 
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 047d0850d4c..10092dce587 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -40,6 +40,7 @@ use rustc_middle::{bug, span_bug};
 use rustc_session::Session;
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::{sym, BytePos, Span, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{self, ObligationCauseCode, SelectionContext};
 
 use std::iter;
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 8d380caf916..fca0a3e195d 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -2582,7 +2582,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             (hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr), _, &ty::Ref(_, checked, _))
-                if self.can_sub(self.param_env, checked, expected) =>
+                if self.can_eq(self.param_env, checked, expected) =>
             {
                 let make_sugg = |start: Span, end: BytePos| {
                     // skip `(` for tuples such as `(c) = (&123)`.
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 63b30d79aba..6a7af5510e0 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -33,6 +33,7 @@ use rustc_span::edit_distance::{
 };
 use rustc_span::symbol::sym;
 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt as _;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
 use rustc_trait_selection::traits::query::method_autoderef::{
@@ -857,7 +858,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 let args = self.fresh_args_for_item(self.span, method.def_id);
                 let fty = self.tcx.fn_sig(method.def_id).instantiate(self.tcx, args);
                 let fty = self.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, fty);
-                self.can_sub(self.param_env, fty.output(), expected)
+                self.can_eq(self.param_env, fty.output(), expected)
             }),
             _ => false,
         }
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index 5e0f37ed792..be526e1c26c 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -19,6 +19,7 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span, DUMMY_SP};
 use rustc_target::abi::FieldIdx;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
 use ty::VariantDef;
 
diff --git a/compiler/rustc_infer/src/infer/context.rs b/compiler/rustc_infer/src/infer/context.rs
index 209996b12e2..f35a8162d96 100644
--- a/compiler/rustc_infer/src/infer/context.rs
+++ b/compiler/rustc_infer/src/infer/context.rs
@@ -151,6 +151,10 @@ impl<'tcx> InferCtxtLike for InferCtxt<'tcx> {
             .eq_structurally_relating_aliases_no_trace(lhs, rhs)
     }
 
+    fn shallow_resolve(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        self.shallow_resolve(ty)
+    }
+
     fn resolve_vars_if_possible<T>(&self, value: T) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
index fd50d1eb438..d5e7de897d0 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
@@ -820,7 +820,7 @@ fn foo(&self) -> Self::T { String::new() }
                                 tcx.defaultness(item.id.owner_id)
                             {
                                 let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
-                                if self.infcx.can_eq(param_env, assoc_ty, found) {
+                                if self.infcx.can_eq_shallow(param_env, assoc_ty, found) {
                                     diag.span_label(
                                         item.span,
                                         "associated type defaults can't be assumed inside the \
@@ -843,7 +843,7 @@ fn foo(&self) -> Self::T { String::new() }
                         let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
                         if let hir::Defaultness::Default { has_value: true } =
                             tcx.defaultness(item.id.owner_id)
-                            && self.infcx.can_eq(param_env, assoc_ty, found)
+                            && self.infcx.can_eq_shallow(param_env, assoc_ty, found)
                         {
                             diag.span_label(
                                 item.span,
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index edbb741036f..9f55939c165 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -768,19 +768,9 @@ impl<'tcx> InferCtxt<'tcx> {
             .collect()
     }
 
-    pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, expected: T, actual: T) -> bool
-    where
-        T: at::ToTrace<'tcx>,
-    {
-        let origin = &ObligationCause::dummy();
-        self.probe(|_| {
-            // We're only answering whether there could be a subtyping relation, and with
-            // opaque types, "there could be one", via registering a hidden type.
-            self.at(origin, param_env).sub(DefineOpaqueTypes::Yes, expected, actual).is_ok()
-        })
-    }
-
-    pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
+    // FIXME(-Znext-solver): Get rid of this method, it's never correct. Either that,
+    // or we need to process the obligations.
+    pub fn can_eq_shallow<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
     where
         T: at::ToTrace<'tcx>,
     {
diff --git a/compiler/rustc_infer/src/traits/util.rs b/compiler/rustc_infer/src/traits/util.rs
index b269bfcbfeb..f54d0418595 100644
--- a/compiler/rustc_infer/src/traits/util.rs
+++ b/compiler/rustc_infer/src/traits/util.rs
@@ -1,12 +1,10 @@
-use smallvec::smallvec;
-
 use crate::traits::{self, Obligation, ObligationCauseCode, PredicateObligation};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::ty::ToPolyTraitRef;
-use rustc_middle::ty::{self, Ty, TyCtxt, Upcast};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::Ident;
 use rustc_span::Span;
-use rustc_type_ir::outlives::{push_outlives_components, Component};
+pub use rustc_type_ir::elaborate::*;
 
 pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -64,50 +62,9 @@ impl<'tcx> Extend<ty::Predicate<'tcx>> for PredicateSet<'tcx> {
     }
 }
 
-///////////////////////////////////////////////////////////////////////////
-// `Elaboration` iterator
-///////////////////////////////////////////////////////////////////////////
-
-/// "Elaboration" is the process of identifying all the predicates that
-/// are implied by a source predicate. Currently, this basically means
-/// walking the "supertraits" and other similar assumptions. For example,
-/// if we know that `T: Ord`, the elaborator would deduce that `T: PartialOrd`
-/// holds as well. Similarly, if we have `trait Foo: 'static`, and we know that
-/// `T: Foo`, then we know that `T: 'static`.
-pub struct Elaborator<'tcx, O> {
-    stack: Vec<O>,
-    visited: PredicateSet<'tcx>,
-    mode: Filter,
-}
-
-enum Filter {
-    All,
-    OnlySelf,
-}
-
-/// Describes how to elaborate an obligation into a sub-obligation.
-///
 /// For [`Obligation`], a sub-obligation is combined with the current obligation's
-/// param-env and cause code. For [`ty::Predicate`], none of this is needed, since
-/// there is no param-env or cause code to copy over.
-pub trait Elaboratable<'tcx> {
-    fn predicate(&self) -> ty::Predicate<'tcx>;
-
-    // Makes a new `Self` but with a different clause that comes from elaboration.
-    fn child(&self, clause: ty::Clause<'tcx>) -> Self;
-
-    // Makes a new `Self` but with a different clause and a different cause
-    // code (if `Self` has one, such as [`PredicateObligation`]).
-    fn child_with_derived_cause(
-        &self,
-        clause: ty::Clause<'tcx>,
-        span: Span,
-        parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
-        index: usize,
-    ) -> Self;
-}
-
-impl<'tcx> Elaboratable<'tcx> for PredicateObligation<'tcx> {
+/// param-env and cause code.
+impl<'tcx> Elaboratable<TyCtxt<'tcx>> for PredicateObligation<'tcx> {
     fn predicate(&self) -> ty::Predicate<'tcx> {
         self.predicate
     }
@@ -145,270 +102,6 @@ impl<'tcx> Elaboratable<'tcx> for PredicateObligation<'tcx> {
     }
 }
 
-impl<'tcx> Elaboratable<'tcx> for ty::Predicate<'tcx> {
-    fn predicate(&self) -> ty::Predicate<'tcx> {
-        *self
-    }
-
-    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
-        clause.as_predicate()
-    }
-
-    fn child_with_derived_cause(
-        &self,
-        clause: ty::Clause<'tcx>,
-        _span: Span,
-        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
-        _index: usize,
-    ) -> Self {
-        clause.as_predicate()
-    }
-}
-
-impl<'tcx> Elaboratable<'tcx> for (ty::Predicate<'tcx>, Span) {
-    fn predicate(&self) -> ty::Predicate<'tcx> {
-        self.0
-    }
-
-    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
-        (clause.as_predicate(), self.1)
-    }
-
-    fn child_with_derived_cause(
-        &self,
-        clause: ty::Clause<'tcx>,
-        _span: Span,
-        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
-        _index: usize,
-    ) -> Self {
-        (clause.as_predicate(), self.1)
-    }
-}
-
-impl<'tcx> Elaboratable<'tcx> for (ty::Clause<'tcx>, Span) {
-    fn predicate(&self) -> ty::Predicate<'tcx> {
-        self.0.as_predicate()
-    }
-
-    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
-        (clause, self.1)
-    }
-
-    fn child_with_derived_cause(
-        &self,
-        clause: ty::Clause<'tcx>,
-        _span: Span,
-        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
-        _index: usize,
-    ) -> Self {
-        (clause, self.1)
-    }
-}
-
-impl<'tcx> Elaboratable<'tcx> for ty::Clause<'tcx> {
-    fn predicate(&self) -> ty::Predicate<'tcx> {
-        self.as_predicate()
-    }
-
-    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
-        clause
-    }
-
-    fn child_with_derived_cause(
-        &self,
-        clause: ty::Clause<'tcx>,
-        _span: Span,
-        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
-        _index: usize,
-    ) -> Self {
-        clause
-    }
-}
-
-pub fn elaborate<'tcx, O: Elaboratable<'tcx>>(
-    tcx: TyCtxt<'tcx>,
-    obligations: impl IntoIterator<Item = O>,
-) -> Elaborator<'tcx, O> {
-    let mut elaborator =
-        Elaborator { stack: Vec::new(), visited: PredicateSet::new(tcx), mode: Filter::All };
-    elaborator.extend_deduped(obligations);
-    elaborator
-}
-
-impl<'tcx, O: Elaboratable<'tcx>> Elaborator<'tcx, O> {
-    fn extend_deduped(&mut self, obligations: impl IntoIterator<Item = O>) {
-        // Only keep those bounds that we haven't already seen.
-        // This is necessary to prevent infinite recursion in some
-        // cases. One common case is when people define
-        // `trait Sized: Sized { }` rather than `trait Sized { }`.
-        // let visited = &mut self.visited;
-        self.stack.extend(obligations.into_iter().filter(|o| self.visited.insert(o.predicate())));
-    }
-
-    /// Filter to only the supertraits of trait predicates, i.e. only the predicates
-    /// that have `Self` as their self type, instead of all implied predicates.
-    pub fn filter_only_self(mut self) -> Self {
-        self.mode = Filter::OnlySelf;
-        self
-    }
-
-    fn elaborate(&mut self, elaboratable: &O) {
-        let tcx = self.visited.tcx;
-
-        // We only elaborate clauses.
-        let Some(clause) = elaboratable.predicate().as_clause() else {
-            return;
-        };
-
-        let bound_clause = clause.kind();
-        match bound_clause.skip_binder() {
-            ty::ClauseKind::Trait(data) => {
-                // Negative trait bounds do not imply any supertrait bounds
-                if data.polarity != ty::PredicatePolarity::Positive {
-                    return;
-                }
-                // Get predicates implied by the trait, or only super predicates if we only care about self predicates.
-                let predicates = match self.mode {
-                    Filter::All => tcx.explicit_implied_predicates_of(data.def_id()),
-                    Filter::OnlySelf => tcx.explicit_super_predicates_of(data.def_id()),
-                };
-
-                let obligations =
-                    predicates.predicates.iter().enumerate().map(|(index, &(clause, span))| {
-                        elaboratable.child_with_derived_cause(
-                            clause.instantiate_supertrait(tcx, bound_clause.rebind(data.trait_ref)),
-                            span,
-                            bound_clause.rebind(data),
-                            index,
-                        )
-                    });
-                debug!(?data, ?obligations, "super_predicates");
-                self.extend_deduped(obligations);
-            }
-            ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty_max, r_min)) => {
-                // We know that `T: 'a` for some type `T`. We can
-                // often elaborate this. For example, if we know that
-                // `[U]: 'a`, that implies that `U: 'a`. Similarly, if
-                // we know `&'a U: 'b`, then we know that `'a: 'b` and
-                // `U: 'b`.
-                //
-                // We can basically ignore bound regions here. So for
-                // example `for<'c> Foo<'a,'c>: 'b` can be elaborated to
-                // `'a: 'b`.
-
-                // Ignore `for<'a> T: 'a` -- we might in the future
-                // consider this as evidence that `T: 'static`, but
-                // I'm a bit wary of such constructions and so for now
-                // I want to be conservative. --nmatsakis
-                if r_min.is_bound() {
-                    return;
-                }
-
-                let mut components = smallvec![];
-                push_outlives_components(tcx, ty_max, &mut components);
-                self.extend_deduped(
-                    components
-                        .into_iter()
-                        .filter_map(|component| match component {
-                            Component::Region(r) => {
-                                if r.is_bound() {
-                                    None
-                                } else {
-                                    Some(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
-                                        r, r_min,
-                                    )))
-                                }
-                            }
-
-                            Component::Param(p) => {
-                                let ty = Ty::new_param(tcx, p.index, p.name);
-                                Some(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty, r_min)))
-                            }
-
-                            Component::Placeholder(p) => {
-                                let ty = Ty::new_placeholder(tcx, p);
-                                Some(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty, r_min)))
-                            }
-
-                            Component::UnresolvedInferenceVariable(_) => None,
-
-                            Component::Alias(alias_ty) => {
-                                // We might end up here if we have `Foo<<Bar as Baz>::Assoc>: 'a`.
-                                // With this, we can deduce that `<Bar as Baz>::Assoc: 'a`.
-                                Some(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
-                                    alias_ty.to_ty(tcx),
-                                    r_min,
-                                )))
-                            }
-
-                            Component::EscapingAlias(_) => {
-                                // We might be able to do more here, but we don't
-                                // want to deal with escaping vars right now.
-                                None
-                            }
-                        })
-                        .map(|clause| elaboratable.child(bound_clause.rebind(clause).upcast(tcx))),
-                );
-            }
-            ty::ClauseKind::RegionOutlives(..) => {
-                // Nothing to elaborate from `'a: 'b`.
-            }
-            ty::ClauseKind::WellFormed(..) => {
-                // Currently, we do not elaborate WF predicates,
-                // although we easily could.
-            }
-            ty::ClauseKind::Projection(..) => {
-                // Nothing to elaborate in a projection predicate.
-            }
-            ty::ClauseKind::ConstEvaluatable(..) => {
-                // Currently, we do not elaborate const-evaluatable
-                // predicates.
-            }
-            ty::ClauseKind::ConstArgHasType(..) => {
-                // Nothing to elaborate
-            }
-        }
-    }
-}
-
-impl<'tcx, O: Elaboratable<'tcx>> Iterator for Elaborator<'tcx, O> {
-    type Item = O;
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        (self.stack.len(), None)
-    }
-
-    fn next(&mut self) -> Option<Self::Item> {
-        // Extract next item from top-most stack frame, if any.
-        if let Some(obligation) = self.stack.pop() {
-            self.elaborate(&obligation);
-            Some(obligation)
-        } else {
-            None
-        }
-    }
-}
-
-///////////////////////////////////////////////////////////////////////////
-// Supertrait iterator
-///////////////////////////////////////////////////////////////////////////
-
-pub fn supertraits<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
-) -> FilterToTraits<Elaborator<'tcx, ty::Clause<'tcx>>> {
-    elaborate(tcx, [trait_ref.upcast(tcx)]).filter_only_self().filter_to_traits()
-}
-
-pub fn transitive_bounds<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
-) -> FilterToTraits<Elaborator<'tcx, ty::Clause<'tcx>>> {
-    elaborate(tcx, trait_refs.map(|trait_ref| trait_ref.upcast(tcx)))
-        .filter_only_self()
-        .filter_to_traits()
-}
-
 /// A specialized variant of `elaborate` that only elaborates trait references that may
 /// define the given associated item with the name `assoc_name`. It uses the
 /// `explicit_supertraits_containing_assoc_item` query to avoid enumerating super-predicates that
@@ -443,37 +136,3 @@ pub fn transitive_bounds_that_define_assoc_item<'tcx>(
         None
     })
 }
-
-///////////////////////////////////////////////////////////////////////////
-// Other
-///////////////////////////////////////////////////////////////////////////
-
-impl<'tcx> Elaborator<'tcx, ty::Clause<'tcx>> {
-    fn filter_to_traits(self) -> FilterToTraits<Self> {
-        FilterToTraits { base_iterator: self }
-    }
-}
-
-/// A filter around an iterator of predicates that makes it yield up
-/// just trait references.
-pub struct FilterToTraits<I> {
-    base_iterator: I,
-}
-
-impl<'tcx, I: Iterator<Item = ty::Clause<'tcx>>> Iterator for FilterToTraits<I> {
-    type Item = ty::PolyTraitRef<'tcx>;
-
-    fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
-        while let Some(pred) = self.base_iterator.next() {
-            if let Some(data) = pred.as_trait_clause() {
-                return Some(data.map_bound(|t| t.trait_ref));
-            }
-        }
-        None
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        let (_, upper) = self.base_iterator.size_hint();
-        (0, upper)
-    }
-}
diff --git a/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs b/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
index 8b669bcc13f..5ee73dbfdc6 100644
--- a/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
+++ b/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
@@ -76,9 +76,7 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
         // For every projection predicate in the opaque type's explicit bounds,
         // check that the type that we're assigning actually satisfies the bounds
         // of the associated type.
-        for (pred, pred_span) in
-            cx.tcx.explicit_item_bounds(def_id).instantiate_identity_iter_copied()
-        {
+        for (pred, pred_span) in cx.tcx.explicit_item_bounds(def_id).iter_identity_copied() {
             infcx.enter_forall(pred.kind(), |predicate| {
                 let ty::ClauseKind::Projection(proj) = predicate else {
                     return;
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 195a0f72475..65d42ed8054 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -298,9 +298,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                 ty::Alias(ty::Opaque | ty::Projection, ty::AliasTy { def_id: def, .. }) => {
                     elaborate(
                         cx.tcx,
-                        cx.tcx
-                            .explicit_item_super_predicates(def)
-                            .instantiate_identity_iter_copied(),
+                        cx.tcx.explicit_item_super_predicates(def).iter_identity_copied(),
                     )
                     // We only care about self bounds for the impl-trait
                     .filter_only_self()
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 2ade6964ca8..bc93248252d 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -80,6 +80,7 @@ declare_lint_pass! {
         PRIVATE_BOUNDS,
         PRIVATE_INTERFACES,
         PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
+        PTR_CAST_ADD_AUTO_TO_OBJECT,
         PUB_USE_OF_PRIVATE_EXTERN_CRATE,
         REDUNDANT_LIFETIMES,
         REFINING_IMPL_TRAIT_INTERNAL,
@@ -4189,6 +4190,7 @@ declare_lint! {
         reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
         reference: "issue #123748 <https://github.com/rust-lang/rust/issues/123748>",
     };
+    @edition Edition2024 => Deny;
     report_in_external_macro
 }
 
@@ -4938,6 +4940,58 @@ declare_lint! {
 }
 
 declare_lint! {
+    /// The `ptr_cast_add_auto_to_object` lint detects casts of raw pointers to trait
+    /// objects, which add auto traits.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,edition2021,compile_fail
+    /// let ptr: *const dyn core::any::Any = &();
+    /// _ = ptr as *const dyn core::any::Any + Send;
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Adding an auto trait can make the vtable invalid, potentially causing
+    /// UB in safe code afterwards. For example:
+    ///
+    /// ```ignore (causes a warning)
+    /// #![feature(arbitrary_self_types)]
+    ///
+    /// trait Trait {
+    ///     fn f(self: *const Self)
+    ///     where
+    ///         Self: Send;
+    /// }
+    ///
+    /// impl Trait for *const () {
+    ///     fn f(self: *const Self) {
+    ///         unreachable!()
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     let unsend: *const () = &();
+    ///     let unsend: *const dyn Trait = &unsend;
+    ///     let send_bad: *const (dyn Trait + Send) = unsend as _;
+    ///     send_bad.f(); // this crashes, since vtable for `*const ()` does not have an entry for `f`
+    /// }
+    /// ```
+    ///
+    /// Generally you must ensure that vtable is right for the pointer's type,
+    /// before passing the pointer to safe code.
+    pub PTR_CAST_ADD_AUTO_TO_OBJECT,
+    Warn,
+    "detects `as` casts from pointers to `dyn Trait` to pointers to `dyn Trait + Auto`",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
+        reference: "issue #127323 <https://github.com/rust-lang/rust/issues/127323>",
+    };
+}
+
+declare_lint! {
     /// The `out_of_scope_macro_calls` lint detects `macro_rules` called when they are not in scope,
     /// above their definition, which may happen in key-value attributes.
     ///
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 305ba1ef3bb..2f3a6ee601b 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -31,9 +31,18 @@ pub struct Map<'hir> {
 
 /// An iterator that walks up the ancestor tree of a given `HirId`.
 /// Constructed using `tcx.hir().parent_iter(hir_id)`.
-pub struct ParentHirIterator<'hir> {
+struct ParentHirIterator<'hir> {
     current_id: HirId,
     map: Map<'hir>,
+    // Cache the current value of `hir_owner_nodes` to avoid repeatedly calling the same query for
+    // the same owner, which will uselessly record many times the same query dependency.
+    current_owner_nodes: Option<&'hir OwnerNodes<'hir>>,
+}
+
+impl<'hir> ParentHirIterator<'hir> {
+    fn new(map: Map<'hir>, current_id: HirId) -> ParentHirIterator<'hir> {
+        ParentHirIterator { current_id, map, current_owner_nodes: None }
+    }
 }
 
 impl<'hir> Iterator for ParentHirIterator<'hir> {
@@ -44,13 +53,22 @@ impl<'hir> Iterator for ParentHirIterator<'hir> {
             return None;
         }
 
-        // There are nodes that do not have entries, so we need to skip them.
-        let parent_id = self.map.tcx.parent_hir_id(self.current_id);
+        let HirId { owner, local_id } = self.current_id;
 
-        if parent_id == self.current_id {
-            self.current_id = CRATE_HIR_ID;
-            return None;
-        }
+        let parent_id = if local_id == ItemLocalId::ZERO {
+            // We go from an owner to its parent, so clear the cache.
+            self.current_owner_nodes = None;
+            self.map.tcx.hir_owner_parent(owner)
+        } else {
+            let owner_nodes =
+                self.current_owner_nodes.get_or_insert_with(|| self.map.tcx.hir_owner_nodes(owner));
+            let parent_local_id = owner_nodes.nodes[local_id].parent;
+            // HIR indexing should have checked that.
+            debug_assert_ne!(parent_local_id, local_id);
+            HirId { owner, local_id: parent_local_id }
+        };
+
+        debug_assert_ne!(parent_id, self.current_id);
 
         self.current_id = parent_id;
         return Some(parent_id);
@@ -479,7 +497,7 @@ impl<'hir> Map<'hir> {
     /// until the crate root is reached. Prefer this over your own loop using `parent_id`.
     #[inline]
     pub fn parent_id_iter(self, current_id: HirId) -> impl Iterator<Item = HirId> + 'hir {
-        ParentHirIterator { current_id, map: self }
+        ParentHirIterator::new(self, current_id)
     }
 
     /// Returns an iterator for the nodes in the ancestor tree of the `current_id`
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index af19ed95193..82625ae3d47 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -854,6 +854,16 @@ impl<'tcx> TerminatorKind<'tcx> {
                 }
                 write!(fmt, ")")
             }
+            TailCall { func, args, .. } => {
+                write!(fmt, "tailcall {func:?}(")?;
+                for (index, arg) in args.iter().enumerate() {
+                    if index > 0 {
+                        write!(fmt, ", ")?;
+                    }
+                    write!(fmt, "{:?}", arg)?;
+                }
+                write!(fmt, ")")
+            }
             Assert { cond, expected, msg, .. } => {
                 write!(fmt, "assert(")?;
                 if !expected {
@@ -921,7 +931,12 @@ impl<'tcx> TerminatorKind<'tcx> {
     pub fn fmt_successor_labels(&self) -> Vec<Cow<'static, str>> {
         use self::TerminatorKind::*;
         match *self {
-            Return | UnwindResume | UnwindTerminate(_) | Unreachable | CoroutineDrop => vec![],
+            Return
+            | TailCall { .. }
+            | UnwindResume
+            | UnwindTerminate(_)
+            | Unreachable
+            | CoroutineDrop => vec![],
             Goto { .. } => vec!["".into()],
             SwitchInt { ref targets, .. } => targets
                 .values
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 2c2884f1897..620fa962d79 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -744,6 +744,36 @@ pub enum TerminatorKind<'tcx> {
         fn_span: Span,
     },
 
+    /// Tail call.
+    ///
+    /// Roughly speaking this is a chimera of [`Call`] and [`Return`], with some caveats.
+    /// Semantically tail calls consists of two actions:
+    /// - pop of the current stack frame
+    /// - a call to the `func`, with the return address of the **current** caller
+    ///   - so that a `return` inside `func` returns to the caller of the caller
+    ///     of the function that is currently being executed
+    ///
+    /// Note that in difference with [`Call`] this is missing
+    /// - `destination` (because it's always the return place)
+    /// - `target` (because it's always taken from the current stack frame)
+    /// - `unwind` (because it's always taken from the current stack frame)
+    ///
+    /// [`Call`]: TerminatorKind::Call
+    /// [`Return`]: TerminatorKind::Return
+    TailCall {
+        /// The function that’s being called.
+        func: Operand<'tcx>,
+        /// Arguments the function is called with.
+        /// These are owned by the callee, which is free to modify them.
+        /// This allows the memory occupied by "by-value" arguments to be
+        /// reused across function calls without duplicating the contents.
+        args: Box<[Spanned<Operand<'tcx>>]>,
+        // FIXME(explicit_tail_calls): should we have the span for `become`? is this span accurate? do we need it?
+        /// This `Span` is the span of the function, without the dot and receiver
+        /// (e.g. `foo(a, b)` in `x.foo(a, b)`
+        fn_span: Span,
+    },
+
     /// Evaluates the operand, which must have type `bool`. If it is not equal to `expected`,
     /// initiates a panic. Initiating a panic corresponds to a `Call` terminator with some
     /// unspecified constant as the function to call, all the operands stored in the `AssertMessage`
@@ -870,6 +900,7 @@ impl TerminatorKind<'_> {
             TerminatorKind::Unreachable => "Unreachable",
             TerminatorKind::Drop { .. } => "Drop",
             TerminatorKind::Call { .. } => "Call",
+            TerminatorKind::TailCall { .. } => "TailCall",
             TerminatorKind::Assert { .. } => "Assert",
             TerminatorKind::Yield { .. } => "Yield",
             TerminatorKind::CoroutineDrop => "CoroutineDrop",
diff --git a/compiler/rustc_middle/src/mir/terminator.rs b/compiler/rustc_middle/src/mir/terminator.rs
index ed592612358..5b035d9579d 100644
--- a/compiler/rustc_middle/src/mir/terminator.rs
+++ b/compiler/rustc_middle/src/mir/terminator.rs
@@ -439,6 +439,7 @@ mod helper {
                 | CoroutineDrop
                 | Return
                 | Unreachable
+                | TailCall { .. }
                 | Call { target: None, unwind: _, .. } => (&[]).into_iter().copied().chain(None),
                 InlineAsm { ref targets, unwind: UnwindAction::Cleanup(u), .. } => {
                     targets.iter().copied().chain(Some(u))
@@ -479,6 +480,7 @@ mod helper {
                 | CoroutineDrop
                 | Return
                 | Unreachable
+                | TailCall { .. }
                 | Call { target: None, unwind: _, .. } => (&mut []).into_iter().chain(None),
                 InlineAsm { ref mut targets, unwind: UnwindAction::Cleanup(ref mut u), .. } => {
                     targets.iter_mut().chain(Some(u))
@@ -501,6 +503,7 @@ impl<'tcx> TerminatorKind<'tcx> {
             | TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::CoroutineDrop
             | TerminatorKind::Yield { .. }
@@ -521,6 +524,7 @@ impl<'tcx> TerminatorKind<'tcx> {
             | TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::CoroutineDrop
             | TerminatorKind::Yield { .. }
@@ -606,9 +610,12 @@ impl<'tcx> TerminatorKind<'tcx> {
     pub fn edges(&self) -> TerminatorEdges<'_, 'tcx> {
         use TerminatorKind::*;
         match *self {
-            Return | UnwindResume | UnwindTerminate(_) | CoroutineDrop | Unreachable => {
-                TerminatorEdges::None
-            }
+            Return
+            | TailCall { .. }
+            | UnwindResume
+            | UnwindTerminate(_)
+            | CoroutineDrop
+            | Unreachable => TerminatorEdges::None,
 
             Goto { target } => TerminatorEdges::Single(target),
 
diff --git a/compiler/rustc_middle/src/mir/visit.rs b/compiler/rustc_middle/src/mir/visit.rs
index 7628a1ed2fe..0d3c419748b 100644
--- a/compiler/rustc_middle/src/mir/visit.rs
+++ b/compiler/rustc_middle/src/mir/visit.rs
@@ -540,6 +540,17 @@ macro_rules! make_mir_visitor {
                         );
                     }
 
+                    TerminatorKind::TailCall {
+                        func,
+                        args,
+                        fn_span: _,
+                    } => {
+                        self.visit_operand(func, location);
+                        for arg in args {
+                            self.visit_operand(&$($mutability)? arg.node, location);
+                        }
+                    },
+
                     TerminatorKind::Assert {
                         cond,
                         expected: _,
diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index b4e3fae1b43..b74775142e4 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -7,7 +7,6 @@ pub mod select;
 pub mod solve;
 pub mod specialization_graph;
 mod structural_impls;
-pub mod util;
 
 use crate::mir::ConstraintCategory;
 use crate::ty::abstract_const::NotConstEvaluatable;
diff --git a/compiler/rustc_middle/src/traits/util.rs b/compiler/rustc_middle/src/traits/util.rs
deleted file mode 100644
index 7437be7a74c..00000000000
--- a/compiler/rustc_middle/src/traits/util.rs
+++ /dev/null
@@ -1,62 +0,0 @@
-use rustc_data_structures::fx::FxHashSet;
-
-use crate::ty::{Clause, PolyTraitRef, ToPolyTraitRef, TyCtxt, Upcast};
-
-/// Given a [`PolyTraitRef`], get the [`Clause`]s implied by the trait's definition.
-///
-/// This only exists in `rustc_middle` because the more powerful elaborator depends on
-/// `rustc_infer` for elaborating outlives bounds -- this should only be used for pretty
-/// printing.
-pub fn super_predicates_for_pretty_printing<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: PolyTraitRef<'tcx>,
-) -> impl Iterator<Item = Clause<'tcx>> {
-    let clause = trait_ref.upcast(tcx);
-    Elaborator { tcx, visited: FxHashSet::from_iter([clause]), stack: vec![clause] }
-}
-
-/// Like [`super_predicates_for_pretty_printing`], except it only returns traits and filters out
-/// all other [`Clause`]s.
-pub fn supertraits_for_pretty_printing<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: PolyTraitRef<'tcx>,
-) -> impl Iterator<Item = PolyTraitRef<'tcx>> {
-    super_predicates_for_pretty_printing(tcx, trait_ref).filter_map(|clause| {
-        clause.as_trait_clause().map(|trait_clause| trait_clause.to_poly_trait_ref())
-    })
-}
-
-struct Elaborator<'tcx> {
-    tcx: TyCtxt<'tcx>,
-    visited: FxHashSet<Clause<'tcx>>,
-    stack: Vec<Clause<'tcx>>,
-}
-
-impl<'tcx> Elaborator<'tcx> {
-    fn elaborate(&mut self, trait_ref: PolyTraitRef<'tcx>) {
-        let super_predicates =
-            self.tcx.explicit_super_predicates_of(trait_ref.def_id()).predicates.iter().filter_map(
-                |&(pred, _)| {
-                    let clause = pred.instantiate_supertrait(self.tcx, trait_ref);
-                    self.visited.insert(clause).then_some(clause)
-                },
-            );
-
-        self.stack.extend(super_predicates);
-    }
-}
-
-impl<'tcx> Iterator for Elaborator<'tcx> {
-    type Item = Clause<'tcx>;
-
-    fn next(&mut self) -> Option<Clause<'tcx>> {
-        if let Some(clause) = self.stack.pop() {
-            if let Some(trait_clause) = clause.as_trait_clause() {
-                self.elaborate(trait_clause.to_poly_trait_ref());
-            }
-            Some(clause)
-        } else {
-            None
-        }
-    }
-}
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index 8e221cdc603..88ee32eae95 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -229,6 +229,10 @@ impl<'tcx> rustc_type_ir::inherent::AdtDef<TyCtxt<'tcx>> for AdtDef<'tcx> {
     fn sized_constraint(self, tcx: TyCtxt<'tcx>) -> Option<ty::EarlyBinder<'tcx, Ty<'tcx>>> {
         self.sized_constraint(tcx)
     }
+
+    fn is_fundamental(self) -> bool {
+        self.is_fundamental()
+    }
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable, TyEncodable, TyDecodable)]
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index dca48069974..aee42bfe3aa 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -37,7 +37,7 @@ use crate::ty::{GenericArg, GenericArgs, GenericArgsRef};
 use rustc_ast::{self as ast, attr};
 use rustc_data_structures::defer;
 use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::sharded::{IntoPointer, ShardedHashMap};
@@ -347,12 +347,16 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     fn explicit_super_predicates_of(
         self,
         def_id: DefId,
-    ) -> ty::EarlyBinder<'tcx, impl IntoIterator<Item = ty::Clause<'tcx>>> {
+    ) -> ty::EarlyBinder<'tcx, impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>> {
+        ty::EarlyBinder::bind(self.explicit_super_predicates_of(def_id).instantiate_identity(self))
+    }
+
+    fn explicit_implied_predicates_of(
+        self,
+        def_id: DefId,
+    ) -> ty::EarlyBinder<'tcx, impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>> {
         ty::EarlyBinder::bind(
-            self.explicit_super_predicates_of(def_id)
-                .instantiate_identity(self)
-                .predicates
-                .into_iter(),
+            self.explicit_implied_predicates_of(def_id).instantiate_identity(self),
         )
     }
 
@@ -524,12 +528,12 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self.is_object_safe(trait_def_id)
     }
 
-    fn trait_may_be_implemented_via_object(self, trait_def_id: DefId) -> bool {
-        self.trait_def(trait_def_id).implement_via_object
+    fn trait_is_fundamental(self, def_id: DefId) -> bool {
+        self.trait_def(def_id).is_fundamental
     }
 
-    fn supertrait_def_ids(self, trait_def_id: DefId) -> impl IntoIterator<Item = DefId> {
-        self.supertrait_def_ids(trait_def_id)
+    fn trait_may_be_implemented_via_object(self, trait_def_id: DefId) -> bool {
+        self.trait_def(trait_def_id).implement_via_object
     }
 
     fn delay_bug(self, msg: impl ToString) -> ErrorGuaranteed {
@@ -569,6 +573,13 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     ) -> Ty<'tcx> {
         placeholder.find_const_ty_from_env(param_env)
     }
+
+    fn anonymize_bound_vars<T: TypeFoldable<TyCtxt<'tcx>>>(
+        self,
+        binder: ty::Binder<'tcx, T>,
+    ) -> ty::Binder<'tcx, T> {
+        self.anonymize_bound_vars(binder)
+    }
 }
 
 macro_rules! bidirectional_lang_item_map {
@@ -635,6 +646,10 @@ bidirectional_lang_item_map! {
 }
 
 impl<'tcx> rustc_type_ir::inherent::DefId<TyCtxt<'tcx>> for DefId {
+    fn is_local(self) -> bool {
+        self.is_local()
+    }
+
     fn as_local(self) -> Option<LocalDefId> {
         self.as_local()
     }
@@ -2484,25 +2499,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// to identify which traits may define a given associated type to help avoid cycle errors,
     /// and to make size estimates for vtable layout computation.
     pub fn supertrait_def_ids(self, trait_def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
-        let mut set = FxHashSet::default();
-        let mut stack = vec![trait_def_id];
-
-        set.insert(trait_def_id);
-
-        iter::from_fn(move || -> Option<DefId> {
-            let trait_did = stack.pop()?;
-            let generic_predicates = self.explicit_super_predicates_of(trait_did);
-
-            for (predicate, _) in generic_predicates.predicates {
-                if let ty::ClauseKind::Trait(data) = predicate.kind().skip_binder() {
-                    if set.insert(data.def_id()) {
-                        stack.push(data.def_id());
-                    }
-                }
-            }
-
-            Some(trait_did)
-        })
+        rustc_type_ir::elaborate::supertrait_def_ids(self, trait_def_id)
     }
 
     /// Given a closure signature, returns an equivalent fn signature. Detuples
diff --git a/compiler/rustc_middle/src/ty/elaborate_impl.rs b/compiler/rustc_middle/src/ty/elaborate_impl.rs
new file mode 100644
index 00000000000..8c89a2d884b
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/elaborate_impl.rs
@@ -0,0 +1,84 @@
+use rustc_span::Span;
+use rustc_type_ir::elaborate::Elaboratable;
+
+use crate::ty::{self, TyCtxt};
+
+impl<'tcx> Elaboratable<TyCtxt<'tcx>> for ty::Clause<'tcx> {
+    fn predicate(&self) -> ty::Predicate<'tcx> {
+        self.as_predicate()
+    }
+
+    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
+        clause
+    }
+
+    fn child_with_derived_cause(
+        &self,
+        clause: ty::Clause<'tcx>,
+        _span: Span,
+        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
+        _index: usize,
+    ) -> Self {
+        clause
+    }
+}
+
+impl<'tcx> Elaboratable<TyCtxt<'tcx>> for ty::Predicate<'tcx> {
+    fn predicate(&self) -> ty::Predicate<'tcx> {
+        *self
+    }
+
+    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
+        clause.as_predicate()
+    }
+
+    fn child_with_derived_cause(
+        &self,
+        clause: ty::Clause<'tcx>,
+        _span: Span,
+        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
+        _index: usize,
+    ) -> Self {
+        clause.as_predicate()
+    }
+}
+
+impl<'tcx> Elaboratable<TyCtxt<'tcx>> for (ty::Predicate<'tcx>, Span) {
+    fn predicate(&self) -> ty::Predicate<'tcx> {
+        self.0
+    }
+
+    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
+        (clause.as_predicate(), self.1)
+    }
+
+    fn child_with_derived_cause(
+        &self,
+        clause: ty::Clause<'tcx>,
+        _span: Span,
+        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
+        _index: usize,
+    ) -> Self {
+        (clause.as_predicate(), self.1)
+    }
+}
+
+impl<'tcx> Elaboratable<TyCtxt<'tcx>> for (ty::Clause<'tcx>, Span) {
+    fn predicate(&self) -> ty::Predicate<'tcx> {
+        self.0.as_predicate()
+    }
+
+    fn child(&self, clause: ty::Clause<'tcx>) -> Self {
+        (clause, self.1)
+    }
+
+    fn child_with_derived_cause(
+        &self,
+        clause: ty::Clause<'tcx>,
+        _span: Span,
+        _parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
+        _index: usize,
+    ) -> Self {
+        (clause, self.1)
+    }
+}
diff --git a/compiler/rustc_middle/src/ty/generics.rs b/compiler/rustc_middle/src/ty/generics.rs
index 844023df1e3..11ed0bdaa70 100644
--- a/compiler/rustc_middle/src/ty/generics.rs
+++ b/compiler/rustc_middle/src/ty/generics.rs
@@ -394,7 +394,7 @@ impl<'tcx> GenericPredicates<'tcx> {
     }
 
     pub fn instantiate_own_identity(&self) -> impl Iterator<Item = (Clause<'tcx>, Span)> {
-        EarlyBinder::bind(self.predicates).instantiate_identity_iter_copied()
+        EarlyBinder::bind(self.predicates).iter_identity_copied()
     }
 
     #[instrument(level = "debug", skip(self, tcx))]
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 7d57d88f40f..4470db47474 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -148,6 +148,7 @@ mod closure;
 mod consts;
 mod context;
 mod diagnostics;
+mod elaborate_impl;
 mod erase_regions;
 mod generic_args;
 mod generics;
diff --git a/compiler/rustc_middle/src/ty/predicate.rs b/compiler/rustc_middle/src/ty/predicate.rs
index e9b37503bb3..5d6352c57ce 100644
--- a/compiler/rustc_middle/src/ty/predicate.rs
+++ b/compiler/rustc_middle/src/ty/predicate.rs
@@ -46,6 +46,10 @@ pub struct Predicate<'tcx>(
 );
 
 impl<'tcx> rustc_type_ir::inherent::Predicate<TyCtxt<'tcx>> for Predicate<'tcx> {
+    fn as_clause(self) -> Option<ty::Clause<'tcx>> {
+        self.as_clause()
+    }
+
     fn is_coinductive(self, interner: TyCtxt<'tcx>) -> bool {
         self.is_coinductive(interner)
     }
@@ -173,7 +177,11 @@ pub struct Clause<'tcx>(
     pub(super) Interned<'tcx, WithCachedTypeInfo<ty::Binder<'tcx, PredicateKind<'tcx>>>>,
 );
 
-impl<'tcx> rustc_type_ir::inherent::Clause<TyCtxt<'tcx>> for Clause<'tcx> {}
+impl<'tcx> rustc_type_ir::inherent::Clause<TyCtxt<'tcx>> for Clause<'tcx> {
+    fn instantiate_supertrait(self, tcx: TyCtxt<'tcx>, trait_ref: ty::PolyTraitRef<'tcx>) -> Self {
+        self.instantiate_supertrait(tcx, trait_ref)
+    }
+}
 
 impl<'tcx> rustc_type_ir::inherent::IntoKind for Clause<'tcx> {
     type Kind = ty::Binder<'tcx, ClauseKind<'tcx>>;
@@ -341,6 +349,14 @@ impl<'tcx> ty::List<ty::PolyExistentialPredicate<'tcx>> {
             _ => None,
         })
     }
+
+    pub fn without_auto_traits(
+        &self,
+    ) -> impl Iterator<Item = ty::PolyExistentialPredicate<'tcx>> + '_ {
+        self.iter().filter(|predicate| {
+            !matches!(predicate.as_ref().skip_binder(), ExistentialPredicate::AutoTrait(_))
+        })
+    }
 }
 
 pub type PolyTraitRef<'tcx> = ty::Binder<'tcx, TraitRef<'tcx>>;
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 7e64c507406..df080b2887b 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -1,7 +1,6 @@
 use crate::mir::interpret::{AllocRange, GlobalAlloc, Pointer, Provenance, Scalar};
 use crate::query::IntoQueryParam;
 use crate::query::Providers;
-use crate::traits::util::{super_predicates_for_pretty_printing, supertraits_for_pretty_printing};
 use crate::ty::GenericArgKind;
 use crate::ty::{
     ConstInt, Expr, ParamConst, ScalarInt, Term, TermKind, TypeFoldable, TypeSuperFoldable,
@@ -23,6 +22,7 @@ use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::FileNameDisplayPreference;
 use rustc_target::abi::Size;
 use rustc_target::spec::abi::Abi;
+use rustc_type_ir::{elaborate, Upcast as _};
 use smallvec::SmallVec;
 
 use std::cell::Cell;
@@ -1255,14 +1255,14 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 entry.has_fn_once = true;
                 return;
             } else if self.tcx().is_lang_item(trait_def_id, LangItem::FnMut) {
-                let super_trait_ref = supertraits_for_pretty_printing(self.tcx(), trait_ref)
+                let super_trait_ref = elaborate::supertraits(self.tcx(), trait_ref)
                     .find(|super_trait_ref| super_trait_ref.def_id() == fn_once_trait)
                     .unwrap();
 
                 fn_traits.entry(super_trait_ref).or_default().fn_mut_trait_ref = Some(trait_ref);
                 return;
             } else if self.tcx().is_lang_item(trait_def_id, LangItem::Fn) {
-                let super_trait_ref = supertraits_for_pretty_printing(self.tcx(), trait_ref)
+                let super_trait_ref = elaborate::supertraits(self.tcx(), trait_ref)
                     .find(|super_trait_ref| super_trait_ref.def_id() == fn_once_trait)
                     .unwrap();
 
@@ -1343,10 +1343,11 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     let bound_principal_with_self = bound_principal
                         .with_self_ty(cx.tcx(), cx.tcx().types.trait_object_dummy_self);
 
-                    let super_projections: Vec<_> =
-                        super_predicates_for_pretty_printing(cx.tcx(), bound_principal_with_self)
-                            .filter_map(|clause| clause.as_projection_clause())
-                            .collect();
+                    let clause: ty::Clause<'tcx> = bound_principal_with_self.upcast(cx.tcx());
+                    let super_projections: Vec<_> = elaborate::elaborate(cx.tcx(), [clause])
+                        .filter_only_self()
+                        .filter_map(|clause| clause.as_projection_clause())
+                        .collect();
 
                     let mut projections: Vec<_> = predicates
                         .projection_bounds()
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 52690ae678d..d2b444a066b 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -811,6 +811,14 @@ impl<'tcx> rustc_type_ir::inherent::Ty<TyCtxt<'tcx>> for Ty<'tcx> {
         Ty::new_var(tcx, vid)
     }
 
+    fn new_param(tcx: TyCtxt<'tcx>, param: ty::ParamTy) -> Self {
+        Ty::new_param(tcx, param.index, param.name)
+    }
+
+    fn new_placeholder(tcx: TyCtxt<'tcx>, placeholder: ty::PlaceholderType) -> Self {
+        Ty::new_placeholder(tcx, placeholder)
+    }
+
     fn new_bound(interner: TyCtxt<'tcx>, debruijn: ty::DebruijnIndex, var: ty::BoundTy) -> Self {
         Ty::new_bound(interner, debruijn, var)
     }
diff --git a/compiler/rustc_middle/src/ty/trait_def.rs b/compiler/rustc_middle/src/ty/trait_def.rs
index 4dba97c3b5b..076a74ca6f8 100644
--- a/compiler/rustc_middle/src/ty/trait_def.rs
+++ b/compiler/rustc_middle/src/ty/trait_def.rs
@@ -31,7 +31,7 @@ pub struct TraitDef {
     /// and thus `impl`s of it are allowed to overlap.
     pub is_marker: bool,
 
-    /// If `true`, then this trait has to `#[rustc_coinductive]` attribute or
+    /// If `true`, then this trait has the `#[rustc_coinductive]` attribute or
     /// is an auto trait. This indicates that trait solver cycles involving an
     /// `X: ThisTrait` goal are accepted.
     ///
@@ -40,6 +40,11 @@ pub struct TraitDef {
     /// also have already switched to the new trait solver.
     pub is_coinductive: bool,
 
+    /// If `true`, then this trait has the `#[fundamental]` attribute. This
+    /// affects how conherence computes whether a trait may have trait implementations
+    /// added in the future.
+    pub is_fundamental: bool,
+
     /// If `true`, then this trait has the `#[rustc_skip_during_method_dispatch(array)]`
     /// attribute, indicating that editions before 2021 should not consider this trait
     /// during method dispatch if the receiver is an array.
diff --git a/compiler/rustc_mir_build/src/build/expr/stmt.rs b/compiler/rustc_mir_build/src/build/expr/stmt.rs
index 2bdeb579a02..88b76c46c90 100644
--- a/compiler/rustc_mir_build/src/build/expr/stmt.rs
+++ b/compiler/rustc_mir_build/src/build/expr/stmt.rs
@@ -2,7 +2,9 @@ use crate::build::scope::BreakableTarget;
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 use rustc_middle::middle::region;
 use rustc_middle::mir::*;
+use rustc_middle::span_bug;
 use rustc_middle::thir::*;
+use rustc_span::source_map::Spanned;
 use tracing::debug;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -91,9 +93,42 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             ExprKind::Return { value } => {
                 this.break_scope(block, value, BreakableTarget::Return, source_info)
             }
-            // FIXME(explicit_tail_calls): properly lower tail calls here
             ExprKind::Become { value } => {
-                this.break_scope(block, Some(value), BreakableTarget::Return, source_info)
+                let v = &this.thir[value];
+                let ExprKind::Scope { value, lint_level, region_scope } = v.kind else {
+                    span_bug!(v.span, "`thir_check_tail_calls` should have disallowed this {v:?}")
+                };
+
+                let v = &this.thir[value];
+                let ExprKind::Call { ref args, fun, fn_span, .. } = v.kind else {
+                    span_bug!(v.span, "`thir_check_tail_calls` should have disallowed this {v:?}")
+                };
+
+                this.in_scope((region_scope, source_info), lint_level, |this| {
+                    let fun = unpack!(block = this.as_local_operand(block, fun));
+                    let args: Box<[_]> = args
+                        .into_iter()
+                        .copied()
+                        .map(|arg| Spanned {
+                            node: unpack!(block = this.as_local_call_operand(block, arg)),
+                            span: this.thir.exprs[arg].span,
+                        })
+                        .collect();
+
+                    this.record_operands_moved(&args);
+
+                    debug!("expr_into_dest: fn_span={:?}", fn_span);
+
+                    unpack!(block = this.break_for_tail_call(block, &args, source_info));
+
+                    this.cfg.terminate(
+                        block,
+                        source_info,
+                        TerminatorKind::TailCall { func: fun, args, fn_span },
+                    );
+
+                    this.cfg.start_new_block().unit()
+                })
             }
             _ => {
                 assert!(
diff --git a/compiler/rustc_mir_build/src/build/scope.rs b/compiler/rustc_mir_build/src/build/scope.rs
index 5b6de39bb2e..948301e2ece 100644
--- a/compiler/rustc_mir_build/src/build/scope.rs
+++ b/compiler/rustc_mir_build/src/build/scope.rs
@@ -745,6 +745,91 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         self.cfg.terminate(block, source_info, TerminatorKind::UnwindResume);
     }
 
+    /// Sets up the drops for explict tail calls.
+    ///
+    /// Unlike other kinds of early exits, tail calls do not go through the drop tree.
+    /// Instead, all scheduled drops are immediately added to the CFG.
+    pub(crate) fn break_for_tail_call(
+        &mut self,
+        mut block: BasicBlock,
+        args: &[Spanned<Operand<'tcx>>],
+        source_info: SourceInfo,
+    ) -> BlockAnd<()> {
+        let arg_drops: Vec<_> = args
+            .iter()
+            .rev()
+            .filter_map(|arg| match &arg.node {
+                Operand::Copy(_) => bug!("copy op in tail call args"),
+                Operand::Move(place) => {
+                    let local =
+                        place.as_local().unwrap_or_else(|| bug!("projection in tail call args"));
+
+                    Some(DropData { source_info, local, kind: DropKind::Value })
+                }
+                Operand::Constant(_) => None,
+            })
+            .collect();
+
+        let mut unwind_to = self.diverge_cleanup_target(
+            self.scopes.scopes.iter().rev().nth(1).unwrap().region_scope,
+            DUMMY_SP,
+        );
+        let unwind_drops = &mut self.scopes.unwind_drops;
+
+        // the innermost scope contains only the destructors for the tail call arguments
+        // we only want to drop these in case of a panic, so we skip it
+        for scope in self.scopes.scopes[1..].iter().rev().skip(1) {
+            // FIXME(explicit_tail_calls) code duplication with `build_scope_drops`
+            for drop_data in scope.drops.iter().rev() {
+                let source_info = drop_data.source_info;
+                let local = drop_data.local;
+
+                match drop_data.kind {
+                    DropKind::Value => {
+                        // `unwind_to` should drop the value that we're about to
+                        // schedule. If dropping this value panics, then we continue
+                        // with the *next* value on the unwind path.
+                        debug_assert_eq!(unwind_drops.drops[unwind_to].data.local, drop_data.local);
+                        debug_assert_eq!(unwind_drops.drops[unwind_to].data.kind, drop_data.kind);
+                        unwind_to = unwind_drops.drops[unwind_to].next;
+
+                        let mut unwind_entry_point = unwind_to;
+
+                        // the tail call arguments must be dropped if any of these drops panic
+                        for drop in arg_drops.iter().copied() {
+                            unwind_entry_point = unwind_drops.add_drop(drop, unwind_entry_point);
+                        }
+
+                        unwind_drops.add_entry_point(block, unwind_entry_point);
+
+                        let next = self.cfg.start_new_block();
+                        self.cfg.terminate(
+                            block,
+                            source_info,
+                            TerminatorKind::Drop {
+                                place: local.into(),
+                                target: next,
+                                unwind: UnwindAction::Continue,
+                                replace: false,
+                            },
+                        );
+                        block = next;
+                    }
+                    DropKind::Storage => {
+                        // Only temps and vars need their storage dead.
+                        assert!(local.index() > self.arg_count);
+                        self.cfg.push(
+                            block,
+                            Statement { source_info, kind: StatementKind::StorageDead(local) },
+                        );
+                    }
+                }
+            }
+        }
+
+        block.unit()
+    }
+
     fn leave_top_scope(&mut self, block: BasicBlock) -> BasicBlock {
         // If we are emitting a `drop` statement, we need to have the cached
         // diverge cleanup pads ready in case that drop panics.
@@ -1523,6 +1608,7 @@ impl<'tcx> DropTreeBuilder<'tcx> for Unwind {
             | TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::Yield { .. }
             | TerminatorKind::CoroutineDrop
diff --git a/compiler/rustc_mir_build/src/lints.rs b/compiler/rustc_mir_build/src/lints.rs
index 1c7aa9f9ed0..263e777d03a 100644
--- a/compiler/rustc_mir_build/src/lints.rs
+++ b/compiler/rustc_mir_build/src/lints.rs
@@ -217,12 +217,28 @@ impl<'mir, 'tcx, C: TerminatorClassifier<'tcx>> TriColorVisitor<BasicBlocks<'tcx
             | TerminatorKind::FalseUnwind { .. }
             | TerminatorKind::Goto { .. }
             | TerminatorKind::SwitchInt { .. } => ControlFlow::Continue(()),
+
+            // Note that tail call terminator technically returns to the caller,
+            // but for purposes of this lint it makes sense to count it as possibly recursive,
+            // since it's still a call.
+            //
+            // If this'll be repurposed for something else, this might need to be changed.
+            TerminatorKind::TailCall { .. } => ControlFlow::Continue(()),
         }
     }
 
     fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
         // When we examine a node for the last time, remember it if it is a recursive call.
         let terminator = self.body[bb].terminator();
+
+        // FIXME(explicit_tail_calls): highlight tail calls as "recursive call site"
+        //
+        // We don't want to lint functions that recurse only through tail calls
+        // (such as `fn g() { become () }`), so just adding `| TailCall { ... }`
+        // here won't work.
+        //
+        // But at the same time we would like to highlight both calls in a function like
+        // `fn f() { if false { become f() } else { f() } }`, so we need to figure something out.
         if self.classifier.is_recursive_terminator(self.tcx, self.body, terminator) {
             self.reachable_recursive_calls.push(terminator.source_info.span);
         }
diff --git a/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs b/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs
index 706bb796349..574da949b0e 100644
--- a/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs
@@ -145,6 +145,7 @@ where
             | TerminatorKind::InlineAsm { .. }
             | TerminatorKind::UnwindResume
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::SwitchInt { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::Yield { .. } => {}
diff --git a/compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs b/compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs
index 29169c31263..f850a710277 100644
--- a/compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs
@@ -288,6 +288,7 @@ impl<'tcx> crate::GenKillAnalysis<'tcx> for MaybeRequiresStorage<'_, 'tcx> {
             | TerminatorKind::Goto { .. }
             | TerminatorKind::UnwindResume
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::SwitchInt { .. }
             | TerminatorKind::Unreachable => {}
         }
@@ -325,6 +326,7 @@ impl<'tcx> crate::GenKillAnalysis<'tcx> for MaybeRequiresStorage<'_, 'tcx> {
             | TerminatorKind::Goto { .. }
             | TerminatorKind::UnwindResume
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::SwitchInt { .. }
             | TerminatorKind::Unreachable => {}
         }
diff --git a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs b/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
index 1fb77bef3d4..7b39db821d8 100644
--- a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
+++ b/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
@@ -489,6 +489,12 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
                     self.gather_init(destination.as_ref(), InitKind::NonPanicPathOnly);
                 }
             }
+            TerminatorKind::TailCall { ref func, ref args, .. } => {
+                self.gather_operand(func);
+                for arg in args {
+                    self.gather_operand(&arg.node);
+                }
+            }
             TerminatorKind::InlineAsm {
                 template: _,
                 ref operands,
diff --git a/compiler/rustc_mir_dataflow/src/value_analysis.rs b/compiler/rustc_mir_dataflow/src/value_analysis.rs
index 7c1ff6fda53..1582c2e8a90 100644
--- a/compiler/rustc_mir_dataflow/src/value_analysis.rs
+++ b/compiler/rustc_mir_dataflow/src/value_analysis.rs
@@ -269,6 +269,9 @@ pub trait ValueAnalysis<'tcx> {
             TerminatorKind::SwitchInt { discr, targets } => {
                 return self.handle_switch_int(discr, targets, state);
             }
+            TerminatorKind::TailCall { .. } => {
+                // FIXME(explicit_tail_calls): determine if we need to do something here (probably not)
+            }
             TerminatorKind::Goto { .. }
             | TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index 9d44001f915..fa5da89e8ba 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -1367,6 +1367,10 @@ fn can_unwind<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) -> bool {
             | TerminatorKind::Call { .. }
             | TerminatorKind::InlineAsm { .. }
             | TerminatorKind::Assert { .. } => return true,
+
+            TerminatorKind::TailCall { .. } => {
+                unreachable!("tail calls can't be present in generators")
+            }
         }
     }
 
@@ -1916,6 +1920,7 @@ impl<'tcx> Visitor<'tcx> for EnsureCoroutineFieldAssignmentsNeverAlias<'_> {
             | TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::Drop { .. }
             | TerminatorKind::Assert { .. }
diff --git a/compiler/rustc_mir_transform/src/cost_checker.rs b/compiler/rustc_mir_transform/src/cost_checker.rs
index 3333bebff3a..a1c1422912e 100644
--- a/compiler/rustc_mir_transform/src/cost_checker.rs
+++ b/compiler/rustc_mir_transform/src/cost_checker.rs
@@ -40,7 +40,9 @@ impl<'b, 'tcx> CostChecker<'b, 'tcx> {
         fn is_call_like(bbd: &BasicBlockData<'_>) -> bool {
             use TerminatorKind::*;
             match bbd.terminator().kind {
-                Call { .. } | Drop { .. } | Assert { .. } | InlineAsm { .. } => true,
+                Call { .. } | TailCall { .. } | Drop { .. } | Assert { .. } | InlineAsm { .. } => {
+                    true
+                }
 
                 Goto { .. }
                 | SwitchInt { .. }
@@ -137,6 +139,9 @@ impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
                     self.penalty += LANDINGPAD_PENALTY;
                 }
             }
+            TerminatorKind::TailCall { .. } => {
+                self.penalty += CALL_PENALTY;
+            }
             TerminatorKind::SwitchInt { discr, targets } => {
                 if discr.constant().is_some() {
                     // Not only will this become a `Goto`, but likely other
diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index 360dccb240d..83fb9ff9743 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -358,9 +358,12 @@ fn bcb_filtered_successors<'a, 'tcx>(terminator: &'a Terminator<'tcx>) -> Covera
         }
 
         // These terminators have no coverage-relevant successors.
-        CoroutineDrop | Return | Unreachable | UnwindResume | UnwindTerminate(_) => {
-            CoverageSuccessors::NotChainable(&[])
-        }
+        CoroutineDrop
+        | Return
+        | TailCall { .. }
+        | Unreachable
+        | UnwindResume
+        | UnwindTerminate(_) => CoverageSuccessors::NotChainable(&[]),
     }
 }
 
diff --git a/compiler/rustc_mir_transform/src/coverage/mod.rs b/compiler/rustc_mir_transform/src/coverage/mod.rs
index d55bde311c1..2efca40d180 100644
--- a/compiler/rustc_mir_transform/src/coverage/mod.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mod.rs
@@ -8,6 +8,10 @@ mod spans;
 mod tests;
 mod unexpand;
 
+use rustc_hir as hir;
+use rustc_hir::intravisit::{walk_expr, Visitor};
+use rustc_middle::hir::map::Map;
+use rustc_middle::hir::nested_filter;
 use rustc_middle::mir::coverage::{
     CodeRegion, CoverageKind, DecisionInfo, FunctionCoverageInfo, Mapping, MappingKind,
 };
@@ -465,6 +469,9 @@ struct ExtractedHirInfo {
     /// Must have the same context and filename as the body span.
     fn_sig_span_extended: Option<Span>,
     body_span: Span,
+    /// "Holes" are regions within the body span that should not be included in
+    /// coverage spans for this function (e.g. closures and nested items).
+    hole_spans: Vec<Span>,
 }
 
 fn extract_hir_info<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> ExtractedHirInfo {
@@ -480,7 +487,7 @@ fn extract_hir_info<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> ExtractedHir
 
     let mut body_span = hir_body.value.span;
 
-    use rustc_hir::{Closure, Expr, ExprKind, Node};
+    use hir::{Closure, Expr, ExprKind, Node};
     // Unexpand a closure's body span back to the context of its declaration.
     // This helps with closure bodies that consist of just a single bang-macro,
     // and also with closure bodies produced by async desugaring.
@@ -507,11 +514,78 @@ fn extract_hir_info<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> ExtractedHir
 
     let function_source_hash = hash_mir_source(tcx, hir_body);
 
-    ExtractedHirInfo { function_source_hash, is_async_fn, fn_sig_span_extended, body_span }
+    let hole_spans = extract_hole_spans_from_hir(tcx, body_span, hir_body);
+
+    ExtractedHirInfo {
+        function_source_hash,
+        is_async_fn,
+        fn_sig_span_extended,
+        body_span,
+        hole_spans,
+    }
 }
 
-fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx rustc_hir::Body<'tcx>) -> u64 {
+fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx hir::Body<'tcx>) -> u64 {
     // FIXME(cjgillot) Stop hashing HIR manually here.
     let owner = hir_body.id().hir_id.owner;
     tcx.hir_owner_nodes(owner).opt_hash_including_bodies.unwrap().to_smaller_hash().as_u64()
 }
+
+fn extract_hole_spans_from_hir<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body_span: Span, // Usually `hir_body.value.span`, but not always
+    hir_body: &hir::Body<'tcx>,
+) -> Vec<Span> {
+    struct HolesVisitor<'hir, F> {
+        hir: Map<'hir>,
+        visit_hole_span: F,
+    }
+
+    impl<'hir, F: FnMut(Span)> Visitor<'hir> for HolesVisitor<'hir, F> {
+        /// - We need `NestedFilter::INTRA = true` so that `visit_item` will be called.
+        /// - Bodies of nested items don't actually get visited, because of the
+        ///   `visit_item` override.
+        /// - For nested bodies that are not part of an item, we do want to visit any
+        ///   items contained within them.
+        type NestedFilter = nested_filter::All;
+
+        fn nested_visit_map(&mut self) -> Self::Map {
+            self.hir
+        }
+
+        fn visit_item(&mut self, item: &'hir hir::Item<'hir>) {
+            (self.visit_hole_span)(item.span);
+            // Having visited this item, we don't care about its children,
+            // so don't call `walk_item`.
+        }
+
+        // We override `visit_expr` instead of the more specific expression
+        // visitors, so that we have direct access to the expression span.
+        fn visit_expr(&mut self, expr: &'hir hir::Expr<'hir>) {
+            match expr.kind {
+                hir::ExprKind::Closure(_) | hir::ExprKind::ConstBlock(_) => {
+                    (self.visit_hole_span)(expr.span);
+                    // Having visited this expression, we don't care about its
+                    // children, so don't call `walk_expr`.
+                }
+
+                // For other expressions, recursively visit as normal.
+                _ => walk_expr(self, expr),
+            }
+        }
+    }
+
+    let mut hole_spans = vec![];
+    let mut visitor = HolesVisitor {
+        hir: tcx.hir(),
+        visit_hole_span: |hole_span| {
+            // Discard any holes that aren't directly visible within the body span.
+            if body_span.contains(hole_span) && body_span.eq_ctxt(hole_span) {
+                hole_spans.push(hole_span);
+            }
+        },
+    };
+
+    visitor.visit_body(hir_body);
+    hole_spans
+}
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 7612c01c52e..dbc26a2808e 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -8,7 +8,7 @@ use rustc_span::Span;
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
 use crate::coverage::mappings;
 use crate::coverage::spans::from_mir::{
-    extract_covspans_and_holes_from_mir, ExtractedCovspans, Hole, SpanFromMir,
+    extract_covspans_from_mir, ExtractedCovspans, Hole, SpanFromMir,
 };
 use crate::coverage::ExtractedHirInfo;
 
@@ -20,8 +20,8 @@ pub(super) fn extract_refined_covspans(
     basic_coverage_blocks: &CoverageGraph,
     code_mappings: &mut impl Extend<mappings::CodeMapping>,
 ) {
-    let ExtractedCovspans { mut covspans, mut holes } =
-        extract_covspans_and_holes_from_mir(mir_body, hir_info, basic_coverage_blocks);
+    let ExtractedCovspans { mut covspans } =
+        extract_covspans_from_mir(mir_body, hir_info, basic_coverage_blocks);
 
     // First, perform the passes that need macro information.
     covspans.sort_by(|a, b| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb));
@@ -45,6 +45,7 @@ pub(super) fn extract_refined_covspans(
     covspans.dedup_by(|b, a| a.span.source_equal(b.span));
 
     // Sort the holes, and merge overlapping/adjacent holes.
+    let mut holes = hir_info.hole_spans.iter().map(|&span| Hole { span }).collect::<Vec<_>>();
     holes.sort_by(|a, b| compare_spans(a.span, b.span));
     holes.dedup_by(|b, a| a.merge_if_overlapping_or_adjacent(b));
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
index 2ca166929ee..32bd25bf4b9 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
@@ -1,8 +1,7 @@
 use rustc_middle::bug;
 use rustc_middle::mir::coverage::CoverageKind;
 use rustc_middle::mir::{
-    self, AggregateKind, FakeReadCause, Rvalue, Statement, StatementKind, Terminator,
-    TerminatorKind,
+    self, FakeReadCause, Statement, StatementKind, Terminator, TerminatorKind,
 };
 use rustc_span::{Span, Symbol};
 
@@ -15,13 +14,12 @@ use crate::coverage::ExtractedHirInfo;
 
 pub(crate) struct ExtractedCovspans {
     pub(crate) covspans: Vec<SpanFromMir>,
-    pub(crate) holes: Vec<Hole>,
 }
 
 /// Traverses the MIR body to produce an initial collection of coverage-relevant
 /// spans, each associated with a node in the coverage graph (BCB) and possibly
 /// other metadata.
-pub(crate) fn extract_covspans_and_holes_from_mir(
+pub(crate) fn extract_covspans_from_mir(
     mir_body: &mir::Body<'_>,
     hir_info: &ExtractedHirInfo,
     basic_coverage_blocks: &CoverageGraph,
@@ -29,21 +27,13 @@ pub(crate) fn extract_covspans_and_holes_from_mir(
     let &ExtractedHirInfo { body_span, .. } = hir_info;
 
     let mut covspans = vec![];
-    let mut holes = vec![];
 
     for (bcb, bcb_data) in basic_coverage_blocks.iter_enumerated() {
-        bcb_to_initial_coverage_spans(
-            mir_body,
-            body_span,
-            bcb,
-            bcb_data,
-            &mut covspans,
-            &mut holes,
-        );
+        bcb_to_initial_coverage_spans(mir_body, body_span, bcb, bcb_data, &mut covspans);
     }
 
     // Only add the signature span if we found at least one span in the body.
-    if !covspans.is_empty() || !holes.is_empty() {
+    if !covspans.is_empty() {
         // If there is no usable signature span, add a fake one (before refinement)
         // to avoid an ugly gap between the body start and the first real span.
         // FIXME: Find a more principled way to solve this problem.
@@ -51,7 +41,7 @@ pub(crate) fn extract_covspans_and_holes_from_mir(
         covspans.push(SpanFromMir::for_fn_sig(fn_sig_span));
     }
 
-    ExtractedCovspans { covspans, holes }
+    ExtractedCovspans { covspans }
 }
 
 // Generate a set of coverage spans from the filtered set of `Statement`s and `Terminator`s of
@@ -65,7 +55,6 @@ fn bcb_to_initial_coverage_spans<'a, 'tcx>(
     bcb: BasicCoverageBlock,
     bcb_data: &'a BasicCoverageBlockData,
     initial_covspans: &mut Vec<SpanFromMir>,
-    holes: &mut Vec<Hole>,
 ) {
     for &bb in &bcb_data.basic_blocks {
         let data = &mir_body[bb];
@@ -81,13 +70,7 @@ fn bcb_to_initial_coverage_spans<'a, 'tcx>(
             let expn_span = filtered_statement_span(statement)?;
             let (span, visible_macro) = unexpand(expn_span)?;
 
-            // A statement that looks like the assignment of a closure expression
-            // is treated as a "hole" span, to be carved out of other spans.
-            if is_closure_like(statement) {
-                holes.push(Hole { span });
-            } else {
-                initial_covspans.push(SpanFromMir::new(span, visible_macro, bcb));
-            }
+            initial_covspans.push(SpanFromMir::new(span, visible_macro, bcb));
             Some(())
         };
         for statement in data.statements.iter() {
@@ -105,18 +88,6 @@ fn bcb_to_initial_coverage_spans<'a, 'tcx>(
     }
 }
 
-fn is_closure_like(statement: &Statement<'_>) -> bool {
-    match statement.kind {
-        StatementKind::Assign(box (_, Rvalue::Aggregate(box ref agg_kind, _))) => match agg_kind {
-            AggregateKind::Closure(_, _)
-            | AggregateKind::Coroutine(_, _)
-            | AggregateKind::CoroutineClosure(..) => true,
-            _ => false,
-        },
-        _ => false,
-    }
-}
-
 /// If the MIR `Statement` has a span contributive to computing coverage spans,
 /// return it; otherwise return `None`.
 fn filtered_statement_span(statement: &Statement<'_>) -> Option<Span> {
@@ -193,7 +164,8 @@ fn filtered_terminator_span(terminator: &Terminator<'_>) -> Option<Span> {
         | TerminatorKind::Goto { .. } => None,
 
         // Call `func` operand can have a more specific span when part of a chain of calls
-        | TerminatorKind::Call { ref func, .. } => {
+        TerminatorKind::Call { ref func, .. }
+        | TerminatorKind::TailCall { ref func, .. } => {
             let mut span = terminator.source_info.span;
             if let mir::Operand::Constant(box constant) = func {
                 if constant.span.lo() > span.lo() {
diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs
index b1016c0867c..ab73a8af317 100644
--- a/compiler/rustc_mir_transform/src/dest_prop.rs
+++ b/compiler/rustc_mir_transform/src/dest_prop.rs
@@ -628,6 +628,12 @@ impl WriteInfo {
                     self.add_operand(&arg.node);
                 }
             }
+            TerminatorKind::TailCall { func, args, .. } => {
+                self.add_operand(func);
+                for arg in args {
+                    self.add_operand(&arg.node);
+                }
+            }
             TerminatorKind::InlineAsm { operands, .. } => {
                 for asm_operand in operands {
                     match asm_operand {
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 2b7d9be6d35..1002746e553 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -1391,11 +1391,15 @@ fn op_to_prop_const<'tcx>(
         let (prov, offset) = pointer.into_parts();
         let alloc_id = prov.alloc_id();
         intern_const_alloc_for_constprop(ecx, alloc_id).ok()?;
-        if matches!(ecx.tcx.global_alloc(alloc_id), GlobalAlloc::Memory(_)) {
-            // `alloc_id` may point to a static. Codegen will choke on an `Indirect` with anything
-            // by `GlobalAlloc::Memory`, so do fall through to copying if needed.
-            // FIXME: find a way to treat this more uniformly
-            // (probably by fixing codegen)
+
+        // `alloc_id` may point to a static. Codegen will choke on an `Indirect` with anything
+        // by `GlobalAlloc::Memory`, so do fall through to copying if needed.
+        // FIXME: find a way to treat this more uniformly (probably by fixing codegen)
+        if let GlobalAlloc::Memory(alloc) = ecx.tcx.global_alloc(alloc_id)
+            // Transmuting a constant is just an offset in the allocation. If the alignment of the
+            // allocation is not enough, fallback to copying into a properly aligned value.
+            && alloc.inner().align >= op.layout.align.abi
+        {
             return Some(ConstValue::Indirect { alloc_id, offset });
         }
     }
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index 5075e072754..fe73715480f 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -383,6 +383,8 @@ impl<'tcx> Inliner<'tcx> {
     ) -> Option<CallSite<'tcx>> {
         // Only consider direct calls to functions
         let terminator = bb_data.terminator();
+
+        // FIXME(explicit_tail_calls): figure out if we can inline tail calls
         if let TerminatorKind::Call { ref func, fn_span, .. } = terminator.kind {
             let func_ty = func.ty(caller_body, self.tcx);
             if let ty::FnDef(def_id, args) = *func_ty.kind() {
@@ -550,6 +552,9 @@ impl<'tcx> Inliner<'tcx> {
                 // inline-asm is detected. LLVM will still possibly do an inline later on
                 // if the no-attribute function ends up with the same instruction set anyway.
                 return Err("Cannot move inline-asm across instruction sets");
+            } else if let TerminatorKind::TailCall { .. } = term.kind {
+                // FIXME(explicit_tail_calls): figure out how exactly functions containing tail calls can be inlined (and if they even should)
+                return Err("can't inline functions with tail calls");
             } else {
                 work_list.extend(term.successors())
             }
@@ -1038,6 +1043,10 @@ impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
                 *target = self.map_block(*target);
                 *unwind = self.map_unwind(*unwind);
             }
+            TerminatorKind::TailCall { .. } => {
+                // check_mir_body forbids tail calls
+                unreachable!()
+            }
             TerminatorKind::Call { ref mut target, ref mut unwind, .. } => {
                 if let Some(ref mut tgt) = *target {
                     *tgt = self.map_block(*tgt);
diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs
index 85a61f95ca3..97ec0cb39de 100644
--- a/compiler/rustc_mir_transform/src/jump_threading.rs
+++ b/compiler/rustc_mir_transform/src/jump_threading.rs
@@ -596,6 +596,7 @@ impl<'tcx, 'a> TOFinder<'tcx, 'a> {
             TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::CoroutineDrop => bug!("{term:?} has no terminators"),
             // Disallowed during optimizations.
diff --git a/compiler/rustc_mir_transform/src/known_panics_lint.rs b/compiler/rustc_mir_transform/src/known_panics_lint.rs
index 8d6c00bbedb..82ad8879d17 100644
--- a/compiler/rustc_mir_transform/src/known_panics_lint.rs
+++ b/compiler/rustc_mir_transform/src/known_panics_lint.rs
@@ -799,6 +799,7 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
             | TerminatorKind::UnwindResume
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::Drop { .. }
             | TerminatorKind::Yield { .. }
diff --git a/compiler/rustc_mir_transform/src/mentioned_items.rs b/compiler/rustc_mir_transform/src/mentioned_items.rs
index db2bb60bdac..d928d7cf764 100644
--- a/compiler/rustc_mir_transform/src/mentioned_items.rs
+++ b/compiler/rustc_mir_transform/src/mentioned_items.rs
@@ -38,7 +38,7 @@ impl<'tcx> Visitor<'tcx> for MentionedItemsVisitor<'_, 'tcx> {
         self.super_terminator(terminator, location);
         let span = || self.body.source_info(location).span;
         match &terminator.kind {
-            mir::TerminatorKind::Call { func, .. } => {
+            mir::TerminatorKind::Call { func, .. } | mir::TerminatorKind::TailCall { func, .. } => {
                 let callee_ty = func.ty(self.body, self.tcx);
                 self.mentioned_items
                     .push(Spanned { node: MentionedItem::Fn(callee_ty), span: span() });
diff --git a/compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs b/compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs
index fb52bfa468a..1df5737e859 100644
--- a/compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs
+++ b/compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs
@@ -75,6 +75,7 @@ impl RemoveNoopLandingPads {
             | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Unreachable
             | TerminatorKind::Call { .. }
+            | TerminatorKind::TailCall { .. }
             | TerminatorKind::Assert { .. }
             | TerminatorKind::Drop { .. }
             | TerminatorKind::InlineAsm { .. } => false,
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index 2018a8fe667..ab5c25c4937 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -400,40 +400,44 @@ impl<'a, 'tcx> Visitor<'tcx> for CfgChecker<'a, 'tcx> {
                 self.check_edge(location, *target, EdgeKind::Normal);
                 self.check_unwind_edge(location, *unwind);
             }
-            TerminatorKind::Call { args, destination, target, unwind, .. } => {
-                if let Some(target) = target {
-                    self.check_edge(location, *target, EdgeKind::Normal);
-                }
-                self.check_unwind_edge(location, *unwind);
+            TerminatorKind::Call { args, .. } | TerminatorKind::TailCall { args, .. } => {
+                // FIXME(explicit_tail_calls): refactor this & add tail-call specific checks
+                if let TerminatorKind::Call { target, unwind, destination, .. } = terminator.kind {
+                    if let Some(target) = target {
+                        self.check_edge(location, target, EdgeKind::Normal);
+                    }
+                    self.check_unwind_edge(location, unwind);
+
+                    // The code generation assumes that there are no critical call edges. The assumption
+                    // is used to simplify inserting code that should be executed along the return edge
+                    // from the call. FIXME(tmiasko): Since this is a strictly code generation concern,
+                    // the code generation should be responsible for handling it.
+                    if self.mir_phase >= MirPhase::Runtime(RuntimePhase::Optimized)
+                        && self.is_critical_call_edge(target, unwind)
+                    {
+                        self.fail(
+                            location,
+                            format!(
+                                "encountered critical edge in `Call` terminator {:?}",
+                                terminator.kind,
+                            ),
+                        );
+                    }
 
-                // The code generation assumes that there are no critical call edges. The assumption
-                // is used to simplify inserting code that should be executed along the return edge
-                // from the call. FIXME(tmiasko): Since this is a strictly code generation concern,
-                // the code generation should be responsible for handling it.
-                if self.mir_phase >= MirPhase::Runtime(RuntimePhase::Optimized)
-                    && self.is_critical_call_edge(*target, *unwind)
-                {
-                    self.fail(
-                        location,
-                        format!(
-                            "encountered critical edge in `Call` terminator {:?}",
-                            terminator.kind,
-                        ),
-                    );
+                    // The call destination place and Operand::Move place used as an argument might be
+                    // passed by a reference to the callee. Consequently they cannot be packed.
+                    if is_within_packed(self.tcx, &self.body.local_decls, destination).is_some() {
+                        // This is bad! The callee will expect the memory to be aligned.
+                        self.fail(
+                            location,
+                            format!(
+                                "encountered packed place in `Call` terminator destination: {:?}",
+                                terminator.kind,
+                            ),
+                        );
+                    }
                 }
 
-                // The call destination place and Operand::Move place used as an argument might be
-                // passed by a reference to the callee. Consequently they cannot be packed.
-                if is_within_packed(self.tcx, &self.body.local_decls, *destination).is_some() {
-                    // This is bad! The callee will expect the memory to be aligned.
-                    self.fail(
-                        location,
-                        format!(
-                            "encountered packed place in `Call` terminator destination: {:?}",
-                            terminator.kind,
-                        ),
-                    );
-                }
                 for arg in args {
                     if let Operand::Move(place) = &arg.node {
                         if is_within_packed(self.tcx, &self.body.local_decls, *place).is_some() {
@@ -1498,15 +1502,22 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     }
                 }
             }
-            TerminatorKind::Call { func, .. } => {
+            TerminatorKind::Call { func, .. } | TerminatorKind::TailCall { func, .. } => {
                 let func_ty = func.ty(&self.body.local_decls, self.tcx);
                 match func_ty.kind() {
                     ty::FnPtr(..) | ty::FnDef(..) => {}
                     _ => self.fail(
                         location,
-                        format!("encountered non-callable type {func_ty} in `Call` terminator"),
+                        format!(
+                            "encountered non-callable type {func_ty} in `{}` terminator",
+                            terminator.kind.name()
+                        ),
                     ),
                 }
+
+                if let TerminatorKind::TailCall { .. } = terminator.kind {
+                    // FIXME(explicit_tail_calls): implement tail-call specific checks here (such as signature matching, forbidding closures, etc)
+                }
             }
             TerminatorKind::Assert { cond, .. } => {
                 let cond_ty = cond.ty(&self.body.local_decls, self.tcx);
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 005a22f642f..bfd505c0672 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -755,7 +755,8 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
         };
 
         match terminator.kind {
-            mir::TerminatorKind::Call { ref func, ref args, ref fn_span, .. } => {
+            mir::TerminatorKind::Call { ref func, ref args, ref fn_span, .. }
+            | mir::TerminatorKind::TailCall { ref func, ref args, ref fn_span } => {
                 let callee_ty = func.ty(self.body, tcx);
                 // *Before* monomorphizing, record that we already handled this mention.
                 self.used_mentioned_items.insert(MentionedItem::Fn(callee_ty));
diff --git a/compiler/rustc_next_trait_solver/src/coherence.rs b/compiler/rustc_next_trait_solver/src/coherence.rs
new file mode 100644
index 00000000000..55f602d907b
--- /dev/null
+++ b/compiler/rustc_next_trait_solver/src/coherence.rs
@@ -0,0 +1,469 @@
+use std::fmt::Debug;
+use std::ops::ControlFlow;
+
+use rustc_type_ir::inherent::*;
+use rustc_type_ir::visit::{TypeVisitable, TypeVisitableExt, TypeVisitor};
+use rustc_type_ir::{self as ty, InferCtxtLike, Interner};
+use tracing::instrument;
+
+/// Whether we do the orphan check relative to this crate or to some remote crate.
+#[derive(Copy, Clone, Debug)]
+pub enum InCrate {
+    Local { mode: OrphanCheckMode },
+    Remote,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum OrphanCheckMode {
+    /// Proper orphan check.
+    Proper,
+    /// Improper orphan check for backward compatibility.
+    ///
+    /// In this mode, type params inside projections are considered to be covered
+    /// even if the projection may normalize to a type that doesn't actually cover
+    /// them. This is unsound. See also [#124559] and [#99554].
+    ///
+    /// [#124559]: https://github.com/rust-lang/rust/issues/124559
+    /// [#99554]: https://github.com/rust-lang/rust/issues/99554
+    Compat,
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum Conflict {
+    Upstream,
+    Downstream,
+}
+
+/// Returns whether all impls which would apply to the `trait_ref`
+/// e.g. `Ty: Trait<Arg>` are already known in the local crate.
+///
+/// This both checks whether any downstream or sibling crates could
+/// implement it and whether an upstream crate can add this impl
+/// without breaking backwards compatibility.
+#[instrument(level = "debug", skip(infcx, lazily_normalize_ty), ret)]
+pub fn trait_ref_is_knowable<Infcx, I, E>(
+    infcx: &Infcx,
+    trait_ref: ty::TraitRef<I>,
+    mut lazily_normalize_ty: impl FnMut(I::Ty) -> Result<I::Ty, E>,
+) -> Result<Result<(), Conflict>, E>
+where
+    Infcx: InferCtxtLike<Interner = I>,
+    I: Interner,
+    E: Debug,
+{
+    if orphan_check_trait_ref(infcx, trait_ref, InCrate::Remote, &mut lazily_normalize_ty)?.is_ok()
+    {
+        // A downstream or cousin crate is allowed to implement some
+        // generic parameters of this trait-ref.
+        return Ok(Err(Conflict::Downstream));
+    }
+
+    if trait_ref_is_local_or_fundamental(infcx.cx(), trait_ref) {
+        // This is a local or fundamental trait, so future-compatibility
+        // is no concern. We know that downstream/cousin crates are not
+        // allowed to implement a generic parameter of this trait ref,
+        // which means impls could only come from dependencies of this
+        // crate, which we already know about.
+        return Ok(Ok(()));
+    }
+
+    // This is a remote non-fundamental trait, so if another crate
+    // can be the "final owner" of the generic parameters of this trait-ref,
+    // they are allowed to implement it future-compatibly.
+    //
+    // However, if we are a final owner, then nobody else can be,
+    // and if we are an intermediate owner, then we don't care
+    // about future-compatibility, which means that we're OK if
+    // we are an owner.
+    if orphan_check_trait_ref(
+        infcx,
+        trait_ref,
+        InCrate::Local { mode: OrphanCheckMode::Proper },
+        &mut lazily_normalize_ty,
+    )?
+    .is_ok()
+    {
+        Ok(Ok(()))
+    } else {
+        Ok(Err(Conflict::Upstream))
+    }
+}
+
+pub fn trait_ref_is_local_or_fundamental<I: Interner>(tcx: I, trait_ref: ty::TraitRef<I>) -> bool {
+    trait_ref.def_id.is_local() || tcx.trait_is_fundamental(trait_ref.def_id)
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum IsFirstInputType {
+    No,
+    Yes,
+}
+
+impl From<bool> for IsFirstInputType {
+    fn from(b: bool) -> IsFirstInputType {
+        match b {
+            false => IsFirstInputType::No,
+            true => IsFirstInputType::Yes,
+        }
+    }
+}
+
+#[derive(derivative::Derivative)]
+#[derivative(Debug(bound = "T: Debug"))]
+pub enum OrphanCheckErr<I: Interner, T> {
+    NonLocalInputType(Vec<(I::Ty, IsFirstInputType)>),
+    UncoveredTyParams(UncoveredTyParams<I, T>),
+}
+
+#[derive(derivative::Derivative)]
+#[derivative(Debug(bound = "T: Debug"))]
+pub struct UncoveredTyParams<I: Interner, T> {
+    pub uncovered: T,
+    pub local_ty: Option<I::Ty>,
+}
+
+/// Checks whether a trait-ref is potentially implementable by a crate.
+///
+/// The current rule is that a trait-ref orphan checks in a crate C:
+///
+/// 1. Order the parameters in the trait-ref in generic parameters order
+/// - Self first, others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
+/// 2. Of these type parameters, there is at least one type parameter
+///    in which, walking the type as a tree, you can reach a type local
+///    to C where all types in-between are fundamental types. Call the
+///    first such parameter the "local key parameter".
+///     - e.g., `Box<LocalType>` is OK, because you can visit LocalType
+///       going through `Box`, which is fundamental.
+///     - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
+///       the same reason.
+///     - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
+///       not local), `Vec<LocalType>` is bad, because `Vec<->` is between
+///       the local type and the type parameter.
+/// 3. Before this local type, no generic type parameter of the impl must
+///    be reachable through fundamental types.
+///     - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
+///     - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is
+///       reachable through the fundamental type `Box`.
+/// 4. Every type in the local key parameter not known in C, going
+///    through the parameter's type tree, must appear only as a subtree of
+///    a type local to C, with only fundamental types between the type
+///    local to C and the local key parameter.
+///     - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
+///     is bad, because the only local type with `T` as a subtree is
+///     `LocalType<T>`, and `Vec<->` is between it and the type parameter.
+///     - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
+///     the second occurrence of `T` is not a subtree of *any* local type.
+///     - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
+///     `LocalType<Vec<T>>`, which is local and has no types between it and
+///     the type parameter.
+///
+/// The orphan rules actually serve several different purposes:
+///
+/// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
+///    every type local to one crate is unknown in the other) can't implement
+///    the same trait-ref. This follows because it can be seen that no such
+///    type can orphan-check in 2 such crates.
+///
+///    To check that a local impl follows the orphan rules, we check it in
+///    InCrate::Local mode, using type parameters for the "generic" types.
+///
+///    In InCrate::Local mode the orphan check succeeds if the current crate
+///    is definitely allowed to implement the given trait (no false positives).
+///
+/// 2. They ground negative reasoning for coherence. If a user wants to
+///    write both a conditional blanket impl and a specific impl, we need to
+///    make sure they do not overlap. For example, if we write
+///    ```ignore (illustrative)
+///    impl<T> IntoIterator for Vec<T>
+///    impl<T: Iterator> IntoIterator for T
+///    ```
+///    We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
+///    We can observe that this holds in the current crate, but we need to make
+///    sure this will also hold in all unknown crates (both "independent" crates,
+///    which we need for link-safety, and also child crates, because we don't want
+///    child crates to get error for impl conflicts in a *dependency*).
+///
+///    For that, we only allow negative reasoning if, for every assignment to the
+///    inference variables, every unknown crate would get an orphan error if they
+///    try to implement this trait-ref. To check for this, we use InCrate::Remote
+///    mode. That is sound because we already know all the impls from known crates.
+///
+///    In InCrate::Remote mode the orphan check succeeds if a foreign crate
+///    *could* implement the given trait (no false negatives).
+///
+/// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
+///    add "non-blanket" impls without breaking negative reasoning in dependent
+///    crates. This is the "rebalancing coherence" (RFC 1023) restriction.
+///
+///    For that, we only allow a crate to perform negative reasoning on
+///    non-local-non-`#[fundamental]` if there's a local key parameter as per (2).
+///
+///    Because we never perform negative reasoning generically (coherence does
+///    not involve type parameters), this can be interpreted as doing the full
+///    orphan check (using InCrate::Local mode), instantiating non-local known
+///    types for all inference variables.
+///
+///    This allows for crates to future-compatibly add impls as long as they
+///    can't apply to types with a key parameter in a child crate - applying
+///    the rules, this basically means that every type parameter in the impl
+///    must appear behind a non-fundamental type (because this is not a
+///    type-system requirement, crate owners might also go for "semantic
+///    future-compatibility" involving things such as sealed traits, but
+///    the above requirement is sufficient, and is necessary in "open world"
+///    cases).
+///
+/// Note that this function is never called for types that have both type
+/// parameters and inference variables.
+#[instrument(level = "trace", skip(infcx, lazily_normalize_ty), ret)]
+pub fn orphan_check_trait_ref<Infcx, I, E: Debug>(
+    infcx: &Infcx,
+    trait_ref: ty::TraitRef<I>,
+    in_crate: InCrate,
+    lazily_normalize_ty: impl FnMut(I::Ty) -> Result<I::Ty, E>,
+) -> Result<Result<(), OrphanCheckErr<I, I::Ty>>, E>
+where
+    Infcx: InferCtxtLike<Interner = I>,
+    I: Interner,
+    E: Debug,
+{
+    if trait_ref.has_param() {
+        panic!("orphan check only expects inference variables: {trait_ref:?}");
+    }
+
+    let mut checker = OrphanChecker::new(infcx, in_crate, lazily_normalize_ty);
+    Ok(match trait_ref.visit_with(&mut checker) {
+        ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)),
+        ControlFlow::Break(residual) => match residual {
+            OrphanCheckEarlyExit::NormalizationFailure(err) => return Err(err),
+            OrphanCheckEarlyExit::UncoveredTyParam(ty) => {
+                // Does there exist some local type after the `ParamTy`.
+                checker.search_first_local_ty = true;
+                let local_ty = match trait_ref.visit_with(&mut checker) {
+                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(local_ty)) => Some(local_ty),
+                    _ => None,
+                };
+                Err(OrphanCheckErr::UncoveredTyParams(UncoveredTyParams {
+                    uncovered: ty,
+                    local_ty,
+                }))
+            }
+            OrphanCheckEarlyExit::LocalTy(_) => Ok(()),
+        },
+    })
+}
+
+struct OrphanChecker<'a, Infcx, I: Interner, F> {
+    infcx: &'a Infcx,
+    in_crate: InCrate,
+    in_self_ty: bool,
+    lazily_normalize_ty: F,
+    /// Ignore orphan check failures and exclusively search for the first local type.
+    search_first_local_ty: bool,
+    non_local_tys: Vec<(I::Ty, IsFirstInputType)>,
+}
+
+impl<'a, Infcx, I, F, E> OrphanChecker<'a, Infcx, I, F>
+where
+    Infcx: InferCtxtLike<Interner = I>,
+    I: Interner,
+    F: FnOnce(I::Ty) -> Result<I::Ty, E>,
+{
+    fn new(infcx: &'a Infcx, in_crate: InCrate, lazily_normalize_ty: F) -> Self {
+        OrphanChecker {
+            infcx,
+            in_crate,
+            in_self_ty: true,
+            lazily_normalize_ty,
+            search_first_local_ty: false,
+            non_local_tys: Vec::new(),
+        }
+    }
+
+    fn found_non_local_ty(&mut self, t: I::Ty) -> ControlFlow<OrphanCheckEarlyExit<I, E>> {
+        self.non_local_tys.push((t, self.in_self_ty.into()));
+        ControlFlow::Continue(())
+    }
+
+    fn found_uncovered_ty_param(&mut self, ty: I::Ty) -> ControlFlow<OrphanCheckEarlyExit<I, E>> {
+        if self.search_first_local_ty {
+            return ControlFlow::Continue(());
+        }
+
+        ControlFlow::Break(OrphanCheckEarlyExit::UncoveredTyParam(ty))
+    }
+
+    fn def_id_is_local(&mut self, def_id: I::DefId) -> bool {
+        match self.in_crate {
+            InCrate::Local { .. } => def_id.is_local(),
+            InCrate::Remote => false,
+        }
+    }
+}
+
+enum OrphanCheckEarlyExit<I: Interner, E> {
+    NormalizationFailure(E),
+    UncoveredTyParam(I::Ty),
+    LocalTy(I::Ty),
+}
+
+impl<'a, Infcx, I, F, E> TypeVisitor<I> for OrphanChecker<'a, Infcx, I, F>
+where
+    Infcx: InferCtxtLike<Interner = I>,
+    I: Interner,
+    F: FnMut(I::Ty) -> Result<I::Ty, E>,
+{
+    type Result = ControlFlow<OrphanCheckEarlyExit<I, E>>;
+
+    fn visit_region(&mut self, _r: I::Region) -> Self::Result {
+        ControlFlow::Continue(())
+    }
+
+    fn visit_ty(&mut self, ty: I::Ty) -> Self::Result {
+        let ty = self.infcx.shallow_resolve(ty);
+        let ty = match (self.lazily_normalize_ty)(ty) {
+            Ok(norm_ty) if norm_ty.is_ty_var() => ty,
+            Ok(norm_ty) => norm_ty,
+            Err(err) => return ControlFlow::Break(OrphanCheckEarlyExit::NormalizationFailure(err)),
+        };
+
+        let result = match ty.kind() {
+            ty::Bool
+            | ty::Char
+            | ty::Int(..)
+            | ty::Uint(..)
+            | ty::Float(..)
+            | ty::Str
+            | ty::FnDef(..)
+            | ty::Pat(..)
+            | ty::FnPtr(_)
+            | ty::Array(..)
+            | ty::Slice(..)
+            | ty::RawPtr(..)
+            | ty::Never
+            | ty::Tuple(..) => self.found_non_local_ty(ty),
+
+            ty::Param(..) => panic!("unexpected ty param"),
+
+            ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => {
+                match self.in_crate {
+                    InCrate::Local { .. } => self.found_uncovered_ty_param(ty),
+                    // The inference variable might be unified with a local
+                    // type in that remote crate.
+                    InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
+                }
+            }
+
+            // A rigid alias may normalize to anything.
+            // * If it references an infer var, placeholder or bound ty, it may
+            //   normalize to that, so we have to treat it as an uncovered ty param.
+            // * Otherwise it may normalize to any non-type-generic type
+            //   be it local or non-local.
+            ty::Alias(kind, _) => {
+                if ty.has_type_flags(
+                    ty::TypeFlags::HAS_TY_PLACEHOLDER
+                        | ty::TypeFlags::HAS_TY_BOUND
+                        | ty::TypeFlags::HAS_TY_INFER,
+                ) {
+                    match self.in_crate {
+                        InCrate::Local { mode } => match kind {
+                            ty::Projection => {
+                                if let OrphanCheckMode::Compat = mode {
+                                    ControlFlow::Continue(())
+                                } else {
+                                    self.found_uncovered_ty_param(ty)
+                                }
+                            }
+                            _ => self.found_uncovered_ty_param(ty),
+                        },
+                        InCrate::Remote => {
+                            // The inference variable might be unified with a local
+                            // type in that remote crate.
+                            ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
+                        }
+                    }
+                } else {
+                    // Regarding *opaque types* specifically, we choose to treat them as non-local,
+                    // even those that appear within the same crate. This seems somewhat surprising
+                    // at first, but makes sense when you consider that opaque types are supposed
+                    // to hide the underlying type *within the same crate*. When an opaque type is
+                    // used from outside the module where it is declared, it should be impossible to
+                    // observe anything about it other than the traits that it implements.
+                    //
+                    // The alternative would be to look at the underlying type to determine whether
+                    // or not the opaque type itself should be considered local.
+                    //
+                    // However, this could make it a breaking change to switch the underlying hidden
+                    // type from a local type to a remote type. This would violate the rule that
+                    // opaque types should be completely opaque apart from the traits that they
+                    // implement, so we don't use this behavior.
+                    // Addendum: Moreover, revealing the underlying type is likely to cause cycle
+                    // errors as we rely on coherence / the specialization graph during typeck.
+
+                    self.found_non_local_ty(ty)
+                }
+            }
+
+            // For fundamental types, we just look inside of them.
+            ty::Ref(_, ty, _) => ty.visit_with(self),
+            ty::Adt(def, args) => {
+                if self.def_id_is_local(def.def_id()) {
+                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
+                } else if def.is_fundamental() {
+                    args.visit_with(self)
+                } else {
+                    self.found_non_local_ty(ty)
+                }
+            }
+            ty::Foreign(def_id) => {
+                if self.def_id_is_local(def_id) {
+                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
+                } else {
+                    self.found_non_local_ty(ty)
+                }
+            }
+            ty::Dynamic(tt, ..) => {
+                let principal = tt.principal().map(|p| p.def_id());
+                if principal.is_some_and(|p| self.def_id_is_local(p)) {
+                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
+                } else {
+                    self.found_non_local_ty(ty)
+                }
+            }
+            ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
+            ty::Closure(did, ..) | ty::CoroutineClosure(did, ..) | ty::Coroutine(did, ..) => {
+                if self.def_id_is_local(did) {
+                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
+                } else {
+                    self.found_non_local_ty(ty)
+                }
+            }
+            // This should only be created when checking whether we have to check whether some
+            // auto trait impl applies. There will never be multiple impls, so we can just
+            // act as if it were a local type here.
+            ty::CoroutineWitness(..) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
+        };
+        // A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so
+        // the first type we visit is always the self type.
+        self.in_self_ty = false;
+        result
+    }
+
+    /// All possible values for a constant parameter already exist
+    /// in the crate defining the trait, so they are always non-local[^1].
+    ///
+    /// Because there's no way to have an impl where the first local
+    /// generic argument is a constant, we also don't have to fail
+    /// the orphan check when encountering a parameter or a generic constant.
+    ///
+    /// This means that we can completely ignore constants during the orphan check.
+    ///
+    /// See `tests/ui/coherence/const-generics-orphan-check-ok.rs` for examples.
+    ///
+    /// [^1]: This might not hold for function pointers or trait objects in the future.
+    /// As these should be quite rare as const arguments and especially rare as impl
+    /// parameters, allowing uncovered const parameters in impls seems more useful
+    /// than allowing `impl<T> Trait<local_fn_ptr, T> for i32` to compile.
+    fn visit_const(&mut self, _c: I::Const) -> Self::Result {
+        ControlFlow::Continue(())
+    }
+}
diff --git a/compiler/rustc_next_trait_solver/src/delegate.rs b/compiler/rustc_next_trait_solver/src/delegate.rs
index 31032dc679a..6a3d58b5906 100644
--- a/compiler/rustc_next_trait_solver/src/delegate.rs
+++ b/compiler/rustc_next_trait_solver/src/delegate.rs
@@ -1,4 +1,3 @@
-use std::fmt::Debug;
 use std::ops::Deref;
 
 use rustc_type_ir::fold::TypeFoldable;
@@ -32,12 +31,6 @@ pub trait SolverDelegate:
     // FIXME: Uplift the leak check into this crate.
     fn leak_check(&self, max_input_universe: ty::UniverseIndex) -> Result<(), NoSolution>;
 
-    // FIXME: This is only here because elaboration lives in `rustc_infer`!
-    fn elaborate_supertraits(
-        cx: Self::Interner,
-        trait_ref: ty::Binder<Self::Interner, ty::TraitRef<Self::Interner>>,
-    ) -> impl Iterator<Item = ty::Binder<Self::Interner, ty::TraitRef<Self::Interner>>>;
-
     fn try_const_eval_resolve(
         &self,
         param_env: <Self::Interner as Interner>::ParamEnv,
@@ -99,14 +92,6 @@ pub trait SolverDelegate:
 
     fn reset_opaque_types(&self);
 
-    fn trait_ref_is_knowable<E: Debug>(
-        &self,
-        trait_ref: ty::TraitRef<Self::Interner>,
-        lazily_normalize_ty: impl FnMut(
-            <Self::Interner as Interner>::Ty,
-        ) -> Result<<Self::Interner as Interner>::Ty, E>,
-    ) -> Result<bool, E>;
-
     fn fetch_eligible_assoc_item(
         &self,
         param_env: <Self::Interner as Interner>::ParamEnv,
diff --git a/compiler/rustc_next_trait_solver/src/lib.rs b/compiler/rustc_next_trait_solver/src/lib.rs
index 761475d3d6b..0a5b4278058 100644
--- a/compiler/rustc_next_trait_solver/src/lib.rs
+++ b/compiler/rustc_next_trait_solver/src/lib.rs
@@ -5,6 +5,7 @@
 //! So if you got to this crate from the old solver, it's totally normal.
 
 pub mod canonicalizer;
+pub mod coherence;
 pub mod delegate;
 pub mod relate;
 pub mod resolve;
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
index 38a4f7dfe25..01dde9ca587 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -2,6 +2,7 @@
 
 pub(super) mod structural_traits;
 
+use rustc_type_ir::elaborate;
 use rustc_type_ir::fold::TypeFoldable;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
@@ -667,7 +668,7 @@ where
         // a projection goal.
         if let Some(principal) = bounds.principal() {
             let principal_trait_ref = principal.with_self_ty(cx, self_ty);
-            for (idx, assumption) in D::elaborate_supertraits(cx, principal_trait_ref).enumerate() {
+            for (idx, assumption) in elaborate::supertraits(cx, principal_trait_ref).enumerate() {
                 candidates.extend(G::probe_and_consider_object_bound_candidate(
                     self,
                     CandidateSource::BuiltinImpl(BuiltinImplSource::Object(idx)),
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index 3447b39fa5b..7df14e81ab5 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -669,7 +669,9 @@ where
     let cx = ecx.cx();
     let mut requirements = vec![];
     requirements.extend(
-        cx.explicit_super_predicates_of(trait_ref.def_id).iter_instantiated(cx, trait_ref.args),
+        cx.explicit_super_predicates_of(trait_ref.def_id)
+            .iter_instantiated(cx, trait_ref.args)
+            .map(|(pred, _)| pred),
     );
 
     // FIXME(associated_const_equality): Also add associated consts to
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
index d8a3acc655a..c90f8e76163 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
@@ -11,6 +11,7 @@ use rustc_type_ir::{self as ty, CanonicalVarValues, InferCtxtLike, Interner};
 use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
 use tracing::{instrument, trace};
 
+use crate::coherence;
 use crate::delegate::SolverDelegate;
 use crate::solve::inspect::{self, ProofTreeBuilder};
 use crate::solve::search_graph::SearchGraph;
@@ -906,7 +907,8 @@ where
     ) -> Result<bool, NoSolution> {
         let delegate = self.delegate;
         let lazily_normalize_ty = |ty| self.structurally_normalize_ty(param_env, ty);
-        delegate.trait_ref_is_knowable(trait_ref, lazily_normalize_ty)
+        coherence::trait_ref_is_knowable(&**delegate, trait_ref, lazily_normalize_ty)
+            .map(|is_knowable| is_knowable.is_ok())
     }
 
     pub(super) fn fetch_eligible_assoc_item(
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index b2a59eece0d..4474bbc2351 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -6,7 +6,7 @@ use rustc_type_ir::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
 use rustc_type_ir::visit::TypeVisitableExt as _;
-use rustc_type_ir::{self as ty, Interner, TraitPredicate, Upcast as _};
+use rustc_type_ir::{self as ty, elaborate, Interner, TraitPredicate, Upcast as _};
 use tracing::{instrument, trace};
 
 use crate::delegate::SolverDelegate;
@@ -787,7 +787,7 @@ where
             ));
         } else if let Some(a_principal) = a_data.principal() {
             for new_a_principal in
-                D::elaborate_supertraits(self.cx(), a_principal.with_self_ty(cx, a_ty)).skip(1)
+                elaborate::supertraits(self.cx(), a_principal.with_self_ty(cx, a_ty)).skip(1)
             {
                 responses.extend(self.consider_builtin_upcast_to_principal(
                     goal,
@@ -862,8 +862,7 @@ where
             .auto_traits()
             .into_iter()
             .chain(a_data.principal_def_id().into_iter().flat_map(|principal_def_id| {
-                self.cx()
-                    .supertrait_def_ids(principal_def_id)
+                elaborate::supertrait_def_ids(self.cx(), principal_def_id)
                     .into_iter()
                     .filter(|def_id| self.cx().trait_is_auto(*def_id))
             }))
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index 58fef9b6c45..a8fe35f45b3 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -282,7 +282,7 @@ impl<'a> Parser<'a> {
     pub fn parse_inner_attributes(&mut self) -> PResult<'a, ast::AttrVec> {
         let mut attrs = ast::AttrVec::new();
         loop {
-            let start_pos: u32 = self.num_bump_calls.try_into().unwrap();
+            let start_pos = self.num_bump_calls;
             // Only try to parse if it is an inner attribute (has `!`).
             let attr = if self.check(&token::Pound) && self.look_ahead(1, |t| t == &token::Not) {
                 Some(self.parse_attribute(InnerAttrPolicy::Permitted)?)
@@ -303,7 +303,7 @@ impl<'a> Parser<'a> {
                 None
             };
             if let Some(attr) = attr {
-                let end_pos: u32 = self.num_bump_calls.try_into().unwrap();
+                let end_pos = self.num_bump_calls;
                 // If we are currently capturing tokens, mark the location of this inner attribute.
                 // If capturing ends up creating a `LazyAttrTokenStream`, we will include
                 // this replace range with it, removing the inner attribute from the final
@@ -313,7 +313,7 @@ impl<'a> Parser<'a> {
                 // corresponding macro).
                 let range = start_pos..end_pos;
                 if let Capturing::Yes = self.capture_state.capturing {
-                    self.capture_state.inner_attr_ranges.insert(attr.id, (range, vec![]));
+                    self.capture_state.inner_attr_ranges.insert(attr.id, (range, None));
                 }
                 attrs.push(attr);
             } else {
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
index 13a647adfe3..38f18022e3c 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -1,6 +1,6 @@
 use super::{Capturing, FlatToken, ForceCollect, Parser, ReplaceRange, TokenCursor, TrailingToken};
 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
-use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree, AttributesData, DelimSpacing};
+use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree, AttrsTarget, DelimSpacing};
 use rustc_ast::tokenstream::{DelimSpan, LazyAttrTokenStream, Spacing, ToAttrTokenStream};
 use rustc_ast::{self as ast};
 use rustc_ast::{AttrVec, Attribute, HasAttrs, HasTokens};
@@ -8,7 +8,6 @@ use rustc_errors::PResult;
 use rustc_session::parse::ParseSess;
 use rustc_span::{sym, Span, DUMMY_SP};
 
-use std::ops::Range;
 use std::{iter, mem};
 
 /// A wrapper type to ensure that the parser handles outer attributes correctly.
@@ -88,7 +87,6 @@ fn has_cfg_or_cfg_attr(attrs: &[Attribute]) -> bool {
 //
 // This also makes `Parser` very cheap to clone, since
 // there is no intermediate collection buffer to clone.
-#[derive(Clone)]
 struct LazyAttrTokenStreamImpl {
     start_token: (Token, Spacing),
     cursor_snapshot: TokenCursor,
@@ -146,24 +144,23 @@ impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
             // start position, we ensure that any replace range which encloses
             // another replace range will capture the *replaced* tokens for the inner
             // range, not the original tokens.
-            for (range, new_tokens) in replace_ranges.into_iter().rev() {
+            for (range, target) in replace_ranges.into_iter().rev() {
                 assert!(!range.is_empty(), "Cannot replace an empty range: {range:?}");
-                // Replace ranges are only allowed to decrease the number of tokens.
-                assert!(
-                    range.len() >= new_tokens.len(),
-                    "Range {range:?} has greater len than {new_tokens:?}"
-                );
-
-                // Replace any removed tokens with `FlatToken::Empty`.
-                // This keeps the total length of `tokens` constant throughout the
-                // replacement process, allowing us to use all of the `ReplaceRanges` entries
-                // without adjusting indices.
-                let filler = iter::repeat((FlatToken::Empty, Spacing::Alone))
-                    .take(range.len() - new_tokens.len());
 
+                // Replace the tokens in range with zero or one `FlatToken::AttrsTarget`s, plus
+                // enough `FlatToken::Empty`s to fill up the rest of the range. This keeps the
+                // total length of `tokens` constant throughout the replacement process, allowing
+                // us to use all of the `ReplaceRanges` entries without adjusting indices.
+                let target_len = target.is_some() as usize;
                 tokens.splice(
                     (range.start as usize)..(range.end as usize),
-                    new_tokens.into_iter().chain(filler),
+                    target
+                        .into_iter()
+                        .map(|target| (FlatToken::AttrsTarget(target), Spacing::Alone))
+                        .chain(
+                            iter::repeat((FlatToken::Empty, Spacing::Alone))
+                                .take(range.len() - target_len),
+                        ),
                 );
             }
             make_attr_token_stream(tokens.into_iter(), self.break_last_token)
@@ -316,7 +313,7 @@ impl<'a> Parser<'a> {
                 .iter()
                 .cloned()
                 .chain(inner_attr_replace_ranges.iter().cloned())
-                .map(|(range, tokens)| ((range.start - start_pos)..(range.end - start_pos), tokens))
+                .map(|(range, data)| ((range.start - start_pos)..(range.end - start_pos), data))
                 .collect()
         };
 
@@ -346,18 +343,14 @@ impl<'a> Parser<'a> {
             && matches!(self.capture_state.capturing, Capturing::Yes)
             && has_cfg_or_cfg_attr(final_attrs)
         {
-            let attr_data = AttributesData { attrs: final_attrs.iter().cloned().collect(), tokens };
+            assert!(!self.break_last_token, "Should not have unglued last token with cfg attr");
 
-            // Replace the entire AST node that we just parsed, including attributes,
-            // with a `FlatToken::AttrTarget`. If this AST node is inside an item
-            // that has `#[derive]`, then this will allow us to cfg-expand this
-            // AST node.
+            // Replace the entire AST node that we just parsed, including attributes, with
+            // `target`. If this AST node is inside an item that has `#[derive]`, then this will
+            // allow us to cfg-expand this AST node.
             let start_pos = if has_outer_attrs { attrs.start_pos } else { start_pos };
-            let new_tokens = vec![(FlatToken::AttrTarget(attr_data), Spacing::Alone)];
-
-            assert!(!self.break_last_token, "Should not have unglued last token with cfg attr");
-            let range: Range<u32> = (start_pos.try_into().unwrap())..(end_pos.try_into().unwrap());
-            self.capture_state.replace_ranges.push((range, new_tokens));
+            let target = AttrsTarget { attrs: final_attrs.iter().cloned().collect(), tokens };
+            self.capture_state.replace_ranges.push((start_pos..end_pos, Some(target)));
             self.capture_state.replace_ranges.extend(inner_attr_replace_ranges);
         }
 
@@ -419,11 +412,11 @@ fn make_attr_token_stream(
                 .expect("Bottom token frame is missing!")
                 .inner
                 .push(AttrTokenTree::Token(token, spacing)),
-            FlatToken::AttrTarget(data) => stack
+            FlatToken::AttrsTarget(target) => stack
                 .last_mut()
                 .expect("Bottom token frame is missing!")
                 .inner
-                .push(AttrTokenTree::Attributes(data)),
+                .push(AttrTokenTree::AttrsTarget(target)),
             FlatToken::Empty => {}
         }
         token_and_spacing = iter.next();
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 5f16a3e1f37..45ca267fe5d 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -20,7 +20,7 @@ use path::PathStyle;
 
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, IdentIsRaw, Nonterminal, Token, TokenKind};
-use rustc_ast::tokenstream::{AttributesData, DelimSpacing, DelimSpan, Spacing};
+use rustc_ast::tokenstream::{AttrsTarget, DelimSpacing, DelimSpan, Spacing};
 use rustc_ast::tokenstream::{TokenStream, TokenTree, TokenTreeCursor};
 use rustc_ast::util::case::Case;
 use rustc_ast::{
@@ -203,13 +203,13 @@ struct ClosureSpans {
 }
 
 /// Indicates a range of tokens that should be replaced by
-/// the tokens in the provided vector. This is used in two
+/// the tokens in the provided `AttrsTarget`. This is used in two
 /// places during token collection:
 ///
 /// 1. During the parsing of an AST node that may have a `#[derive]`
 /// attribute, we parse a nested AST node that has `#[cfg]` or `#[cfg_attr]`
 /// In this case, we use a `ReplaceRange` to replace the entire inner AST node
-/// with `FlatToken::AttrTarget`, allowing us to perform eager cfg-expansion
+/// with `FlatToken::AttrsTarget`, allowing us to perform eager cfg-expansion
 /// on an `AttrTokenStream`.
 ///
 /// 2. When we parse an inner attribute while collecting tokens. We
@@ -219,7 +219,7 @@ struct ClosureSpans {
 /// the first macro inner attribute to invoke a proc-macro).
 /// When create a `TokenStream`, the inner attributes get inserted
 /// into the proper place in the token stream.
-type ReplaceRange = (Range<u32>, Vec<(FlatToken, Spacing)>);
+type ReplaceRange = (Range<u32>, Option<AttrsTarget>);
 
 /// Controls how we capture tokens. Capturing can be expensive,
 /// so we try to avoid performing capturing in cases where
@@ -1608,11 +1608,10 @@ enum FlatToken {
     /// A token - this holds both delimiter (e.g. '{' and '}')
     /// and non-delimiter tokens
     Token(Token),
-    /// Holds the `AttributesData` for an AST node. The
-    /// `AttributesData` is inserted directly into the
-    /// constructed `AttrTokenStream` as
-    /// an `AttrTokenTree::Attributes`.
-    AttrTarget(AttributesData),
+    /// Holds the `AttrsTarget` for an AST node. The `AttrsTarget` is inserted
+    /// directly into the constructed `AttrTokenStream` as an
+    /// `AttrTokenTree::AttrsTarget`.
+    AttrsTarget(AttrsTarget),
     /// A special 'empty' token that is ignored during the conversion
     /// to an `AttrTokenStream`. This is used to simplify the
     /// handling of replace ranges.
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index 4e0f2792d97..92cf73870ff 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -321,8 +321,14 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
             // The fields are not expanded yet.
             return;
         }
-        let def_ids = fields.iter().map(|field| self.r.local_def_id(field.id).to_def_id());
-        self.r.field_def_ids.insert(def_id, self.r.tcx.arena.alloc_from_iter(def_ids));
+        let fields = fields
+            .iter()
+            .enumerate()
+            .map(|(i, field)| {
+                field.ident.unwrap_or_else(|| Ident::from_str_and_span(&format!("{i}"), field.span))
+            })
+            .collect();
+        self.r.field_names.insert(def_id, fields);
     }
 
     fn insert_field_visibilities_local(&mut self, def_id: DefId, fields: &[ast::FieldDef]) {
diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index 80619c59cc3..a4fdb4a0baf 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -8,6 +8,7 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_span::hygiene::LocalExpnId;
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::Span;
+use std::mem;
 use tracing::debug;
 
 pub(crate) fn collect_definitions(
@@ -15,8 +16,9 @@ pub(crate) fn collect_definitions(
     fragment: &AstFragment,
     expansion: LocalExpnId,
 ) {
-    let (parent_def, impl_trait_context) = resolver.invocation_parents[&expansion];
-    fragment.visit_with(&mut DefCollector { resolver, parent_def, expansion, impl_trait_context });
+    let (parent_def, impl_trait_context, in_attr) = resolver.invocation_parents[&expansion];
+    let mut visitor = DefCollector { resolver, parent_def, expansion, impl_trait_context, in_attr };
+    fragment.visit_with(&mut visitor);
 }
 
 /// Creates `DefId`s for nodes in the AST.
@@ -24,6 +26,7 @@ struct DefCollector<'a, 'b, 'tcx> {
     resolver: &'a mut Resolver<'b, 'tcx>,
     parent_def: LocalDefId,
     impl_trait_context: ImplTraitContext,
+    in_attr: bool,
     expansion: LocalExpnId,
 }
 
@@ -53,7 +56,7 @@ impl<'a, 'b, 'tcx> DefCollector<'a, 'b, 'tcx> {
     }
 
     fn with_parent<F: FnOnce(&mut Self)>(&mut self, parent_def: LocalDefId, f: F) {
-        let orig_parent_def = std::mem::replace(&mut self.parent_def, parent_def);
+        let orig_parent_def = mem::replace(&mut self.parent_def, parent_def);
         f(self);
         self.parent_def = orig_parent_def;
     }
@@ -63,7 +66,7 @@ impl<'a, 'b, 'tcx> DefCollector<'a, 'b, 'tcx> {
         impl_trait_context: ImplTraitContext,
         f: F,
     ) {
-        let orig_itc = std::mem::replace(&mut self.impl_trait_context, impl_trait_context);
+        let orig_itc = mem::replace(&mut self.impl_trait_context, impl_trait_context);
         f(self);
         self.impl_trait_context = orig_itc;
     }
@@ -105,8 +108,10 @@ impl<'a, 'b, 'tcx> DefCollector<'a, 'b, 'tcx> {
 
     fn visit_macro_invoc(&mut self, id: NodeId) {
         let id = id.placeholder_to_expn_id();
-        let old_parent =
-            self.resolver.invocation_parents.insert(id, (self.parent_def, self.impl_trait_context));
+        let old_parent = self
+            .resolver
+            .invocation_parents
+            .insert(id, (self.parent_def, self.impl_trait_context, self.in_attr));
         assert!(old_parent.is_none(), "parent `LocalDefId` is reset for an invocation");
     }
 }
@@ -413,4 +418,10 @@ impl<'a, 'b, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'b, 'tcx> {
             visit::walk_crate(self, krate)
         }
     }
+
+    fn visit_attribute(&mut self, attr: &'a Attribute) -> Self::Result {
+        let orig_in_attr = mem::replace(&mut self.in_attr, true);
+        visit::walk_attribute(self, attr);
+        self.in_attr = orig_in_attr;
+    }
 }
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 50a4e03d233..ffd495aa985 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1726,11 +1726,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         )) = binding.kind
         {
             let def_id = self.tcx.parent(ctor_def_id);
-            return self
-                .field_def_ids(def_id)?
-                .iter()
-                .map(|&field_id| self.def_span(field_id))
-                .reduce(Span::to); // None for `struct Foo()`
+            return self.field_idents(def_id)?.iter().map(|&f| f.span).reduce(Span::to); // None for `struct Foo()`
         }
         None
     }
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index ad4e222f4de..1d37264f96a 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1744,7 +1744,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                             ) {
                                 self.r.dcx().emit_err(errors::LendingIteratorReportError {
                                     lifetime: lifetime.ident.span,
-                                    ty: ty.span(),
+                                    ty: ty.span,
                                 });
                             } else {
                                 self.r.dcx().emit_err(errors::AnonymousLivetimeNonGatReportError {
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index 764cc350182..941fb6436df 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -1532,17 +1532,17 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                     if !this.has_private_fields(def_id) {
                         // If the fields of the type are private, we shouldn't be suggesting using
                         // the struct literal syntax at all, as that will cause a subsequent error.
-                        let field_ids = this.r.field_def_ids(def_id);
-                        let (fields, applicability) = match field_ids {
-                            Some(field_ids) => {
-                                let fields = field_ids.iter().map(|&id| this.r.tcx.item_name(id));
-
+                        let fields = this.r.field_idents(def_id);
+                        let has_fields = fields.as_ref().is_some_and(|f| !f.is_empty());
+                        let (fields, applicability) = match fields {
+                            Some(fields) => {
                                 let fields = if let Some(old_fields) = old_fields {
                                     fields
+                                        .iter()
                                         .enumerate()
                                         .map(|(idx, new)| (new, old_fields.get(idx)))
                                         .map(|(new, old)| {
-                                            let new = new.to_ident_string();
+                                            let new = new.name.to_ident_string();
                                             if let Some(Some(old)) = old
                                                 && new != *old
                                             {
@@ -1553,17 +1553,17 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                                         })
                                         .collect::<Vec<String>>()
                                 } else {
-                                    fields.map(|f| format!("{f}{tail}")).collect::<Vec<String>>()
+                                    fields
+                                        .iter()
+                                        .map(|f| format!("{f}{tail}"))
+                                        .collect::<Vec<String>>()
                                 };
 
                                 (fields.join(", "), applicability)
                             }
                             None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
                         };
-                        let pad = match field_ids {
-                            Some([]) => "",
-                            _ => " ",
-                        };
+                        let pad = if has_fields { " " } else { "" };
                         err.span_suggestion(
                             span,
                             format!("use struct {descr} syntax instead"),
@@ -1723,12 +1723,9 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             &args[..],
                         );
                         // Use spans of the tuple struct definition.
-                        self.r.field_def_ids(def_id).map(|field_ids| {
-                            field_ids
-                                .iter()
-                                .map(|&field_id| self.r.def_span(field_id))
-                                .collect::<Vec<_>>()
-                        })
+                        self.r
+                            .field_idents(def_id)
+                            .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
                     }
                     _ => None,
                 };
@@ -1791,7 +1788,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), ctor_def_id), _) if ns == ValueNS => {
                 let def_id = self.r.tcx.parent(ctor_def_id);
                 err.span_label(self.r.def_span(def_id), format!("`{path_str}` defined here"));
-                let fields = self.r.field_def_ids(def_id).map_or_else(
+                let fields = self.r.field_idents(def_id).map_or_else(
                     || "/* fields */".to_string(),
                     |field_ids| vec!["_"; field_ids.len()].join(", "),
                 );
@@ -2017,12 +2014,9 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                     if let Some(Res::Def(DefKind::Struct | DefKind::Union, did)) =
                         resolution.full_res()
                     {
-                        if let Some(field_ids) = self.r.field_def_ids(did) {
-                            if let Some(field_id) = field_ids
-                                .iter()
-                                .find(|&&field_id| ident.name == self.r.tcx.item_name(field_id))
-                            {
-                                return Some(AssocSuggestion::Field(self.r.def_span(*field_id)));
+                        if let Some(fields) = self.r.field_idents(did) {
+                            if let Some(field) = fields.iter().find(|id| ident.name == id.name) {
+                                return Some(AssocSuggestion::Field(field.span));
                             }
                         }
                     }
@@ -2418,7 +2412,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 match kind {
                     CtorKind::Const => false,
                     CtorKind::Fn => {
-                        !self.r.field_def_ids(def_id).is_some_and(|field_ids| field_ids.is_empty())
+                        !self.r.field_idents(def_id).is_some_and(|field_ids| field_ids.is_empty())
                     }
                 }
             };
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 38963ef4ef0..7cb5a3fb2fd 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -991,7 +991,7 @@ pub struct Resolver<'a, 'tcx> {
     extern_prelude: FxHashMap<Ident, ExternPreludeEntry<'a>>,
 
     /// N.B., this is used only for better diagnostics, not name resolution itself.
-    field_def_ids: LocalDefIdMap<&'tcx [DefId]>,
+    field_names: LocalDefIdMap<Vec<Ident>>,
 
     /// Span of the privacy modifier in fields of an item `DefId` accessible with dot syntax.
     /// Used for hints during error reporting.
@@ -1139,7 +1139,7 @@ pub struct Resolver<'a, 'tcx> {
     /// When collecting definitions from an AST fragment produced by a macro invocation `ExpnId`
     /// we know what parent node that fragment should be attached to thanks to this table,
     /// and how the `impl Trait` fragments were introduced.
-    invocation_parents: FxHashMap<LocalExpnId, (LocalDefId, ImplTraitContext)>,
+    invocation_parents: FxHashMap<LocalExpnId, (LocalDefId, ImplTraitContext, bool /*in_attr*/)>,
 
     /// Some way to know that we are in a *trait* impl in `visit_assoc_item`.
     /// FIXME: Replace with a more general AST map (together with some other fields).
@@ -1371,7 +1371,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         node_id_to_def_id.insert(CRATE_NODE_ID, crate_feed);
 
         let mut invocation_parents = FxHashMap::default();
-        invocation_parents.insert(LocalExpnId::ROOT, (CRATE_DEF_ID, ImplTraitContext::Existential));
+        invocation_parents
+            .insert(LocalExpnId::ROOT, (CRATE_DEF_ID, ImplTraitContext::Existential, false));
 
         let mut extern_prelude: FxHashMap<Ident, ExternPreludeEntry<'_>> = tcx
             .sess
@@ -1406,7 +1407,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             prelude: None,
             extern_prelude,
 
-            field_def_ids: Default::default(),
+            field_names: Default::default(),
             field_visibility_spans: FxHashMap::default(),
 
             determined_imports: Vec::new(),
@@ -2127,10 +2128,18 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         }
     }
 
-    fn field_def_ids(&self, def_id: DefId) -> Option<&'tcx [DefId]> {
+    fn field_idents(&self, def_id: DefId) -> Option<Vec<Ident>> {
         match def_id.as_local() {
-            Some(def_id) => self.field_def_ids.get(&def_id).copied(),
-            None => Some(self.tcx.associated_item_def_ids(def_id)),
+            Some(def_id) => self.field_names.get(&def_id).cloned(),
+            None => Some(
+                self.tcx
+                    .associated_item_def_ids(def_id)
+                    .iter()
+                    .map(|&def_id| {
+                        Ident::new(self.tcx.item_name(def_id), self.tcx.def_span(def_id))
+                    })
+                    .collect(),
+            ),
         }
     }
 
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 026a2ca1412..cb9bebd33d3 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -297,11 +297,12 @@ impl<'a, 'tcx> ResolverExpand for Resolver<'a, 'tcx> {
             .invocation_parents
             .get(&invoc_id)
             .or_else(|| self.invocation_parents.get(&eager_expansion_root))
-            .map(|&(mod_def_id, _)| mod_def_id)
-            .filter(|&mod_def_id| {
-                invoc.fragment_kind == AstFragmentKind::Expr
+            .filter(|&&(mod_def_id, _, in_attr)| {
+                in_attr
+                    && invoc.fragment_kind == AstFragmentKind::Expr
                     && self.tcx.def_kind(mod_def_id) == DefKind::Mod
-            });
+            })
+            .map(|&(mod_def_id, ..)| mod_def_id);
         let (ext, res) = self.smart_resolve_macro_path(
             path,
             kind,
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/mir.rs b/compiler/rustc_smir/src/rustc_smir/convert/mir.rs
index 9d5a14b5145..8bfaa112c2f 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/mir.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/mir.rs
@@ -644,6 +644,7 @@ impl<'tcx> Stable<'tcx> for mir::TerminatorKind<'tcx> {
                 target: target.map(|t| t.as_usize()),
                 unwind: unwind.stable(tables),
             },
+            mir::TerminatorKind::TailCall { func: _, args: _, fn_span: _ } => todo!(),
             mir::TerminatorKind::Assert { cond, expected, msg, target, unwind } => {
                 TerminatorKind::Assert {
                     cond: cond.stable(tables),
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index c95649e2ffb..ad087620ae0 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -1,3 +1,4 @@
+use crate::infer::at::ToTrace;
 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
 use crate::traits::{self, Obligation, ObligationCause, ObligationCtxt, SelectionContext};
 
@@ -17,6 +18,16 @@ pub use rustc_infer::infer::*;
 
 #[extension(pub trait InferCtxtExt<'tcx>)]
 impl<'tcx> InferCtxt<'tcx> {
+    fn can_eq<T: ToTrace<'tcx>>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool {
+        self.probe(|_| {
+            let ocx = ObligationCtxt::new(self);
+            let Ok(()) = ocx.eq(&ObligationCause::dummy(), param_env, a, b) else {
+                return false;
+            };
+            ocx.select_where_possible().is_empty()
+        })
+    }
+
     fn type_is_copy_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
         let ty = self.resolve_vars_if_possible(ty);
 
diff --git a/compiler/rustc_trait_selection/src/lib.rs b/compiler/rustc_trait_selection/src/lib.rs
index 50c618bb3bd..37008baca28 100644
--- a/compiler/rustc_trait_selection/src/lib.rs
+++ b/compiler/rustc_trait_selection/src/lib.rs
@@ -26,6 +26,7 @@
 #![feature(never_type)]
 #![feature(rustdoc_internals)]
 #![feature(type_alias_impl_trait)]
+#![feature(unwrap_infallible)]
 #![recursion_limit = "512"] // For rustdoc
 // tidy-alphabetical-end
 
diff --git a/compiler/rustc_trait_selection/src/solve/delegate.rs b/compiler/rustc_trait_selection/src/solve/delegate.rs
index f98744e906f..f67518a577e 100644
--- a/compiler/rustc_trait_selection/src/solve/delegate.rs
+++ b/compiler/rustc_trait_selection/src/solve/delegate.rs
@@ -8,14 +8,12 @@ use rustc_infer::infer::canonical::{
 };
 use rustc_infer::infer::{InferCtxt, RegionVariableOrigin, TyCtxtInferExt};
 use rustc_infer::traits::solve::Goal;
-use rustc_infer::traits::util::supertraits;
 use rustc_infer::traits::{ObligationCause, Reveal};
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt as _};
 use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
 use rustc_type_ir::solve::{Certainty, NoSolution, SolverMode};
 
-use crate::traits::coherence::trait_ref_is_knowable;
 use crate::traits::specialization_graph;
 
 #[repr(transparent)]
@@ -82,13 +80,6 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
         self.0.leak_check(max_input_universe, None).map_err(|_| NoSolution)
     }
 
-    fn elaborate_supertraits(
-        interner: TyCtxt<'tcx>,
-        trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-    ) -> impl Iterator<Item = ty::Binder<'tcx, ty::TraitRef<'tcx>>> {
-        supertraits(interner, trait_ref)
-    }
-
     fn try_const_eval_resolve(
         &self,
         param_env: ty::ParamEnv<'tcx>,
@@ -200,15 +191,6 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
         let _ = self.take_opaque_types();
     }
 
-    fn trait_ref_is_knowable<E: std::fmt::Debug>(
-        &self,
-        trait_ref: ty::TraitRef<'tcx>,
-        lazily_normalize_ty: impl FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
-    ) -> Result<bool, E> {
-        trait_ref_is_knowable(&self.0, trait_ref, lazily_normalize_ty)
-            .map(|is_knowable| is_knowable.is_ok())
-    }
-
     fn fetch_eligible_assoc_item(
         &self,
         param_env: ty::ParamEnv<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 9f0d84e7d45..fc390bf318d 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -25,42 +25,14 @@ use rustc_middle::traits::specialization_graph::OverlapMode;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
 use rustc_middle::ty::{self, Ty, TyCtxt};
+pub use rustc_next_trait_solver::coherence::*;
 use rustc_span::symbol::sym;
 use rustc_span::{Span, DUMMY_SP};
 use std::fmt::Debug;
-use std::ops::ControlFlow;
 
 use super::error_reporting::suggest_new_overflow_limit;
 use super::ObligationCtxt;
 
-/// Whether we do the orphan check relative to this crate or to some remote crate.
-#[derive(Copy, Clone, Debug)]
-pub enum InCrate {
-    Local { mode: OrphanCheckMode },
-    Remote,
-}
-
-#[derive(Copy, Clone, Debug)]
-pub enum OrphanCheckMode {
-    /// Proper orphan check.
-    Proper,
-    /// Improper orphan check for backward compatibility.
-    ///
-    /// In this mode, type params inside projections are considered to be covered
-    /// even if the projection may normalize to a type that doesn't actually cover
-    /// them. This is unsound. See also [#124559] and [#99554].
-    ///
-    /// [#124559]: https://github.com/rust-lang/rust/issues/124559
-    /// [#99554]: https://github.com/rust-lang/rust/issues/99554
-    Compat,
-}
-
-#[derive(Debug, Copy, Clone)]
-pub enum Conflict {
-    Upstream,
-    Downstream,
-}
-
 pub struct OverlapResult<'tcx> {
     pub impl_header: ty::ImplHeader<'tcx>,
     pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause<'tcx>>,
@@ -612,426 +584,6 @@ fn try_prove_negated_where_clause<'tcx>(
     true
 }
 
-/// Returns whether all impls which would apply to the `trait_ref`
-/// e.g. `Ty: Trait<Arg>` are already known in the local crate.
-///
-/// This both checks whether any downstream or sibling crates could
-/// implement it and whether an upstream crate can add this impl
-/// without breaking backwards compatibility.
-#[instrument(level = "debug", skip(infcx, lazily_normalize_ty), ret)]
-pub fn trait_ref_is_knowable<'tcx, E: Debug>(
-    infcx: &InferCtxt<'tcx>,
-    trait_ref: ty::TraitRef<'tcx>,
-    mut lazily_normalize_ty: impl FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
-) -> Result<Result<(), Conflict>, E> {
-    if orphan_check_trait_ref(infcx, trait_ref, InCrate::Remote, &mut lazily_normalize_ty)?.is_ok()
-    {
-        // A downstream or cousin crate is allowed to implement some
-        // generic parameters of this trait-ref.
-        return Ok(Err(Conflict::Downstream));
-    }
-
-    if trait_ref_is_local_or_fundamental(infcx.tcx, trait_ref) {
-        // This is a local or fundamental trait, so future-compatibility
-        // is no concern. We know that downstream/cousin crates are not
-        // allowed to implement a generic parameter of this trait ref,
-        // which means impls could only come from dependencies of this
-        // crate, which we already know about.
-        return Ok(Ok(()));
-    }
-
-    // This is a remote non-fundamental trait, so if another crate
-    // can be the "final owner" of the generic parameters of this trait-ref,
-    // they are allowed to implement it future-compatibly.
-    //
-    // However, if we are a final owner, then nobody else can be,
-    // and if we are an intermediate owner, then we don't care
-    // about future-compatibility, which means that we're OK if
-    // we are an owner.
-    if orphan_check_trait_ref(
-        infcx,
-        trait_ref,
-        InCrate::Local { mode: OrphanCheckMode::Proper },
-        &mut lazily_normalize_ty,
-    )?
-    .is_ok()
-    {
-        Ok(Ok(()))
-    } else {
-        Ok(Err(Conflict::Upstream))
-    }
-}
-
-pub fn trait_ref_is_local_or_fundamental<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: ty::TraitRef<'tcx>,
-) -> bool {
-    trait_ref.def_id.is_local() || tcx.has_attr(trait_ref.def_id, sym::fundamental)
-}
-
-#[derive(Debug, Copy, Clone)]
-pub enum IsFirstInputType {
-    No,
-    Yes,
-}
-
-impl From<bool> for IsFirstInputType {
-    fn from(b: bool) -> IsFirstInputType {
-        match b {
-            false => IsFirstInputType::No,
-            true => IsFirstInputType::Yes,
-        }
-    }
-}
-
-#[derive(Debug)]
-pub enum OrphanCheckErr<'tcx, T> {
-    NonLocalInputType(Vec<(Ty<'tcx>, IsFirstInputType)>),
-    UncoveredTyParams(UncoveredTyParams<'tcx, T>),
-}
-
-#[derive(Debug)]
-pub struct UncoveredTyParams<'tcx, T> {
-    pub uncovered: T,
-    pub local_ty: Option<Ty<'tcx>>,
-}
-
-/// Checks whether a trait-ref is potentially implementable by a crate.
-///
-/// The current rule is that a trait-ref orphan checks in a crate C:
-///
-/// 1. Order the parameters in the trait-ref in generic parameters order
-/// - Self first, others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
-/// 2. Of these type parameters, there is at least one type parameter
-///    in which, walking the type as a tree, you can reach a type local
-///    to C where all types in-between are fundamental types. Call the
-///    first such parameter the "local key parameter".
-///     - e.g., `Box<LocalType>` is OK, because you can visit LocalType
-///       going through `Box`, which is fundamental.
-///     - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
-///       the same reason.
-///     - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
-///       not local), `Vec<LocalType>` is bad, because `Vec<->` is between
-///       the local type and the type parameter.
-/// 3. Before this local type, no generic type parameter of the impl must
-///    be reachable through fundamental types.
-///     - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
-///     - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is
-///       reachable through the fundamental type `Box`.
-/// 4. Every type in the local key parameter not known in C, going
-///    through the parameter's type tree, must appear only as a subtree of
-///    a type local to C, with only fundamental types between the type
-///    local to C and the local key parameter.
-///     - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
-///     is bad, because the only local type with `T` as a subtree is
-///     `LocalType<T>`, and `Vec<->` is between it and the type parameter.
-///     - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
-///     the second occurrence of `T` is not a subtree of *any* local type.
-///     - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
-///     `LocalType<Vec<T>>`, which is local and has no types between it and
-///     the type parameter.
-///
-/// The orphan rules actually serve several different purposes:
-///
-/// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
-///    every type local to one crate is unknown in the other) can't implement
-///    the same trait-ref. This follows because it can be seen that no such
-///    type can orphan-check in 2 such crates.
-///
-///    To check that a local impl follows the orphan rules, we check it in
-///    InCrate::Local mode, using type parameters for the "generic" types.
-///
-///    In InCrate::Local mode the orphan check succeeds if the current crate
-///    is definitely allowed to implement the given trait (no false positives).
-///
-/// 2. They ground negative reasoning for coherence. If a user wants to
-///    write both a conditional blanket impl and a specific impl, we need to
-///    make sure they do not overlap. For example, if we write
-///    ```ignore (illustrative)
-///    impl<T> IntoIterator for Vec<T>
-///    impl<T: Iterator> IntoIterator for T
-///    ```
-///    We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
-///    We can observe that this holds in the current crate, but we need to make
-///    sure this will also hold in all unknown crates (both "independent" crates,
-///    which we need for link-safety, and also child crates, because we don't want
-///    child crates to get error for impl conflicts in a *dependency*).
-///
-///    For that, we only allow negative reasoning if, for every assignment to the
-///    inference variables, every unknown crate would get an orphan error if they
-///    try to implement this trait-ref. To check for this, we use InCrate::Remote
-///    mode. That is sound because we already know all the impls from known crates.
-///
-///    In InCrate::Remote mode the orphan check succeeds if a foreign crate
-///    *could* implement the given trait (no false negatives).
-///
-/// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
-///    add "non-blanket" impls without breaking negative reasoning in dependent
-///    crates. This is the "rebalancing coherence" (RFC 1023) restriction.
-///
-///    For that, we only allow a crate to perform negative reasoning on
-///    non-local-non-`#[fundamental]` if there's a local key parameter as per (2).
-///
-///    Because we never perform negative reasoning generically (coherence does
-///    not involve type parameters), this can be interpreted as doing the full
-///    orphan check (using InCrate::Local mode), instantiating non-local known
-///    types for all inference variables.
-///
-///    This allows for crates to future-compatibly add impls as long as they
-///    can't apply to types with a key parameter in a child crate - applying
-///    the rules, this basically means that every type parameter in the impl
-///    must appear behind a non-fundamental type (because this is not a
-///    type-system requirement, crate owners might also go for "semantic
-///    future-compatibility" involving things such as sealed traits, but
-///    the above requirement is sufficient, and is necessary in "open world"
-///    cases).
-///
-/// Note that this function is never called for types that have both type
-/// parameters and inference variables.
-#[instrument(level = "trace", skip(infcx, lazily_normalize_ty), ret)]
-pub fn orphan_check_trait_ref<'tcx, E: Debug>(
-    infcx: &InferCtxt<'tcx>,
-    trait_ref: ty::TraitRef<'tcx>,
-    in_crate: InCrate,
-    lazily_normalize_ty: impl FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
-) -> Result<Result<(), OrphanCheckErr<'tcx, Ty<'tcx>>>, E> {
-    if trait_ref.has_param() {
-        bug!("orphan check only expects inference variables: {trait_ref:?}");
-    }
-
-    let mut checker = OrphanChecker::new(infcx, in_crate, lazily_normalize_ty);
-    Ok(match trait_ref.visit_with(&mut checker) {
-        ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)),
-        ControlFlow::Break(residual) => match residual {
-            OrphanCheckEarlyExit::NormalizationFailure(err) => return Err(err),
-            OrphanCheckEarlyExit::UncoveredTyParam(ty) => {
-                // Does there exist some local type after the `ParamTy`.
-                checker.search_first_local_ty = true;
-                let local_ty = match trait_ref.visit_with(&mut checker).break_value() {
-                    Some(OrphanCheckEarlyExit::LocalTy(local_ty)) => Some(local_ty),
-                    _ => None,
-                };
-                Err(OrphanCheckErr::UncoveredTyParams(UncoveredTyParams {
-                    uncovered: ty,
-                    local_ty,
-                }))
-            }
-            OrphanCheckEarlyExit::LocalTy(_) => Ok(()),
-        },
-    })
-}
-
-struct OrphanChecker<'a, 'tcx, F> {
-    infcx: &'a InferCtxt<'tcx>,
-    in_crate: InCrate,
-    in_self_ty: bool,
-    lazily_normalize_ty: F,
-    /// Ignore orphan check failures and exclusively search for the first local type.
-    search_first_local_ty: bool,
-    non_local_tys: Vec<(Ty<'tcx>, IsFirstInputType)>,
-}
-
-impl<'a, 'tcx, F, E> OrphanChecker<'a, 'tcx, F>
-where
-    F: FnOnce(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
-{
-    fn new(infcx: &'a InferCtxt<'tcx>, in_crate: InCrate, lazily_normalize_ty: F) -> Self {
-        OrphanChecker {
-            infcx,
-            in_crate,
-            in_self_ty: true,
-            lazily_normalize_ty,
-            search_first_local_ty: false,
-            non_local_tys: Vec::new(),
-        }
-    }
-
-    fn found_non_local_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<OrphanCheckEarlyExit<'tcx, E>> {
-        self.non_local_tys.push((t, self.in_self_ty.into()));
-        ControlFlow::Continue(())
-    }
-
-    fn found_uncovered_ty_param(
-        &mut self,
-        ty: Ty<'tcx>,
-    ) -> ControlFlow<OrphanCheckEarlyExit<'tcx, E>> {
-        if self.search_first_local_ty {
-            return ControlFlow::Continue(());
-        }
-
-        ControlFlow::Break(OrphanCheckEarlyExit::UncoveredTyParam(ty))
-    }
-
-    fn def_id_is_local(&mut self, def_id: DefId) -> bool {
-        match self.in_crate {
-            InCrate::Local { .. } => def_id.is_local(),
-            InCrate::Remote => false,
-        }
-    }
-}
-
-enum OrphanCheckEarlyExit<'tcx, E> {
-    NormalizationFailure(E),
-    UncoveredTyParam(Ty<'tcx>),
-    LocalTy(Ty<'tcx>),
-}
-
-impl<'a, 'tcx, F, E> TypeVisitor<TyCtxt<'tcx>> for OrphanChecker<'a, 'tcx, F>
-where
-    F: FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
-{
-    type Result = ControlFlow<OrphanCheckEarlyExit<'tcx, E>>;
-
-    fn visit_region(&mut self, _r: ty::Region<'tcx>) -> Self::Result {
-        ControlFlow::Continue(())
-    }
-
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
-        let ty = self.infcx.shallow_resolve(ty);
-        let ty = match (self.lazily_normalize_ty)(ty) {
-            Ok(norm_ty) if norm_ty.is_ty_var() => ty,
-            Ok(norm_ty) => norm_ty,
-            Err(err) => return ControlFlow::Break(OrphanCheckEarlyExit::NormalizationFailure(err)),
-        };
-
-        let result = match *ty.kind() {
-            ty::Bool
-            | ty::Char
-            | ty::Int(..)
-            | ty::Uint(..)
-            | ty::Float(..)
-            | ty::Str
-            | ty::FnDef(..)
-            | ty::Pat(..)
-            | ty::FnPtr(_)
-            | ty::Array(..)
-            | ty::Slice(..)
-            | ty::RawPtr(..)
-            | ty::Never
-            | ty::Tuple(..) => self.found_non_local_ty(ty),
-
-            ty::Param(..) => bug!("unexpected ty param"),
-
-            ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => {
-                match self.in_crate {
-                    InCrate::Local { .. } => self.found_uncovered_ty_param(ty),
-                    // The inference variable might be unified with a local
-                    // type in that remote crate.
-                    InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
-                }
-            }
-
-            // A rigid alias may normalize to anything.
-            // * If it references an infer var, placeholder or bound ty, it may
-            //   normalize to that, so we have to treat it as an uncovered ty param.
-            // * Otherwise it may normalize to any non-type-generic type
-            //   be it local or non-local.
-            ty::Alias(kind, _) => {
-                if ty.has_type_flags(
-                    ty::TypeFlags::HAS_TY_PLACEHOLDER
-                        | ty::TypeFlags::HAS_TY_BOUND
-                        | ty::TypeFlags::HAS_TY_INFER,
-                ) {
-                    match self.in_crate {
-                        InCrate::Local { mode } => match kind {
-                            ty::Projection if let OrphanCheckMode::Compat = mode => {
-                                ControlFlow::Continue(())
-                            }
-                            _ => self.found_uncovered_ty_param(ty),
-                        },
-                        InCrate::Remote => {
-                            // The inference variable might be unified with a local
-                            // type in that remote crate.
-                            ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
-                        }
-                    }
-                } else {
-                    // Regarding *opaque types* specifically, we choose to treat them as non-local,
-                    // even those that appear within the same crate. This seems somewhat surprising
-                    // at first, but makes sense when you consider that opaque types are supposed
-                    // to hide the underlying type *within the same crate*. When an opaque type is
-                    // used from outside the module where it is declared, it should be impossible to
-                    // observe anything about it other than the traits that it implements.
-                    //
-                    // The alternative would be to look at the underlying type to determine whether
-                    // or not the opaque type itself should be considered local.
-                    //
-                    // However, this could make it a breaking change to switch the underlying hidden
-                    // type from a local type to a remote type. This would violate the rule that
-                    // opaque types should be completely opaque apart from the traits that they
-                    // implement, so we don't use this behavior.
-                    // Addendum: Moreover, revealing the underlying type is likely to cause cycle
-                    // errors as we rely on coherence / the specialization graph during typeck.
-
-                    self.found_non_local_ty(ty)
-                }
-            }
-
-            // For fundamental types, we just look inside of them.
-            ty::Ref(_, ty, _) => ty.visit_with(self),
-            ty::Adt(def, args) => {
-                if self.def_id_is_local(def.did()) {
-                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
-                } else if def.is_fundamental() {
-                    args.visit_with(self)
-                } else {
-                    self.found_non_local_ty(ty)
-                }
-            }
-            ty::Foreign(def_id) => {
-                if self.def_id_is_local(def_id) {
-                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
-                } else {
-                    self.found_non_local_ty(ty)
-                }
-            }
-            ty::Dynamic(tt, ..) => {
-                let principal = tt.principal().map(|p| p.def_id());
-                if principal.is_some_and(|p| self.def_id_is_local(p)) {
-                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
-                } else {
-                    self.found_non_local_ty(ty)
-                }
-            }
-            ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
-            ty::Closure(did, ..) | ty::CoroutineClosure(did, ..) | ty::Coroutine(did, ..) => {
-                if self.def_id_is_local(did) {
-                    ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
-                } else {
-                    self.found_non_local_ty(ty)
-                }
-            }
-            // This should only be created when checking whether we have to check whether some
-            // auto trait impl applies. There will never be multiple impls, so we can just
-            // act as if it were a local type here.
-            ty::CoroutineWitness(..) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
-        };
-        // A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so
-        // the first type we visit is always the self type.
-        self.in_self_ty = false;
-        result
-    }
-
-    /// All possible values for a constant parameter already exist
-    /// in the crate defining the trait, so they are always non-local[^1].
-    ///
-    /// Because there's no way to have an impl where the first local
-    /// generic argument is a constant, we also don't have to fail
-    /// the orphan check when encountering a parameter or a generic constant.
-    ///
-    /// This means that we can completely ignore constants during the orphan check.
-    ///
-    /// See `tests/ui/coherence/const-generics-orphan-check-ok.rs` for examples.
-    ///
-    /// [^1]: This might not hold for function pointers or trait objects in the future.
-    /// As these should be quite rare as const arguments and especially rare as impl
-    /// parameters, allowing uncovered const parameters in impls seems more useful
-    /// than allowing `impl<T> Trait<local_fn_ptr, T> for i32` to compile.
-    fn visit_const(&mut self, _c: ty::Const<'tcx>) -> Self::Result {
-        ControlFlow::Continue(())
-    }
-}
-
 /// Compute the `intercrate_ambiguity_causes` for the new solver using
 /// "proof trees".
 ///
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index 32c8a454b40..94b28426f43 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -1,5 +1,10 @@
 use super::{ObligationCauseCode, PredicateObligation};
+use crate::errors::{
+    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
+};
 use crate::infer::error_reporting::TypeErrCtxt;
+use crate::infer::InferCtxtExt;
+use crate::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt;
 use rustc_ast::AttrArgs;
 use rustc_ast::AttrArgsEq;
 use rustc_ast::AttrKind;
@@ -21,12 +26,6 @@ use rustc_span::Span;
 use std::iter;
 use std::path::PathBuf;
 
-use crate::errors::{
-    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
-};
-
-use crate::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt;
-
 /// The symbols which are always allowed in a format string
 static ALLOWED_FORMAT_SYMBOLS: &[Symbol] = &[
     kw::SelfUpper,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index a0a8e5963f1..52edffce614 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -3472,6 +3472,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     )
                 });
             }
+            // Suppress `compare_type_predicate_entailment` errors for RPITITs, since they
+            // should be implied by the parent method.
+            ObligationCauseCode::CompareImplItem { trait_item_def_id, .. }
+                if tcx.is_impl_trait_in_trait(trait_item_def_id) => {}
             ObligationCauseCode::CompareImplItem { trait_item_def_id, kind, .. } => {
                 let item_name = tcx.item_name(trait_item_def_id);
                 let msg = format!(
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
index 17b6dd2bc58..5461f9e65af 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
@@ -1073,7 +1073,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             // mismatched, then we have a totally different error to report.
             if self.enter_forall(found_args, |found_args| {
                 self.enter_forall(expected_args, |expected_args| {
-                    !self.can_sub(obligation.param_env, expected_args, found_args)
+                    !self.can_eq(obligation.param_env, expected_args, found_args)
                 })
             }) {
                 return None;
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 5b2c8fb1950..1c6993bdd37 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -203,7 +203,7 @@ fn bounds_reference_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span
     tcx.associated_items(trait_def_id)
         .in_definition_order()
         .filter(|item| item.kind == ty::AssocKind::Type)
-        .flat_map(|item| tcx.explicit_item_bounds(item.def_id).instantiate_identity_iter_copied())
+        .flat_map(|item| tcx.explicit_item_bounds(item.def_id).iter_identity_copied())
         .filter_map(|c| predicate_references_self(tcx, c))
         .collect()
 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 68cc04bc8e6..cc082ad98aa 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -18,7 +18,7 @@ use super::{
     TraitQueryMode,
 };
 
-use crate::infer::{InferCtxt, InferOk, TypeFreshener};
+use crate::infer::{InferCtxt, InferCtxtExt, InferOk, TypeFreshener};
 use crate::solve::InferCtxtSelectExt as _;
 use crate::traits::error_reporting::TypeErrCtxtExt;
 use crate::traits::normalize::normalize_with_depth;
@@ -1523,7 +1523,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // bound regions.
         let trait_ref = predicate.skip_binder().trait_ref;
 
-        coherence::trait_ref_is_knowable::<!>(self.infcx, trait_ref, |ty| Ok(ty)).unwrap()
+        coherence::trait_ref_is_knowable(self.infcx, trait_ref, |ty| Ok::<_, !>(ty)).into_ok()
     }
 
     /// Returns `true` if the global caches can be used.
diff --git a/compiler/rustc_ty_utils/src/opaque_types.rs b/compiler/rustc_ty_utils/src/opaque_types.rs
index 686f2f04ad9..5e91320f897 100644
--- a/compiler/rustc_ty_utils/src/opaque_types.rs
+++ b/compiler/rustc_ty_utils/src/opaque_types.rs
@@ -169,10 +169,8 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
                 // Collect opaque types nested within the associated type bounds of this opaque type.
                 // We use identity args here, because we already know that the opaque type uses
                 // only generic parameters, and thus instantiating would not give us more information.
-                for (pred, span) in self
-                    .tcx
-                    .explicit_item_bounds(alias_ty.def_id)
-                    .instantiate_identity_iter_copied()
+                for (pred, span) in
+                    self.tcx.explicit_item_bounds(alias_ty.def_id).iter_identity_copied()
                 {
                     trace!(?pred);
                     self.visit_spanned(span, pred);
diff --git a/compiler/rustc_ty_utils/src/sig_types.rs b/compiler/rustc_ty_utils/src/sig_types.rs
index 97a1b94263e..eb6cb369974 100644
--- a/compiler/rustc_ty_utils/src/sig_types.rs
+++ b/compiler/rustc_ty_utils/src/sig_types.rs
@@ -62,7 +62,7 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
             }
         }
         DefKind::OpaqueTy => {
-            for (pred, span) in tcx.explicit_item_bounds(item).instantiate_identity_iter_copied() {
+            for (pred, span) in tcx.explicit_item_bounds(item).iter_identity_copied() {
                 try_visit!(visitor.visit(span, pred));
             }
         }
diff --git a/compiler/rustc_type_ir/src/binder.rs b/compiler/rustc_type_ir/src/binder.rs
index 491ef34430c..2531219baec 100644
--- a/compiler/rustc_type_ir/src/binder.rs
+++ b/compiler/rustc_type_ir/src/binder.rs
@@ -448,7 +448,7 @@ where
 
     /// Similar to [`instantiate_identity`](EarlyBinder::instantiate_identity),
     /// but on an iterator of `TypeFoldable` values.
-    pub fn instantiate_identity_iter(self) -> Iter::IntoIter {
+    pub fn iter_identity(self) -> Iter::IntoIter {
         self.value.into_iter()
     }
 }
@@ -515,9 +515,7 @@ where
 
     /// Similar to [`instantiate_identity`](EarlyBinder::instantiate_identity),
     /// but on an iterator of values that deref to a `TypeFoldable`.
-    pub fn instantiate_identity_iter_copied(
-        self,
-    ) -> impl Iterator<Item = <Iter::Item as Deref>::Target> {
+    pub fn iter_identity_copied(self) -> impl Iterator<Item = <Iter::Item as Deref>::Target> {
         self.value.into_iter().map(|v| *v)
     }
 }
diff --git a/compiler/rustc_type_ir/src/elaborate.rs b/compiler/rustc_type_ir/src/elaborate.rs
new file mode 100644
index 00000000000..0def7d12f74
--- /dev/null
+++ b/compiler/rustc_type_ir/src/elaborate.rs
@@ -0,0 +1,305 @@
+use std::marker::PhantomData;
+
+use smallvec::smallvec;
+
+use crate::data_structures::HashSet;
+use crate::outlives::{push_outlives_components, Component};
+use crate::{self as ty, Interner};
+use crate::{inherent::*, Upcast as _};
+
+/// "Elaboration" is the process of identifying all the predicates that
+/// are implied by a source predicate. Currently, this basically means
+/// walking the "supertraits" and other similar assumptions. For example,
+/// if we know that `T: Ord`, the elaborator would deduce that `T: PartialOrd`
+/// holds as well. Similarly, if we have `trait Foo: 'static`, and we know that
+/// `T: Foo`, then we know that `T: 'static`.
+pub struct Elaborator<I: Interner, O> {
+    cx: I,
+    stack: Vec<O>,
+    visited: HashSet<ty::Binder<I, ty::PredicateKind<I>>>,
+    mode: Filter,
+}
+
+enum Filter {
+    All,
+    OnlySelf,
+}
+
+/// Describes how to elaborate an obligation into a sub-obligation.
+pub trait Elaboratable<I: Interner> {
+    fn predicate(&self) -> I::Predicate;
+
+    // Makes a new `Self` but with a different clause that comes from elaboration.
+    fn child(&self, clause: I::Clause) -> Self;
+
+    // Makes a new `Self` but with a different clause and a different cause
+    // code (if `Self` has one, such as [`PredicateObligation`]).
+    fn child_with_derived_cause(
+        &self,
+        clause: I::Clause,
+        span: I::Span,
+        parent_trait_pred: ty::Binder<I, ty::TraitPredicate<I>>,
+        index: usize,
+    ) -> Self;
+}
+
+pub fn elaborate<I: Interner, O: Elaboratable<I>>(
+    cx: I,
+    obligations: impl IntoIterator<Item = O>,
+) -> Elaborator<I, O> {
+    let mut elaborator =
+        Elaborator { cx, stack: Vec::new(), visited: HashSet::default(), mode: Filter::All };
+    elaborator.extend_deduped(obligations);
+    elaborator
+}
+
+impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
+    fn extend_deduped(&mut self, obligations: impl IntoIterator<Item = O>) {
+        // Only keep those bounds that we haven't already seen.
+        // This is necessary to prevent infinite recursion in some
+        // cases. One common case is when people define
+        // `trait Sized: Sized { }` rather than `trait Sized { }`.
+        self.stack.extend(
+            obligations.into_iter().filter(|o| {
+                self.visited.insert(self.cx.anonymize_bound_vars(o.predicate().kind()))
+            }),
+        );
+    }
+
+    /// Filter to only the supertraits of trait predicates, i.e. only the predicates
+    /// that have `Self` as their self type, instead of all implied predicates.
+    pub fn filter_only_self(mut self) -> Self {
+        self.mode = Filter::OnlySelf;
+        self
+    }
+
+    fn elaborate(&mut self, elaboratable: &O) {
+        let cx = self.cx;
+
+        // We only elaborate clauses.
+        let Some(clause) = elaboratable.predicate().as_clause() else {
+            return;
+        };
+
+        let bound_clause = clause.kind();
+        match bound_clause.skip_binder() {
+            ty::ClauseKind::Trait(data) => {
+                // Negative trait bounds do not imply any supertrait bounds
+                if data.polarity != ty::PredicatePolarity::Positive {
+                    return;
+                }
+
+                let map_to_child_clause =
+                    |(index, (clause, span)): (usize, (I::Clause, I::Span))| {
+                        elaboratable.child_with_derived_cause(
+                            clause.instantiate_supertrait(cx, bound_clause.rebind(data.trait_ref)),
+                            span,
+                            bound_clause.rebind(data),
+                            index,
+                        )
+                    };
+
+                // Get predicates implied by the trait, or only super predicates if we only care about self predicates.
+                match self.mode {
+                    Filter::All => self.extend_deduped(
+                        cx.explicit_implied_predicates_of(data.def_id())
+                            .iter_identity()
+                            .enumerate()
+                            .map(map_to_child_clause),
+                    ),
+                    Filter::OnlySelf => self.extend_deduped(
+                        cx.explicit_super_predicates_of(data.def_id())
+                            .iter_identity()
+                            .enumerate()
+                            .map(map_to_child_clause),
+                    ),
+                };
+            }
+            ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty_max, r_min)) => {
+                // We know that `T: 'a` for some type `T`. We can
+                // often elaborate this. For example, if we know that
+                // `[U]: 'a`, that implies that `U: 'a`. Similarly, if
+                // we know `&'a U: 'b`, then we know that `'a: 'b` and
+                // `U: 'b`.
+                //
+                // We can basically ignore bound regions here. So for
+                // example `for<'c> Foo<'a,'c>: 'b` can be elaborated to
+                // `'a: 'b`.
+
+                // Ignore `for<'a> T: 'a` -- we might in the future
+                // consider this as evidence that `T: 'static`, but
+                // I'm a bit wary of such constructions and so for now
+                // I want to be conservative. --nmatsakis
+                if r_min.is_bound() {
+                    return;
+                }
+
+                let mut components = smallvec![];
+                push_outlives_components(cx, ty_max, &mut components);
+                self.extend_deduped(
+                    components
+                        .into_iter()
+                        .filter_map(|component| elaborate_component_to_clause(cx, component, r_min))
+                        .map(|clause| elaboratable.child(bound_clause.rebind(clause).upcast(cx))),
+                );
+            }
+            ty::ClauseKind::RegionOutlives(..) => {
+                // Nothing to elaborate from `'a: 'b`.
+            }
+            ty::ClauseKind::WellFormed(..) => {
+                // Currently, we do not elaborate WF predicates,
+                // although we easily could.
+            }
+            ty::ClauseKind::Projection(..) => {
+                // Nothing to elaborate in a projection predicate.
+            }
+            ty::ClauseKind::ConstEvaluatable(..) => {
+                // Currently, we do not elaborate const-evaluatable
+                // predicates.
+            }
+            ty::ClauseKind::ConstArgHasType(..) => {
+                // Nothing to elaborate
+            }
+        }
+    }
+}
+
+fn elaborate_component_to_clause<I: Interner>(
+    cx: I,
+    component: Component<I>,
+    outlives_region: I::Region,
+) -> Option<ty::ClauseKind<I>> {
+    match component {
+        Component::Region(r) => {
+            if r.is_bound() {
+                None
+            } else {
+                Some(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r, outlives_region)))
+            }
+        }
+
+        Component::Param(p) => {
+            let ty = Ty::new_param(cx, p);
+            Some(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty, outlives_region)))
+        }
+
+        Component::Placeholder(p) => {
+            let ty = Ty::new_placeholder(cx, p);
+            Some(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty, outlives_region)))
+        }
+
+        Component::UnresolvedInferenceVariable(_) => None,
+
+        Component::Alias(alias_ty) => {
+            // We might end up here if we have `Foo<<Bar as Baz>::Assoc>: 'a`.
+            // With this, we can deduce that `<Bar as Baz>::Assoc: 'a`.
+            Some(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
+                alias_ty.to_ty(cx),
+                outlives_region,
+            )))
+        }
+
+        Component::EscapingAlias(_) => {
+            // We might be able to do more here, but we don't
+            // want to deal with escaping vars right now.
+            None
+        }
+    }
+}
+
+impl<I: Interner, O: Elaboratable<I>> Iterator for Elaborator<I, O> {
+    type Item = O;
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.stack.len(), None)
+    }
+
+    fn next(&mut self) -> Option<Self::Item> {
+        // Extract next item from top-most stack frame, if any.
+        if let Some(obligation) = self.stack.pop() {
+            self.elaborate(&obligation);
+            Some(obligation)
+        } else {
+            None
+        }
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////
+// Supertrait iterator
+///////////////////////////////////////////////////////////////////////////
+
+/// Computes the def-ids of the transitive supertraits of `trait_def_id`. This (intentionally)
+/// does not compute the full elaborated super-predicates but just the set of def-ids. It is used
+/// to identify which traits may define a given associated type to help avoid cycle errors,
+/// and to make size estimates for vtable layout computation.
+pub fn supertrait_def_ids<I: Interner>(
+    cx: I,
+    trait_def_id: I::DefId,
+) -> impl Iterator<Item = I::DefId> {
+    let mut set = HashSet::default();
+    let mut stack = vec![trait_def_id];
+
+    set.insert(trait_def_id);
+
+    std::iter::from_fn(move || {
+        let trait_def_id = stack.pop()?;
+
+        for (predicate, _) in cx.explicit_super_predicates_of(trait_def_id).iter_identity() {
+            if let ty::ClauseKind::Trait(data) = predicate.kind().skip_binder() {
+                if set.insert(data.def_id()) {
+                    stack.push(data.def_id());
+                }
+            }
+        }
+
+        Some(trait_def_id)
+    })
+}
+
+pub fn supertraits<I: Interner>(
+    tcx: I,
+    trait_ref: ty::Binder<I, ty::TraitRef<I>>,
+) -> FilterToTraits<I, Elaborator<I, I::Clause>> {
+    elaborate(tcx, [trait_ref.upcast(tcx)]).filter_only_self().filter_to_traits()
+}
+
+pub fn transitive_bounds<I: Interner>(
+    tcx: I,
+    trait_refs: impl Iterator<Item = ty::Binder<I, ty::TraitRef<I>>>,
+) -> FilterToTraits<I, Elaborator<I, I::Clause>> {
+    elaborate(tcx, trait_refs.map(|trait_ref| trait_ref.upcast(tcx)))
+        .filter_only_self()
+        .filter_to_traits()
+}
+
+impl<I: Interner> Elaborator<I, I::Clause> {
+    fn filter_to_traits(self) -> FilterToTraits<I, Self> {
+        FilterToTraits { _cx: PhantomData, base_iterator: self }
+    }
+}
+
+/// A filter around an iterator of predicates that makes it yield up
+/// just trait references.
+pub struct FilterToTraits<I: Interner, It: Iterator<Item = I::Clause>> {
+    _cx: PhantomData<I>,
+    base_iterator: It,
+}
+
+impl<I: Interner, It: Iterator<Item = I::Clause>> Iterator for FilterToTraits<I, It> {
+    type Item = ty::Binder<I, ty::TraitRef<I>>;
+
+    fn next(&mut self) -> Option<ty::Binder<I, ty::TraitRef<I>>> {
+        while let Some(pred) = self.base_iterator.next() {
+            if let Some(data) = pred.as_trait_clause() {
+                return Some(data.map_bound(|t| t.trait_ref));
+            }
+        }
+        None
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.base_iterator.size_hint();
+        (0, upper)
+    }
+}
diff --git a/compiler/rustc_type_ir/src/infer_ctxt.rs b/compiler/rustc_type_ir/src/infer_ctxt.rs
index 2c80ee0a73d..1d0b2345b80 100644
--- a/compiler/rustc_type_ir/src/infer_ctxt.rs
+++ b/compiler/rustc_type_ir/src/infer_ctxt.rs
@@ -3,7 +3,7 @@ use crate::relate::Relate;
 use crate::solve::{Goal, NoSolution, SolverMode};
 use crate::{self as ty, Interner};
 
-pub trait InferCtxtLike {
+pub trait InferCtxtLike: Sized {
     type Interner: Interner;
     fn cx(&self) -> Self::Interner;
 
@@ -73,6 +73,11 @@ pub trait InferCtxtLike {
         rhs: T,
     ) -> Result<Vec<Goal<Self::Interner, <Self::Interner as Interner>::Predicate>>, NoSolution>;
 
+    fn shallow_resolve(
+        &self,
+        ty: <Self::Interner as Interner>::Ty,
+    ) -> <Self::Interner as Interner>::Ty;
+
     fn resolve_vars_if_possible<T>(&self, value: T) -> T
     where
         T: TypeFoldable<Self::Interner>;
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 68c2575258d..de86a8536f7 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -9,6 +9,7 @@ use std::hash::Hash;
 use rustc_ast_ir::Mutability;
 
 use crate::data_structures::HashSet;
+use crate::elaborate::Elaboratable;
 use crate::fold::{TypeFoldable, TypeSuperFoldable};
 use crate::relate::Relate;
 use crate::solve::{CacheData, CanonicalInput, QueryResult, Reveal};
@@ -40,6 +41,10 @@ pub trait Ty<I: Interner<Ty = Self>>:
 
     fn new_var(interner: I, var: ty::TyVid) -> Self;
 
+    fn new_param(interner: I, param: I::ParamTy) -> Self;
+
+    fn new_placeholder(interner: I, param: I::PlaceholderTy) -> Self;
+
     fn new_bound(interner: I, debruijn: ty::DebruijnIndex, var: I::BoundTy) -> Self;
 
     fn new_anon_bound(interner: I, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self;
@@ -429,6 +434,8 @@ pub trait Predicate<I: Interner<Predicate = Self>>:
     + UpcastFrom<I, ty::OutlivesPredicate<I, I::Region>>
     + IntoKind<Kind = ty::Binder<I, ty::PredicateKind<I>>>
 {
+    fn as_clause(self) -> Option<I::Clause>;
+
     fn is_coinductive(self, interner: I) -> bool;
 
     // FIXME: Eventually uplift the impl out of rustc and make this defaulted.
@@ -441,35 +448,35 @@ pub trait Clause<I: Interner<Clause = Self>>:
     + Hash
     + Eq
     + TypeFoldable<I>
-    // FIXME: Remove these, uplift the `Upcast` impls.
+    + UpcastFrom<I, ty::Binder<I, ty::ClauseKind<I>>>
     + UpcastFrom<I, ty::TraitRef<I>>
     + UpcastFrom<I, ty::Binder<I, ty::TraitRef<I>>>
     + UpcastFrom<I, ty::ProjectionPredicate<I>>
     + UpcastFrom<I, ty::Binder<I, ty::ProjectionPredicate<I>>>
     + IntoKind<Kind = ty::Binder<I, ty::ClauseKind<I>>>
+    + Elaboratable<I>
 {
     fn as_trait_clause(self) -> Option<ty::Binder<I, ty::TraitPredicate<I>>> {
         self.kind()
-            .map_bound(|clause| {
-                if let ty::ClauseKind::Trait(t) = clause {
-                    Some(t)
-                } else {
-                    None
-                }
-            })
+            .map_bound(|clause| if let ty::ClauseKind::Trait(t) = clause { Some(t) } else { None })
             .transpose()
     }
+
     fn as_projection_clause(self) -> Option<ty::Binder<I, ty::ProjectionPredicate<I>>> {
         self.kind()
-            .map_bound(|clause| {
-                if let ty::ClauseKind::Projection(p) = clause {
-                    Some(p)
-                } else {
-                    None
-                }
-            })
+            .map_bound(
+                |clause| {
+                    if let ty::ClauseKind::Projection(p) = clause { Some(p) } else { None }
+                },
+            )
             .transpose()
     }
+
+    /// Performs a instantiation suitable for going from a
+    /// poly-trait-ref to supertraits that must hold if that
+    /// poly-trait-ref holds. This is slightly different from a normal
+    /// instantiation in terms of what happens with bound regions.
+    fn instantiate_supertrait(self, tcx: I, trait_ref: ty::Binder<I, ty::TraitRef<I>>) -> Self;
 }
 
 /// Common capabilities of placeholder kinds
@@ -514,6 +521,8 @@ pub trait AdtDef<I: Interner>: Copy + Debug + Hash + Eq {
     fn all_field_tys(self, interner: I) -> ty::EarlyBinder<I, impl IntoIterator<Item = I::Ty>>;
 
     fn sized_constraint(self, interner: I) -> Option<ty::EarlyBinder<I, I::Ty>>;
+
+    fn is_fundamental(self) -> bool;
 }
 
 pub trait ParamEnv<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
@@ -558,6 +567,8 @@ pub trait EvaluationCache<I: Interner> {
 }
 
 pub trait DefId<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
+    fn is_local(self) -> bool;
+
     fn as_local(self) -> Option<I::LocalDefId>;
 }
 
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index 6e013768c3e..fdd1553d389 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -32,7 +32,7 @@ pub trait Interner:
 {
     type DefId: DefId<Self>;
     type LocalDefId: Copy + Debug + Hash + Eq + Into<Self::DefId> + TypeFoldable<Self>;
-    type Span: Copy + Debug + Hash + Eq;
+    type Span: Copy + Debug + Hash + Eq + TypeFoldable<Self>;
 
     type GenericArgs: GenericArgs<Self>;
     type GenericArgsSlice: Copy + Debug + Hash + Eq + SliceLike<Item = Self::GenericArg>;
@@ -213,7 +213,12 @@ pub trait Interner:
     fn explicit_super_predicates_of(
         self,
         def_id: Self::DefId,
-    ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = Self::Clause>>;
+    ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = (Self::Clause, Self::Span)>>;
+
+    fn explicit_implied_predicates_of(
+        self,
+        def_id: Self::DefId,
+    ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = (Self::Clause, Self::Span)>>;
 
     fn has_target_features(self, def_id: Self::DefId) -> bool;
 
@@ -246,10 +251,9 @@ pub trait Interner:
 
     fn trait_is_object_safe(self, trait_def_id: Self::DefId) -> bool;
 
-    fn trait_may_be_implemented_via_object(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_is_fundamental(self, def_id: Self::DefId) -> bool;
 
-    fn supertrait_def_ids(self, trait_def_id: Self::DefId)
-    -> impl IntoIterator<Item = Self::DefId>;
+    fn trait_may_be_implemented_via_object(self, trait_def_id: Self::DefId) -> bool;
 
     fn delay_bug(self, msg: impl ToString) -> Self::ErrorGuaranteed;
 
@@ -268,6 +272,11 @@ pub trait Interner:
         param_env: Self::ParamEnv,
         placeholder: Self::PlaceholderConst,
     ) -> Self::Ty;
+
+    fn anonymize_bound_vars<T: TypeFoldable<Self>>(
+        self,
+        binder: ty::Binder<Self, T>,
+    ) -> ty::Binder<Self, T>;
 }
 
 /// Imagine you have a function `F: FnOnce(&[T]) -> R`, plus an iterator `iter`
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index 2a909b06baf..b14a65fc779 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -20,6 +20,7 @@ pub mod visit;
 #[cfg(feature = "nightly")]
 pub mod codec;
 pub mod data_structures;
+pub mod elaborate;
 pub mod error;
 pub mod fast_reject;
 pub mod fold;
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 1ec095a46f7..65bcb241e4a 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -2374,7 +2374,7 @@ impl dyn Error + Send {
         let err: Box<dyn Error> = self;
         <dyn Error>::downcast(err).map_err(|s| unsafe {
             // Reapply the `Send` marker.
-            Box::from_raw(Box::into_raw(s) as *mut (dyn Error + Send))
+            mem::transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
         })
     }
 }
@@ -2387,8 +2387,8 @@ impl dyn Error + Send + Sync {
     pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
         let err: Box<dyn Error> = self;
         <dyn Error>::downcast(err).map_err(|s| unsafe {
-            // Reapply the `Send + Sync` marker.
-            Box::from_raw(Box::into_raw(s) as *mut (dyn Error + Send + Sync))
+            // Reapply the `Send + Sync` markers.
+            mem::transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
         })
     }
 }
diff --git a/library/alloc/src/collections/btree/map/tests.rs b/library/alloc/src/collections/btree/map/tests.rs
index 56620cf890d..ba1f38dcc3e 100644
--- a/library/alloc/src/collections/btree/map/tests.rs
+++ b/library/alloc/src/collections/btree/map/tests.rs
@@ -1796,18 +1796,18 @@ fn test_ord_absence() {
     }
 
     fn map_debug<K: Debug>(mut map: BTreeMap<K, ()>) {
-        format!("{map:?}");
-        format!("{:?}", map.iter());
-        format!("{:?}", map.iter_mut());
-        format!("{:?}", map.keys());
-        format!("{:?}", map.values());
-        format!("{:?}", map.values_mut());
+        let _ = format!("{map:?}");
+        let _ = format!("{:?}", map.iter());
+        let _ = format!("{:?}", map.iter_mut());
+        let _ = format!("{:?}", map.keys());
+        let _ = format!("{:?}", map.values());
+        let _ = format!("{:?}", map.values_mut());
         if true {
-            format!("{:?}", map.into_iter());
+            let _ = format!("{:?}", map.into_iter());
         } else if true {
-            format!("{:?}", map.into_keys());
+            let _ = format!("{:?}", map.into_keys());
         } else {
-            format!("{:?}", map.into_values());
+            let _ = format!("{:?}", map.into_values());
         }
     }
 
diff --git a/library/alloc/src/collections/btree/set/tests.rs b/library/alloc/src/collections/btree/set/tests.rs
index 688ce57e9da..48bf7674138 100644
--- a/library/alloc/src/collections/btree/set/tests.rs
+++ b/library/alloc/src/collections/btree/set/tests.rs
@@ -705,9 +705,9 @@ fn test_ord_absence() {
     }
 
     fn set_debug<K: Debug>(set: BTreeSet<K>) {
-        format!("{set:?}");
-        format!("{:?}", set.iter());
-        format!("{:?}", set.into_iter());
+        let _ = format!("{set:?}");
+        let _ = format!("{:?}", set.iter());
+        let _ = format!("{:?}", set.into_iter());
     }
 
     fn set_clone<K: Clone>(mut set: BTreeSet<K>) {
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index 01510a61405..077483a174b 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -1495,6 +1495,14 @@ impl<'a, T, A: Allocator> Cursor<'a, T, A> {
     pub fn back(&self) -> Option<&'a T> {
         self.list.back()
     }
+
+    /// Provides a reference to the cursor's parent list.
+    #[must_use]
+    #[inline(always)]
+    #[unstable(feature = "linked_list_cursors", issue = "58533")]
+    pub fn as_list(&self) -> &'a LinkedList<T, A> {
+        self.list
+    }
 }
 
 impl<'a, T, A: Allocator> CursorMut<'a, T, A> {
@@ -1605,6 +1613,18 @@ impl<'a, T, A: Allocator> CursorMut<'a, T, A> {
     pub fn as_cursor(&self) -> Cursor<'_, T, A> {
         Cursor { list: self.list, current: self.current, index: self.index }
     }
+
+    /// Provides a read-only reference to the cursor's parent list.
+    ///
+    /// The lifetime of the returned reference is bound to that of the
+    /// `CursorMut`, which means it cannot outlive the `CursorMut` and that the
+    /// `CursorMut` is frozen for the lifetime of the reference.
+    #[must_use]
+    #[inline(always)]
+    #[unstable(feature = "linked_list_cursors", issue = "58533")]
+    pub fn as_list(&self) -> &LinkedList<T, A> {
+        self.list
+    }
 }
 
 // Now the list editing operations
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index 61d05afccfd..a07f250d7d8 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -164,6 +164,20 @@ impl<T, A: Allocator> VecDeque<T, A> {
         self.buf.ptr()
     }
 
+    /// Appends an element to the buffer.
+    ///
+    /// # Safety
+    ///
+    /// May only be called if `deque.len() < deque.capacity()`
+    #[inline]
+    unsafe fn push_unchecked(&mut self, element: T) {
+        // SAFETY: Because of the precondition, it's guaranteed that there is space
+        // in the logical array after the last element.
+        unsafe { self.buffer_write(self.to_physical_idx(self.len), element) };
+        // This can't overflow because `deque.len() < deque.capacity() <= usize::MAX`.
+        self.len += 1;
+    }
+
     /// Moves an element out of the buffer
     #[inline]
     unsafe fn buffer_read(&mut self, off: usize) -> T {
@@ -2911,6 +2925,14 @@ impl<T, A: Allocator> Extend<T> for VecDeque<T, A> {
     fn extend_reserve(&mut self, additional: usize) {
         self.reserve(additional);
     }
+
+    #[inline]
+    unsafe fn extend_one_unchecked(&mut self, item: T) {
+        // SAFETY: Our preconditions ensure the space has been reserved, and `extend_reserve` is implemented correctly.
+        unsafe {
+            self.push_unchecked(item);
+        }
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -2928,6 +2950,14 @@ impl<'a, T: 'a + Copy, A: Allocator> Extend<&'a T> for VecDeque<T, A> {
     fn extend_reserve(&mut self, additional: usize) {
         self.reserve(additional);
     }
+
+    #[inline]
+    unsafe fn extend_one_unchecked(&mut self, &item: &'a T) {
+        // SAFETY: Our preconditions ensure the space has been reserved, and `extend_reserve` is implemented correctly.
+        unsafe {
+            self.push_unchecked(item);
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/alloc/src/collections/vec_deque/spec_extend.rs b/library/alloc/src/collections/vec_deque/spec_extend.rs
index dccf40ccb38..6a89abc3ef9 100644
--- a/library/alloc/src/collections/vec_deque/spec_extend.rs
+++ b/library/alloc/src/collections/vec_deque/spec_extend.rs
@@ -21,21 +21,12 @@ where
         //     self.push_back(item);
         // }
 
-        // May only be called if `deque.len() < deque.capacity()`
-        unsafe fn push_unchecked<T, A: Allocator>(deque: &mut VecDeque<T, A>, element: T) {
-            // SAFETY: Because of the precondition, it's guaranteed that there is space
-            // in the logical array after the last element.
-            unsafe { deque.buffer_write(deque.to_physical_idx(deque.len), element) };
-            // This can't overflow because `deque.len() < deque.capacity() <= usize::MAX`.
-            deque.len += 1;
-        }
-
         while let Some(element) = iter.next() {
             let (lower, _) = iter.size_hint();
             self.reserve(lower.saturating_add(1));
 
             // SAFETY: We just reserved space for at least one element.
-            unsafe { push_unchecked(self, element) };
+            unsafe { self.push_unchecked(element) };
 
             // Inner loop to avoid repeatedly calling `reserve`.
             while self.len < self.capacity() {
@@ -43,7 +34,7 @@ where
                     return;
                 };
                 // SAFETY: The loop condition guarantees that `self.len() < self.capacity()`.
-                unsafe { push_unchecked(self, element) };
+                unsafe { self.push_unchecked(element) };
             }
         }
     }
diff --git a/library/alloc/src/fmt.rs b/library/alloc/src/fmt.rs
index ae44cab8131..c6bba619ae6 100644
--- a/library/alloc/src/fmt.rs
+++ b/library/alloc/src/fmt.rs
@@ -12,6 +12,7 @@
 //! Some examples of the [`format!`] extension are:
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! format!("Hello");                 // => "Hello"
 //! format!("Hello, {}!", "world");   // => "Hello, world!"
 //! format!("The number is {}", 1);   // => "The number is 1"
@@ -50,6 +51,7 @@
 //! the iterator advances. This leads to behavior like this:
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! format!("{1} {} {0} {}", 1, 2); // => "2 1 1 2"
 //! ```
 //!
@@ -77,6 +79,7 @@
 //! For example, the following [`format!`] expressions all use named arguments:
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! format!("{argument}", argument = "test");   // => "test"
 //! format!("{name} {}", 1, name = 2);          // => "2 1"
 //! format!("{a} {c} {b}", a="a", b='b', c=3);  // => "a 3 b"
@@ -86,6 +89,7 @@
 //! reference a variable with that name in the current scope.
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! let argument = 2 + 2;
 //! format!("{argument}");   // => "4"
 //!
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 703538d0f35..a7715740cbd 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -124,6 +124,7 @@
 #![feature(error_generic_member_access)]
 #![feature(exact_size_is_empty)]
 #![feature(extend_one)]
+#![feature(extend_one_unchecked)]
 #![feature(fmt_internals)]
 #![feature(fn_traits)]
 #![feature(hasher_prefixfree_extras)]
@@ -256,6 +257,7 @@ pub mod vec;
 #[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
 pub mod __export {
     pub use core::format_args;
+    pub use core::hint::must_use;
 }
 
 #[cfg(test)]
diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs
index d5ca5c4ed27..8c6a367869c 100644
--- a/library/alloc/src/macros.rs
+++ b/library/alloc/src/macros.rs
@@ -111,6 +111,7 @@ macro_rules! vec {
 /// # Examples
 ///
 /// ```
+/// # #![allow(unused_must_use)]
 /// format!("test");                             // => "test"
 /// format!("hello {}", "world!");               // => "hello world!"
 /// format!("x = {}, y = {val}", 10, val = 30);  // => "x = 10, y = 30"
@@ -119,10 +120,13 @@ macro_rules! vec {
 /// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable(hint_must_use, liballoc_internals)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "format_macro")]
 macro_rules! format {
-    ($($arg:tt)*) => {{
-        let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
-        res
-    }}
+    ($($arg:tt)*) => {
+        $crate::__export::must_use({
+            let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
+            res
+        })
+    }
 }
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 90672164cb9..1983ea8281a 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -197,11 +197,7 @@ macro_rules! acquire {
 ///
 /// Sharing some immutable data between threads:
 ///
-// Note that we **do not** run these tests here. The windows builders get super
-// unhappy if a thread outlives the main thread and then exits at the same time
-// (something deadlocks) so we just avoid this entirely by not running these
-// tests.
-/// ```no_run
+/// ```
 /// use std::sync::Arc;
 /// use std::thread;
 ///
@@ -220,7 +216,7 @@ macro_rules! acquire {
 ///
 /// [`AtomicUsize`]: core::sync::atomic::AtomicUsize "sync::atomic::AtomicUsize"
 ///
-/// ```no_run
+/// ```
 /// use std::sync::Arc;
 /// use std::sync::atomic::{AtomicUsize, Ordering};
 /// use std::thread;
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index f1706e31bb8..6e9b017ad75 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -3048,6 +3048,16 @@ impl<T, A: Allocator> Extend<T> for Vec<T, A> {
     fn extend_reserve(&mut self, additional: usize) {
         self.reserve(additional);
     }
+
+    #[inline]
+    unsafe fn extend_one_unchecked(&mut self, item: T) {
+        // SAFETY: Our preconditions ensure the space has been reserved, and `extend_reserve` is implemented correctly.
+        unsafe {
+            let len = self.len();
+            ptr::write(self.as_mut_ptr().add(len), item);
+            self.set_len(len + 1);
+        }
+    }
 }
 
 impl<T, A: Allocator> Vec<T, A> {
@@ -3244,6 +3254,16 @@ impl<'a, T: Copy + 'a, A: Allocator> Extend<&'a T> for Vec<T, A> {
     fn extend_reserve(&mut self, additional: usize) {
         self.reserve(additional);
     }
+
+    #[inline]
+    unsafe fn extend_one_unchecked(&mut self, &item: &'a T) {
+        // SAFETY: Our preconditions ensure the space has been reserved, and `extend_reserve` is implemented correctly.
+        unsafe {
+            let len = self.len();
+            ptr::write(self.as_mut_ptr().add(len), item);
+            self.set_len(len + 1);
+        }
+    }
 }
 
 /// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
diff --git a/library/alloc/tests/fmt.rs b/library/alloc/tests/fmt.rs
index 379e09ab69a..ce24a40f4c0 100644
--- a/library/alloc/tests/fmt.rs
+++ b/library/alloc/tests/fmt.rs
@@ -217,19 +217,19 @@ fn test_format_macro_interface() {
 
     // make sure that format! doesn't move out of local variables
     let a = Box::new(3);
-    format!("{a}");
-    format!("{a}");
+    let _ = format!("{a}");
+    let _ = format!("{a}");
 
     // make sure that format! doesn't cause spurious unused-unsafe warnings when
     // it's inside of an outer unsafe block
     unsafe {
         let a: isize = ::std::mem::transmute(3_usize);
-        format!("{a}");
+        let _ = format!("{a}");
     }
 
     // test that trailing commas are acceptable
-    format!("{}", "test",);
-    format!("{foo}", foo = "test",);
+    let _ = format!("{}", "test",);
+    let _ = format!("{foo}", foo = "test",);
 }
 
 // Basic test to make sure that we can invoke the `write!` macro with an
diff --git a/library/core/src/any.rs b/library/core/src/any.rs
index eab11ae288a..59f3b6841d5 100644
--- a/library/core/src/any.rs
+++ b/library/core/src/any.rs
@@ -673,7 +673,7 @@ impl hash::Hash for TypeId {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for TypeId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
-        f.debug_tuple("TypeId").field(&self.as_u128()).finish()
+        write!(f, "TypeId({:#034x})", self.as_u128())
     }
 }
 
diff --git a/library/core/src/ffi/mod.rs b/library/core/src/ffi/mod.rs
index 6d1f10f5211..88adc378477 100644
--- a/library/core/src/ffi/mod.rs
+++ b/library/core/src/ffi/mod.rs
@@ -10,8 +10,6 @@
 #![allow(non_camel_case_types)]
 
 use crate::fmt;
-use crate::marker::PhantomData;
-use crate::ops::{Deref, DerefMut};
 
 #[doc(no_inline)]
 #[stable(feature = "core_c_str", since = "1.64.0")]
@@ -28,6 +26,20 @@ pub use self::c_str::CStr;
 #[unstable(feature = "c_str_module", issue = "112134")]
 pub mod c_str;
 
+#[unstable(
+    feature = "c_variadic",
+    issue = "44930",
+    reason = "the `c_variadic` feature has not been properly tested on all supported platforms"
+)]
+pub use self::va_list::{VaList, VaListImpl};
+
+#[unstable(
+    feature = "c_variadic",
+    issue = "44930",
+    reason = "the `c_variadic` feature has not been properly tested on all supported platforms"
+)]
+pub mod va_list;
+
 macro_rules! type_alias {
     {
       $Docfile:tt, $Alias:ident = $Real:ty;
@@ -205,404 +217,6 @@ impl fmt::Debug for c_void {
     }
 }
 
-/// Basic implementation of a `va_list`.
-// The name is WIP, using `VaListImpl` for now.
-#[cfg(any(
-    all(
-        not(target_arch = "aarch64"),
-        not(target_arch = "powerpc"),
-        not(target_arch = "s390x"),
-        not(target_arch = "x86_64")
-    ),
-    all(target_arch = "aarch64", target_vendor = "apple"),
-    target_family = "wasm",
-    target_os = "uefi",
-    windows,
-))]
-#[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/90435
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-#[lang = "va_list"]
-pub struct VaListImpl<'f> {
-    ptr: *mut c_void,
-
-    // Invariant over `'f`, so each `VaListImpl<'f>` object is tied to
-    // the region of the function it's defined in
-    _marker: PhantomData<&'f mut &'f c_void>,
-}
-
-#[cfg(any(
-    all(
-        not(target_arch = "aarch64"),
-        not(target_arch = "powerpc"),
-        not(target_arch = "s390x"),
-        not(target_arch = "x86_64")
-    ),
-    all(target_arch = "aarch64", target_vendor = "apple"),
-    target_family = "wasm",
-    target_os = "uefi",
-    windows,
-))]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'f> fmt::Debug for VaListImpl<'f> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "va_list* {:p}", self.ptr)
-    }
-}
-
-/// AArch64 ABI implementation of a `va_list`. See the
-/// [AArch64 Procedure Call Standard] for more details.
-///
-/// [AArch64 Procedure Call Standard]:
-/// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf
-#[cfg(all(
-    target_arch = "aarch64",
-    not(target_vendor = "apple"),
-    not(target_os = "uefi"),
-    not(windows),
-))]
-#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
-#[derive(Debug)]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-#[lang = "va_list"]
-pub struct VaListImpl<'f> {
-    stack: *mut c_void,
-    gr_top: *mut c_void,
-    vr_top: *mut c_void,
-    gr_offs: i32,
-    vr_offs: i32,
-    _marker: PhantomData<&'f mut &'f c_void>,
-}
-
-/// PowerPC ABI implementation of a `va_list`.
-#[cfg(all(target_arch = "powerpc", not(target_os = "uefi"), not(windows)))]
-#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
-#[derive(Debug)]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-#[lang = "va_list"]
-pub struct VaListImpl<'f> {
-    gpr: u8,
-    fpr: u8,
-    reserved: u16,
-    overflow_arg_area: *mut c_void,
-    reg_save_area: *mut c_void,
-    _marker: PhantomData<&'f mut &'f c_void>,
-}
-
-/// s390x ABI implementation of a `va_list`.
-#[cfg(target_arch = "s390x")]
-#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
-#[derive(Debug)]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-#[lang = "va_list"]
-pub struct VaListImpl<'f> {
-    gpr: i64,
-    fpr: i64,
-    overflow_arg_area: *mut c_void,
-    reg_save_area: *mut c_void,
-    _marker: PhantomData<&'f mut &'f c_void>,
-}
-
-/// x86_64 ABI implementation of a `va_list`.
-#[cfg(all(target_arch = "x86_64", not(target_os = "uefi"), not(windows)))]
-#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
-#[derive(Debug)]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-#[lang = "va_list"]
-pub struct VaListImpl<'f> {
-    gp_offset: i32,
-    fp_offset: i32,
-    overflow_arg_area: *mut c_void,
-    reg_save_area: *mut c_void,
-    _marker: PhantomData<&'f mut &'f c_void>,
-}
-
-/// A wrapper for a `va_list`
-#[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/90435
-#[derive(Debug)]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-pub struct VaList<'a, 'f: 'a> {
-    #[cfg(any(
-        all(
-            not(target_arch = "aarch64"),
-            not(target_arch = "powerpc"),
-            not(target_arch = "s390x"),
-            not(target_arch = "x86_64")
-        ),
-        all(target_arch = "aarch64", target_vendor = "apple"),
-        target_family = "wasm",
-        target_os = "uefi",
-        windows,
-    ))]
-    inner: VaListImpl<'f>,
-
-    #[cfg(all(
-        any(
-            target_arch = "aarch64",
-            target_arch = "powerpc",
-            target_arch = "s390x",
-            target_arch = "x86_64"
-        ),
-        any(not(target_arch = "aarch64"), not(target_vendor = "apple")),
-        not(target_family = "wasm"),
-        not(target_os = "uefi"),
-        not(windows),
-    ))]
-    inner: &'a mut VaListImpl<'f>,
-
-    _marker: PhantomData<&'a mut VaListImpl<'f>>,
-}
-
-#[cfg(any(
-    all(
-        not(target_arch = "aarch64"),
-        not(target_arch = "powerpc"),
-        not(target_arch = "s390x"),
-        not(target_arch = "x86_64")
-    ),
-    all(target_arch = "aarch64", target_vendor = "apple"),
-    target_family = "wasm",
-    target_os = "uefi",
-    windows,
-))]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'f> VaListImpl<'f> {
-    /// Convert a `VaListImpl` into a `VaList` that is binary-compatible with C's `va_list`.
-    #[inline]
-    pub fn as_va_list<'a>(&'a mut self) -> VaList<'a, 'f> {
-        VaList { inner: VaListImpl { ..*self }, _marker: PhantomData }
-    }
-}
-
-#[cfg(all(
-    any(
-        target_arch = "aarch64",
-        target_arch = "powerpc",
-        target_arch = "s390x",
-        target_arch = "x86_64"
-    ),
-    any(not(target_arch = "aarch64"), not(target_vendor = "apple")),
-    not(target_family = "wasm"),
-    not(target_os = "uefi"),
-    not(windows),
-))]
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'f> VaListImpl<'f> {
-    /// Convert a `VaListImpl` into a `VaList` that is binary-compatible with C's `va_list`.
-    #[inline]
-    pub fn as_va_list<'a>(&'a mut self) -> VaList<'a, 'f> {
-        VaList { inner: self, _marker: PhantomData }
-    }
-}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'a, 'f: 'a> Deref for VaList<'a, 'f> {
-    type Target = VaListImpl<'f>;
-
-    #[inline]
-    fn deref(&self) -> &VaListImpl<'f> {
-        &self.inner
-    }
-}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'a, 'f: 'a> DerefMut for VaList<'a, 'f> {
-    #[inline]
-    fn deref_mut(&mut self) -> &mut VaListImpl<'f> {
-        &mut self.inner
-    }
-}
-
-// The VaArgSafe trait needs to be used in public interfaces, however, the trait
-// itself must not be allowed to be used outside this module. Allowing users to
-// implement the trait for a new type (thereby allowing the va_arg intrinsic to
-// be used on a new type) is likely to cause undefined behavior.
-//
-// FIXME(dlrobertson): In order to use the VaArgSafe trait in a public interface
-// but also ensure it cannot be used elsewhere, the trait needs to be public
-// within a private module. Once RFC 2145 has been implemented look into
-// improving this.
-mod sealed_trait {
-    /// Trait which permits the allowed types to be used with [super::VaListImpl::arg].
-    #[unstable(
-        feature = "c_variadic",
-        reason = "the `c_variadic` feature has not been properly tested on \
-                  all supported platforms",
-        issue = "44930"
-    )]
-    pub unsafe trait VaArgSafe {}
-}
-
-macro_rules! impl_va_arg_safe {
-    ($($t:ty),+) => {
-        $(
-            #[unstable(feature = "c_variadic",
-                       reason = "the `c_variadic` feature has not been properly tested on \
-                                 all supported platforms",
-                       issue = "44930")]
-            unsafe impl sealed_trait::VaArgSafe for $t {}
-        )+
-    }
-}
-
-impl_va_arg_safe! {i8, i16, i32, i64, usize}
-impl_va_arg_safe! {u8, u16, u32, u64, isize}
-impl_va_arg_safe! {f64}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-unsafe impl<T> sealed_trait::VaArgSafe for *mut T {}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-unsafe impl<T> sealed_trait::VaArgSafe for *const T {}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'f> VaListImpl<'f> {
-    /// Advance to the next arg.
-    #[inline]
-    pub unsafe fn arg<T: sealed_trait::VaArgSafe>(&mut self) -> T {
-        // SAFETY: the caller must uphold the safety contract for `va_arg`.
-        unsafe { va_arg(self) }
-    }
-
-    /// Copies the `va_list` at the current location.
-    pub unsafe fn with_copy<F, R>(&self, f: F) -> R
-    where
-        F: for<'copy> FnOnce(VaList<'copy, 'f>) -> R,
-    {
-        let mut ap = self.clone();
-        let ret = f(ap.as_va_list());
-        // SAFETY: the caller must uphold the safety contract for `va_end`.
-        unsafe {
-            va_end(&mut ap);
-        }
-        ret
-    }
-}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'f> Clone for VaListImpl<'f> {
-    #[inline]
-    fn clone(&self) -> Self {
-        let mut dest = crate::mem::MaybeUninit::uninit();
-        // SAFETY: we write to the `MaybeUninit`, thus it is initialized and `assume_init` is legal
-        unsafe {
-            va_copy(dest.as_mut_ptr(), self);
-            dest.assume_init()
-        }
-    }
-}
-
-#[unstable(
-    feature = "c_variadic",
-    reason = "the `c_variadic` feature has not been properly tested on \
-              all supported platforms",
-    issue = "44930"
-)]
-impl<'f> Drop for VaListImpl<'f> {
-    fn drop(&mut self) {
-        // FIXME: this should call `va_end`, but there's no clean way to
-        // guarantee that `drop` always gets inlined into its caller,
-        // so the `va_end` would get directly called from the same function as
-        // the corresponding `va_copy`. `man va_end` states that C requires this,
-        // and LLVM basically follows the C semantics, so we need to make sure
-        // that `va_end` is always called from the same function as `va_copy`.
-        // For more details, see https://github.com/rust-lang/rust/pull/59625
-        // and https://llvm.org/docs/LangRef.html#llvm-va-end-intrinsic.
-        //
-        // This works for now, since `va_end` is a no-op on all current LLVM targets.
-    }
-}
-
-extern "rust-intrinsic" {
-    /// Destroy the arglist `ap` after initialization with `va_start` or
-    /// `va_copy`.
-    #[rustc_nounwind]
-    fn va_end(ap: &mut VaListImpl<'_>);
-
-    /// Copies the current location of arglist `src` to the arglist `dst`.
-    #[rustc_nounwind]
-    fn va_copy<'f>(dest: *mut VaListImpl<'f>, src: &VaListImpl<'f>);
-
-    /// Loads an argument of type `T` from the `va_list` `ap` and increment the
-    /// argument `ap` points to.
-    #[rustc_nounwind]
-    fn va_arg<T: sealed_trait::VaArgSafe>(ap: &mut VaListImpl<'_>) -> T;
-}
-
 // Link the MSVC default lib
 #[cfg(all(windows, target_env = "msvc"))]
 #[link(
diff --git a/library/core/src/ffi/va_list.rs b/library/core/src/ffi/va_list.rs
new file mode 100644
index 00000000000..6a2e8b67d0c
--- /dev/null
+++ b/library/core/src/ffi/va_list.rs
@@ -0,0 +1,301 @@
+//! C's "variable arguments"
+//!
+//! Better known as "varargs".
+
+use crate::ffi::c_void;
+
+#[allow(unused_imports)]
+use crate::fmt;
+use crate::marker::PhantomData;
+use crate::ops::{Deref, DerefMut};
+
+/// Basic implementation of a `va_list`.
+// The name is WIP, using `VaListImpl` for now.
+#[cfg(any(
+    all(
+        not(target_arch = "aarch64"),
+        not(target_arch = "powerpc"),
+        not(target_arch = "s390x"),
+        not(target_arch = "x86_64")
+    ),
+    all(target_arch = "aarch64", target_vendor = "apple"),
+    target_family = "wasm",
+    target_os = "uefi",
+    windows,
+))]
+#[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/90435
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    ptr: *mut c_void,
+
+    // Invariant over `'f`, so each `VaListImpl<'f>` object is tied to
+    // the region of the function it's defined in
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
+#[cfg(any(
+    all(
+        not(target_arch = "aarch64"),
+        not(target_arch = "powerpc"),
+        not(target_arch = "s390x"),
+        not(target_arch = "x86_64")
+    ),
+    all(target_arch = "aarch64", target_vendor = "apple"),
+    target_family = "wasm",
+    target_os = "uefi",
+    windows,
+))]
+impl<'f> fmt::Debug for VaListImpl<'f> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "va_list* {:p}", self.ptr)
+    }
+}
+
+/// AArch64 ABI implementation of a `va_list`. See the
+/// [AArch64 Procedure Call Standard] for more details.
+///
+/// [AArch64 Procedure Call Standard]:
+/// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf
+#[cfg(all(
+    target_arch = "aarch64",
+    not(target_vendor = "apple"),
+    not(target_os = "uefi"),
+    not(windows),
+))]
+#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
+#[derive(Debug)]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    stack: *mut c_void,
+    gr_top: *mut c_void,
+    vr_top: *mut c_void,
+    gr_offs: i32,
+    vr_offs: i32,
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
+/// PowerPC ABI implementation of a `va_list`.
+#[cfg(all(target_arch = "powerpc", not(target_os = "uefi"), not(windows)))]
+#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
+#[derive(Debug)]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    gpr: u8,
+    fpr: u8,
+    reserved: u16,
+    overflow_arg_area: *mut c_void,
+    reg_save_area: *mut c_void,
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
+/// s390x ABI implementation of a `va_list`.
+#[cfg(target_arch = "s390x")]
+#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
+#[derive(Debug)]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    gpr: i64,
+    fpr: i64,
+    overflow_arg_area: *mut c_void,
+    reg_save_area: *mut c_void,
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
+/// x86_64 ABI implementation of a `va_list`.
+#[cfg(all(target_arch = "x86_64", not(target_os = "uefi"), not(windows)))]
+#[cfg_attr(not(doc), repr(C))] // work around https://github.com/rust-lang/rust/issues/66401
+#[derive(Debug)]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    gp_offset: i32,
+    fp_offset: i32,
+    overflow_arg_area: *mut c_void,
+    reg_save_area: *mut c_void,
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
+/// A wrapper for a `va_list`
+#[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/90435
+#[derive(Debug)]
+pub struct VaList<'a, 'f: 'a> {
+    #[cfg(any(
+        all(
+            not(target_arch = "aarch64"),
+            not(target_arch = "powerpc"),
+            not(target_arch = "s390x"),
+            not(target_arch = "x86_64")
+        ),
+        all(target_arch = "aarch64", target_vendor = "apple"),
+        target_family = "wasm",
+        target_os = "uefi",
+        windows,
+    ))]
+    inner: VaListImpl<'f>,
+
+    #[cfg(all(
+        any(
+            target_arch = "aarch64",
+            target_arch = "powerpc",
+            target_arch = "s390x",
+            target_arch = "x86_64"
+        ),
+        any(not(target_arch = "aarch64"), not(target_vendor = "apple")),
+        not(target_family = "wasm"),
+        not(target_os = "uefi"),
+        not(windows),
+    ))]
+    inner: &'a mut VaListImpl<'f>,
+
+    _marker: PhantomData<&'a mut VaListImpl<'f>>,
+}
+
+#[cfg(any(
+    all(
+        not(target_arch = "aarch64"),
+        not(target_arch = "powerpc"),
+        not(target_arch = "s390x"),
+        not(target_arch = "x86_64")
+    ),
+    all(target_arch = "aarch64", target_vendor = "apple"),
+    target_family = "wasm",
+    target_os = "uefi",
+    windows,
+))]
+impl<'f> VaListImpl<'f> {
+    /// Convert a `VaListImpl` into a `VaList` that is binary-compatible with C's `va_list`.
+    #[inline]
+    pub fn as_va_list<'a>(&'a mut self) -> VaList<'a, 'f> {
+        VaList { inner: VaListImpl { ..*self }, _marker: PhantomData }
+    }
+}
+
+#[cfg(all(
+    any(
+        target_arch = "aarch64",
+        target_arch = "powerpc",
+        target_arch = "s390x",
+        target_arch = "x86_64"
+    ),
+    any(not(target_arch = "aarch64"), not(target_vendor = "apple")),
+    not(target_family = "wasm"),
+    not(target_os = "uefi"),
+    not(windows),
+))]
+impl<'f> VaListImpl<'f> {
+    /// Convert a `VaListImpl` into a `VaList` that is binary-compatible with C's `va_list`.
+    #[inline]
+    pub fn as_va_list<'a>(&'a mut self) -> VaList<'a, 'f> {
+        VaList { inner: self, _marker: PhantomData }
+    }
+}
+
+impl<'a, 'f: 'a> Deref for VaList<'a, 'f> {
+    type Target = VaListImpl<'f>;
+
+    #[inline]
+    fn deref(&self) -> &VaListImpl<'f> {
+        &self.inner
+    }
+}
+
+impl<'a, 'f: 'a> DerefMut for VaList<'a, 'f> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut VaListImpl<'f> {
+        &mut self.inner
+    }
+}
+
+// The VaArgSafe trait needs to be used in public interfaces, however, the trait
+// itself must not be allowed to be used outside this module. Allowing users to
+// implement the trait for a new type (thereby allowing the va_arg intrinsic to
+// be used on a new type) is likely to cause undefined behavior.
+//
+// FIXME(dlrobertson): In order to use the VaArgSafe trait in a public interface
+// but also ensure it cannot be used elsewhere, the trait needs to be public
+// within a private module. Once RFC 2145 has been implemented look into
+// improving this.
+mod sealed_trait {
+    /// Trait which permits the allowed types to be used with [super::VaListImpl::arg].
+    pub unsafe trait VaArgSafe {}
+}
+
+macro_rules! impl_va_arg_safe {
+    ($($t:ty),+) => {
+        $(
+            unsafe impl sealed_trait::VaArgSafe for $t {}
+        )+
+    }
+}
+
+impl_va_arg_safe! {i8, i16, i32, i64, usize}
+impl_va_arg_safe! {u8, u16, u32, u64, isize}
+impl_va_arg_safe! {f64}
+
+unsafe impl<T> sealed_trait::VaArgSafe for *mut T {}
+unsafe impl<T> sealed_trait::VaArgSafe for *const T {}
+
+impl<'f> VaListImpl<'f> {
+    /// Advance to the next arg.
+    #[inline]
+    pub unsafe fn arg<T: sealed_trait::VaArgSafe>(&mut self) -> T {
+        // SAFETY: the caller must uphold the safety contract for `va_arg`.
+        unsafe { va_arg(self) }
+    }
+
+    /// Copies the `va_list` at the current location.
+    pub unsafe fn with_copy<F, R>(&self, f: F) -> R
+    where
+        F: for<'copy> FnOnce(VaList<'copy, 'f>) -> R,
+    {
+        let mut ap = self.clone();
+        let ret = f(ap.as_va_list());
+        // SAFETY: the caller must uphold the safety contract for `va_end`.
+        unsafe {
+            va_end(&mut ap);
+        }
+        ret
+    }
+}
+
+impl<'f> Clone for VaListImpl<'f> {
+    #[inline]
+    fn clone(&self) -> Self {
+        let mut dest = crate::mem::MaybeUninit::uninit();
+        // SAFETY: we write to the `MaybeUninit`, thus it is initialized and `assume_init` is legal
+        unsafe {
+            va_copy(dest.as_mut_ptr(), self);
+            dest.assume_init()
+        }
+    }
+}
+
+impl<'f> Drop for VaListImpl<'f> {
+    fn drop(&mut self) {
+        // FIXME: this should call `va_end`, but there's no clean way to
+        // guarantee that `drop` always gets inlined into its caller,
+        // so the `va_end` would get directly called from the same function as
+        // the corresponding `va_copy`. `man va_end` states that C requires this,
+        // and LLVM basically follows the C semantics, so we need to make sure
+        // that `va_end` is always called from the same function as `va_copy`.
+        // For more details, see https://github.com/rust-lang/rust/pull/59625
+        // and https://llvm.org/docs/LangRef.html#llvm-va-end-intrinsic.
+        //
+        // This works for now, since `va_end` is a no-op on all current LLVM targets.
+    }
+}
+
+extern "rust-intrinsic" {
+    /// Destroy the arglist `ap` after initialization with `va_start` or
+    /// `va_copy`.
+    #[rustc_nounwind]
+    fn va_end(ap: &mut VaListImpl<'_>);
+
+    /// Copies the current location of arglist `src` to the arglist `dst`.
+    #[rustc_nounwind]
+    fn va_copy<'f>(dest: *mut VaListImpl<'f>, src: &VaListImpl<'f>);
+
+    /// Loads an argument of type `T` from the `va_list` `ap` and increment the
+    /// argument `ap` points to.
+    #[rustc_nounwind]
+    fn va_arg<T: sealed_trait::VaArgSafe>(ap: &mut VaListImpl<'_>) -> T;
+}
diff --git a/library/core/src/iter/traits/collect.rs b/library/core/src/iter/traits/collect.rs
index 61a45789013..86660f2e375 100644
--- a/library/core/src/iter/traits/collect.rs
+++ b/library/core/src/iter/traits/collect.rs
@@ -1,3 +1,5 @@
+use super::TrustedLen;
+
 /// Conversion from an [`Iterator`].
 ///
 /// By implementing `FromIterator` for a type, you define how it will be
@@ -460,6 +462,27 @@ pub trait Extend<A> {
     fn extend_reserve(&mut self, additional: usize) {
         let _ = additional;
     }
+
+    /// Extends a collection with one element, without checking there is enough capacity for it.
+    ///
+    /// # Safety
+    ///
+    /// **For callers:** This must only be called when we know the collection has enough capacity
+    /// to contain the new item, for example because we previously called `extend_reserve`.
+    ///
+    /// **For implementors:** For a collection to unsafely rely on this method's safety precondition (that is,
+    /// invoke UB if they are violated), it must implement `extend_reserve` correctly. In other words,
+    /// callers may assume that if they `extend_reserve`ed enough space they can call this method.
+
+    // This method is for internal usage only. It is only on the trait because of specialization's limitations.
+    #[unstable(feature = "extend_one_unchecked", issue = "none")]
+    #[doc(hidden)]
+    unsafe fn extend_one_unchecked(&mut self, item: A)
+    where
+        Self: Sized,
+    {
+        self.extend_one(item);
+    }
 }
 
 #[stable(feature = "extend_for_unit", since = "1.28.0")]
@@ -499,33 +522,102 @@ where
     fn extend<T: IntoIterator<Item = (A, B)>>(&mut self, into_iter: T) {
         let (a, b) = self;
         let iter = into_iter.into_iter();
+        SpecTupleExtend::extend(iter, a, b);
+    }
+
+    fn extend_one(&mut self, item: (A, B)) {
+        self.0.extend_one(item.0);
+        self.1.extend_one(item.1);
+    }
+
+    fn extend_reserve(&mut self, additional: usize) {
+        self.0.extend_reserve(additional);
+        self.1.extend_reserve(additional);
+    }
+
+    unsafe fn extend_one_unchecked(&mut self, item: (A, B)) {
+        // SAFETY: Those are our safety preconditions, and we correctly forward `extend_reserve`.
+        unsafe {
+            self.0.extend_one_unchecked(item.0);
+            self.1.extend_one_unchecked(item.1);
+        }
+    }
+}
+
+fn default_extend_tuple<A, B, ExtendA, ExtendB>(
+    iter: impl Iterator<Item = (A, B)>,
+    a: &mut ExtendA,
+    b: &mut ExtendB,
+) where
+    ExtendA: Extend<A>,
+    ExtendB: Extend<B>,
+{
+    fn extend<'a, A, B>(
+        a: &'a mut impl Extend<A>,
+        b: &'a mut impl Extend<B>,
+    ) -> impl FnMut((), (A, B)) + 'a {
+        move |(), (t, u)| {
+            a.extend_one(t);
+            b.extend_one(u);
+        }
+    }
+
+    let (lower_bound, _) = iter.size_hint();
+    if lower_bound > 0 {
+        a.extend_reserve(lower_bound);
+        b.extend_reserve(lower_bound);
+    }
+
+    iter.fold((), extend(a, b));
+}
+
+trait SpecTupleExtend<A, B> {
+    fn extend(self, a: &mut A, b: &mut B);
+}
 
+impl<A, B, ExtendA, ExtendB, Iter> SpecTupleExtend<ExtendA, ExtendB> for Iter
+where
+    ExtendA: Extend<A>,
+    ExtendB: Extend<B>,
+    Iter: Iterator<Item = (A, B)>,
+{
+    default fn extend(self, a: &mut ExtendA, b: &mut ExtendB) {
+        default_extend_tuple(self, a, b);
+    }
+}
+
+impl<A, B, ExtendA, ExtendB, Iter> SpecTupleExtend<ExtendA, ExtendB> for Iter
+where
+    ExtendA: Extend<A>,
+    ExtendB: Extend<B>,
+    Iter: TrustedLen<Item = (A, B)>,
+{
+    fn extend(self, a: &mut ExtendA, b: &mut ExtendB) {
         fn extend<'a, A, B>(
             a: &'a mut impl Extend<A>,
             b: &'a mut impl Extend<B>,
         ) -> impl FnMut((), (A, B)) + 'a {
-            move |(), (t, u)| {
-                a.extend_one(t);
-                b.extend_one(u);
+            // SAFETY: We reserve enough space for the `size_hint`, and the iterator is `TrustedLen`
+            // so its `size_hint` is exact.
+            move |(), (t, u)| unsafe {
+                a.extend_one_unchecked(t);
+                b.extend_one_unchecked(u);
             }
         }
 
-        let (lower_bound, _) = iter.size_hint();
+        let (lower_bound, upper_bound) = self.size_hint();
+
+        if upper_bound.is_none() {
+            // We cannot reserve more than `usize::MAX` items, and this is likely to go out of memory anyway.
+            default_extend_tuple(self, a, b);
+            return;
+        }
+
         if lower_bound > 0 {
             a.extend_reserve(lower_bound);
             b.extend_reserve(lower_bound);
         }
 
-        iter.fold((), extend(a, b));
-    }
-
-    fn extend_one(&mut self, item: (A, B)) {
-        self.0.extend_one(item.0);
-        self.1.extend_one(item.1);
-    }
-
-    fn extend_reserve(&mut self, additional: usize) {
-        self.0.extend_reserve(additional);
-        self.1.extend_reserve(additional);
+        self.fold((), extend(a, b));
     }
 }
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index 9054ade2d79..dd4b6e82343 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -1266,6 +1266,20 @@ impl<T> SizedTypeProperties for T {}
 /// // ^^^ error[E0616]: field `private` of struct `Struct` is private
 /// ```
 ///
+/// Only [`Sized`] fields are supported, but the container may be unsized:
+/// ```
+/// # use core::mem;
+/// #[repr(C)]
+/// pub struct Struct {
+///     a: u8,
+///     b: [u8],
+/// }
+///
+/// assert_eq!(mem::offset_of!(Struct, a), 0); // OK
+/// // assert_eq!(mem::offset_of!(Struct, b), 1);
+/// // ^^^ error[E0277]: doesn't have a size known at compile-time
+/// ```
+///
 /// Note that type layout is, in general, [subject to change and
 /// platform-specific](https://doc.rust-lang.org/reference/type-layout.html). If
 /// layout stability is required, consider using an [explicit `repr` attribute].
diff --git a/library/core/src/num/f16.rs b/library/core/src/num/f16.rs
index 3c58b0af9c2..e74300d6c2f 100644
--- a/library/core/src/num/f16.rs
+++ b/library/core/src/num/f16.rs
@@ -507,8 +507,8 @@ impl f16 {
     ///
     /// ```
     /// #![feature(f16)]
-    /// # // FIXME(f16_f128): remove when `extendhfsf2` and `truncsfhf2` are available
-    /// # #[cfg(target_os = "linux")] {
+    /// # // FIXME(f16_f128): extendhfsf2, truncsfhf2, __gnu_h2f_ieee, __gnu_f2h_ieee missing for many platforms
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
     ///
     /// let x = 2.0_f16;
     /// let abs_difference = (x.recip() - (1.0 / x)).abs();
@@ -528,8 +528,8 @@ impl f16 {
     ///
     /// ```
     /// #![feature(f16)]
-    /// # // FIXME(f16_f128): remove when `extendhfsf2` and `truncsfhf2` are available
-    /// # #[cfg(target_os = "linux")] {
+    /// # // FIXME(f16_f128): extendhfsf2, truncsfhf2, __gnu_h2f_ieee, __gnu_f2h_ieee missing for many platforms
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
     ///
     /// let angle = std::f16::consts::PI;
     ///
@@ -551,8 +551,8 @@ impl f16 {
     ///
     /// ```
     /// #![feature(f16)]
-    /// # // FIXME(f16_f128): remove when `extendhfsf2` and `truncsfhf2` are available
-    /// # #[cfg(target_os = "linux")] {
+    /// # // FIXME(f16_f128): extendhfsf2, truncsfhf2, __gnu_h2f_ieee, __gnu_f2h_ieee missing for many platforms
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
     ///
     /// let angle = 180.0f16;
     ///
@@ -870,6 +870,8 @@ impl f16 {
     ///
     /// ```
     /// #![feature(f16)]
+    /// # // FIXME(f16_f128): extendhfsf2, truncsfhf2, __gnu_h2f_ieee, __gnu_f2h_ieee missing for many platforms
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
     ///
     /// struct GoodBoy {
     ///     name: &'static str,
@@ -897,6 +899,7 @@ impl f16 {
     ///         .zip([-5.0, 0.1, 10.0, 99.0, f16::INFINITY, f16::NAN].iter())
     ///         .for_each(|(a, b)| assert_eq!(a.to_bits(), b.to_bits()))
     /// }
+    /// # }
     /// ```
     #[inline]
     #[must_use]
diff --git a/library/core/tests/fmt/builders.rs b/library/core/tests/fmt/builders.rs
index 487ce46be28..2bdc334b7c0 100644
--- a/library/core/tests/fmt/builders.rs
+++ b/library/core/tests/fmt/builders.rs
@@ -441,7 +441,7 @@ mod debug_map {
             }
         }
 
-        format!("{Foo:?}");
+        let _ = format!("{Foo:?}");
     }
 
     #[test]
@@ -455,7 +455,7 @@ mod debug_map {
             }
         }
 
-        format!("{Foo:?}");
+        let _ = format!("{Foo:?}");
     }
 
     #[test]
@@ -469,7 +469,7 @@ mod debug_map {
             }
         }
 
-        format!("{Foo:?}");
+        let _ = format!("{Foo:?}");
     }
 }
 
diff --git a/library/std/build.rs b/library/std/build.rs
index 55388648a14..c542ba81eed 100644
--- a/library/std/build.rs
+++ b/library/std/build.rs
@@ -99,7 +99,9 @@ fn main() {
         // the compiler-builtins update. <https://github.com/rust-lang/rust/issues/123885>
         ("x86" | "x86_64", _) => false,
         // Missing `__gnu_h2f_ieee` and `__gnu_f2h_ieee`
-        ("powerpc" | "powerpc64" | "powerpc64le", _) => false,
+        ("powerpc" | "powerpc64", _) => false,
+        // Missing `__gnu_h2f_ieee` and `__gnu_f2h_ieee`
+        ("mips" | "mips32r6" | "mips64" | "mips64r6", _) => false,
         // Missing `__extendhfsf` and `__truncsfhf`
         ("riscv32" | "riscv64", _) => false,
         // Most OSs are missing `__extendhfsf` and `__truncsfhf`
diff --git a/library/std/src/os/fd/owned.rs b/library/std/src/os/fd/owned.rs
index 8c7fc4cb2e4..a1f83029d27 100644
--- a/library/std/src/os/fd/owned.rs
+++ b/library/std/src/os/fd/owned.rs
@@ -175,6 +175,11 @@ impl Drop for OwnedFd {
             // the file descriptor was closed or not, and if we retried (for
             // something like EINTR), we might close another valid file descriptor
             // opened after we closed ours.
+            // However, this is usually justified, as some of the major Unices
+            // do make sure to always close the FD, even when `close()` is interrupted,
+            // and the scenario is rare to begin with.
+            // Helpful link to an epic discussion by POSIX workgroup:
+            // http://austingroupbugs.net/view.php?id=529
             #[cfg(not(target_os = "hermit"))]
             {
                 #[cfg(unix)]
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 8d565e26a16..d5121a554bf 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -3192,15 +3192,19 @@ impl Hash for Path {
         let bytes = &bytes[prefix_len..];
 
         let mut component_start = 0;
-        let mut bytes_hashed = 0;
+        // track some extra state to avoid prefix collisions.
+        // ["foo", "bar"] and ["foobar"], will have the same payload bytes
+        // but result in different chunk_bits
+        let mut chunk_bits: usize = 0;
 
         for i in 0..bytes.len() {
             let is_sep = if verbatim { is_verbatim_sep(bytes[i]) } else { is_sep_byte(bytes[i]) };
             if is_sep {
                 if i > component_start {
                     let to_hash = &bytes[component_start..i];
+                    chunk_bits = chunk_bits.wrapping_add(to_hash.len());
+                    chunk_bits = chunk_bits.rotate_right(2);
                     h.write(to_hash);
-                    bytes_hashed += to_hash.len();
                 }
 
                 // skip over separator and optionally a following CurDir item
@@ -3221,11 +3225,12 @@ impl Hash for Path {
 
         if component_start < bytes.len() {
             let to_hash = &bytes[component_start..];
+            chunk_bits = chunk_bits.wrapping_add(to_hash.len());
+            chunk_bits = chunk_bits.rotate_right(2);
             h.write(to_hash);
-            bytes_hashed += to_hash.len();
         }
 
-        h.write_usize(bytes_hashed);
+        h.write_usize(chunk_bits);
     }
 }
 
diff --git a/library/std/src/path/tests.rs b/library/std/src/path/tests.rs
index bb6126e4941..3ade4fb892f 100644
--- a/library/std/src/path/tests.rs
+++ b/library/std/src/path/tests.rs
@@ -1619,6 +1619,20 @@ pub fn test_compare() {
     relative_from: Some("")
     );
 
+    tc!("foo//", "foo",
+    eq: true,
+    starts_with: true,
+    ends_with: true,
+    relative_from: Some("")
+    );
+
+    tc!("foo///", "foo",
+    eq: true,
+    starts_with: true,
+    ends_with: true,
+    relative_from: Some("")
+    );
+
     tc!("foo/.", "foo",
     eq: true,
     starts_with: true,
@@ -1633,6 +1647,20 @@ pub fn test_compare() {
     relative_from: Some("")
     );
 
+    tc!("foo/.//bar", "foo/bar",
+    eq: true,
+    starts_with: true,
+    ends_with: true,
+    relative_from: Some("")
+    );
+
+    tc!("foo//./bar", "foo/bar",
+    eq: true,
+    starts_with: true,
+    ends_with: true,
+    relative_from: Some("")
+    );
+
     tc!("foo/bar", "foo",
     eq: false,
     starts_with: true,
@@ -1640,6 +1668,13 @@ pub fn test_compare() {
     relative_from: Some("bar")
     );
 
+    tc!("foo/bar", "foobar",
+    eq: false,
+    starts_with: false,
+    ends_with: false,
+    relative_from: None
+    );
+
     tc!("foo/bar/baz", "foo/bar",
     eq: false,
     starts_with: true,
diff --git a/library/std/src/sync/once_lock.rs b/library/std/src/sync/once_lock.rs
index f52b9e52c54..fe243550606 100644
--- a/library/std/src/sync/once_lock.rs
+++ b/library/std/src/sync/once_lock.rs
@@ -80,14 +80,21 @@ use crate::sync::Once;
 /// static LIST: OnceList<u32> = OnceList::new();
 /// static COUNTER: AtomicU32 = AtomicU32::new(0);
 ///
-/// let vec = (0..thread::available_parallelism().unwrap().get()).map(|_| thread::spawn(|| {
-///     while let i @ 0..=1000 = COUNTER.fetch_add(1, Ordering::Relaxed) {
-///         LIST.push(i);
+/// # const LEN: u32 = if cfg!(miri) { 50 } else { 1000 };
+/// # /*
+/// const LEN: u32 = 1000;
+/// # */
+/// thread::scope(|s| {
+///     for _ in 0..thread::available_parallelism().unwrap().get() {
+///         s.spawn(|| {
+///             while let i @ 0..LEN = COUNTER.fetch_add(1, Ordering::Relaxed) {
+///                 LIST.push(i);
+///             }
+///         });
 ///     }
-/// })).collect::<Vec<thread::JoinHandle<_>>>();
-/// vec.into_iter().for_each(|handle| handle.join().unwrap());
+/// });
 ///
-/// for i in 0..=1000 {
+/// for i in 0..LEN {
 ///     assert!(LIST.contains(&i));
 /// }
 ///
diff --git a/src/bootstrap/Cargo.lock b/src/bootstrap/Cargo.lock
index 9c24742cff1..c095127da14 100644
--- a/src/bootstrap/Cargo.lock
+++ b/src/bootstrap/Cargo.lock
@@ -54,7 +54,6 @@ dependencies = [
  "junction",
  "libc",
  "object",
- "once_cell",
  "opener",
  "pretty_assertions",
  "semver",
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index 32dd3efa7a6..df7b5b88193 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -49,7 +49,6 @@ home = "0.5"
 ignore = "0.4"
 libc = "0.2"
 object = { version = "0.32", default-features = false, features = ["archive", "coff", "read_core", "unaligned"] }
-once_cell = "1.19"
 opener = "0.5"
 semver = "1.0"
 serde = "1.0"
diff --git a/src/bootstrap/src/core/build_steps/clean.rs b/src/bootstrap/src/core/build_steps/clean.rs
index 479af4af666..a4be6bc56c5 100644
--- a/src/bootstrap/src/core/build_steps/clean.rs
+++ b/src/bootstrap/src/core/build_steps/clean.rs
@@ -85,7 +85,7 @@ macro_rules! clean_crate_tree {
 
                 // NOTE: doesn't use `run_cargo` because we don't want to save a stamp file,
                 // and doesn't use `stream_cargo` to avoid passing `--message-format` which `clean` doesn't accept.
-                builder.run(cargo);
+                cargo.run(builder);
             }
         }
     )+ }
diff --git a/src/bootstrap/src/core/build_steps/compile.rs b/src/bootstrap/src/core/build_steps/compile.rs
index 01b25224de4..11a7a404535 100644
--- a/src/bootstrap/src/core/build_steps/compile.rs
+++ b/src/bootstrap/src/core/build_steps/compile.rs
@@ -27,7 +27,7 @@ use crate::core::builder::crate_description;
 use crate::core::builder::Cargo;
 use crate::core::builder::{Builder, Kind, PathSet, RunConfig, ShouldRun, Step, TaskPath};
 use crate::core::config::{DebuginfoLevel, LlvmLibunwind, RustcLto, TargetSelection};
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::utils::helpers::{
     exe, get_clang_cl_resource_dir, is_debug_info, is_dylib, symlink_dir, t, up_to_date,
 };
@@ -773,20 +773,19 @@ impl Step for StartupObjects {
             let src_file = &src_dir.join(file.to_string() + ".rs");
             let dst_file = &dst_dir.join(file.to_string() + ".o");
             if !up_to_date(src_file, dst_file) {
-                let mut cmd = BootstrapCommand::new(&builder.initial_rustc);
+                let mut cmd = command(&builder.initial_rustc);
                 cmd.env("RUSTC_BOOTSTRAP", "1");
                 if !builder.local_rebuild {
                     // a local_rebuild compiler already has stage1 features
                     cmd.arg("--cfg").arg("bootstrap");
                 }
-                builder.run(
-                    cmd.arg("--target")
-                        .arg(target.rustc_target_arg())
-                        .arg("--emit=obj")
-                        .arg("-o")
-                        .arg(dst_file)
-                        .arg(src_file),
-                );
+                cmd.arg("--target")
+                    .arg(target.rustc_target_arg())
+                    .arg("--emit=obj")
+                    .arg("-o")
+                    .arg(dst_file)
+                    .arg(src_file)
+                    .run(builder);
             }
 
             let target = sysroot_dir.join((*file).to_string() + ".o");
@@ -1488,10 +1487,10 @@ pub fn compiler_file(
     if builder.config.dry_run() {
         return PathBuf::new();
     }
-    let mut cmd = BootstrapCommand::new(compiler);
+    let mut cmd = command(compiler);
     cmd.args(builder.cflags(target, GitRepo::Rustc, c));
     cmd.arg(format!("-print-file-name={file}"));
-    let out = builder.run(cmd.capture_stdout()).stdout();
+    let out = cmd.capture_stdout().run(builder).stdout();
     PathBuf::from(out.trim())
 }
 
@@ -1836,9 +1835,8 @@ impl Step for Assemble {
             let llvm::LlvmResult { llvm_config, .. } =
                 builder.ensure(llvm::Llvm { target: target_compiler.host });
             if !builder.config.dry_run() && builder.config.llvm_tools_enabled {
-                let llvm_bin_dir = builder
-                    .run(BootstrapCommand::new(llvm_config).capture_stdout().arg("--bindir"))
-                    .stdout();
+                let llvm_bin_dir =
+                    command(llvm_config).capture_stdout().arg("--bindir").run(builder).stdout();
                 let llvm_bin_dir = Path::new(llvm_bin_dir.trim());
 
                 // Since we've already built the LLVM tools, install them to the sysroot.
@@ -2163,7 +2161,7 @@ pub fn strip_debug(builder: &Builder<'_>, target: TargetSelection, path: &Path)
     }
 
     let previous_mtime = FileTime::from_last_modification_time(&path.metadata().unwrap());
-    builder.run(BootstrapCommand::new("strip").capture().arg("--strip-debug").arg(path));
+    command("strip").capture().arg("--strip-debug").arg(path).run(builder);
 
     // After running `strip`, we have to set the file modification time to what it was before,
     // otherwise we risk Cargo invalidating its fingerprint and rebuilding the world next time
diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index 3dc871b1ca9..7bc5405e92f 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -25,7 +25,7 @@ use crate::core::build_steps::tool::{self, Tool};
 use crate::core::builder::{Builder, Kind, RunConfig, ShouldRun, Step};
 use crate::core::config::TargetSelection;
 use crate::utils::channel::{self, Info};
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 use crate::utils::helpers::{
     exe, is_dylib, move_file, t, target_supports_cranelift_backend, timeit,
 };
@@ -180,9 +180,9 @@ fn make_win_dist(
     }
 
     //Ask gcc where it keeps its stuff
-    let mut cmd = BootstrapCommand::new(builder.cc(target));
+    let mut cmd = command(builder.cc(target));
     cmd.arg("-print-search-dirs");
-    let gcc_out = builder.run(cmd.capture_stdout()).stdout();
+    let gcc_out = cmd.capture_stdout().run(builder).stdout();
 
     let mut bin_path: Vec<_> = env::split_paths(&env::var_os("PATH").unwrap_or_default()).collect();
     let mut lib_path = Vec::new();
@@ -1023,7 +1023,7 @@ impl Step for PlainSourceTarball {
             }
 
             // Vendor all Cargo dependencies
-            let mut cmd = BootstrapCommand::new(&builder.initial_cargo);
+            let mut cmd = command(&builder.initial_cargo);
             cmd.arg("vendor")
                 .arg("--versioned-dirs")
                 .arg("--sync")
@@ -1061,7 +1061,7 @@ impl Step for PlainSourceTarball {
             }
 
             let config = if !builder.config.dry_run() {
-                builder.run(cmd.capture()).stdout()
+                cmd.capture().run(builder).stdout()
             } else {
                 String::new()
             };
@@ -1599,14 +1599,14 @@ impl Step for Extended {
             let _ = fs::remove_dir_all(&pkg);
 
             let pkgbuild = |component: &str| {
-                let mut cmd = BootstrapCommand::new("pkgbuild");
+                let mut cmd = command("pkgbuild");
                 cmd.arg("--identifier")
                     .arg(format!("org.rust-lang.{}", component))
                     .arg("--scripts")
                     .arg(pkg.join(component))
                     .arg("--nopayload")
                     .arg(pkg.join(component).with_extension("pkg"));
-                builder.run(cmd);
+                cmd.run(builder);
             };
 
             let prepare = |name: &str| {
@@ -1636,7 +1636,7 @@ impl Step for Extended {
             builder.create_dir(&pkg.join("res"));
             builder.create(&pkg.join("res/LICENSE.txt"), &license);
             builder.install(&etc.join("gfx/rust-logo.png"), &pkg.join("res"), 0o644);
-            let mut cmd = BootstrapCommand::new("productbuild");
+            let mut cmd = command("productbuild");
             cmd.arg("--distribution")
                 .arg(xform(&etc.join("pkg/Distribution.xml")))
                 .arg("--resources")
@@ -1649,7 +1649,7 @@ impl Step for Extended {
                 .arg("--package-path")
                 .arg(&pkg);
             let _time = timeit(builder);
-            builder.run(cmd);
+            cmd.run(builder);
         }
 
         if target.is_windows() {
@@ -1703,168 +1703,159 @@ impl Step for Extended {
             let light = wix.join("bin/light.exe");
 
             let heat_flags = ["-nologo", "-gg", "-sfrag", "-srd", "-sreg"];
-            builder.run(
-                BootstrapCommand::new(&heat)
+            command(&heat)
+                .current_dir(&exe)
+                .arg("dir")
+                .arg("rustc")
+                .args(heat_flags)
+                .arg("-cg")
+                .arg("RustcGroup")
+                .arg("-dr")
+                .arg("Rustc")
+                .arg("-var")
+                .arg("var.RustcDir")
+                .arg("-out")
+                .arg(exe.join("RustcGroup.wxs"))
+                .run(builder);
+            if built_tools.contains("rust-docs") {
+                command(&heat)
                     .current_dir(&exe)
                     .arg("dir")
-                    .arg("rustc")
+                    .arg("rust-docs")
                     .args(heat_flags)
                     .arg("-cg")
-                    .arg("RustcGroup")
+                    .arg("DocsGroup")
                     .arg("-dr")
-                    .arg("Rustc")
+                    .arg("Docs")
                     .arg("-var")
-                    .arg("var.RustcDir")
+                    .arg("var.DocsDir")
                     .arg("-out")
-                    .arg(exe.join("RustcGroup.wxs")),
-            );
-            if built_tools.contains("rust-docs") {
-                builder.run(
-                    BootstrapCommand::new(&heat)
-                        .current_dir(&exe)
-                        .arg("dir")
-                        .arg("rust-docs")
-                        .args(heat_flags)
-                        .arg("-cg")
-                        .arg("DocsGroup")
-                        .arg("-dr")
-                        .arg("Docs")
-                        .arg("-var")
-                        .arg("var.DocsDir")
-                        .arg("-out")
-                        .arg(exe.join("DocsGroup.wxs"))
-                        .arg("-t")
-                        .arg(etc.join("msi/squash-components.xsl")),
-                );
+                    .arg(exe.join("DocsGroup.wxs"))
+                    .arg("-t")
+                    .arg(etc.join("msi/squash-components.xsl"))
+                    .run(builder);
             }
-            builder.run(
-                BootstrapCommand::new(&heat)
+            command(&heat)
+                .current_dir(&exe)
+                .arg("dir")
+                .arg("cargo")
+                .args(heat_flags)
+                .arg("-cg")
+                .arg("CargoGroup")
+                .arg("-dr")
+                .arg("Cargo")
+                .arg("-var")
+                .arg("var.CargoDir")
+                .arg("-out")
+                .arg(exe.join("CargoGroup.wxs"))
+                .arg("-t")
+                .arg(etc.join("msi/remove-duplicates.xsl"))
+                .run(builder);
+            command(&heat)
+                .current_dir(&exe)
+                .arg("dir")
+                .arg("rust-std")
+                .args(heat_flags)
+                .arg("-cg")
+                .arg("StdGroup")
+                .arg("-dr")
+                .arg("Std")
+                .arg("-var")
+                .arg("var.StdDir")
+                .arg("-out")
+                .arg(exe.join("StdGroup.wxs"))
+                .run(builder);
+            if built_tools.contains("rust-analyzer") {
+                command(&heat)
                     .current_dir(&exe)
                     .arg("dir")
-                    .arg("cargo")
+                    .arg("rust-analyzer")
                     .args(heat_flags)
                     .arg("-cg")
-                    .arg("CargoGroup")
+                    .arg("RustAnalyzerGroup")
                     .arg("-dr")
-                    .arg("Cargo")
+                    .arg("RustAnalyzer")
                     .arg("-var")
-                    .arg("var.CargoDir")
+                    .arg("var.RustAnalyzerDir")
                     .arg("-out")
-                    .arg(exe.join("CargoGroup.wxs"))
+                    .arg(exe.join("RustAnalyzerGroup.wxs"))
                     .arg("-t")
-                    .arg(etc.join("msi/remove-duplicates.xsl")),
-            );
-            builder.run(
-                BootstrapCommand::new(&heat)
+                    .arg(etc.join("msi/remove-duplicates.xsl"))
+                    .run(builder);
+            }
+            if built_tools.contains("clippy") {
+                command(&heat)
                     .current_dir(&exe)
                     .arg("dir")
-                    .arg("rust-std")
+                    .arg("clippy")
                     .args(heat_flags)
                     .arg("-cg")
-                    .arg("StdGroup")
+                    .arg("ClippyGroup")
                     .arg("-dr")
-                    .arg("Std")
+                    .arg("Clippy")
                     .arg("-var")
-                    .arg("var.StdDir")
+                    .arg("var.ClippyDir")
                     .arg("-out")
-                    .arg(exe.join("StdGroup.wxs")),
-            );
-            if built_tools.contains("rust-analyzer") {
-                builder.run(
-                    BootstrapCommand::new(&heat)
-                        .current_dir(&exe)
-                        .arg("dir")
-                        .arg("rust-analyzer")
-                        .args(heat_flags)
-                        .arg("-cg")
-                        .arg("RustAnalyzerGroup")
-                        .arg("-dr")
-                        .arg("RustAnalyzer")
-                        .arg("-var")
-                        .arg("var.RustAnalyzerDir")
-                        .arg("-out")
-                        .arg(exe.join("RustAnalyzerGroup.wxs"))
-                        .arg("-t")
-                        .arg(etc.join("msi/remove-duplicates.xsl")),
-                );
-            }
-            if built_tools.contains("clippy") {
-                builder.run(
-                    BootstrapCommand::new(&heat)
-                        .current_dir(&exe)
-                        .arg("dir")
-                        .arg("clippy")
-                        .args(heat_flags)
-                        .arg("-cg")
-                        .arg("ClippyGroup")
-                        .arg("-dr")
-                        .arg("Clippy")
-                        .arg("-var")
-                        .arg("var.ClippyDir")
-                        .arg("-out")
-                        .arg(exe.join("ClippyGroup.wxs"))
-                        .arg("-t")
-                        .arg(etc.join("msi/remove-duplicates.xsl")),
-                );
+                    .arg(exe.join("ClippyGroup.wxs"))
+                    .arg("-t")
+                    .arg(etc.join("msi/remove-duplicates.xsl"))
+                    .run(builder);
             }
             if built_tools.contains("miri") {
-                builder.run(
-                    BootstrapCommand::new(&heat)
-                        .current_dir(&exe)
-                        .arg("dir")
-                        .arg("miri")
-                        .args(heat_flags)
-                        .arg("-cg")
-                        .arg("MiriGroup")
-                        .arg("-dr")
-                        .arg("Miri")
-                        .arg("-var")
-                        .arg("var.MiriDir")
-                        .arg("-out")
-                        .arg(exe.join("MiriGroup.wxs"))
-                        .arg("-t")
-                        .arg(etc.join("msi/remove-duplicates.xsl")),
-                );
-            }
-            builder.run(
-                BootstrapCommand::new(&heat)
+                command(&heat)
                     .current_dir(&exe)
                     .arg("dir")
-                    .arg("rust-analysis")
+                    .arg("miri")
                     .args(heat_flags)
                     .arg("-cg")
-                    .arg("AnalysisGroup")
+                    .arg("MiriGroup")
                     .arg("-dr")
-                    .arg("Analysis")
+                    .arg("Miri")
                     .arg("-var")
-                    .arg("var.AnalysisDir")
+                    .arg("var.MiriDir")
                     .arg("-out")
-                    .arg(exe.join("AnalysisGroup.wxs"))
+                    .arg(exe.join("MiriGroup.wxs"))
                     .arg("-t")
-                    .arg(etc.join("msi/remove-duplicates.xsl")),
-            );
+                    .arg(etc.join("msi/remove-duplicates.xsl"))
+                    .run(builder);
+            }
+            command(&heat)
+                .current_dir(&exe)
+                .arg("dir")
+                .arg("rust-analysis")
+                .args(heat_flags)
+                .arg("-cg")
+                .arg("AnalysisGroup")
+                .arg("-dr")
+                .arg("Analysis")
+                .arg("-var")
+                .arg("var.AnalysisDir")
+                .arg("-out")
+                .arg(exe.join("AnalysisGroup.wxs"))
+                .arg("-t")
+                .arg(etc.join("msi/remove-duplicates.xsl"))
+                .run(builder);
             if target.ends_with("windows-gnu") {
-                builder.run(
-                    BootstrapCommand::new(&heat)
-                        .current_dir(&exe)
-                        .arg("dir")
-                        .arg("rust-mingw")
-                        .args(heat_flags)
-                        .arg("-cg")
-                        .arg("GccGroup")
-                        .arg("-dr")
-                        .arg("Gcc")
-                        .arg("-var")
-                        .arg("var.GccDir")
-                        .arg("-out")
-                        .arg(exe.join("GccGroup.wxs")),
-                );
+                command(&heat)
+                    .current_dir(&exe)
+                    .arg("dir")
+                    .arg("rust-mingw")
+                    .args(heat_flags)
+                    .arg("-cg")
+                    .arg("GccGroup")
+                    .arg("-dr")
+                    .arg("Gcc")
+                    .arg("-var")
+                    .arg("var.GccDir")
+                    .arg("-out")
+                    .arg(exe.join("GccGroup.wxs"))
+                    .run(builder);
             }
 
             let candle = |input: &Path| {
                 let output = exe.join(input.file_stem().unwrap()).with_extension("wixobj");
                 let arch = if target.contains("x86_64") { "x64" } else { "x86" };
-                let mut cmd = BootstrapCommand::new(&candle);
+                let mut cmd = command(&candle);
                 cmd.current_dir(&exe)
                     .arg("-nologo")
                     .arg("-dRustcDir=rustc")
@@ -1893,7 +1884,7 @@ impl Step for Extended {
                 if target.ends_with("windows-gnu") {
                     cmd.arg("-dGccDir=rust-mingw");
                 }
-                builder.run(cmd);
+                cmd.run(builder);
             };
             candle(&xform(&etc.join("msi/rust.wxs")));
             candle(&etc.join("msi/ui.wxs"));
@@ -1925,7 +1916,7 @@ impl Step for Extended {
 
             builder.info(&format!("building `msi` installer with {light:?}"));
             let filename = format!("{}-{}.msi", pkgname(builder, "rust"), target.triple);
-            let mut cmd = BootstrapCommand::new(&light);
+            let mut cmd = command(&light);
             cmd.arg("-nologo")
                 .arg("-ext")
                 .arg("WixUIExtension")
@@ -1962,7 +1953,7 @@ impl Step for Extended {
             cmd.arg("-sice:ICE57");
 
             let _time = timeit(builder);
-            builder.run(cmd);
+            cmd.run(builder);
 
             if !builder.config.dry_run() {
                 t!(move_file(exe.join(&filename), distdir(builder).join(&filename)));
@@ -2078,13 +2069,13 @@ fn maybe_install_llvm(
     } else if let llvm::LlvmBuildStatus::AlreadyBuilt(llvm::LlvmResult { llvm_config, .. }) =
         llvm::prebuilt_llvm_config(builder, target)
     {
-        let mut cmd = BootstrapCommand::new(llvm_config);
+        let mut cmd = command(llvm_config);
         cmd.arg("--libfiles");
         builder.verbose(|| println!("running {cmd:?}"));
         let files = if builder.config.dry_run() {
             "".into()
         } else {
-            builder.run(cmd.capture_stdout()).stdout()
+            cmd.capture_stdout().run(builder).stdout()
         };
         let build_llvm_out = &builder.llvm_out(builder.config.build);
         let target_llvm_out = &builder.llvm_out(target);
diff --git a/src/bootstrap/src/core/build_steps/doc.rs b/src/bootstrap/src/core/build_steps/doc.rs
index 823e842693e..4b35d6c5d4c 100644
--- a/src/bootstrap/src/core/build_steps/doc.rs
+++ b/src/bootstrap/src/core/build_steps/doc.rs
@@ -154,7 +154,7 @@ impl<P: Step> Step for RustbookSrc<P> {
             builder.info(&format!("Rustbook ({target}) - {name}"));
             let _ = fs::remove_dir_all(&out);
 
-            builder.run(rustbook_cmd.arg("build").arg(&src).arg("-d").arg(&out));
+            rustbook_cmd.arg("build").arg(&src).arg("-d").arg(&out).run(builder);
 
             for lang in &self.languages {
                 let out = out.join(lang);
@@ -162,10 +162,15 @@ impl<P: Step> Step for RustbookSrc<P> {
                 builder.info(&format!("Rustbook ({target}) - {name} - {lang}"));
                 let _ = fs::remove_dir_all(&out);
 
-                let mut rustbook_cmd = builder.tool_cmd(Tool::Rustbook);
-                builder.run(
-                    rustbook_cmd.arg("build").arg(&src).arg("-d").arg(&out).arg("-l").arg(lang),
-                );
+                builder
+                    .tool_cmd(Tool::Rustbook)
+                    .arg("build")
+                    .arg(&src)
+                    .arg("-d")
+                    .arg(&out)
+                    .arg("-l")
+                    .arg(lang)
+                    .run(builder);
             }
         }
 
@@ -301,7 +306,7 @@ fn invoke_rustdoc(
         cmd.arg("-Z").arg("unstable-options").arg("--disable-minification");
     }
 
-    builder.run(cmd);
+    cmd.run(builder);
 }
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
@@ -395,7 +400,7 @@ impl Step for Standalone {
             } else {
                 cmd.arg("--markdown-css").arg("rust.css");
             }
-            builder.run(cmd);
+            cmd.run(builder);
         }
 
         // We open doc/index.html as the default if invoked as `x.py doc --open`
@@ -494,7 +499,7 @@ impl Step for Releases {
                 cmd.arg("--disable-minification");
             }
 
-            builder.run(cmd);
+            cmd.run(builder);
         }
 
         // We open doc/RELEASES.html as the default if invoked as `x.py doc --open RELEASES.md`
@@ -738,7 +743,7 @@ fn doc_std(
         format!("library{} in {} format", crate_description(requested_crates), format.as_str());
     let _guard = builder.msg_doc(compiler, description, target);
 
-    builder.run(cargo.into_cmd());
+    cargo.into_cmd().run(builder);
     builder.cp_link_r(&out_dir, out);
 }
 
@@ -863,7 +868,7 @@ impl Step for Rustc {
         let proc_macro_out_dir = builder.stage_out(compiler, Mode::Rustc).join("doc");
         symlink_dir_force(&builder.config, &out, &proc_macro_out_dir);
 
-        builder.run(cargo.into_cmd());
+        cargo.into_cmd().run(builder);
 
         if !builder.config.dry_run() {
             // Sanity check on linked compiler crates
@@ -996,7 +1001,7 @@ macro_rules! tool_doc {
                 symlink_dir_force(&builder.config, &out, &proc_macro_out_dir);
 
                 let _guard = builder.msg_doc(compiler, stringify!($tool).to_lowercase(), target);
-                builder.run(cargo.into_cmd());
+                cargo.into_cmd().run(builder);
 
                 if !builder.config.dry_run() {
                     // Sanity check on linked doc directories
@@ -1075,12 +1080,7 @@ impl Step for ErrorIndex {
         builder.info(&format!("Documenting error index ({})", self.target));
         let out = builder.doc_out(self.target);
         t!(fs::create_dir_all(&out));
-        let mut index = tool::ErrorIndex::command(builder);
-        index.arg("html");
-        index.arg(out);
-        index.arg(&builder.version);
-
-        builder.run(index);
+        tool::ErrorIndex::command(builder).arg("html").arg(out).arg(&builder.version).run(builder);
     }
 }
 
@@ -1116,7 +1116,7 @@ impl Step for UnstableBookGen {
         cmd.arg(builder.src.join("src"));
         cmd.arg(out);
 
-        builder.run(cmd);
+        cmd.run(builder);
     }
 }
 
@@ -1211,7 +1211,7 @@ impl Step for RustcBook {
             self.compiler.host,
             self.target,
         );
-        builder.run(cmd);
+        cmd.run(builder);
         drop(doc_generator_guard);
 
         // Run rustbook/mdbook to generate the HTML pages.
diff --git a/src/bootstrap/src/core/build_steps/format.rs b/src/bootstrap/src/core/build_steps/format.rs
index 66286a52813..d3ac2bae1e8 100644
--- a/src/bootstrap/src/core/build_steps/format.rs
+++ b/src/bootstrap/src/core/build_steps/format.rs
@@ -1,7 +1,7 @@
 //! Runs rustfmt on the repository.
 
 use crate::core::builder::Builder;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::utils::helpers::{self, program_out_of_date, t};
 use build_helper::ci::CiEnv;
 use build_helper::git::get_git_modified_files;
@@ -54,13 +54,13 @@ fn rustfmt(src: &Path, rustfmt: &Path, paths: &[PathBuf], check: bool) -> impl F
 fn get_rustfmt_version(build: &Builder<'_>) -> Option<(String, PathBuf)> {
     let stamp_file = build.out.join("rustfmt.stamp");
 
-    let mut cmd = BootstrapCommand::new(match build.initial_rustfmt() {
+    let mut cmd = command(match build.initial_rustfmt() {
         Some(p) => p,
         None => return None,
     });
     cmd.arg("--version");
 
-    let output = build.run(cmd.capture().allow_failure());
+    let output = cmd.capture().allow_failure().run(build);
     if output.is_failure() {
         return None;
     }
@@ -160,29 +160,25 @@ pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
         }
     }
     let git_available =
-        build.run(helpers::git(None).capture().allow_failure().arg("--version")).is_success();
+        helpers::git(None).capture().allow_failure().arg("--version").run(build).is_success();
 
     let mut adjective = None;
     if git_available {
-        let in_working_tree = build
-            .run(
-                helpers::git(Some(&build.src))
-                    .capture()
-                    .allow_failure()
-                    .arg("rev-parse")
-                    .arg("--is-inside-work-tree"),
-            )
+        let in_working_tree = helpers::git(Some(&build.src))
+            .capture()
+            .allow_failure()
+            .arg("rev-parse")
+            .arg("--is-inside-work-tree")
+            .run(build)
             .is_success();
         if in_working_tree {
-            let untracked_paths_output = build
-                .run(
-                    helpers::git(Some(&build.src))
-                        .capture_stdout()
-                        .arg("status")
-                        .arg("--porcelain")
-                        .arg("-z")
-                        .arg("--untracked-files=normal"),
-                )
+            let untracked_paths_output = helpers::git(Some(&build.src))
+                .capture_stdout()
+                .arg("status")
+                .arg("--porcelain")
+                .arg("-z")
+                .arg("--untracked-files=normal")
+                .run(build)
                 .stdout();
             let untracked_paths: Vec<_> = untracked_paths_output
                 .split_terminator('\0')
diff --git a/src/bootstrap/src/core/build_steps/install.rs b/src/bootstrap/src/core/build_steps/install.rs
index 7ee1aca2abc..d3e9d6d7875 100644
--- a/src/bootstrap/src/core/build_steps/install.rs
+++ b/src/bootstrap/src/core/build_steps/install.rs
@@ -10,7 +10,7 @@ use std::path::{Component, Path, PathBuf};
 use crate::core::build_steps::dist;
 use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
 use crate::core::config::{Config, TargetSelection};
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::utils::helpers::t;
 use crate::utils::tarball::GeneratedTarball;
 use crate::{Compiler, Kind};
@@ -102,7 +102,7 @@ fn install_sh(
     let empty_dir = builder.out.join("tmp/empty_dir");
     t!(fs::create_dir_all(&empty_dir));
 
-    let mut cmd = BootstrapCommand::new(SHELL);
+    let mut cmd = command(SHELL);
     cmd.current_dir(&empty_dir)
         .arg(sanitize_sh(&tarball.decompressed_output().join("install.sh")))
         .arg(format!("--prefix={}", prepare_dir(&destdir_env, prefix)))
@@ -113,7 +113,7 @@ fn install_sh(
         .arg(format!("--libdir={}", prepare_dir(&destdir_env, libdir)))
         .arg(format!("--mandir={}", prepare_dir(&destdir_env, mandir)))
         .arg("--disable-ldconfig");
-    builder.run(cmd);
+    cmd.run(builder);
     t!(fs::remove_dir_all(&empty_dir));
 }
 
diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index 4f1c1f87d1c..872823506f8 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -24,7 +24,7 @@ use crate::utils::helpers::{
 };
 use crate::{generate_smart_stamp_hash, CLang, GitRepo, Kind};
 
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use build_helper::ci::CiEnv;
 use build_helper::git::get_git_merge_base;
 
@@ -478,9 +478,8 @@ impl Step for Llvm {
             let LlvmResult { llvm_config, .. } =
                 builder.ensure(Llvm { target: builder.config.build });
             if !builder.config.dry_run() {
-                let llvm_bindir = builder
-                    .run(BootstrapCommand::new(&llvm_config).capture_stdout().arg("--bindir"))
-                    .stdout();
+                let llvm_bindir =
+                    command(&llvm_config).capture_stdout().arg("--bindir").run(builder).stdout();
                 let host_bin = Path::new(llvm_bindir.trim());
                 cfg.define(
                     "LLVM_TABLEGEN",
@@ -530,8 +529,8 @@ impl Step for Llvm {
 
         // Helper to find the name of LLVM's shared library on darwin and linux.
         let find_llvm_lib_name = |extension| {
-            let cmd = BootstrapCommand::new(&res.llvm_config);
-            let version = builder.run(cmd.capture_stdout().arg("--version")).stdout();
+            let version =
+                command(&res.llvm_config).capture_stdout().arg("--version").run(builder).stdout();
             let major = version.split('.').next().unwrap();
 
             match &llvm_version_suffix {
@@ -587,8 +586,7 @@ fn check_llvm_version(builder: &Builder<'_>, llvm_config: &Path) {
         return;
     }
 
-    let cmd = BootstrapCommand::new(llvm_config);
-    let version = builder.run(cmd.capture_stdout().arg("--version")).stdout();
+    let version = command(llvm_config).capture_stdout().arg("--version").run(builder).stdout();
     let mut parts = version.split('.').take(2).filter_map(|s| s.parse::<u32>().ok());
     if let (Some(major), Some(_minor)) = (parts.next(), parts.next()) {
         if major >= 17 {
@@ -755,7 +753,7 @@ fn configure_cmake(
     }
 
     if builder.config.llvm_clang_cl.is_some() {
-        cflags.push(&format!(" --target={target}"));
+        cflags.push(format!(" --target={target}"));
     }
     cfg.define("CMAKE_C_FLAGS", cflags);
     let mut cxxflags: OsString = builder
@@ -774,7 +772,7 @@ fn configure_cmake(
         cxxflags.push(s);
     }
     if builder.config.llvm_clang_cl.is_some() {
-        cxxflags.push(&format!(" --target={target}"));
+        cxxflags.push(format!(" --target={target}"));
     }
     cfg.define("CMAKE_CXX_FLAGS", cxxflags);
     if let Some(ar) = builder.ar(target) {
@@ -915,7 +913,7 @@ impl Step for Lld {
                 // Find clang's runtime library directory and push that as a search path to the
                 // cmake linker flags.
                 let clang_rt_dir = get_clang_cl_resource_dir(clang_cl_path);
-                ldflags.push_all(&format!("/libpath:{}", clang_rt_dir.display()));
+                ldflags.push_all(format!("/libpath:{}", clang_rt_dir.display()));
             }
         }
 
diff --git a/src/bootstrap/src/core/build_steps/perf.rs b/src/bootstrap/src/core/build_steps/perf.rs
index f41b5fe10f1..5b83080a326 100644
--- a/src/bootstrap/src/core/build_steps/perf.rs
+++ b/src/bootstrap/src/core/build_steps/perf.rs
@@ -31,5 +31,5 @@ Consider setting `rust.debuginfo-level = 1` in `config.toml`."#);
         .env("PERF_COLLECTOR", collector)
         .env("PERF_RESULT_DIR", profile_results_dir)
         .args(args);
-    builder.run(&mut cmd);
+    cmd.run(builder);
 }
diff --git a/src/bootstrap/src/core/build_steps/run.rs b/src/bootstrap/src/core/build_steps/run.rs
index 316a03a2171..3a2d3f67522 100644
--- a/src/bootstrap/src/core/build_steps/run.rs
+++ b/src/bootstrap/src/core/build_steps/run.rs
@@ -11,7 +11,7 @@ use crate::core::build_steps::tool::{self, SourceType, Tool};
 use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
 use crate::core::config::flags::get_completion;
 use crate::core::config::TargetSelection;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::Mode;
 
 #[derive(Debug, PartialOrd, Ord, Clone, Hash, PartialEq, Eq)]
@@ -40,8 +40,7 @@ impl Step for BuildManifest {
             panic!("\n\nfailed to specify `dist.upload-addr` in `config.toml`\n\n")
         });
 
-        let today =
-            builder.run(BootstrapCommand::new("date").capture_stdout().arg("+%Y-%m-%d")).stdout();
+        let today = command("date").capture_stdout().arg("+%Y-%m-%d").run(builder).stdout();
 
         cmd.arg(sign);
         cmd.arg(distdir(builder));
@@ -50,7 +49,7 @@ impl Step for BuildManifest {
         cmd.arg(&builder.config.channel);
 
         builder.create_dir(&distdir(builder));
-        builder.run(cmd);
+        cmd.run(builder);
     }
 }
 
@@ -72,7 +71,7 @@ impl Step for BumpStage0 {
     fn run(self, builder: &Builder<'_>) -> Self::Output {
         let mut cmd = builder.tool_cmd(Tool::BumpStage0);
         cmd.args(builder.config.args());
-        builder.run(cmd);
+        cmd.run(builder);
     }
 }
 
@@ -94,7 +93,7 @@ impl Step for ReplaceVersionPlaceholder {
     fn run(self, builder: &Builder<'_>) -> Self::Output {
         let mut cmd = builder.tool_cmd(Tool::ReplaceVersionPlaceholder);
         cmd.arg(&builder.src);
-        builder.run(cmd);
+        cmd.run(builder);
     }
 }
 
@@ -158,7 +157,7 @@ impl Step for Miri {
         // after another --, so this must be at the end.
         miri.args(builder.config.args());
 
-        builder.run(miri.into_cmd());
+        miri.into_cmd().run(builder);
     }
 }
 
@@ -188,7 +187,7 @@ impl Step for CollectLicenseMetadata {
         let mut cmd = builder.tool_cmd(Tool::CollectLicenseMetadata);
         cmd.env("REUSE_EXE", reuse);
         cmd.env("DEST", &dest);
-        builder.run(cmd);
+        cmd.run(builder);
 
         dest
     }
@@ -218,7 +217,7 @@ impl Step for GenerateCopyright {
         let mut cmd = builder.tool_cmd(Tool::GenerateCopyright);
         cmd.env("LICENSE_METADATA", &license_metadata);
         cmd.env("DEST", &dest);
-        builder.run(cmd);
+        cmd.run(builder);
 
         dest
     }
@@ -242,7 +241,7 @@ impl Step for GenerateWindowsSys {
     fn run(self, builder: &Builder<'_>) {
         let mut cmd = builder.tool_cmd(Tool::GenerateWindowsSys);
         cmd.arg(&builder.src);
-        builder.run(cmd);
+        cmd.run(builder);
     }
 }
 
diff --git a/src/bootstrap/src/core/build_steps/suggest.rs b/src/bootstrap/src/core/build_steps/suggest.rs
index 5412b3c807b..2d4409d27c6 100644
--- a/src/bootstrap/src/core/build_steps/suggest.rs
+++ b/src/bootstrap/src/core/build_steps/suggest.rs
@@ -13,13 +13,11 @@ use crate::core::builder::Builder;
 pub fn suggest(builder: &Builder<'_>, run: bool) {
     let git_config = builder.config.git_config();
     let suggestions = builder
-        .run(
-            builder
-                .tool_cmd(Tool::SuggestTests)
-                .capture_stdout()
-                .env("SUGGEST_TESTS_GIT_REPOSITORY", git_config.git_repository)
-                .env("SUGGEST_TESTS_NIGHTLY_BRANCH", git_config.nightly_branch),
-        )
+        .tool_cmd(Tool::SuggestTests)
+        .capture_stdout()
+        .env("SUGGEST_TESTS_GIT_REPOSITORY", git_config.git_repository)
+        .env("SUGGEST_TESTS_NIGHTLY_BRANCH", git_config.nightly_branch)
+        .run(builder)
         .stdout();
 
     let suggestions = suggestions
diff --git a/src/bootstrap/src/core/build_steps/synthetic_targets.rs b/src/bootstrap/src/core/build_steps/synthetic_targets.rs
index a115ba2d8b2..021680302cd 100644
--- a/src/bootstrap/src/core/build_steps/synthetic_targets.rs
+++ b/src/bootstrap/src/core/build_steps/synthetic_targets.rs
@@ -9,7 +9,7 @@
 
 use crate::core::builder::{Builder, ShouldRun, Step};
 use crate::core::config::TargetSelection;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::Compiler;
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -56,7 +56,7 @@ fn create_synthetic_target(
         return TargetSelection::create_synthetic(&name, path.to_str().unwrap());
     }
 
-    let mut cmd = BootstrapCommand::new(builder.rustc(compiler));
+    let mut cmd = command(builder.rustc(compiler));
     cmd.arg("--target").arg(base.rustc_target_arg());
     cmd.args(["-Zunstable-options", "--print", "target-spec-json"]);
 
@@ -64,7 +64,7 @@ fn create_synthetic_target(
     // we cannot use nightly features. So `RUSTC_BOOTSTRAP` is needed here.
     cmd.env("RUSTC_BOOTSTRAP", "1");
 
-    let output = builder.run(cmd.capture()).stdout();
+    let output = cmd.capture().run(builder).stdout();
     let mut spec: serde_json::Value = serde_json::from_slice(output.as_bytes()).unwrap();
     let spec_map = spec.as_object_mut().unwrap();
 
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index dc53bd3cfa7..7f4c4bd53df 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -26,7 +26,7 @@ use crate::core::builder::{Builder, Compiler, Kind, RunConfig, ShouldRun, Step};
 use crate::core::config::flags::get_completion;
 use crate::core::config::flags::Subcommand;
 use crate::core::config::TargetSelection;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 use crate::utils::helpers::{
     self, add_link_lib_path, add_rustdoc_cargo_linker_args, dylib_path, dylib_path_var,
     linker_args, linker_flags, t, target_supports_cranelift_backend, up_to_date, LldThreads,
@@ -155,7 +155,7 @@ You can skip linkcheck with --skip src/tools/linkchecker"
         let _guard =
             builder.msg(Kind::Test, compiler.stage, "Linkcheck", bootstrap_host, bootstrap_host);
         let _time = helpers::timeit(builder);
-        builder.run(linkchecker.delay_failure().arg(builder.out.join(host.triple).join("doc")));
+        linkchecker.delay_failure().arg(builder.out.join(host.triple).join("doc")).run(builder);
     }
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -212,9 +212,11 @@ impl Step for HtmlCheck {
             builder,
         ));
 
-        builder.run(
-            builder.tool_cmd(Tool::HtmlChecker).delay_failure().arg(builder.doc_out(self.target)),
-        );
+        builder
+            .tool_cmd(Tool::HtmlChecker)
+            .delay_failure()
+            .arg(builder.doc_out(self.target))
+            .run(builder);
     }
 }
 
@@ -259,7 +261,7 @@ impl Step for Cargotest {
             .env("RUSTC", builder.rustc(compiler))
             .env("RUSTDOC", builder.rustdoc(compiler));
         add_rustdoc_cargo_linker_args(&mut cmd, builder, compiler.host, LldThreads::No);
-        builder.run(cmd.delay_failure());
+        cmd.delay_failure().run(builder);
     }
 }
 
@@ -460,7 +462,7 @@ impl Miri {
         let mut cargo = BootstrapCommand::from(cargo);
         let _guard =
             builder.msg(Kind::Build, compiler.stage, "miri sysroot", compiler.host, target);
-        builder.run(&mut cargo);
+        cargo.run(builder);
 
         // # Determine where Miri put its sysroot.
         // To this end, we run `cargo miri setup --print-sysroot` and capture the output.
@@ -473,7 +475,7 @@ impl Miri {
             String::new()
         } else {
             builder.verbose(|| println!("running: {cargo:?}"));
-            let stdout = builder.run(cargo.capture_stdout()).stdout();
+            let stdout = cargo.capture_stdout().run(builder).stdout();
             // Output is "<sysroot>\n".
             let sysroot = stdout.trim_end();
             builder.verbose(|| println!("`cargo miri setup --print-sysroot` said: {sysroot:?}"));
@@ -561,7 +563,7 @@ impl Step for Miri {
         {
             let _guard = builder.msg_sysroot_tool(Kind::Test, stage, "miri", host, target);
             let _time = helpers::timeit(builder);
-            builder.run(&mut cargo);
+            cargo.run(builder);
         }
 
         // Run it again for mir-opt-level 4 to catch some miscompilations.
@@ -583,7 +585,7 @@ impl Step for Miri {
                     target,
                 );
                 let _time = helpers::timeit(builder);
-                builder.run(cargo);
+                cargo.run(builder);
             }
         }
     }
@@ -648,11 +650,11 @@ impl Step for CargoMiri {
 
         // Finally, pass test-args and run everything.
         cargo.arg("--").args(builder.config.test_args());
-        let cargo = BootstrapCommand::from(cargo);
+        let mut cargo = BootstrapCommand::from(cargo);
         {
             let _guard = builder.msg_sysroot_tool(Kind::Test, stage, "cargo-miri", host, target);
             let _time = helpers::timeit(builder);
-            builder.run(cargo);
+            cargo.run(builder);
         }
     }
 }
@@ -753,7 +755,7 @@ impl Step for Clippy {
         let _guard = builder.msg_sysroot_tool(Kind::Test, compiler.stage, "clippy", host, host);
 
         // Clippy reports errors if it blessed the outputs
-        if builder.run(cargo.allow_failure()).is_success() {
+        if cargo.allow_failure().run(builder).is_success() {
             // The tests succeeded; nothing to do.
             return;
         }
@@ -806,7 +808,7 @@ impl Step for RustdocTheme {
             .env("RUSTC_BOOTSTRAP", "1");
         cmd.args(linker_args(builder, self.compiler.host, LldThreads::No));
 
-        builder.run(cmd.delay_failure());
+        cmd.delay_failure().run(builder);
     }
 }
 
@@ -832,7 +834,7 @@ impl Step for RustdocJSStd {
     fn run(self, builder: &Builder<'_>) {
         let nodejs =
             builder.config.nodejs.as_ref().expect("need nodejs to run rustdoc-js-std tests");
-        let mut command = BootstrapCommand::new(nodejs);
+        let mut command = command(nodejs);
         command
             .arg(builder.src.join("src/tools/rustdoc-js/tester.js"))
             .arg("--crate-name")
@@ -866,7 +868,7 @@ impl Step for RustdocJSStd {
             builder.config.build,
             self.target,
         );
-        builder.run(command);
+        command.run(builder);
     }
 }
 
@@ -908,12 +910,12 @@ fn get_browser_ui_test_version_inner(
     npm: &Path,
     global: bool,
 ) -> Option<String> {
-    let mut command = BootstrapCommand::new(npm).capture();
+    let mut command = command(npm).capture();
     command.arg("list").arg("--parseable").arg("--long").arg("--depth=0");
     if global {
         command.arg("--global");
     }
-    let lines = builder.run(command.allow_failure()).stdout();
+    let lines = command.allow_failure().run(builder).stdout();
     lines
         .lines()
         .find_map(|l| l.split(':').nth(1)?.strip_prefix("browser-ui-test@"))
@@ -1085,7 +1087,7 @@ HELP: to skip test's attempt to check tidiness, pass `--skip src/tools/tidy` to
         }
 
         builder.info("tidy check");
-        builder.run(cmd.delay_failure());
+        cmd.delay_failure().run(builder);
 
         builder.info("x.py completions check");
         let [bash, zsh, fish, powershell] = ["x.py.sh", "x.py.zsh", "x.py.fish", "x.py.ps1"]
@@ -1292,7 +1294,7 @@ impl Step for RunMakeSupport {
             &[],
         );
 
-        builder.run(cargo.into_cmd());
+        cargo.into_cmd().run(builder);
 
         let lib_name = "librun_make_support.rlib";
         let lib = builder.tools_dir(self.compiler).join(lib_name);
@@ -1804,14 +1806,20 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         }
 
         let lldb_exe = builder.config.lldb.clone().unwrap_or_else(|| PathBuf::from("lldb"));
-        let lldb_version = builder
-            .run(BootstrapCommand::new(&lldb_exe).capture().allow_failure().arg("--version"))
+        let lldb_version = command(&lldb_exe)
+            .capture()
+            .allow_failure()
+            .arg("--version")
+            .run(builder)
             .stdout_if_ok()
             .and_then(|v| if v.trim().is_empty() { None } else { Some(v) });
         if let Some(ref vers) = lldb_version {
             cmd.arg("--lldb-version").arg(vers);
-            let lldb_python_dir = builder
-                .run(BootstrapCommand::new(&lldb_exe).allow_failure().capture_stdout().arg("-P"))
+            let lldb_python_dir = command(&lldb_exe)
+                .allow_failure()
+                .capture_stdout()
+                .arg("-P")
+                .run(builder)
                 .stdout_if_ok()
                 .map(|p| p.lines().next().expect("lldb Python dir not found").to_string());
             if let Some(ref dir) = lldb_python_dir {
@@ -1869,11 +1877,10 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
             let llvm::LlvmResult { llvm_config, .. } =
                 builder.ensure(llvm::Llvm { target: builder.config.build });
             if !builder.config.dry_run() {
-                let llvm_version = builder
-                    .run(BootstrapCommand::new(&llvm_config).capture_stdout().arg("--version"))
-                    .stdout();
+                let llvm_version =
+                    builder.run(command(&llvm_config).capture_stdout().arg("--version")).stdout();
                 let llvm_components = builder
-                    .run(BootstrapCommand::new(&llvm_config).capture_stdout().arg("--components"))
+                    .run(command(&llvm_config).capture_stdout().arg("--components"))
                     .stdout();
                 // Remove trailing newline from llvm-config output.
                 cmd.arg("--llvm-version")
@@ -1893,9 +1900,8 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
             // separate compilations. We can add LLVM's library path to the
             // platform-specific environment variable as a workaround.
             if !builder.config.dry_run() && suite.ends_with("fulldeps") {
-                let llvm_libdir = builder
-                    .run(BootstrapCommand::new(&llvm_config).capture_stdout().arg("--libdir"))
-                    .stdout();
+                let llvm_libdir =
+                    builder.run(command(&llvm_config).capture_stdout().arg("--libdir")).stdout();
                 add_link_lib_path(vec![llvm_libdir.trim().into()], &mut cmd);
             }
 
@@ -2169,9 +2175,11 @@ impl BookTest {
             compiler.host,
         );
         let _time = helpers::timeit(builder);
-        let cmd = rustbook_cmd.delay_failure();
-        let toolstate =
-            if builder.run(cmd).is_success() { ToolState::TestPass } else { ToolState::TestFail };
+        let toolstate = if rustbook_cmd.delay_failure().run(builder).is_success() {
+            ToolState::TestPass
+        } else {
+            ToolState::TestFail
+        };
         builder.save_toolstate(self.name, toolstate);
     }
 
@@ -2300,7 +2308,7 @@ impl Step for ErrorIndex {
         let guard =
             builder.msg(Kind::Test, compiler.stage, "error-index", compiler.host, compiler.host);
         let _time = helpers::timeit(builder);
-        builder.run(tool.capture());
+        tool.capture().run(builder);
         drop(guard);
         // The tests themselves need to link to std, so make sure it is
         // available.
@@ -2333,7 +2341,7 @@ fn markdown_test(builder: &Builder<'_>, compiler: Compiler, markdown: &Path) ->
     if !builder.config.verbose_tests {
         cmd = cmd.capture();
     }
-    builder.run(cmd).is_success()
+    cmd.run(builder).is_success()
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -2359,7 +2367,7 @@ impl Step for RustcGuide {
         let src = builder.src.join(relative_path);
         let mut rustbook_cmd = builder.tool_cmd(Tool::Rustbook).delay_failure();
         rustbook_cmd.arg("linkcheck").arg(&src);
-        let toolstate = if builder.run(rustbook_cmd).is_success() {
+        let toolstate = if rustbook_cmd.run(builder).is_success() {
             ToolState::TestPass
         } else {
             ToolState::TestFail
@@ -2863,19 +2871,19 @@ impl Step for RemoteCopyLibs {
 
         // Spawn the emulator and wait for it to come online
         let tool = builder.tool_exe(Tool::RemoteTestClient);
-        let mut cmd = BootstrapCommand::new(&tool);
+        let mut cmd = command(&tool);
         cmd.arg("spawn-emulator").arg(target.triple).arg(&server).arg(builder.tempdir());
         if let Some(rootfs) = builder.qemu_rootfs(target) {
             cmd.arg(rootfs);
         }
-        builder.run(cmd);
+        cmd.run(builder);
 
         // Push all our dylibs to the emulator
         for f in t!(builder.sysroot_libdir(compiler, target).read_dir()) {
             let f = t!(f);
             let name = f.file_name().into_string().unwrap();
             if helpers::is_dylib(&name) {
-                builder.run(BootstrapCommand::new(&tool).arg("push").arg(f.path()));
+                builder.run(command(&tool).arg("push").arg(f.path()));
             }
         }
     }
@@ -2906,22 +2914,20 @@ impl Step for Distcheck {
         builder.ensure(dist::PlainSourceTarball);
         builder.ensure(dist::Src);
 
-        let mut cmd = BootstrapCommand::new("tar");
+        let mut cmd = command("tar");
         cmd.arg("-xf")
             .arg(builder.ensure(dist::PlainSourceTarball).tarball())
             .arg("--strip-components=1")
             .current_dir(&dir);
-        builder.run(cmd);
+        cmd.run(builder);
         builder.run(
-            BootstrapCommand::new("./configure")
+            command("./configure")
                 .args(&builder.config.configure_args)
                 .arg("--enable-vendor")
                 .current_dir(&dir),
         );
         builder.run(
-            BootstrapCommand::new(helpers::make(&builder.config.build.triple))
-                .arg("check")
-                .current_dir(&dir),
+            command(helpers::make(&builder.config.build.triple)).arg("check").current_dir(&dir),
         );
 
         // Now make sure that rust-src has all of libstd's dependencies
@@ -2930,16 +2936,16 @@ impl Step for Distcheck {
         let _ = fs::remove_dir_all(&dir);
         t!(fs::create_dir_all(&dir));
 
-        let mut cmd = BootstrapCommand::new("tar");
+        let mut cmd = command("tar");
         cmd.arg("-xf")
             .arg(builder.ensure(dist::Src).tarball())
             .arg("--strip-components=1")
             .current_dir(&dir);
-        builder.run(cmd);
+        cmd.run(builder);
 
         let toml = dir.join("rust-src/lib/rustlib/src/rust/library/std/Cargo.toml");
         builder.run(
-            BootstrapCommand::new(&builder.initial_cargo)
+            command(&builder.initial_cargo)
                 // Will read the libstd Cargo.toml
                 // which uses the unstable `public-dependency` feature.
                 .env("RUSTC_BOOTSTRAP", "1")
@@ -2968,7 +2974,7 @@ impl Step for Bootstrap {
         // Some tests require cargo submodule to be present.
         builder.build.update_submodule(Path::new("src/tools/cargo"));
 
-        let mut check_bootstrap = BootstrapCommand::new(builder.python());
+        let mut check_bootstrap = command(builder.python());
         check_bootstrap
             .args(["-m", "unittest", "bootstrap_test.py"])
             .env("BUILD_DIR", &builder.out)
@@ -2976,9 +2982,9 @@ impl Step for Bootstrap {
             .current_dir(builder.src.join("src/bootstrap/"));
         // NOTE: we intentionally don't pass test_args here because the args for unittest and cargo test are mutually incompatible.
         // Use `python -m unittest` manually if you want to pass arguments.
-        builder.run(check_bootstrap.delay_failure());
+        check_bootstrap.delay_failure().run(builder);
 
-        let mut cmd = BootstrapCommand::new(&builder.initial_cargo);
+        let mut cmd = command(&builder.initial_cargo);
         cmd.arg("test")
             .args(["--features", "bootstrap-self-test"])
             .current_dir(builder.src.join("src/bootstrap"))
@@ -3053,7 +3059,7 @@ impl Step for TierCheck {
             self.compiler.host,
             self.compiler.host,
         );
-        builder.run(BootstrapCommand::from(cargo).delay_failure());
+        BootstrapCommand::from(cargo).delay_failure().run(builder);
     }
 }
 
@@ -3129,7 +3135,7 @@ impl Step for RustInstaller {
             return;
         }
 
-        let mut cmd = BootstrapCommand::new(builder.src.join("src/tools/rust-installer/test.sh"));
+        let mut cmd = command(builder.src.join("src/tools/rust-installer/test.sh"));
         let tmpdir = testdir(builder, compiler.host).join("rust-installer");
         let _ = std::fs::remove_dir_all(&tmpdir);
         let _ = std::fs::create_dir_all(&tmpdir);
@@ -3138,7 +3144,7 @@ impl Step for RustInstaller {
         cmd.env("CARGO", &builder.initial_cargo);
         cmd.env("RUSTC", &builder.initial_rustc);
         cmd.env("TMP_DIR", &tmpdir);
-        builder.run(cmd.delay_failure());
+        cmd.delay_failure().run(builder);
     }
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -3332,7 +3338,7 @@ impl Step for CodegenCranelift {
             .arg("testsuite.extended_sysroot");
         cargo.args(builder.config.test_args());
 
-        builder.run(cargo.into_cmd());
+        cargo.into_cmd().run(builder);
     }
 }
 
@@ -3457,6 +3463,6 @@ impl Step for CodegenGCC {
             .arg("--std-tests");
         cargo.args(builder.config.test_args());
 
-        builder.run(cargo.into_cmd());
+        cargo.into_cmd().run(builder);
     }
 }
diff --git a/src/bootstrap/src/core/build_steps/tool.rs b/src/bootstrap/src/core/build_steps/tool.rs
index 5fb282db90a..ad92a01bce7 100644
--- a/src/bootstrap/src/core/build_steps/tool.rs
+++ b/src/bootstrap/src/core/build_steps/tool.rs
@@ -8,7 +8,7 @@ use crate::core::builder;
 use crate::core::builder::{Builder, Cargo as CargoCommand, RunConfig, ShouldRun, Step};
 use crate::core::config::TargetSelection;
 use crate::utils::channel::GitInfo;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 use crate::utils::helpers::{add_dylib_path, exe, t};
 use crate::Compiler;
 use crate::Mode;
@@ -438,7 +438,7 @@ impl ErrorIndex {
         // for rustc_private and libLLVM.so, and `sysroot_lib` for libstd, etc.
         let host = builder.config.build;
         let compiler = builder.compiler_for(builder.top_stage, host, host);
-        let mut cmd = BootstrapCommand::new(builder.ensure(ErrorIndex { compiler }));
+        let mut cmd = command(builder.ensure(ErrorIndex { compiler }));
         let mut dylib_paths = builder.rustc_lib_paths(compiler);
         dylib_paths.push(PathBuf::from(&builder.sysroot_libdir(compiler, compiler.host)));
         add_dylib_path(dylib_paths, &mut cmd);
@@ -602,7 +602,7 @@ impl Step for Rustdoc {
             &self.compiler.host,
             &target,
         );
-        builder.run(cargo.into_cmd());
+        cargo.into_cmd().run(builder);
 
         // Cargo adds a number of paths to the dylib search path on windows, which results in
         // the wrong rustdoc being executed. To avoid the conflicting rustdocs, we name the "tool"
@@ -857,7 +857,7 @@ impl Step for LlvmBitcodeLinker {
             &self.extra_features,
         );
 
-        builder.run(cargo.into_cmd());
+        cargo.into_cmd().run(builder);
 
         let tool_out = builder
             .cargo_out(self.compiler, Mode::ToolRustc, self.target)
@@ -912,21 +912,20 @@ impl Step for LibcxxVersionTool {
             }
 
             let compiler = builder.cxx(self.target).unwrap();
-            let mut cmd = BootstrapCommand::new(compiler);
+            let mut cmd = command(compiler);
 
             cmd.arg("-o")
                 .arg(&executable)
                 .arg(builder.src.join("src/tools/libcxx-version/main.cpp"));
 
-            builder.run(cmd);
+            cmd.run(builder);
 
             if !executable.exists() {
                 panic!("Something went wrong. {} is not present", executable.display());
             }
         }
 
-        let version_output =
-            builder.run(BootstrapCommand::new(executable).capture_stdout()).stdout();
+        let version_output = command(executable).capture_stdout().run(builder).stdout();
 
         let version_str = version_output.split_once("version:").unwrap().1;
         let version = version_str.trim().parse::<usize>().unwrap();
@@ -1050,7 +1049,7 @@ impl<'a> Builder<'a> {
     /// Gets a `BootstrapCommand` which is ready to run `tool` in `stage` built for
     /// `host`.
     pub fn tool_cmd(&self, tool: Tool) -> BootstrapCommand {
-        let mut cmd = BootstrapCommand::new(self.tool_exe(tool));
+        let mut cmd = command(self.tool_exe(tool));
         let compiler = self.compiler(0, self.config.build);
         let host = &compiler.host;
         // Prepares the `cmd` provided to be able to run the `compiler` provided.
diff --git a/src/bootstrap/src/core/build_steps/vendor.rs b/src/bootstrap/src/core/build_steps/vendor.rs
index 0b999a24a1f..62342ee4792 100644
--- a/src/bootstrap/src/core/build_steps/vendor.rs
+++ b/src/bootstrap/src/core/build_steps/vendor.rs
@@ -1,5 +1,5 @@
 use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use std::path::{Path, PathBuf};
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
@@ -27,7 +27,7 @@ impl Step for Vendor {
     }
 
     fn run(self, builder: &Builder<'_>) -> Self::Output {
-        let mut cmd = BootstrapCommand::new(&builder.initial_cargo);
+        let mut cmd = command(&builder.initial_cargo);
         cmd.arg("vendor");
 
         if self.versioned_dirs {
@@ -59,6 +59,6 @@ impl Step for Vendor {
 
         cmd.current_dir(self.root_dir);
 
-        builder.run(cmd);
+        cmd.run(builder);
     }
 }
diff --git a/src/bootstrap/src/core/builder.rs b/src/bootstrap/src/core/builder.rs
index 4da912994c3..65cc1fa7478 100644
--- a/src/bootstrap/src/core/builder.rs
+++ b/src/bootstrap/src/core/builder.rs
@@ -8,6 +8,7 @@ use std::fs;
 use std::hash::Hash;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
+use std::sync::LazyLock;
 use std::time::{Duration, Instant};
 
 use crate::core::build_steps::tool::{self, SourceType};
@@ -23,12 +24,10 @@ use crate::utils::helpers::{check_cfg_arg, libdir, linker_flags, t, LldThreads};
 use crate::EXTRA_CHECK_CFGS;
 use crate::{Build, CLang, Crate, DocTests, GitRepo, Mode};
 
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 pub use crate::Compiler;
 
 use clap::ValueEnum;
-// FIXME: replace with std::lazy after it gets stabilized and reaches beta
-use once_cell::sync::Lazy;
 
 #[cfg(test)]
 mod tests;
@@ -498,7 +497,7 @@ impl StepDescription {
 
 enum ReallyDefault<'a> {
     Bool(bool),
-    Lazy(Lazy<bool, Box<dyn Fn() -> bool + 'a>>),
+    Lazy(LazyLock<bool, Box<dyn Fn() -> bool + 'a>>),
 }
 
 pub struct ShouldRun<'a> {
@@ -529,7 +528,7 @@ impl<'a> ShouldRun<'a> {
     }
 
     pub fn lazy_default_condition(mut self, lazy_cond: Box<dyn Fn() -> bool + 'a>) -> Self {
-        self.is_really_default = ReallyDefault::Lazy(Lazy::new(lazy_cond));
+        self.is_really_default = ReallyDefault::Lazy(LazyLock::new(lazy_cond));
         self
     }
 
@@ -1254,7 +1253,7 @@ impl<'a> Builder<'a> {
         if run_compiler.stage == 0 {
             // `ensure(Clippy { stage: 0 })` *builds* clippy with stage0, it doesn't use the beta clippy.
             let cargo_clippy = self.build.config.download_clippy();
-            let mut cmd = BootstrapCommand::new(cargo_clippy);
+            let mut cmd = command(cargo_clippy);
             cmd.env("CARGO", &self.initial_cargo);
             return cmd;
         }
@@ -1273,7 +1272,7 @@ impl<'a> Builder<'a> {
         let mut dylib_path = helpers::dylib_path();
         dylib_path.insert(0, self.sysroot(run_compiler).join("lib"));
 
-        let mut cmd = BootstrapCommand::new(cargo_clippy);
+        let mut cmd = command(cargo_clippy);
         cmd.env(helpers::dylib_path_var(), env::join_paths(&dylib_path).unwrap());
         cmd.env("CARGO", &self.initial_cargo);
         cmd
@@ -1295,7 +1294,7 @@ impl<'a> Builder<'a> {
             extra_features: Vec::new(),
         });
         // Invoke cargo-miri, make sure it can find miri and cargo.
-        let mut cmd = BootstrapCommand::new(cargo_miri);
+        let mut cmd = command(cargo_miri);
         cmd.env("MIRI", &miri);
         cmd.env("CARGO", &self.initial_cargo);
         // Need to add the `run_compiler` libs. Those are the libs produces *by* `build_compiler`,
@@ -1311,7 +1310,7 @@ impl<'a> Builder<'a> {
     }
 
     pub fn rustdoc_cmd(&self, compiler: Compiler) -> BootstrapCommand {
-        let mut cmd = BootstrapCommand::new(self.bootstrap_out.join("rustdoc"));
+        let mut cmd = command(self.bootstrap_out.join("rustdoc"));
         cmd.env("RUSTC_STAGE", compiler.stage.to_string())
             .env("RUSTC_SYSROOT", self.sysroot(compiler))
             // Note that this is *not* the sysroot_libdir because rustdoc must be linked
@@ -1365,7 +1364,7 @@ impl<'a> Builder<'a> {
             cargo = self.cargo_miri_cmd(compiler);
             cargo.arg("miri").arg(subcmd);
         } else {
-            cargo = BootstrapCommand::new(&self.initial_cargo);
+            cargo = command(&self.initial_cargo);
             cargo.arg(cmd);
         }
 
@@ -1918,9 +1917,8 @@ impl<'a> Builder<'a> {
         // platform-specific environment variable as a workaround.
         if mode == Mode::ToolRustc || mode == Mode::Codegen {
             if let Some(llvm_config) = self.llvm_config(target) {
-                let llvm_libdir = self
-                    .run(BootstrapCommand::new(llvm_config).capture_stdout().arg("--libdir"))
-                    .stdout();
+                let llvm_libdir =
+                    command(llvm_config).capture_stdout().arg("--libdir").run(self).stdout();
                 add_link_lib_path(vec![llvm_libdir.trim().into()], &mut cargo);
             }
         }
@@ -2527,7 +2525,7 @@ impl Cargo {
 
         if let Some(target_linker) = builder.linker(target) {
             let target = crate::envify(&target.triple);
-            self.command.env(&format!("CARGO_TARGET_{target}_LINKER"), target_linker);
+            self.command.env(format!("CARGO_TARGET_{target}_LINKER"), target_linker);
         }
         // We want to set -Clinker using Cargo, therefore we only call `linker_flags` and not
         // `linker_args` here.
diff --git a/src/bootstrap/src/core/download.rs b/src/bootstrap/src/core/download.rs
index c35398e2eb7..a7f4bb0cf14 100644
--- a/src/bootstrap/src/core/download.rs
+++ b/src/bootstrap/src/core/download.rs
@@ -11,7 +11,7 @@ use std::{
 use build_helper::ci::CiEnv;
 use xz2::bufread::XzDecoder;
 
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 use crate::utils::helpers::hex_encode;
 use crate::utils::helpers::{check_run, exe, move_file, program_out_of_date};
 use crate::{t, Config};
@@ -212,7 +212,7 @@ impl Config {
     fn download_http_with_retries(&self, tempfile: &Path, url: &str, help_on_error: &str) {
         println!("downloading {url}");
         // Try curl. If that fails and we are on windows, fallback to PowerShell.
-        let mut curl = BootstrapCommand::new("curl");
+        let mut curl = command("curl");
         curl.args([
             "-y",
             "30",
diff --git a/src/bootstrap/src/core/metadata.rs b/src/bootstrap/src/core/metadata.rs
index 49d17107125..b18da844014 100644
--- a/src/bootstrap/src/core/metadata.rs
+++ b/src/bootstrap/src/core/metadata.rs
@@ -2,7 +2,7 @@ use std::path::PathBuf;
 
 use serde_derive::Deserialize;
 
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::{t, Build, Crate};
 
 /// For more information, see the output of
@@ -70,7 +70,7 @@ pub fn build(build: &mut Build) {
 /// particular crate (e.g., `x build sysroot` to build library/sysroot).
 fn workspace_members(build: &Build) -> Vec<Package> {
     let collect_metadata = |manifest_path| {
-        let mut cargo = BootstrapCommand::new(&build.initial_cargo);
+        let mut cargo = command(&build.initial_cargo);
         cargo
             // Will read the libstd Cargo.toml
             // which uses the unstable `public-dependency` feature.
@@ -81,7 +81,7 @@ fn workspace_members(build: &Build) -> Vec<Package> {
             .arg("--no-deps")
             .arg("--manifest-path")
             .arg(build.src.join(manifest_path));
-        let metadata_output = build.run(cargo.capture_stdout().run_always()).stdout();
+        let metadata_output = cargo.capture_stdout().run_always().run(build).stdout();
         let Output { packages, .. } = t!(serde_json::from_str(&metadata_output));
         packages
     };
diff --git a/src/bootstrap/src/core/sanity.rs b/src/bootstrap/src/core/sanity.rs
index 78862ccb8cd..9995da3a1e5 100644
--- a/src/bootstrap/src/core/sanity.rs
+++ b/src/bootstrap/src/core/sanity.rs
@@ -23,7 +23,7 @@ use std::collections::HashSet;
 
 use crate::builder::Kind;
 use crate::core::config::Target;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::command;
 use crate::Build;
 
 pub struct Finder {
@@ -209,9 +209,7 @@ than building it.
 
     #[cfg(not(feature = "bootstrap-self-test"))]
     let stage0_supported_target_list: HashSet<String> = crate::utils::helpers::output(
-        &mut BootstrapCommand::new(&build.config.initial_rustc)
-            .args(["--print", "target-list"])
-            .command,
+        &mut command(&build.config.initial_rustc).args(["--print", "target-list"]).command,
     )
     .lines()
     .map(|s| s.to_string())
@@ -354,8 +352,7 @@ than building it.
             // There are three builds of cmake on windows: MSVC, MinGW, and
             // Cygwin. The Cygwin build does not have generators for Visual
             // Studio, so detect that here and error.
-            let out =
-                build.run(BootstrapCommand::new("cmake").capture_stdout().arg("--help")).stdout();
+            let out = command("cmake").capture_stdout().arg("--help").run(build).stdout();
             if !out.contains("Visual Studio") {
                 panic!(
                     "
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index ffdd9bc885a..f16afb29796 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -41,7 +41,7 @@ use crate::core::builder::Kind;
 use crate::core::config::{flags, LldMode};
 use crate::core::config::{DryRun, Target};
 use crate::core::config::{LlvmLibunwind, TargetSelection};
-use crate::utils::exec::{BehaviorOnFailure, BootstrapCommand, CommandOutput};
+use crate::utils::exec::{command, BehaviorOnFailure, BootstrapCommand, CommandOutput};
 use crate::utils::helpers::{self, dir_is_empty, exe, libdir, mtime, output, symlink_dir};
 
 mod core;
@@ -510,9 +510,10 @@ impl Build {
         }
 
         println!("Updating submodule {}", relative_path.display());
-        self.run(
-            helpers::git(Some(&self.src)).args(["submodule", "-q", "sync"]).arg(relative_path),
-        );
+        helpers::git(Some(&self.src))
+            .args(["submodule", "-q", "sync"])
+            .arg(relative_path)
+            .run(self);
 
         // Try passing `--progress` to start, then run git again without if that fails.
         let update = |progress: bool| {
@@ -548,23 +549,25 @@ impl Build {
         };
         // NOTE: doesn't use `try_run` because this shouldn't print an error if it fails.
         if !update(true).command.status().map_or(false, |status| status.success()) {
-            self.run(update(false));
+            update(false).run(self);
         }
 
         // Save any local changes, but avoid running `git stash pop` if there are none (since it will exit with an error).
         // diff-index reports the modifications through the exit status
-        let has_local_modifications = self
-            .run(submodule_git().allow_failure().args(["diff-index", "--quiet", "HEAD"]))
+        let has_local_modifications = submodule_git()
+            .allow_failure()
+            .args(["diff-index", "--quiet", "HEAD"])
+            .run(self)
             .is_failure();
         if has_local_modifications {
-            self.run(submodule_git().args(["stash", "push"]));
+            submodule_git().args(["stash", "push"]).run(self);
         }
 
-        self.run(submodule_git().args(["reset", "-q", "--hard"]));
-        self.run(submodule_git().args(["clean", "-qdfx"]));
+        submodule_git().args(["reset", "-q", "--hard"]).run(self);
+        submodule_git().args(["clean", "-qdfx"]).run(self);
 
         if has_local_modifications {
-            self.run(submodule_git().args(["stash", "pop"]));
+            submodule_git().args(["stash", "pop"]).run(self);
         }
     }
 
@@ -575,14 +578,12 @@ impl Build {
         if !self.config.submodules(self.rust_info()) {
             return;
         }
-        let output = self
-            .run(
-                helpers::git(Some(&self.src))
-                    .capture()
-                    .args(["config", "--file"])
-                    .arg(self.config.src.join(".gitmodules"))
-                    .args(["--get-regexp", "path"]),
-            )
+        let output = helpers::git(Some(&self.src))
+            .capture()
+            .args(["config", "--file"])
+            .arg(self.config.src.join(".gitmodules"))
+            .args(["--get-regexp", "path"])
+            .run(self)
             .stdout();
         for line in output.lines() {
             // Look for `submodule.$name.path = $path`
@@ -860,16 +861,14 @@ impl Build {
         if let Some(s) = target_config.and_then(|c| c.llvm_filecheck.as_ref()) {
             s.to_path_buf()
         } else if let Some(s) = target_config.and_then(|c| c.llvm_config.as_ref()) {
-            let llvm_bindir =
-                self.run(BootstrapCommand::new(s).capture_stdout().arg("--bindir")).stdout();
+            let llvm_bindir = command(s).capture_stdout().arg("--bindir").run(self).stdout();
             let filecheck = Path::new(llvm_bindir.trim()).join(exe("FileCheck", target));
             if filecheck.exists() {
                 filecheck
             } else {
                 // On Fedora the system LLVM installs FileCheck in the
                 // llvm subdirectory of the libdir.
-                let llvm_libdir =
-                    self.run(BootstrapCommand::new(s).capture_stdout().arg("--libdir")).stdout();
+                let llvm_libdir = command(s).capture_stdout().arg("--libdir").run(self).stdout();
                 let lib_filecheck =
                     Path::new(llvm_libdir.trim()).join("llvm").join(exe("FileCheck", target));
                 if lib_filecheck.exists() {
@@ -935,8 +934,7 @@ impl Build {
 
     /// Execute a command and return its output.
     /// This method should be used for all command executions in bootstrap.
-    fn run<C: AsMut<BootstrapCommand>>(&self, mut command: C) -> CommandOutput {
-        let command = command.as_mut();
+    fn run(&self, command: &mut BootstrapCommand) -> CommandOutput {
         if self.config.dry_run() && !command.run_always {
             return CommandOutput::default();
         }
@@ -1496,18 +1494,17 @@ impl Build {
             // Figure out how many merge commits happened since we branched off master.
             // That's our beta number!
             // (Note that we use a `..` range, not the `...` symmetric difference.)
-            self.run(
-                helpers::git(Some(&self.src))
-                    .capture()
-                    .arg("rev-list")
-                    .arg("--count")
-                    .arg("--merges")
-                    .arg(format!(
-                        "refs/remotes/origin/{}..HEAD",
-                        self.config.stage0_metadata.config.nightly_branch
-                    )),
-            )
-            .stdout()
+            helpers::git(Some(&self.src))
+                .capture()
+                .arg("rev-list")
+                .arg("--count")
+                .arg("--merges")
+                .arg(format!(
+                    "refs/remotes/origin/{}..HEAD",
+                    self.config.stage0_metadata.config.nightly_branch
+                ))
+                .run(self)
+                .stdout()
         });
         let n = count.trim().parse().unwrap();
         self.prerelease_version.set(Some(n));
diff --git a/src/bootstrap/src/utils/cache.rs b/src/bootstrap/src/utils/cache.rs
index e18dcbb47be..d60b54dc703 100644
--- a/src/bootstrap/src/utils/cache.rs
+++ b/src/bootstrap/src/utils/cache.rs
@@ -9,10 +9,7 @@ use std::marker::PhantomData;
 use std::mem;
 use std::ops::Deref;
 use std::path::PathBuf;
-use std::sync::Mutex;
-
-// FIXME: replace with std::lazy after it gets stabilized and reaches beta
-use once_cell::sync::Lazy;
+use std::sync::{LazyLock, Mutex};
 
 use crate::core::builder::Step;
 
@@ -196,7 +193,7 @@ impl Interner {
     }
 }
 
-pub static INTERNER: Lazy<Interner> = Lazy::new(Interner::default);
+pub static INTERNER: LazyLock<Interner> = LazyLock::new(Interner::default);
 
 /// This is essentially a `HashMap` which allows storing any type in its input and
 /// any type in its output. It is a write-once cache; values are never evicted,
diff --git a/src/bootstrap/src/utils/cc_detect.rs b/src/bootstrap/src/utils/cc_detect.rs
index b80df545202..d6fa7fc0bbe 100644
--- a/src/bootstrap/src/utils/cc_detect.rs
+++ b/src/bootstrap/src/utils/cc_detect.rs
@@ -26,7 +26,7 @@ use std::path::{Path, PathBuf};
 use std::{env, iter};
 
 use crate::core::config::TargetSelection;
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 use crate::{Build, CLang, GitRepo};
 
 // The `cc` crate doesn't provide a way to obtain a path to the detected archiver,
@@ -183,14 +183,14 @@ fn default_compiler(
             }
 
             let cmd = BootstrapCommand::from(c.to_command());
-            let output = build.run(cmd.capture_stdout().arg("--version")).stdout();
+            let output = cmd.capture_stdout().arg("--version").run(build).stdout();
             let i = output.find(" 4.")?;
             match output[i + 3..].chars().next().unwrap() {
                 '0'..='6' => {}
                 _ => return None,
             }
             let alternative = format!("e{gnu_compiler}");
-            if build.run(BootstrapCommand::new(&alternative).capture()).is_success() {
+            if command(&alternative).capture().run(build).is_success() {
                 Some(PathBuf::from(alternative))
             } else {
                 None
diff --git a/src/bootstrap/src/utils/exec.rs b/src/bootstrap/src/utils/exec.rs
index 086d10c6351..ba963f52dc2 100644
--- a/src/bootstrap/src/utils/exec.rs
+++ b/src/bootstrap/src/utils/exec.rs
@@ -1,3 +1,4 @@
+use crate::Build;
 use std::ffi::OsStr;
 use std::path::Path;
 use std::process::{Command, CommandArgs, CommandEnvs, ExitStatus, Output, Stdio};
@@ -108,14 +109,17 @@ impl BootstrapCommand {
         self
     }
 
+    #[must_use]
     pub fn delay_failure(self) -> Self {
         Self { failure_behavior: BehaviorOnFailure::DelayFail, ..self }
     }
 
+    #[must_use]
     pub fn fail_fast(self) -> Self {
         Self { failure_behavior: BehaviorOnFailure::Exit, ..self }
     }
 
+    #[must_use]
     pub fn allow_failure(self) -> Self {
         Self { failure_behavior: BehaviorOnFailure::Ignore, ..self }
     }
@@ -126,21 +130,20 @@ impl BootstrapCommand {
     }
 
     /// Capture all output of the command, do not print it.
+    #[must_use]
     pub fn capture(self) -> Self {
         Self { stdout: OutputMode::Capture, stderr: OutputMode::Capture, ..self }
     }
 
     /// Capture stdout of the command, do not print it.
+    #[must_use]
     pub fn capture_stdout(self) -> Self {
         Self { stdout: OutputMode::Capture, ..self }
     }
-}
 
-/// This implementation exists to make it possible to pass both [BootstrapCommand] and
-/// `&mut BootstrapCommand` to `Build.run()`.
-impl AsMut<BootstrapCommand> for BootstrapCommand {
-    fn as_mut(&mut self) -> &mut BootstrapCommand {
-        self
+    /// Run the command, returning its output.
+    pub fn run(&mut self, builder: &Build) -> CommandOutput {
+        builder.run(self)
     }
 }
 
@@ -164,6 +167,13 @@ enum CommandStatus {
     DidNotStart,
 }
 
+/// Create a new BootstrapCommand. This is a helper function to make command creation
+/// shorter than `BootstrapCommand::new`.
+#[must_use]
+pub fn command<S: AsRef<OsStr>>(program: S) -> BootstrapCommand {
+    BootstrapCommand::new(program)
+}
+
 /// Represents the output of an executed process.
 #[allow(unused)]
 pub struct CommandOutput {
@@ -173,10 +183,12 @@ pub struct CommandOutput {
 }
 
 impl CommandOutput {
+    #[must_use]
     pub fn did_not_start() -> Self {
         Self { status: CommandStatus::DidNotStart, stdout: vec![], stderr: vec![] }
     }
 
+    #[must_use]
     pub fn is_success(&self) -> bool {
         match self.status {
             CommandStatus::Finished(status) => status.success(),
@@ -184,10 +196,12 @@ impl CommandOutput {
         }
     }
 
+    #[must_use]
     pub fn is_failure(&self) -> bool {
         !self.is_success()
     }
 
+    #[must_use]
     pub fn status(&self) -> Option<ExitStatus> {
         match self.status {
             CommandStatus::Finished(status) => Some(status),
@@ -195,14 +209,17 @@ impl CommandOutput {
         }
     }
 
+    #[must_use]
     pub fn stdout(&self) -> String {
         String::from_utf8(self.stdout.clone()).expect("Cannot parse process stdout as UTF-8")
     }
 
+    #[must_use]
     pub fn stdout_if_ok(&self) -> Option<String> {
         if self.is_success() { Some(self.stdout()) } else { None }
     }
 
+    #[must_use]
     pub fn stderr(&self) -> String {
         String::from_utf8(self.stderr.clone()).expect("Cannot parse process stderr as UTF-8")
     }
diff --git a/src/bootstrap/src/utils/helpers.rs b/src/bootstrap/src/utils/helpers.rs
index 2575b7939b4..5dd3ba96786 100644
--- a/src/bootstrap/src/utils/helpers.rs
+++ b/src/bootstrap/src/utils/helpers.rs
@@ -47,7 +47,7 @@ macro_rules! t {
         }
     };
 }
-use crate::utils::exec::BootstrapCommand;
+use crate::utils::exec::{command, BootstrapCommand};
 pub use t;
 
 pub fn exe(name: &str, target: TargetSelection) -> String {
@@ -369,9 +369,9 @@ fn lld_flag_no_threads(builder: &Builder<'_>, lld_mode: LldMode, is_windows: boo
     let (windows_flag, other_flag) = LLD_NO_THREADS.get_or_init(|| {
         let newer_version = match lld_mode {
             LldMode::External => {
-                let mut cmd = BootstrapCommand::new("lld").capture_stdout();
+                let mut cmd = command("lld").capture_stdout();
                 cmd.arg("-flavor").arg("ld").arg("--version");
-                let out = builder.run(cmd).stdout();
+                let out = cmd.run(builder).stdout();
                 match (out.find(char::is_numeric), out.find('.')) {
                     (Some(b), Some(e)) => out.as_str()[b..e].parse::<i32>().ok().unwrap_or(14) > 10,
                     _ => true,
@@ -499,10 +499,10 @@ pub fn check_cfg_arg(name: &str, values: Option<&[&str]>) -> String {
 /// Whenever a git invocation is needed, this function should be preferred over
 /// manually building a git `BootstrapCommand`. This approach allows us to manage
 /// bootstrap-specific needs/hacks from a single source, rather than applying them on next to every
-/// `BootstrapCommand::new("git")`, which is painful to ensure that the required change is applied
+/// git command creation, which is painful to ensure that the required change is applied
 /// on each one of them correctly.
 pub fn git(source_dir: Option<&Path>) -> BootstrapCommand {
-    let mut git = BootstrapCommand::new("git");
+    let mut git = command("git");
 
     if let Some(source_dir) = source_dir {
         git.current_dir(source_dir);
diff --git a/src/bootstrap/src/utils/tarball.rs b/src/bootstrap/src/utils/tarball.rs
index 1a35dc1fd38..4f0104e4bba 100644
--- a/src/bootstrap/src/utils/tarball.rs
+++ b/src/bootstrap/src/utils/tarball.rs
@@ -379,7 +379,7 @@ impl<'a> Tarball<'a> {
             cmd.args(["--override-file-mtime", timestamp.trim()]);
         }
 
-        self.builder.run(cmd);
+        cmd.run(self.builder);
 
         // Ensure there are no symbolic links in the tarball. In particular,
         // rustup-toolchain-install-master and most versions of Windows can't handle symbolic links.
diff --git a/src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md b/src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md
index 2b3d15e93c8..c3eda26ca8e 100644
--- a/src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md
+++ b/src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md
@@ -107,7 +107,7 @@ flag, for example:
 
 Users need to install or built wasi-sdk since release 20.0
 https://github.com/WebAssembly/wasi-sdk/releases/tag/wasi-sdk-20
-and specify path to *wasi-root* `.cargo/config.toml`
+and specify path to *wasi-root* `config.toml`
 
 ```toml
 [target.wasm32-wasip1-threads]
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index b5660cd8492..aa596897fc4 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1404,8 +1404,7 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
 
             let mut predicates = tcx.explicit_predicates_of(assoc_item.def_id).predicates;
             if let ty::TraitContainer = assoc_item.container {
-                let bounds =
-                    tcx.explicit_item_bounds(assoc_item.def_id).instantiate_identity_iter_copied();
+                let bounds = tcx.explicit_item_bounds(assoc_item.def_id).iter_identity_copied();
                 predicates = tcx.arena.alloc_from_iter(bounds.chain(predicates.iter().copied()));
             }
             let mut generics = clean_ty_generics(
diff --git a/src/tools/cargo b/src/tools/cargo
-Subproject a515d463427b3912ec0365d106791f88c1c14e1
+Subproject 154fdac39ae9629954e19e9986fd2cf2cdd8d96
diff --git a/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs b/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
index 42b10f69c0c..f206b2ceebc 100644
--- a/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
+++ b/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
@@ -330,7 +330,8 @@ fn check_terminator<'tcx>(
             target: _,
             unwind: _,
             fn_span: _,
-        } => {
+        }
+        | TerminatorKind::TailCall { func, args, fn_span: _ } => {
             let fn_ty = func.ty(body, tcx);
             if let ty::FnDef(fn_def_id, _) = *fn_ty.kind() {
                 if !is_const_fn(tcx, fn_def_id, msrv) {
diff --git a/src/tools/clippy/clippy_utils/src/ty.rs b/src/tools/clippy/clippy_utils/src/ty.rs
index e5d20564196..acaeb93f44a 100644
--- a/src/tools/clippy/clippy_utils/src/ty.rs
+++ b/src/tools/clippy/clippy_utils/src/ty.rs
@@ -99,7 +99,7 @@ pub fn contains_ty_adt_constructor_opaque<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'
                     for (predicate, _span) in cx
                         .tcx
                         .explicit_item_super_predicates(def_id)
-                        .instantiate_identity_iter_copied()
+                        .iter_identity_copied()
                     {
                         match predicate.kind().skip_binder() {
                             // For `impl Trait<U>`, it will register a predicate of `T: Trait<U>`, so we go through
diff --git a/src/tools/clippy/tests/ui/or_fun_call.fixed b/src/tools/clippy/tests/ui/or_fun_call.fixed
index 7657ef470c5..c76f7a81843 100644
--- a/src/tools/clippy/tests/ui/or_fun_call.fixed
+++ b/src/tools/clippy/tests/ui/or_fun_call.fixed
@@ -98,7 +98,7 @@ fn or_fun_call() {
 
     let opt = Some(1);
     let hello = "Hello";
-    let _ = opt.ok_or(format!("{} world.", hello));
+    let _ = opt.ok_or_else(|| format!("{} world.", hello));
 
     // index
     let map = HashMap::<u64, u64>::new();
diff --git a/src/tools/clippy/tests/ui/or_fun_call.stderr b/src/tools/clippy/tests/ui/or_fun_call.stderr
index b5a30f29923..3070db22fc5 100644
--- a/src/tools/clippy/tests/ui/or_fun_call.stderr
+++ b/src/tools/clippy/tests/ui/or_fun_call.stderr
@@ -100,6 +100,12 @@ error: use of `unwrap_or` to construct default value
 LL |     let _ = stringy.unwrap_or(String::new());
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
 
+error: use of `ok_or` followed by a function call
+  --> tests/ui/or_fun_call.rs:101:17
+   |
+LL |     let _ = opt.ok_or(format!("{} world.", hello));
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `ok_or_else(|| format!("{} world.", hello))`
+
 error: use of `unwrap_or` followed by a function call
   --> tests/ui/or_fun_call.rs:105:21
    |
@@ -190,5 +196,5 @@ error: use of `unwrap_or_else` to construct default value
 LL |         let _ = stringy.unwrap_or_else(String::new);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
 
-error: aborting due to 31 previous errors
+error: aborting due to 32 previous errors
 
diff --git a/src/tools/miri/rust-version b/src/tools/miri/rust-version
index 25d559d789f..e90d3732ca5 100644
--- a/src/tools/miri/rust-version
+++ b/src/tools/miri/rust-version
@@ -1 +1 @@
-51917e2e69702e5752bce6a4f3bfd285d0f4ae39
+99b7134389e9766462601a2fc4013840b9d31745
diff --git a/src/tools/miri/src/machine.rs b/src/tools/miri/src/machine.rs
index 02bfd6ec815..adb84593561 100644
--- a/src/tools/miri/src/machine.rs
+++ b/src/tools/miri/src/machine.rs
@@ -1455,7 +1455,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
         ecx: &mut InterpCx<'tcx, Self>,
         frame: Frame<'tcx, Provenance, FrameExtra<'tcx>>,
         unwinding: bool,
-    ) -> InterpResult<'tcx, StackPopJump> {
+    ) -> InterpResult<'tcx, ReturnAction> {
         if frame.extra.is_user_relevant {
             // All that we store is whether or not the frame we just removed is local, so now we
             // have no idea where the next topmost local frame is. So we recompute it.
diff --git a/src/tools/miri/src/shims/panic.rs b/src/tools/miri/src/shims/panic.rs
index ef832f5bbbd..306dce5edcd 100644
--- a/src/tools/miri/src/shims/panic.rs
+++ b/src/tools/miri/src/shims/panic.rs
@@ -113,7 +113,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         &mut self,
         mut extra: FrameExtra<'tcx>,
         unwinding: bool,
-    ) -> InterpResult<'tcx, StackPopJump> {
+    ) -> InterpResult<'tcx, ReturnAction> {
         let this = self.eval_context_mut();
         trace!("handle_stack_pop_unwind(extra = {:?}, unwinding = {})", extra, unwinding);
 
@@ -150,9 +150,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             )?;
 
             // We pushed a new stack frame, the engine should not do any jumping now!
-            Ok(StackPopJump::NoJump)
+            Ok(ReturnAction::NoJump)
         } else {
-            Ok(StackPopJump::Normal)
+            Ok(ReturnAction::Normal)
         }
     }
 
diff --git a/src/tools/miri/tests/fail/tail_calls/cc-mismatch.rs b/src/tools/miri/tests/fail/tail_calls/cc-mismatch.rs
new file mode 100644
index 00000000000..5f00dbf2573
--- /dev/null
+++ b/src/tools/miri/tests/fail/tail_calls/cc-mismatch.rs
@@ -0,0 +1,10 @@
+//@error-in-other-file: Undefined Behavior: calling a function with calling convention C using calling convention Rust
+#![feature(explicit_tail_calls)]
+#![allow(incomplete_features)]
+
+fn main() {
+    let f = unsafe { std::mem::transmute::<extern "C" fn(), fn()>(f) };
+    become f();
+}
+
+extern "C" fn f() {}
diff --git a/src/tools/miri/tests/fail/tail_calls/cc-mismatch.stderr b/src/tools/miri/tests/fail/tail_calls/cc-mismatch.stderr
new file mode 100644
index 00000000000..b157e9f0b21
--- /dev/null
+++ b/src/tools/miri/tests/fail/tail_calls/cc-mismatch.stderr
@@ -0,0 +1,25 @@
+error: Undefined Behavior: calling a function with calling convention C using calling convention Rust
+  --> RUSTLIB/core/src/ops/function.rs:LL:CC
+   |
+LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ calling a function with calling convention C using calling convention Rust
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `<fn() as std::ops::FnOnce<()>>::call_once - shim(fn())` at RUSTLIB/core/src/ops/function.rs:LL:CC
+   = note: inside `std::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>` at RUSTLIB/std/src/sys/backtrace.rs:LL:CC
+   = note: inside closure at RUSTLIB/std/src/rt.rs:LL:CC
+   = note: inside `std::ops::function::impls::<impl std::ops::FnOnce<()> for &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>::call_once` at RUSTLIB/core/src/ops/function.rs:LL:CC
+   = note: inside `std::panicking::r#try::do_call::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>` at RUSTLIB/std/src/panicking.rs:LL:CC
+   = note: inside `std::panicking::r#try::<i32, &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>` at RUSTLIB/std/src/panicking.rs:LL:CC
+   = note: inside `std::panic::catch_unwind::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>` at RUSTLIB/std/src/panic.rs:LL:CC
+   = note: inside closure at RUSTLIB/std/src/rt.rs:LL:CC
+   = note: inside `std::panicking::r#try::do_call::<{closure@std::rt::lang_start_internal::{closure#2}}, isize>` at RUSTLIB/std/src/panicking.rs:LL:CC
+   = note: inside `std::panicking::r#try::<isize, {closure@std::rt::lang_start_internal::{closure#2}}>` at RUSTLIB/std/src/panicking.rs:LL:CC
+   = note: inside `std::panic::catch_unwind::<{closure@std::rt::lang_start_internal::{closure#2}}, isize>` at RUSTLIB/std/src/panic.rs:LL:CC
+   = note: inside `std::rt::lang_start_internal` at RUSTLIB/std/src/rt.rs:LL:CC
+   = note: inside `std::rt::lang_start::<()>` at RUSTLIB/std/src/rt.rs:LL:CC
+
+error: aborting due to 1 previous error
+
diff --git a/src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.rs b/src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.rs
new file mode 100644
index 00000000000..6df132d3255
--- /dev/null
+++ b/src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.rs
@@ -0,0 +1,17 @@
+#![feature(explicit_tail_calls)]
+#![allow(incomplete_features)]
+
+fn main() {
+    // FIXME(explicit_tail_calls):
+    //   the error should point to `become g(x)`,
+    //   but tail calls mess up the backtrace it seems like...
+    f(0);
+    //~^ error: Undefined Behavior: calling a function with argument of type i32 passing data of type u32
+}
+
+fn f(x: u32) {
+    let g = unsafe { std::mem::transmute::<fn(i32), fn(u32)>(g) };
+    become g(x);
+}
+
+fn g(_: i32) {}
diff --git a/src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.stderr b/src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.stderr
new file mode 100644
index 00000000000..8823ab9b970
--- /dev/null
+++ b/src/tools/miri/tests/fail/tail_calls/signature-mismatch-arg.stderr
@@ -0,0 +1,17 @@
+error: Undefined Behavior: calling a function with argument of type i32 passing data of type u32
+  --> $DIR/signature-mismatch-arg.rs:LL:CC
+   |
+LL |     f(0);
+   |     ^^^^ calling a function with argument of type i32 passing data of type u32
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue with Miri
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/signature-mismatch-arg.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+
diff --git a/src/tools/miri/tests/pass/intptrcast.rs b/src/tools/miri/tests/pass/intptrcast.rs
index 4e9fa12c181..fb1a1dfae5d 100644
--- a/src/tools/miri/tests/pass/intptrcast.rs
+++ b/src/tools/miri/tests/pass/intptrcast.rs
@@ -35,7 +35,7 @@ fn cast_dangling() {
 fn format() {
     // Pointer string formatting! We can't check the output as it changes when libstd changes,
     // but we can make sure Miri does not error.
-    format!("{:?}", &mut 13 as *mut _);
+    let _ = format!("{:?}", &mut 13 as *mut _);
 }
 
 fn transmute() {
@@ -52,7 +52,7 @@ fn ptr_bitops1() {
     let one = bytes.as_ptr().wrapping_offset(1);
     let three = bytes.as_ptr().wrapping_offset(3);
     let res = (one as usize) | (three as usize);
-    format!("{}", res);
+    let _ = format!("{}", res);
 }
 
 fn ptr_bitops2() {
diff --git a/src/tools/miri/tests/pass/packed_struct.rs b/src/tools/miri/tests/pass/packed_struct.rs
index b86235e0c67..039eb5adef0 100644
--- a/src/tools/miri/tests/pass/packed_struct.rs
+++ b/src/tools/miri/tests/pass/packed_struct.rs
@@ -138,7 +138,7 @@ fn test_derive() {
     assert_eq!(x.partial_cmp(&y).unwrap(), x.cmp(&y));
     x.hash(&mut DefaultHasher::new());
     P::default();
-    format!("{:?}", x);
+    let _ = format!("{:?}", x);
 }
 
 fn main() {
diff --git a/src/tools/miri/tests/pass/shims/fs.rs b/src/tools/miri/tests/pass/shims/fs.rs
index 35980fad15d..16d3e8cab30 100644
--- a/src/tools/miri/tests/pass/shims/fs.rs
+++ b/src/tools/miri/tests/pass/shims/fs.rs
@@ -202,7 +202,7 @@ fn test_errors() {
     // Opening a non-existing file should fail with a "not found" error.
     assert_eq!(ErrorKind::NotFound, File::open(&path).unwrap_err().kind());
     // Make sure we can also format this.
-    format!("{0}: {0:?}", File::open(&path).unwrap_err());
+    let _ = format!("{0}: {0:?}", File::open(&path).unwrap_err());
     // Removing a non-existing file should fail with a "not found" error.
     assert_eq!(ErrorKind::NotFound, remove_file(&path).unwrap_err().kind());
     // Reading the metadata of a non-existing file should fail with a "not found" error.
@@ -301,5 +301,5 @@ fn test_from_raw_os_error() {
     let error = Error::from_raw_os_error(code);
     assert!(matches!(error.kind(), ErrorKind::Uncategorized));
     // Make sure we can also format this.
-    format!("{error:?}");
+    let _ = format!("{error:?}");
 }
diff --git a/src/tools/miri/tests/pass/shims/io.rs b/src/tools/miri/tests/pass/shims/io.rs
index d20fc75b793..420ef95a0cb 100644
--- a/src/tools/miri/tests/pass/shims/io.rs
+++ b/src/tools/miri/tests/pass/shims/io.rs
@@ -15,5 +15,5 @@ fn main() {
         panic!("unsupported OS")
     };
     let err = io::Error::from_raw_os_error(raw_os_error);
-    format!("{err}: {err:?}");
+    let _ = format!("{err}: {err:?}");
 }
diff --git a/src/tools/miri/tests/pass/tail_call.rs b/src/tools/miri/tests/pass/tail_call.rs
new file mode 100644
index 00000000000..f6200706398
--- /dev/null
+++ b/src/tools/miri/tests/pass/tail_call.rs
@@ -0,0 +1,39 @@
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+fn main() {
+    assert_eq!(factorial(10), 3_628_800);
+    assert_eq!(mutually_recursive_identity(1000), 1000);
+}
+
+fn factorial(n: u32) -> u32 {
+    fn factorial_acc(n: u32, acc: u32) -> u32 {
+        match n {
+            0 => acc,
+            _ => become factorial_acc(n - 1, acc * n),
+        }
+    }
+
+    factorial_acc(n, 1)
+}
+
+// this is of course very silly, but we need to demonstrate mutual recursion somehow so...
+fn mutually_recursive_identity(x: u32) -> u32 {
+    fn switch(src: u32, tgt: u32) -> u32 {
+        match src {
+            0 => tgt,
+            _ if src % 7 == 0 => become advance_with_extra_steps(src, tgt),
+            _ => become advance(src, tgt),
+        }
+    }
+
+    fn advance(src: u32, tgt: u32) -> u32 {
+        become switch(src - 1, tgt + 1)
+    }
+
+    fn advance_with_extra_steps(src: u32, tgt: u32) -> u32 {
+        become advance(src, tgt)
+    }
+
+    switch(x, 0)
+}
diff --git a/src/tools/miri/tests/pass/vecdeque.rs b/src/tools/miri/tests/pass/vecdeque.rs
index 77c4ca5a04e..9153c428e18 100644
--- a/src/tools/miri/tests/pass/vecdeque.rs
+++ b/src/tools/miri/tests/pass/vecdeque.rs
@@ -31,8 +31,8 @@ fn main() {
     }
 
     // Regression test for Debug impl's
-    format!("{:?} {:?}", dst, dst.iter());
-    format!("{:?}", VecDeque::<u32>::new().iter());
+    let _ = format!("{:?} {:?}", dst, dst.iter());
+    let _ = format!("{:?}", VecDeque::<u32>::new().iter());
 
     for a in dst {
         assert_eq!(*a, 2);
diff --git a/src/tools/run-make-support/src/diff/mod.rs b/src/tools/run-make-support/src/diff/mod.rs
index 3e0bdc1c6f6..24fa88af82e 100644
--- a/src/tools/run-make-support/src/diff/mod.rs
+++ b/src/tools/run-make-support/src/diff/mod.rs
@@ -87,9 +87,7 @@ impl Diff {
         self
     }
 
-    #[track_caller]
-    pub fn run(&mut self) {
-        self.drop_bomb.defuse();
+    fn run_common(&self) -> (&str, &str, String, String) {
         let expected = self.expected.as_ref().expect("expected text not set");
         let mut actual = self.actual.as_ref().expect("actual text not set").to_string();
         let expected_name = self.expected_name.as_ref().unwrap();
@@ -104,6 +102,14 @@ impl Diff {
             .header(expected_name, actual_name)
             .to_string();
 
+        (expected_name, actual_name, output, actual)
+    }
+
+    #[track_caller]
+    pub fn run(&mut self) {
+        self.drop_bomb.defuse();
+        let (expected_name, actual_name, output, actual) = self.run_common();
+
         if !output.is_empty() {
             // If we can bless (meaning we have a file to write into and the `RUSTC_BLESS_TEST`
             // environment variable set), then we write into the file and return.
@@ -120,4 +126,26 @@ impl Diff {
             )
         }
     }
+
+    #[track_caller]
+    pub fn run_fail(&mut self) {
+        self.drop_bomb.defuse();
+        let (expected_name, actual_name, output, actual) = self.run_common();
+
+        if output.is_empty() {
+            // If we can bless (meaning we have a file to write into and the `RUSTC_BLESS_TEST`
+            // environment variable set), then we write into the file and return.
+            if let Some(ref expected_file) = self.expected_file {
+                if std::env::var("RUSTC_BLESS_TEST").is_ok() {
+                    println!("Blessing `{}`", expected_file.display());
+                    fs_wrapper::write(expected_file, actual);
+                    return;
+                }
+            }
+            panic!(
+                "test failed: `{}` is not different from `{}`\n\n{}",
+                expected_name, actual_name, output
+            )
+        }
+    }
 }
diff --git a/src/tools/run-make-support/src/fs_wrapper.rs b/src/tools/run-make-support/src/fs_wrapper.rs
index 8a2bfce8b4a..0f0d6f6618c 100644
--- a/src/tools/run-make-support/src/fs_wrapper.rs
+++ b/src/tools/run-make-support/src/fs_wrapper.rs
@@ -1,7 +1,7 @@
 use std::fs;
 use std::path::Path;
 
-/// A wrapper around [`std::fs::remove_file`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::remove_file`] which includes the file path in the panic message.
 #[track_caller]
 pub fn remove_file<P: AsRef<Path>>(path: P) {
     fs::remove_file(path.as_ref())
@@ -18,21 +18,21 @@ pub fn copy<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) {
     ));
 }
 
-/// A wrapper around [`std::fs::File::create`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::File::create`] which includes the file path in the panic message.
 #[track_caller]
 pub fn create_file<P: AsRef<Path>>(path: P) {
     fs::File::create(path.as_ref())
         .expect(&format!("the file in path \"{}\" could not be created", path.as_ref().display()));
 }
 
-/// A wrapper around [`std::fs::read`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::read`] which includes the file path in the panic message.
 #[track_caller]
 pub fn read<P: AsRef<Path>>(path: P) -> Vec<u8> {
     fs::read(path.as_ref())
         .expect(&format!("the file in path \"{}\" could not be read", path.as_ref().display()))
 }
 
-/// A wrapper around [`std::fs::read_to_string`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::read_to_string`] which includes the file path in the panic message.
 #[track_caller]
 pub fn read_to_string<P: AsRef<Path>>(path: P) -> String {
     fs::read_to_string(path.as_ref()).expect(&format!(
@@ -41,14 +41,14 @@ pub fn read_to_string<P: AsRef<Path>>(path: P) -> String {
     ))
 }
 
-/// A wrapper around [`std::fs::read_dir`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::read_dir`] which includes the file path in the panic message.
 #[track_caller]
 pub fn read_dir<P: AsRef<Path>>(path: P) -> fs::ReadDir {
     fs::read_dir(path.as_ref())
         .expect(&format!("the directory in path \"{}\" could not be read", path.as_ref().display()))
 }
 
-/// A wrapper around [`std::fs::write`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::write`] which includes the file path in the panic message.
 #[track_caller]
 pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) {
     fs::write(path.as_ref(), contents.as_ref()).expect(&format!(
@@ -57,7 +57,7 @@ pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) {
     ));
 }
 
-/// A wrapper around [`std::fs::remove_dir_all`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::remove_dir_all`] which includes the file path in the panic message.
 #[track_caller]
 pub fn remove_dir_all<P: AsRef<Path>>(path: P) {
     fs::remove_dir_all(path.as_ref()).expect(&format!(
@@ -66,7 +66,7 @@ pub fn remove_dir_all<P: AsRef<Path>>(path: P) {
     ));
 }
 
-/// A wrapper around [`std::fs::create_dir`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::create_dir`] which includes the file path in the panic message.
 #[track_caller]
 pub fn create_dir<P: AsRef<Path>>(path: P) {
     fs::create_dir(path.as_ref()).expect(&format!(
@@ -75,7 +75,7 @@ pub fn create_dir<P: AsRef<Path>>(path: P) {
     ));
 }
 
-/// A wrapper around [`std::fs::create_dir_all`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::create_dir_all`] which includes the file path in the panic message.
 #[track_caller]
 pub fn create_dir_all<P: AsRef<Path>>(path: P) {
     fs::create_dir_all(path.as_ref()).expect(&format!(
@@ -84,7 +84,7 @@ pub fn create_dir_all<P: AsRef<Path>>(path: P) {
     ));
 }
 
-/// A wrapper around [`std::fs::metadata`] which includes the file path in the panic message..
+/// A wrapper around [`std::fs::metadata`] which includes the file path in the panic message.
 #[track_caller]
 pub fn metadata<P: AsRef<Path>>(path: P) -> fs::Metadata {
     fs::metadata(path.as_ref()).expect(&format!(
diff --git a/src/tools/run-make-support/src/lib.rs b/src/tools/run-make-support/src/lib.rs
index 7bb89106de1..5655318267a 100644
--- a/src/tools/run-make-support/src/lib.rs
+++ b/src/tools/run-make-support/src/lib.rs
@@ -35,7 +35,7 @@ pub use llvm::{
     LlvmProfdata, LlvmReadobj,
 };
 pub use run::{cmd, run, run_fail, run_with_args};
-pub use rustc::{aux_build, rustc, Rustc};
+pub use rustc::{aux_build, bare_rustc, rustc, Rustc};
 pub use rustdoc::{bare_rustdoc, rustdoc, Rustdoc};
 
 #[track_caller]
@@ -296,12 +296,27 @@ pub fn not_contains<P: AsRef<Path>>(path: P, expected: &str) -> bool {
 }
 
 /// Returns true if the filename at `path` is not in `expected`.
-pub fn filename_not_in_denylist<P: AsRef<Path>>(path: P, expected: &[String]) -> bool {
+pub fn filename_not_in_denylist<P: AsRef<Path>, V: AsRef<[String]>>(path: P, expected: V) -> bool {
+    let expected = expected.as_ref();
     path.as_ref()
         .file_name()
         .is_some_and(|name| !expected.contains(&name.to_str().unwrap().to_owned()))
 }
 
+/// Gathers all files in the current working directory that have the extension `ext`, and counts
+/// the number of lines within that contain a match with the regex pattern `re`.
+pub fn count_regex_matches_in_files_with_extension(re: &regex::Regex, ext: &str) -> usize {
+    let fetched_files = shallow_find_files(cwd(), |path| has_extension(path, ext));
+
+    let mut count = 0;
+    for file in fetched_files {
+        let content = fs_wrapper::read_to_string(file);
+        count += content.lines().filter(|line| re.is_match(&line)).count();
+    }
+
+    count
+}
+
 /// Use `cygpath -w` on a path to get a Windows path string back. This assumes that `cygpath` is
 /// available on the platform!
 #[track_caller]
diff --git a/src/tools/run-make-support/src/rustc.rs b/src/tools/run-make-support/src/rustc.rs
index 885b361f72a..a2a7c8064dc 100644
--- a/src/tools/run-make-support/src/rustc.rs
+++ b/src/tools/run-make-support/src/rustc.rs
@@ -10,6 +10,12 @@ pub fn rustc() -> Rustc {
     Rustc::new()
 }
 
+/// Construct a plain `rustc` invocation with no flags set.
+#[track_caller]
+pub fn bare_rustc() -> Rustc {
+    Rustc::bare()
+}
+
 /// Construct a new `rustc` aux-build invocation.
 #[track_caller]
 pub fn aux_build() -> Rustc {
@@ -30,7 +36,6 @@ fn setup_common() -> Command {
     let rustc = env_var("RUSTC");
     let mut cmd = Command::new(rustc);
     set_host_rpath(&mut cmd);
-    cmd.arg("-L").arg(cwd());
     cmd
 }
 
@@ -40,6 +45,14 @@ impl Rustc {
     /// Construct a new `rustc` invocation.
     #[track_caller]
     pub fn new() -> Self {
+        let mut cmd = setup_common();
+        cmd.arg("-L").arg(cwd());
+        Self { cmd }
+    }
+
+    /// Construct a bare `rustc` invocation with no flags set.
+    #[track_caller]
+    pub fn bare() -> Self {
         let cmd = setup_common();
         Self { cmd }
     }
diff --git a/src/tools/rust-analyzer/crates/stdx/src/anymap.rs b/src/tools/rust-analyzer/crates/stdx/src/anymap.rs
index d189b56a468..4eafcfb060f 100644
--- a/src/tools/rust-analyzer/crates/stdx/src/anymap.rs
+++ b/src/tools/rust-analyzer/crates/stdx/src/anymap.rs
@@ -68,8 +68,6 @@ pub type RawMap<A> = hash_map::HashMap<TypeId, Box<A>, BuildHasherDefault<TypeId
 /// The type parameter `A` allows you to use a different value type; normally you will want
 /// it to be `core::any::Any` (also known as `std::any::Any`), but there are other choices:
 ///
-/// - If you want the entire map to be cloneable, use `CloneAny` instead of `Any`; with
-///   that, you can only add types that implement `Clone` to the map.
 /// - You can add on `+ Send` or `+ Send + Sync` (e.g. `Map<dyn Any + Send>`) to add those
 ///   auto traits.
 ///
@@ -79,9 +77,6 @@ pub type RawMap<A> = hash_map::HashMap<TypeId, Box<A>, BuildHasherDefault<TypeId
 ///   also spelled [`AnyMap`] for convenience.
 /// - <code>[Map]&lt;dyn [core::any::Any] + Send&gt;</code>
 /// - <code>[Map]&lt;dyn [core::any::Any] + Send + Sync&gt;</code>
-/// - <code>[Map]&lt;dyn [CloneAny]&gt;</code>
-/// - <code>[Map]&lt;dyn [CloneAny] + Send&gt;</code>
-/// - <code>[Map]&lt;dyn [CloneAny] + Send + Sync&gt;</code>
 ///
 /// ## Example
 ///
@@ -205,12 +200,6 @@ mod tests {
         assert_debug::<Map<dyn Any>>();
         assert_debug::<Map<dyn Any + Send>>();
         assert_debug::<Map<dyn Any + Send + Sync>>();
-        assert_send::<Map<dyn CloneAny + Send>>();
-        assert_send::<Map<dyn CloneAny + Send + Sync>>();
-        assert_sync::<Map<dyn CloneAny + Send + Sync>>();
-        assert_debug::<Map<dyn CloneAny>>();
-        assert_debug::<Map<dyn CloneAny + Send>>();
-        assert_debug::<Map<dyn CloneAny + Send + Sync>>();
     }
 
     #[test]
@@ -232,53 +221,6 @@ mod tests {
     }
 }
 
-// impl some traits for dyn Any
-use core::fmt;
-
-#[doc(hidden)]
-pub trait CloneToAny {
-    /// Clone `self` into a new `Box<dyn CloneAny>` object.
-    fn clone_to_any(&self) -> Box<dyn CloneAny>;
-}
-
-impl<T: Any + Clone> CloneToAny for T {
-    #[inline]
-    fn clone_to_any(&self) -> Box<dyn CloneAny> {
-        Box::new(self.clone())
-    }
-}
-
-macro_rules! impl_clone {
-    ($t:ty) => {
-        impl Clone for Box<$t> {
-            #[inline]
-            fn clone(&self) -> Box<$t> {
-                // SAFETY: this dance is to reapply any Send/Sync marker. I’m not happy about this
-                // approach, given that I used to do it in safe code, but then came a dodgy
-                // future-compatibility warning where_clauses_object_safety, which is spurious for
-                // auto traits but still super annoying (future-compatibility lints seem to mean
-                // your bin crate needs a corresponding allow!). Although I explained my plight¹
-                // and it was all explained and agreed upon, no action has been taken. So I finally
-                // caved and worked around it by doing it this way, which matches what’s done for
-                // core::any², so it’s probably not *too* bad.
-                //
-                // ¹ https://github.com/rust-lang/rust/issues/51443#issuecomment-421988013
-                // ² https://github.com/rust-lang/rust/blob/e7825f2b690c9a0d21b6f6d84c404bb53b151b38/library/alloc/src/boxed.rs#L1613-L1616
-                let clone: Box<dyn CloneAny> = (**self).clone_to_any();
-                let raw: *mut dyn CloneAny = Box::into_raw(clone);
-                unsafe { Box::from_raw(raw as *mut $t) }
-            }
-        }
-
-        impl fmt::Debug for $t {
-            #[inline]
-            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                f.pad(stringify!($t))
-            }
-        }
-    };
-}
-
 /// Methods for downcasting from an `Any`-like trait object.
 ///
 /// This should only be implemented on trait objects for subtraits of `Any`, though you can
@@ -350,16 +292,3 @@ macro_rules! implement {
 implement!(Any);
 implement!(Any + Send);
 implement!(Any + Send + Sync);
-
-/// [`Any`], but with cloning.
-///
-/// Every type with no non-`'static` references that implements `Clone` implements `CloneAny`.
-/// See [`core::any`] for more details on `Any` in general.
-pub trait CloneAny: Any + CloneToAny {}
-impl<T: Any + Clone> CloneAny for T {}
-implement!(CloneAny);
-implement!(CloneAny + Send);
-implement!(CloneAny + Send + Sync);
-impl_clone!(dyn CloneAny);
-impl_clone!(dyn CloneAny + Send);
-impl_clone!(dyn CloneAny + Send + Sync);
diff --git a/src/tools/tidy/src/allowed_run_make_makefiles.txt b/src/tools/tidy/src/allowed_run_make_makefiles.txt
index ff98bd538db..d26d6fe360d 100644
--- a/src/tools/tidy/src/allowed_run_make_makefiles.txt
+++ b/src/tools/tidy/src/allowed_run_make_makefiles.txt
@@ -23,8 +23,6 @@ run-make/dep-info-spaces/Makefile
 run-make/dep-info/Makefile
 run-make/dump-ice-to-disk/Makefile
 run-make/dump-mono-stats/Makefile
-run-make/emit-path-unhashed/Makefile
-run-make/emit-shared-files/Makefile
 run-make/emit-to-stdout/Makefile
 run-make/env-dep-info/Makefile
 run-make/export-executable-symbols/Makefile
@@ -49,7 +47,6 @@ run-make/foreign-rust-exceptions/Makefile
 run-make/incr-add-rust-src-component/Makefile
 run-make/incr-foreign-head-span/Makefile
 run-make/interdependent-c-libraries/Makefile
-run-make/intrinsic-unreachable/Makefile
 run-make/issue-107094/Makefile
 run-make/issue-109934-lto-debuginfo/Makefile
 run-make/issue-14698/Makefile
@@ -62,7 +59,6 @@ run-make/issue-28595/Makefile
 run-make/issue-33329/Makefile
 run-make/issue-35164/Makefile
 run-make/issue-36710/Makefile
-run-make/issue-37839/Makefile
 run-make/issue-47551/Makefile
 run-make/issue-69368/Makefile
 run-make/issue-83045/Makefile
@@ -101,9 +97,6 @@ run-make/no-builtins-attribute/Makefile
 run-make/no-duplicate-libs/Makefile
 run-make/obey-crate-type-flag/Makefile
 run-make/panic-abort-eh_frame/Makefile
-run-make/pass-linker-flags-flavor/Makefile
-run-make/pass-linker-flags-from-dep/Makefile
-run-make/pass-linker-flags/Makefile
 run-make/pass-non-c-like-enum-to-c/Makefile
 run-make/pdb-buildinfo-cl-cmd/Makefile
 run-make/pgo-gen-lto/Makefile
@@ -132,9 +125,6 @@ run-make/rustc-macro-dep-files/Makefile
 run-make/sanitizer-cdylib-link/Makefile
 run-make/sanitizer-dylib-link/Makefile
 run-make/sanitizer-staticlib-link/Makefile
-run-make/sepcomp-cci-copies/Makefile
-run-make/sepcomp-inlining/Makefile
-run-make/sepcomp-separate/Makefile
 run-make/share-generics-dylib/Makefile
 run-make/silly-file-names/Makefile
 run-make/simd-ffi/Makefile
@@ -149,14 +139,9 @@ run-make/symbol-mangling-hashed/Makefile
 run-make/symbol-visibility/Makefile
 run-make/symbols-include-type-name/Makefile
 run-make/sysroot-crates-are-unstable/Makefile
-run-make/target-cpu-native/Makefile
-run-make/target-specs/Makefile
-run-make/target-without-atomic-cas/Makefile
 run-make/test-benches/Makefile
 run-make/thumb-none-cortex-m/Makefile
 run-make/thumb-none-qemu/Makefile
-run-make/track-path-dep-info/Makefile
-run-make/track-pgo-dep-info/Makefile
 run-make/translation/Makefile
 run-make/type-mismatch-same-crate-name/Makefile
 run-make/unstable-flag-required/Makefile
diff --git a/src/tools/tidy/src/pal.rs b/src/tools/tidy/src/pal.rs
index 7e5656926ab..2f8abc77566 100644
--- a/src/tools/tidy/src/pal.rs
+++ b/src/tools/tidy/src/pal.rs
@@ -45,6 +45,8 @@ const EXCEPTION_PATHS: &[&str] = &[
     // pointer regardless of the target architecture. As a result,
     // we must use `#[cfg(windows)]` to conditionally compile the
     // correct `VaList` structure for windows.
+    "library/core/src/ffi/va_list.rs",
+    // We placed a linkage against Windows libraries here
     "library/core/src/ffi/mod.rs",
     "library/std/src/sys", // Platform-specific code for std lives here.
     "library/std/src/os",  // Platform-specific public interfaces
diff --git a/src/tools/tidy/src/style.rs b/src/tools/tidy/src/style.rs
index e4d54d2a2b5..8e693c35adc 100644
--- a/src/tools/tidy/src/style.rs
+++ b/src/tools/tidy/src/style.rs
@@ -110,6 +110,7 @@ const ROOT_PROBLEMATIC_CONSTS: &[u32] = &[
     173390526, 721077,
 ];
 
+// Returns all permutations of problematic consts, over 2000 elements.
 fn generate_problematic_strings(
     consts: &[u32],
     letter_digit: &FxHashMap<char, char>,
@@ -319,6 +320,8 @@ pub fn check(path: &Path, bad: &mut bool) {
         ROOT_PROBLEMATIC_CONSTS,
         &[('A', '4'), ('B', '8'), ('E', '3')].iter().cloned().collect(),
     );
+    // This creates a RegexSet as regex contains performance optimizations to be able to deal with these over
+    // 2000 needles efficiently. This runs over the entire source code, so performance matters.
     let problematic_regex = RegexSet::new(problematic_consts_strings.as_slice()).unwrap();
 
     walk(path, skip, &mut |entry, contents| {
diff --git a/tests/coverage-run-rustdoc/doctest.coverage b/tests/coverage-run-rustdoc/doctest.coverage
index 1bbf364759b..396811c5487 100644
--- a/tests/coverage-run-rustdoc/doctest.coverage
+++ b/tests/coverage-run-rustdoc/doctest.coverage
@@ -34,10 +34,10 @@ $DIR/doctest.rs:
    LL|       |//!
    LL|       |//! doctest returning a result:
    LL|      1|//! ```
-   LL|      1|//! #[derive(Debug, PartialEq)]
-   LL|      1|//! struct SomeError {
-   LL|      1|//!     msg: String,
-   LL|      1|//! }
+   LL|       |//! #[derive(Debug, PartialEq)]
+   LL|       |//! struct SomeError {
+   LL|       |//!     msg: String,
+   LL|       |//! }
    LL|      1|//! let mut res = Err(SomeError { msg: String::from("a message") });
    LL|      1|//! if res.is_ok() {
    LL|      0|//!     res?;
diff --git a/tests/coverage/async.cov-map b/tests/coverage/async.cov-map
index 7d16372375a..9e5a4bdc60f 100644
--- a/tests/coverage/async.cov-map
+++ b/tests/coverage/async.cov-map
@@ -167,15 +167,16 @@ Number of file 0 mappings: 14
     = ((c6 + c7) + c8)
 
 Function name: async::j
-Raw bytes (53): 0x[01, 01, 02, 07, 0d, 05, 09, 09, 01, 35, 01, 13, 0c, 05, 14, 09, 00, 0a, 01, 00, 0e, 00, 1b, 05, 00, 1f, 00, 27, 09, 01, 09, 00, 0a, 11, 00, 0e, 00, 1a, 09, 00, 1e, 00, 20, 0d, 01, 0e, 00, 10, 03, 02, 01, 00, 02]
+Raw bytes (58): 0x[01, 01, 02, 07, 0d, 05, 09, 0a, 01, 35, 01, 00, 0d, 01, 0b, 0b, 00, 0c, 05, 01, 09, 00, 0a, 01, 00, 0e, 00, 1b, 05, 00, 1f, 00, 27, 09, 01, 09, 00, 0a, 11, 00, 0e, 00, 1a, 09, 00, 1e, 00, 20, 0d, 01, 0e, 00, 10, 03, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 2
 - expression 0 operands: lhs = Expression(1, Add), rhs = Counter(3)
 - expression 1 operands: lhs = Counter(1), rhs = Counter(2)
-Number of file 0 mappings: 9
-- Code(Counter(0)) at (prev + 53, 1) to (start + 19, 12)
-- Code(Counter(1)) at (prev + 20, 9) to (start + 0, 10)
+Number of file 0 mappings: 10
+- Code(Counter(0)) at (prev + 53, 1) to (start + 0, 13)
+- Code(Counter(0)) at (prev + 11, 11) to (start + 0, 12)
+- Code(Counter(1)) at (prev + 1, 9) to (start + 0, 10)
 - Code(Counter(0)) at (prev + 0, 14) to (start + 0, 27)
 - Code(Counter(1)) at (prev + 0, 31) to (start + 0, 39)
 - Code(Counter(2)) at (prev + 1, 9) to (start + 0, 10)
@@ -186,7 +187,7 @@ Number of file 0 mappings: 9
     = ((c1 + c2) + c3)
 
 Function name: async::j::c
-Raw bytes (26): 0x[01, 01, 01, 01, 05, 04, 01, 37, 05, 01, 12, 05, 02, 0d, 00, 0e, 02, 0a, 0d, 00, 0e, 01, 02, 05, 00, 06]
+Raw bytes (26): 0x[01, 01, 01, 01, 05, 04, 01, 37, 05, 01, 12, 05, 02, 0d, 00, 0e, 02, 02, 0d, 00, 0e, 01, 02, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 1
@@ -194,40 +195,40 @@ Number of expressions: 1
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 55, 5) to (start + 1, 18)
 - Code(Counter(1)) at (prev + 2, 13) to (start + 0, 14)
-- Code(Expression(0, Sub)) at (prev + 10, 13) to (start + 0, 14)
+- Code(Expression(0, Sub)) at (prev + 2, 13) to (start + 0, 14)
     = (c0 - c1)
 - Code(Counter(0)) at (prev + 2, 5) to (start + 0, 6)
 
 Function name: async::j::d
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 46, 05, 00, 17]
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 3e, 05, 00, 17]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 70, 5) to (start + 0, 23)
+- Code(Counter(0)) at (prev + 62, 5) to (start + 0, 23)
 
 Function name: async::j::f
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 47, 05, 00, 17]
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 3f, 05, 00, 17]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 71, 5) to (start + 0, 23)
+- Code(Counter(0)) at (prev + 63, 5) to (start + 0, 23)
 
 Function name: async::k (unused)
-Raw bytes (29): 0x[01, 01, 00, 05, 00, 4f, 01, 01, 0c, 00, 02, 0e, 00, 10, 00, 01, 0e, 00, 10, 00, 01, 0e, 00, 10, 00, 02, 01, 00, 02]
+Raw bytes (29): 0x[01, 01, 00, 05, 00, 47, 01, 01, 0c, 00, 02, 0e, 00, 10, 00, 01, 0e, 00, 10, 00, 01, 0e, 00, 10, 00, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 5
-- Code(Zero) at (prev + 79, 1) to (start + 1, 12)
+- Code(Zero) at (prev + 71, 1) to (start + 1, 12)
 - Code(Zero) at (prev + 2, 14) to (start + 0, 16)
 - Code(Zero) at (prev + 1, 14) to (start + 0, 16)
 - Code(Zero) at (prev + 1, 14) to (start + 0, 16)
 - Code(Zero) at (prev + 2, 1) to (start + 0, 2)
 
 Function name: async::l
-Raw bytes (37): 0x[01, 01, 04, 01, 07, 05, 09, 0f, 02, 09, 05, 05, 01, 57, 01, 01, 0c, 02, 02, 0e, 00, 10, 05, 01, 0e, 00, 10, 09, 01, 0e, 00, 10, 0b, 02, 01, 00, 02]
+Raw bytes (37): 0x[01, 01, 04, 01, 07, 05, 09, 0f, 02, 09, 05, 05, 01, 4f, 01, 01, 0c, 02, 02, 0e, 00, 10, 05, 01, 0e, 00, 10, 09, 01, 0e, 00, 10, 0b, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 4
@@ -236,7 +237,7 @@ Number of expressions: 4
 - expression 2 operands: lhs = Expression(3, Add), rhs = Expression(0, Sub)
 - expression 3 operands: lhs = Counter(2), rhs = Counter(1)
 Number of file 0 mappings: 5
-- Code(Counter(0)) at (prev + 87, 1) to (start + 1, 12)
+- Code(Counter(0)) at (prev + 79, 1) to (start + 1, 12)
 - Code(Expression(0, Sub)) at (prev + 2, 14) to (start + 0, 16)
     = (c0 - (c1 + c2))
 - Code(Counter(1)) at (prev + 1, 14) to (start + 0, 16)
@@ -245,26 +246,26 @@ Number of file 0 mappings: 5
     = ((c2 + c1) + (c0 - (c1 + c2)))
 
 Function name: async::m
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 5f, 01, 00, 19]
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 57, 01, 00, 19]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 95, 1) to (start + 0, 25)
+- Code(Counter(0)) at (prev + 87, 1) to (start + 0, 25)
 
 Function name: async::m::{closure#0} (unused)
-Raw bytes (9): 0x[01, 01, 00, 01, 00, 5f, 19, 00, 22]
+Raw bytes (9): 0x[01, 01, 00, 01, 00, 57, 19, 00, 22]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 1
-- Code(Zero) at (prev + 95, 25) to (start + 0, 34)
+- Code(Zero) at (prev + 87, 25) to (start + 0, 34)
 
 Function name: async::main
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 61, 01, 08, 02]
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 59, 01, 08, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 97, 1) to (start + 8, 2)
+- Code(Counter(0)) at (prev + 89, 1) to (start + 8, 2)
 
diff --git a/tests/coverage/async.coverage b/tests/coverage/async.coverage
index e943911d310..f5473829b02 100644
--- a/tests/coverage/async.coverage
+++ b/tests/coverage/async.coverage
@@ -53,25 +53,15 @@
    LL|      1|}
    LL|       |
    LL|      1|fn j(x: u8) {
-   LL|      1|    // non-async versions of `c()`, `d()`, and `f()` to make it similar to async `i()`.
+   LL|       |    // non-async versions of `c()`, `d()`, and `f()` to make it similar to async `i()`.
    LL|      1|    fn c(x: u8) -> u8 {
    LL|      1|        if x == 8 {
-   LL|      1|            1 // This line appears covered, but the 1-character expression span covering the `1`
-                          ^0
-   LL|      1|              // is not executed. (`llvm-cov show` displays a `^0` below the `1` ). This is because
-   LL|      1|              // `fn j()` executes the open brace for the function body, followed by the function's
-   LL|      1|              // first executable statement, `match x`. Inner function declarations are not
-   LL|      1|              // "visible" to the MIR for `j()`, so the code region counts all lines between the
-   LL|      1|              // open brace and the first statement as executed, which is, in a sense, true.
-   LL|      1|              // `llvm-cov show` overcomes this kind of situation by showing the actual counts
-   LL|      1|              // of the enclosed coverages, (that is, the `1` expression was not executed, and
-   LL|      1|              // accurately displays a `0`).
-   LL|      1|        } else {
+   LL|      0|            1
+   LL|       |        } else {
    LL|      1|            0
-   LL|      1|        }
+   LL|       |        }
    LL|      1|    }
-   LL|      1|    fn d() -> u8 { 1 } // inner function is defined in-line, but the function is not executed
-                  ^0
+   LL|      0|    fn d() -> u8 { 1 } // inner function is defined in-line, but the function is not executed
    LL|      1|    fn f() -> u8 { 1 }
    LL|      1|    match x {
    LL|      1|        y if c(x) == y + 1 => { d(); }
diff --git a/tests/coverage/async.rs b/tests/coverage/async.rs
index 5018ade0125..7e6ad761ecd 100644
--- a/tests/coverage/async.rs
+++ b/tests/coverage/async.rs
@@ -54,15 +54,7 @@ fn j(x: u8) {
     // non-async versions of `c()`, `d()`, and `f()` to make it similar to async `i()`.
     fn c(x: u8) -> u8 {
         if x == 8 {
-            1 // This line appears covered, but the 1-character expression span covering the `1`
-              // is not executed. (`llvm-cov show` displays a `^0` below the `1` ). This is because
-              // `fn j()` executes the open brace for the function body, followed by the function's
-              // first executable statement, `match x`. Inner function declarations are not
-              // "visible" to the MIR for `j()`, so the code region counts all lines between the
-              // open brace and the first statement as executed, which is, in a sense, true.
-              // `llvm-cov show` overcomes this kind of situation by showing the actual counts
-              // of the enclosed coverages, (that is, the `1` expression was not executed, and
-              // accurately displays a `0`).
+            1
         } else {
             0
         }
diff --git a/tests/coverage/attr/nested.cov-map b/tests/coverage/attr/nested.cov-map
index 0f2d5542f75..466aec8956e 100644
--- a/tests/coverage/attr/nested.cov-map
+++ b/tests/coverage/attr/nested.cov-map
@@ -1,18 +1,18 @@
 Function name: nested::closure_expr
-Raw bytes (14): 0x[01, 01, 00, 02, 01, 44, 01, 01, 0f, 01, 0b, 05, 01, 02]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 3f, 01, 01, 0f, 01, 0b, 05, 01, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 2
-- Code(Counter(0)) at (prev + 68, 1) to (start + 1, 15)
+- Code(Counter(0)) at (prev + 63, 1) to (start + 1, 15)
 - Code(Counter(0)) at (prev + 11, 5) to (start + 1, 2)
 
 Function name: nested::closure_tail
-Raw bytes (14): 0x[01, 01, 00, 02, 01, 53, 01, 01, 0f, 01, 11, 05, 01, 02]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 4e, 01, 01, 0f, 01, 11, 05, 01, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
 Number of file 0 mappings: 2
-- Code(Counter(0)) at (prev + 83, 1) to (start + 1, 15)
+- Code(Counter(0)) at (prev + 78, 1) to (start + 1, 15)
 - Code(Counter(0)) at (prev + 17, 5) to (start + 1, 2)
 
diff --git a/tests/coverage/attr/nested.coverage b/tests/coverage/attr/nested.coverage
index bdd117b7dfa..2d64fe698ea 100644
--- a/tests/coverage/attr/nested.coverage
+++ b/tests/coverage/attr/nested.coverage
@@ -4,11 +4,6 @@
    LL|       |// Demonstrates the interaction between #[coverage(off)] and various kinds of
    LL|       |// nested function.
    LL|       |
-   LL|       |// FIXME(#126625): Coverage attributes should apply recursively to nested functions.
-   LL|       |// FIXME(#126626): When an inner (non-closure) function has `#[coverage(off)]`,
-   LL|       |// its lines can still be marked with misleading execution counts from its enclosing
-   LL|       |// function.
-   LL|       |
    LL|       |#[coverage(off)]
    LL|       |fn do_stuff() {}
    LL|       |
diff --git a/tests/coverage/attr/nested.rs b/tests/coverage/attr/nested.rs
index c7ff835f44f..8213e29b6fc 100644
--- a/tests/coverage/attr/nested.rs
+++ b/tests/coverage/attr/nested.rs
@@ -4,11 +4,6 @@
 // Demonstrates the interaction between #[coverage(off)] and various kinds of
 // nested function.
 
-// FIXME(#126625): Coverage attributes should apply recursively to nested functions.
-// FIXME(#126626): When an inner (non-closure) function has `#[coverage(off)]`,
-// its lines can still be marked with misleading execution counts from its enclosing
-// function.
-
 #[coverage(off)]
 fn do_stuff() {}
 
diff --git a/tests/coverage/attr/off-on-sandwich.cov-map b/tests/coverage/attr/off-on-sandwich.cov-map
index ed77d7d17e6..d5fbac6ebf7 100644
--- a/tests/coverage/attr/off-on-sandwich.cov-map
+++ b/tests/coverage/attr/off-on-sandwich.cov-map
@@ -1,24 +1,27 @@
 Function name: off_on_sandwich::dense_a::dense_b
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 14, 05, 07, 06]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 0f, 05, 02, 12, 01, 07, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 20, 5) to (start + 7, 6)
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 15, 5) to (start + 2, 18)
+- Code(Counter(0)) at (prev + 7, 5) to (start + 0, 6)
 
 Function name: off_on_sandwich::sparse_a::sparse_b::sparse_c
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 26, 09, 0b, 0a]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 21, 09, 02, 17, 01, 0b, 09, 00, 0a]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 38, 9) to (start + 11, 10)
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 33, 9) to (start + 2, 23)
+- Code(Counter(0)) at (prev + 11, 9) to (start + 0, 10)
 
 Function name: off_on_sandwich::sparse_a::sparse_b::sparse_c::sparse_d
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 29, 0d, 07, 0e]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 24, 0d, 02, 1b, 01, 07, 0d, 00, 0e]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 41, 13) to (start + 7, 14)
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 36, 13) to (start + 2, 27)
+- Code(Counter(0)) at (prev + 7, 13) to (start + 0, 14)
 
diff --git a/tests/coverage/attr/off-on-sandwich.coverage b/tests/coverage/attr/off-on-sandwich.coverage
index 58c128b8342..675697906ee 100644
--- a/tests/coverage/attr/off-on-sandwich.coverage
+++ b/tests/coverage/attr/off-on-sandwich.coverage
@@ -4,11 +4,6 @@
    LL|       |// Demonstrates the interaction of `#[coverage(off)]` and `#[coverage(on)]`
    LL|       |// in nested functions.
    LL|       |
-   LL|       |// FIXME(#126625): Coverage attributes should apply recursively to nested functions.
-   LL|       |// FIXME(#126626): When an inner (non-closure) function has `#[coverage(off)]`,
-   LL|       |// its lines can still be marked with misleading execution counts from its enclosing
-   LL|       |// function.
-   LL|       |
    LL|       |#[coverage(off)]
    LL|       |fn do_stuff() {}
    LL|       |
@@ -20,10 +15,10 @@
    LL|      2|    fn dense_b() {
    LL|      2|        dense_c();
    LL|      2|        dense_c();
-   LL|      2|        #[coverage(off)]
-   LL|      2|        fn dense_c() {
-   LL|      2|            do_stuff();
-   LL|      2|        }
+   LL|       |        #[coverage(off)]
+   LL|       |        fn dense_c() {
+   LL|       |            do_stuff();
+   LL|       |        }
    LL|      2|    }
    LL|       |}
    LL|       |
@@ -41,10 +36,10 @@
    LL|      8|            fn sparse_d() {
    LL|      8|                sparse_e();
    LL|      8|                sparse_e();
-   LL|      8|                #[coverage(off)]
-   LL|      8|                fn sparse_e() {
-   LL|      8|                    do_stuff();
-   LL|      8|                }
+   LL|       |                #[coverage(off)]
+   LL|       |                fn sparse_e() {
+   LL|       |                    do_stuff();
+   LL|       |                }
    LL|      8|            }
    LL|      4|        }
    LL|       |    }
diff --git a/tests/coverage/attr/off-on-sandwich.rs b/tests/coverage/attr/off-on-sandwich.rs
index 6b21b180223..261634e0029 100644
--- a/tests/coverage/attr/off-on-sandwich.rs
+++ b/tests/coverage/attr/off-on-sandwich.rs
@@ -4,11 +4,6 @@
 // Demonstrates the interaction of `#[coverage(off)]` and `#[coverage(on)]`
 // in nested functions.
 
-// FIXME(#126625): Coverage attributes should apply recursively to nested functions.
-// FIXME(#126626): When an inner (non-closure) function has `#[coverage(off)]`,
-// its lines can still be marked with misleading execution counts from its enclosing
-// function.
-
 #[coverage(off)]
 fn do_stuff() {}
 
diff --git a/tests/coverage/closure_macro.cov-map b/tests/coverage/closure_macro.cov-map
index 156947f4e21..eb5f94d1080 100644
--- a/tests/coverage/closure_macro.cov-map
+++ b/tests/coverage/closure_macro.cov-map
@@ -7,15 +7,16 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 29, 1) to (start + 2, 2)
 
 Function name: closure_macro::main
-Raw bytes (31): 0x[01, 01, 01, 01, 05, 05, 01, 21, 01, 01, 21, 02, 02, 09, 00, 0f, 05, 00, 54, 00, 55, 02, 02, 09, 02, 0b, 01, 03, 01, 00, 02]
+Raw bytes (36): 0x[01, 01, 01, 01, 05, 06, 01, 21, 01, 01, 21, 02, 02, 09, 00, 0f, 01, 00, 12, 00, 54, 05, 00, 54, 00, 55, 02, 02, 09, 02, 0b, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-Number of file 0 mappings: 5
+Number of file 0 mappings: 6
 - Code(Counter(0)) at (prev + 33, 1) to (start + 1, 33)
 - Code(Expression(0, Sub)) at (prev + 2, 9) to (start + 0, 15)
     = (c0 - c1)
+- Code(Counter(0)) at (prev + 0, 18) to (start + 0, 84)
 - Code(Counter(1)) at (prev + 0, 84) to (start + 0, 85)
 - Code(Expression(0, Sub)) at (prev + 2, 9) to (start + 2, 11)
     = (c0 - c1)
diff --git a/tests/coverage/closure_macro_async.cov-map b/tests/coverage/closure_macro_async.cov-map
index 0f2b4e01748..1286d663bd4 100644
--- a/tests/coverage/closure_macro_async.cov-map
+++ b/tests/coverage/closure_macro_async.cov-map
@@ -15,15 +15,16 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 35, 1) to (start + 0, 43)
 
 Function name: closure_macro_async::test::{closure#0}
-Raw bytes (31): 0x[01, 01, 01, 01, 05, 05, 01, 23, 2b, 01, 21, 02, 02, 09, 00, 0f, 05, 00, 54, 00, 55, 02, 02, 09, 02, 0b, 01, 03, 01, 00, 02]
+Raw bytes (36): 0x[01, 01, 01, 01, 05, 06, 01, 23, 2b, 01, 21, 02, 02, 09, 00, 0f, 01, 00, 12, 00, 54, 05, 00, 54, 00, 55, 02, 02, 09, 02, 0b, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-Number of file 0 mappings: 5
+Number of file 0 mappings: 6
 - Code(Counter(0)) at (prev + 35, 43) to (start + 1, 33)
 - Code(Expression(0, Sub)) at (prev + 2, 9) to (start + 0, 15)
     = (c0 - c1)
+- Code(Counter(0)) at (prev + 0, 18) to (start + 0, 84)
 - Code(Counter(1)) at (prev + 0, 84) to (start + 0, 85)
 - Code(Expression(0, Sub)) at (prev + 2, 9) to (start + 2, 11)
     = (c0 - c1)
diff --git a/tests/coverage/holes.cov-map b/tests/coverage/holes.cov-map
new file mode 100644
index 00000000000..9350bd9a405
--- /dev/null
+++ b/tests/coverage/holes.cov-map
@@ -0,0 +1,47 @@
+Function name: <holes::main::MyStruct>::_method (unused)
+Raw bytes (9): 0x[01, 01, 00, 01, 00, 25, 09, 00, 1d]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Zero) at (prev + 37, 9) to (start + 0, 29)
+
+Function name: holes::main
+Raw bytes (44): 0x[01, 01, 00, 08, 01, 08, 01, 06, 11, 01, 0f, 05, 00, 12, 01, 04, 05, 00, 12, 01, 07, 05, 00, 12, 01, 06, 05, 00, 12, 01, 06, 05, 03, 0f, 01, 0a, 05, 03, 0f, 01, 0a, 05, 01, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 8
+- Code(Counter(0)) at (prev + 8, 1) to (start + 6, 17)
+- Code(Counter(0)) at (prev + 15, 5) to (start + 0, 18)
+- Code(Counter(0)) at (prev + 4, 5) to (start + 0, 18)
+- Code(Counter(0)) at (prev + 7, 5) to (start + 0, 18)
+- Code(Counter(0)) at (prev + 6, 5) to (start + 0, 18)
+- Code(Counter(0)) at (prev + 6, 5) to (start + 3, 15)
+- Code(Counter(0)) at (prev + 10, 5) to (start + 3, 15)
+- Code(Counter(0)) at (prev + 10, 5) to (start + 1, 2)
+
+Function name: holes::main::_unused_fn (unused)
+Raw bytes (9): 0x[01, 01, 00, 01, 00, 19, 05, 00, 17]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Zero) at (prev + 25, 5) to (start + 0, 23)
+
+Function name: holes::main::{closure#0} (unused)
+Raw bytes (9): 0x[01, 01, 00, 01, 00, 12, 09, 02, 0a]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Zero) at (prev + 18, 9) to (start + 2, 10)
+
+Function name: holes::main::{closure#1} (unused)
+Raw bytes (9): 0x[01, 01, 00, 01, 00, 3d, 09, 02, 0a]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Zero) at (prev + 61, 9) to (start + 2, 10)
+
diff --git a/tests/coverage/holes.coverage b/tests/coverage/holes.coverage
new file mode 100644
index 00000000000..6e65435f7e3
--- /dev/null
+++ b/tests/coverage/holes.coverage
@@ -0,0 +1,68 @@
+   LL|       |//@ edition: 2021
+   LL|       |
+   LL|       |// Nested items/closures should be treated as "holes", so that their spans are
+   LL|       |// not displayed as executable code in the enclosing function.
+   LL|       |
+   LL|       |use core::hint::black_box;
+   LL|       |
+   LL|      1|fn main() {
+   LL|      1|    black_box(());
+   LL|      1|
+   LL|      1|    // Splitting this across multiple lines makes it easier to see where the
+   LL|      1|    // coverage mapping regions begin and end.
+   LL|      1|    #[rustfmt::skip]
+   LL|      1|    let _closure =
+   LL|       |        |
+   LL|       |            _arg: (),
+   LL|       |        |
+   LL|      0|        {
+   LL|      0|            black_box(());
+   LL|      0|        }
+   LL|       |        ;
+   LL|       |
+   LL|      1|    black_box(());
+   LL|       |
+   LL|      0|    fn _unused_fn() {}
+   LL|       |
+   LL|      1|    black_box(());
+   LL|       |
+   LL|       |    struct MyStruct {
+   LL|       |        _x: u32,
+   LL|       |        _y: u32,
+   LL|       |    }
+   LL|       |
+   LL|      1|    black_box(());
+   LL|       |
+   LL|       |    impl MyStruct {
+   LL|      0|        fn _method(&self) {}
+   LL|       |    }
+   LL|       |
+   LL|      1|    black_box(());
+   LL|       |
+   LL|       |    macro_rules! _my_macro {
+   LL|       |        () => {};
+   LL|       |    }
+   LL|       |
+   LL|      1|    black_box(());
+   LL|      1|
+   LL|      1|    #[rustfmt::skip]
+   LL|      1|    let _const =
+   LL|       |        const
+   LL|       |        {
+   LL|       |            7 + 4
+   LL|       |        }
+   LL|       |        ;
+   LL|       |
+   LL|      1|    black_box(());
+   LL|      1|
+   LL|      1|    #[rustfmt::skip]
+   LL|      1|    let _async =
+   LL|       |        async
+   LL|      0|        {
+   LL|      0|            7 + 4
+   LL|      0|        }
+   LL|       |        ;
+   LL|       |
+   LL|      1|    black_box(());
+   LL|      1|}
+
diff --git a/tests/coverage/holes.rs b/tests/coverage/holes.rs
new file mode 100644
index 00000000000..b3a71e759c8
--- /dev/null
+++ b/tests/coverage/holes.rs
@@ -0,0 +1,67 @@
+//@ edition: 2021
+
+// Nested items/closures should be treated as "holes", so that their spans are
+// not displayed as executable code in the enclosing function.
+
+use core::hint::black_box;
+
+fn main() {
+    black_box(());
+
+    // Splitting this across multiple lines makes it easier to see where the
+    // coverage mapping regions begin and end.
+    #[rustfmt::skip]
+    let _closure =
+        |
+            _arg: (),
+        |
+        {
+            black_box(());
+        }
+        ;
+
+    black_box(());
+
+    fn _unused_fn() {}
+
+    black_box(());
+
+    struct MyStruct {
+        _x: u32,
+        _y: u32,
+    }
+
+    black_box(());
+
+    impl MyStruct {
+        fn _method(&self) {}
+    }
+
+    black_box(());
+
+    macro_rules! _my_macro {
+        () => {};
+    }
+
+    black_box(());
+
+    #[rustfmt::skip]
+    let _const =
+        const
+        {
+            7 + 4
+        }
+        ;
+
+    black_box(());
+
+    #[rustfmt::skip]
+    let _async =
+        async
+        {
+            7 + 4
+        }
+        ;
+
+    black_box(());
+}
diff --git a/tests/coverage/no_cov_crate.cov-map b/tests/coverage/no_cov_crate.cov-map
index 281efb6d00d..75234f6c3b7 100644
--- a/tests/coverage/no_cov_crate.cov-map
+++ b/tests/coverage/no_cov_crate.cov-map
@@ -31,20 +31,22 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 77, 1) to (start + 11, 2)
 
 Function name: no_cov_crate::nested_fns::outer
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 31, 05, 0c, 06]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 31, 05, 02, 23, 01, 0c, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 49, 5) to (start + 12, 6)
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 49, 5) to (start + 2, 35)
+- Code(Counter(0)) at (prev + 12, 5) to (start + 0, 6)
 
 Function name: no_cov_crate::nested_fns::outer_both_covered
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 3f, 05, 0b, 06]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 3f, 05, 02, 17, 01, 0b, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 63, 5) to (start + 11, 6)
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 63, 5) to (start + 2, 23)
+- Code(Counter(0)) at (prev + 11, 5) to (start + 0, 6)
 
 Function name: no_cov_crate::nested_fns::outer_both_covered::inner
 Raw bytes (26): 0x[01, 01, 01, 01, 05, 04, 01, 43, 09, 01, 17, 05, 01, 18, 02, 0e, 02, 02, 14, 02, 0e, 01, 03, 09, 00, 0a]
diff --git a/tests/coverage/no_cov_crate.coverage b/tests/coverage/no_cov_crate.coverage
index 29ad1f979cf..6a43e52652e 100644
--- a/tests/coverage/no_cov_crate.coverage
+++ b/tests/coverage/no_cov_crate.coverage
@@ -49,21 +49,21 @@
    LL|      1|    pub fn outer(is_true: bool) {
    LL|      1|        println!("called and covered");
    LL|      1|        inner_not_covered(is_true);
-   LL|      1|
-   LL|      1|        #[coverage(off)]
-   LL|      1|        fn inner_not_covered(is_true: bool) {
-   LL|      1|            if is_true {
-   LL|      1|                println!("called but not covered");
-   LL|      1|            } else {
-   LL|      1|                println!("absolutely not covered");
-   LL|      1|            }
-   LL|      1|        }
+   LL|       |
+   LL|       |        #[coverage(off)]
+   LL|       |        fn inner_not_covered(is_true: bool) {
+   LL|       |            if is_true {
+   LL|       |                println!("called but not covered");
+   LL|       |            } else {
+   LL|       |                println!("absolutely not covered");
+   LL|       |            }
+   LL|       |        }
    LL|      1|    }
    LL|       |
    LL|      1|    pub fn outer_both_covered(is_true: bool) {
    LL|      1|        println!("called and covered");
    LL|      1|        inner(is_true);
-   LL|      1|
+   LL|       |
    LL|      1|        fn inner(is_true: bool) {
    LL|      1|            if is_true {
    LL|      1|                println!("called and covered");
diff --git a/tests/crashes/125099.rs b/tests/crashes/125099.rs
deleted file mode 100644
index bfc8c8fdcf6..00000000000
--- a/tests/crashes/125099.rs
+++ /dev/null
@@ -1,24 +0,0 @@
-//@ known-bug: rust-lang/rust#125099
-
-pub trait ContFn<T>: Fn(T) -> Self::Future {
-    type Future;
-}
-impl<T, F> ContFn<T> for F
-where
-    F: Fn(T),
-{
-    type Future = ();
-}
-
-pub trait SeqHandler {
-    type Requires;
-    fn process<F: ContFn<Self::Requires>>() -> impl Sized;
-}
-
-pub struct ConvertToU64;
-impl SeqHandler for ConvertToU64 {
-    type Requires = u64;
-    fn process<F: ContFn<Self::Requires>>() -> impl Sized {}
-}
-
-fn main() {}
diff --git a/tests/crashes/127332.rs b/tests/crashes/127332.rs
deleted file mode 100644
index 5c14af01cec..00000000000
--- a/tests/crashes/127332.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-//@ known-bug: rust-lang/rust #127332
-
-async fn fun() {
-    enum Foo {
-        A { x: u32 },
-    }
-    let orig = Foo::A { x: 5 };
-    Foo::A { x: 6, ..orig };
-}
diff --git a/tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-abort.diff b/tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-abort.diff
new file mode 100644
index 00000000000..44673ea00a9
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-abort.diff
@@ -0,0 +1,108 @@
+- // MIR for `f` before ElaborateDrops
++ // MIR for `f` after ElaborateDrops
+  
+  fn f() -> () {
+      let mut _0: ();
+      let mut _1: !;
+      let _2: std::string::String;
+      let _6: ();
+      let mut _7: std::string::String;
++     let mut _8: bool;
+      scope 1 {
+          debug _a => _2;
+          let _3: i32;
+          scope 2 {
+              debug _b => _3;
+              let _4: std::string::String;
+              scope 3 {
+                  debug _c => _4;
+                  let _5: std::string::String;
+                  scope 4 {
+                      debug _d => _5;
+                  }
+              }
+          }
+      }
+  
+      bb0: {
++         _8 = const false;
+          StorageLive(_2);
+          _2 = String::new() -> [return: bb1, unwind: bb12];
+      }
+  
+      bb1: {
+          StorageLive(_3);
+          _3 = const 12_i32;
+          StorageLive(_4);
+          _4 = String::new() -> [return: bb2, unwind: bb11];
+      }
+  
+      bb2: {
++         _8 = const true;
+          StorageLive(_5);
+          _5 = String::new() -> [return: bb3, unwind: bb10];
+      }
+  
+      bb3: {
+          StorageLive(_6);
+          StorageLive(_7);
++         _8 = const false;
+          _7 = move _4;
+          _6 = std::mem::drop::<String>(move _7) -> [return: bb4, unwind: bb8];
+      }
+  
+      bb4: {
+          StorageDead(_7);
+          StorageDead(_6);
+          drop(_5) -> [return: bb5, unwind: bb10];
+      }
+  
+      bb5: {
+          StorageDead(_5);
+-         drop(_4) -> [return: bb6, unwind: bb11];
++         goto -> bb6;
+      }
+  
+      bb6: {
++         _8 = const false;
+          StorageDead(_4);
+          StorageDead(_3);
+          drop(_2) -> [return: bb7, unwind: bb12];
+      }
+  
+      bb7: {
+          StorageDead(_2);
+          tailcall g();
+      }
+  
+      bb8 (cleanup): {
+-         drop(_7) -> [return: bb9, unwind terminate(cleanup)];
++         goto -> bb9;
+      }
+  
+      bb9 (cleanup): {
+          drop(_5) -> [return: bb10, unwind terminate(cleanup)];
+      }
+  
+      bb10 (cleanup): {
+-         drop(_4) -> [return: bb11, unwind terminate(cleanup)];
++         goto -> bb14;
+      }
+  
+      bb11 (cleanup): {
+          drop(_2) -> [return: bb12, unwind terminate(cleanup)];
+      }
+  
+      bb12 (cleanup): {
+          resume;
++     }
++ 
++     bb13 (cleanup): {
++         drop(_4) -> [return: bb11, unwind terminate(cleanup)];
++     }
++ 
++     bb14 (cleanup): {
++         switchInt(_8) -> [0: bb11, otherwise: bb13];
+      }
+  }
+  
diff --git a/tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-unwind.diff b/tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-unwind.diff
new file mode 100644
index 00000000000..a6d33a24595
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f.ElaborateDrops.panic-unwind.diff
@@ -0,0 +1,109 @@
+- // MIR for `f` before ElaborateDrops
++ // MIR for `f` after ElaborateDrops
+  
+  fn f() -> () {
+      let mut _0: ();
+      let mut _1: !;
+      let _2: std::string::String;
+      let _6: ();
+      let mut _7: std::string::String;
++     let mut _8: bool;
+      scope 1 {
+          debug _a => _2;
+          let _3: i32;
+          scope 2 {
+              debug _b => _3;
+              let _4: std::string::String;
+              scope 3 {
+                  debug _c => _4;
+                  let _5: std::string::String;
+                  scope 4 {
+                      debug _d => _5;
+                  }
+              }
+          }
+      }
+  
+      bb0: {
++         _8 = const false;
+          StorageLive(_2);
+          _2 = String::new() -> [return: bb1, unwind continue];
+      }
+  
+      bb1: {
+          StorageLive(_3);
+          _3 = const 12_i32;
+          StorageLive(_4);
+          _4 = String::new() -> [return: bb2, unwind: bb11];
+      }
+  
+      bb2: {
++         _8 = const true;
+          StorageLive(_5);
+          _5 = String::new() -> [return: bb3, unwind: bb10];
+      }
+  
+      bb3: {
+          StorageLive(_6);
+          StorageLive(_7);
++         _8 = const false;
+          _7 = move _4;
+          _6 = std::mem::drop::<String>(move _7) -> [return: bb4, unwind: bb8];
+      }
+  
+      bb4: {
+          StorageDead(_7);
+          StorageDead(_6);
+          drop(_5) -> [return: bb5, unwind: bb10];
+      }
+  
+      bb5: {
+          StorageDead(_5);
+-         drop(_4) -> [return: bb6, unwind: bb11];
++         goto -> bb6;
+      }
+  
+      bb6: {
++         _8 = const false;
+          StorageDead(_4);
+          StorageDead(_3);
+-         drop(_2) -> [return: bb7, unwind continue];
++         drop(_2) -> [return: bb7, unwind: bb12];
+      }
+  
+      bb7: {
+          StorageDead(_2);
+          tailcall g();
+      }
+  
+      bb8 (cleanup): {
+-         drop(_7) -> [return: bb9, unwind terminate(cleanup)];
++         goto -> bb9;
+      }
+  
+      bb9 (cleanup): {
+          drop(_5) -> [return: bb10, unwind terminate(cleanup)];
+      }
+  
+      bb10 (cleanup): {
+-         drop(_4) -> [return: bb11, unwind terminate(cleanup)];
++         goto -> bb14;
+      }
+  
+      bb11 (cleanup): {
+          drop(_2) -> [return: bb12, unwind terminate(cleanup)];
+      }
+  
+      bb12 (cleanup): {
+          resume;
++     }
++ 
++     bb13 (cleanup): {
++         drop(_4) -> [return: bb11, unwind terminate(cleanup)];
++     }
++ 
++     bb14 (cleanup): {
++         switchInt(_8) -> [0: bb11, otherwise: bb13];
+      }
+  }
+  
diff --git a/tests/mir-opt/tail_call_drops.f.built.after.panic-abort.mir b/tests/mir-opt/tail_call_drops.f.built.after.panic-abort.mir
new file mode 100644
index 00000000000..2c3d62491d7
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f.built.after.panic-abort.mir
@@ -0,0 +1,118 @@
+// MIR for `f` after built
+
+fn f() -> () {
+    let mut _0: ();
+    let mut _1: !;
+    let _2: std::string::String;
+    let _6: ();
+    let mut _7: std::string::String;
+    scope 1 {
+        debug _a => _2;
+        let _3: i32;
+        scope 2 {
+            debug _b => _3;
+            let _4: std::string::String;
+            scope 3 {
+                debug _c => _4;
+                let _5: std::string::String;
+                scope 4 {
+                    debug _d => _5;
+                }
+            }
+        }
+    }
+
+    bb0: {
+        StorageLive(_2);
+        _2 = String::new() -> [return: bb1, unwind: bb17];
+    }
+
+    bb1: {
+        FakeRead(ForLet(None), _2);
+        StorageLive(_3);
+        _3 = const 12_i32;
+        FakeRead(ForLet(None), _3);
+        StorageLive(_4);
+        _4 = String::new() -> [return: bb2, unwind: bb16];
+    }
+
+    bb2: {
+        FakeRead(ForLet(None), _4);
+        StorageLive(_5);
+        _5 = String::new() -> [return: bb3, unwind: bb15];
+    }
+
+    bb3: {
+        FakeRead(ForLet(None), _5);
+        StorageLive(_6);
+        StorageLive(_7);
+        _7 = move _4;
+        _6 = std::mem::drop::<String>(move _7) -> [return: bb4, unwind: bb13];
+    }
+
+    bb4: {
+        StorageDead(_7);
+        StorageDead(_6);
+        drop(_5) -> [return: bb5, unwind: bb15];
+    }
+
+    bb5: {
+        StorageDead(_5);
+        drop(_4) -> [return: bb6, unwind: bb16];
+    }
+
+    bb6: {
+        StorageDead(_4);
+        StorageDead(_3);
+        drop(_2) -> [return: bb7, unwind: bb17];
+    }
+
+    bb7: {
+        StorageDead(_2);
+        tailcall g();
+    }
+
+    bb8: {
+        drop(_5) -> [return: bb9, unwind: bb15];
+    }
+
+    bb9: {
+        StorageDead(_5);
+        drop(_4) -> [return: bb10, unwind: bb16];
+    }
+
+    bb10: {
+        StorageDead(_4);
+        StorageDead(_3);
+        drop(_2) -> [return: bb11, unwind: bb17];
+    }
+
+    bb11: {
+        StorageDead(_2);
+        unreachable;
+    }
+
+    bb12: {
+        return;
+    }
+
+    bb13 (cleanup): {
+        drop(_7) -> [return: bb14, unwind terminate(cleanup)];
+    }
+
+    bb14 (cleanup): {
+        drop(_5) -> [return: bb15, unwind terminate(cleanup)];
+    }
+
+    bb15 (cleanup): {
+        drop(_4) -> [return: bb16, unwind terminate(cleanup)];
+    }
+
+    bb16 (cleanup): {
+        drop(_2) -> [return: bb17, unwind terminate(cleanup)];
+    }
+
+    bb17 (cleanup): {
+        resume;
+    }
+}
diff --git a/tests/mir-opt/tail_call_drops.f.built.after.panic-unwind.mir b/tests/mir-opt/tail_call_drops.f.built.after.panic-unwind.mir
new file mode 100644
index 00000000000..2c3d62491d7
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f.built.after.panic-unwind.mir
@@ -0,0 +1,118 @@
+// MIR for `f` after built
+
+fn f() -> () {
+    let mut _0: ();
+    let mut _1: !;
+    let _2: std::string::String;
+    let _6: ();
+    let mut _7: std::string::String;
+    scope 1 {
+        debug _a => _2;
+        let _3: i32;
+        scope 2 {
+            debug _b => _3;
+            let _4: std::string::String;
+            scope 3 {
+                debug _c => _4;
+                let _5: std::string::String;
+                scope 4 {
+                    debug _d => _5;
+                }
+            }
+        }
+    }
+
+    bb0: {
+        StorageLive(_2);
+        _2 = String::new() -> [return: bb1, unwind: bb17];
+    }
+
+    bb1: {
+        FakeRead(ForLet(None), _2);
+        StorageLive(_3);
+        _3 = const 12_i32;
+        FakeRead(ForLet(None), _3);
+        StorageLive(_4);
+        _4 = String::new() -> [return: bb2, unwind: bb16];
+    }
+
+    bb2: {
+        FakeRead(ForLet(None), _4);
+        StorageLive(_5);
+        _5 = String::new() -> [return: bb3, unwind: bb15];
+    }
+
+    bb3: {
+        FakeRead(ForLet(None), _5);
+        StorageLive(_6);
+        StorageLive(_7);
+        _7 = move _4;
+        _6 = std::mem::drop::<String>(move _7) -> [return: bb4, unwind: bb13];
+    }
+
+    bb4: {
+        StorageDead(_7);
+        StorageDead(_6);
+        drop(_5) -> [return: bb5, unwind: bb15];
+    }
+
+    bb5: {
+        StorageDead(_5);
+        drop(_4) -> [return: bb6, unwind: bb16];
+    }
+
+    bb6: {
+        StorageDead(_4);
+        StorageDead(_3);
+        drop(_2) -> [return: bb7, unwind: bb17];
+    }
+
+    bb7: {
+        StorageDead(_2);
+        tailcall g();
+    }
+
+    bb8: {
+        drop(_5) -> [return: bb9, unwind: bb15];
+    }
+
+    bb9: {
+        StorageDead(_5);
+        drop(_4) -> [return: bb10, unwind: bb16];
+    }
+
+    bb10: {
+        StorageDead(_4);
+        StorageDead(_3);
+        drop(_2) -> [return: bb11, unwind: bb17];
+    }
+
+    bb11: {
+        StorageDead(_2);
+        unreachable;
+    }
+
+    bb12: {
+        return;
+    }
+
+    bb13 (cleanup): {
+        drop(_7) -> [return: bb14, unwind terminate(cleanup)];
+    }
+
+    bb14 (cleanup): {
+        drop(_5) -> [return: bb15, unwind terminate(cleanup)];
+    }
+
+    bb15 (cleanup): {
+        drop(_4) -> [return: bb16, unwind terminate(cleanup)];
+    }
+
+    bb16 (cleanup): {
+        drop(_2) -> [return: bb17, unwind terminate(cleanup)];
+    }
+
+    bb17 (cleanup): {
+        resume;
+    }
+}
diff --git a/tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-abort.diff b/tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-abort.diff
new file mode 100644
index 00000000000..c7df2bb2207
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-abort.diff
@@ -0,0 +1,184 @@
+- // MIR for `f_with_arg` before ElaborateDrops
++ // MIR for `f_with_arg` after ElaborateDrops
+  
+  fn f_with_arg(_1: String, _2: String) -> () {
+      debug _arg1 => _1;
+      debug _arg2 => _2;
+      let mut _0: ();
+      let mut _3: !;
+      let _4: std::string::String;
+      let _8: ();
+      let mut _9: std::string::String;
+      let mut _10: std::string::String;
+      let mut _11: std::string::String;
++     let mut _12: bool;
+      scope 1 {
+          debug _a => _4;
+          let _5: i32;
+          scope 2 {
+              debug _b => _5;
+              let _6: std::string::String;
+              scope 3 {
+                  debug _c => _6;
+                  let _7: std::string::String;
+                  scope 4 {
+                      debug _d => _7;
+                  }
+              }
+          }
+      }
+  
+      bb0: {
++         _12 = const false;
+          StorageLive(_4);
+          _4 = String::new() -> [return: bb1, unwind: bb27];
+      }
+  
+      bb1: {
+          StorageLive(_5);
+          _5 = const 12_i32;
+          StorageLive(_6);
+          _6 = String::new() -> [return: bb2, unwind: bb26];
+      }
+  
+      bb2: {
++         _12 = const true;
+          StorageLive(_7);
+          _7 = String::new() -> [return: bb3, unwind: bb25];
+      }
+  
+      bb3: {
+          StorageLive(_8);
+          StorageLive(_9);
++         _12 = const false;
+          _9 = move _6;
+          _8 = std::mem::drop::<String>(move _9) -> [return: bb4, unwind: bb23];
+      }
+  
+      bb4: {
+          StorageDead(_9);
+          StorageDead(_8);
+          StorageLive(_10);
+          _10 = String::new() -> [return: bb5, unwind: bb24];
+      }
+  
+      bb5: {
+          StorageLive(_11);
+          _11 = String::new() -> [return: bb6, unwind: bb22];
+      }
+  
+      bb6: {
+          drop(_7) -> [return: bb7, unwind: bb20];
+      }
+  
+      bb7: {
+          StorageDead(_7);
+-         drop(_6) -> [return: bb8, unwind: bb18];
++         goto -> bb8;
+      }
+  
+      bb8: {
++         _12 = const false;
+          StorageDead(_6);
+          StorageDead(_5);
+          drop(_4) -> [return: bb9, unwind: bb16];
+      }
+  
+      bb9: {
+          StorageDead(_4);
+          drop(_2) -> [return: bb10, unwind: bb14];
+      }
+  
+      bb10: {
+          drop(_1) -> [return: bb11, unwind: bb12];
+      }
+  
+      bb11: {
+          tailcall g_with_arg(Spanned { node: move _10, span: $DIR/tail_call_drops.rs:36:23: 36:36 (#0) }, Spanned { node: move _11, span: $DIR/tail_call_drops.rs:36:38: 36:51 (#0) });
+      }
+  
+      bb12 (cleanup): {
+          drop(_10) -> [return: bb13, unwind terminate(cleanup)];
+      }
+  
+      bb13 (cleanup): {
+          drop(_11) -> [return: bb29, unwind terminate(cleanup)];
+      }
+  
+      bb14 (cleanup): {
+          drop(_10) -> [return: bb15, unwind terminate(cleanup)];
+      }
+  
+      bb15 (cleanup): {
+          drop(_11) -> [return: bb28, unwind terminate(cleanup)];
+      }
+  
+      bb16 (cleanup): {
+          drop(_10) -> [return: bb17, unwind terminate(cleanup)];
+      }
+  
+      bb17 (cleanup): {
+          drop(_11) -> [return: bb27, unwind terminate(cleanup)];
+      }
+  
+      bb18 (cleanup): {
+-         drop(_10) -> [return: bb19, unwind terminate(cleanup)];
++         goto -> bb19;
+      }
+  
+      bb19 (cleanup): {
+-         drop(_11) -> [return: bb26, unwind terminate(cleanup)];
++         goto -> bb26;
+      }
+  
+      bb20 (cleanup): {
+          drop(_10) -> [return: bb21, unwind terminate(cleanup)];
+      }
+  
+      bb21 (cleanup): {
+          drop(_11) -> [return: bb25, unwind terminate(cleanup)];
+      }
+  
+      bb22 (cleanup): {
+          drop(_10) -> [return: bb24, unwind terminate(cleanup)];
+      }
+  
+      bb23 (cleanup): {
+-         drop(_9) -> [return: bb24, unwind terminate(cleanup)];
++         goto -> bb24;
+      }
+  
+      bb24 (cleanup): {
+          drop(_7) -> [return: bb25, unwind terminate(cleanup)];
+      }
+  
+      bb25 (cleanup): {
+-         drop(_6) -> [return: bb26, unwind terminate(cleanup)];
++         goto -> bb31;
+      }
+  
+      bb26 (cleanup): {
+          drop(_4) -> [return: bb27, unwind terminate(cleanup)];
+      }
+  
+      bb27 (cleanup): {
+          drop(_2) -> [return: bb28, unwind terminate(cleanup)];
+      }
+  
+      bb28 (cleanup): {
+          drop(_1) -> [return: bb29, unwind terminate(cleanup)];
+      }
+  
+      bb29 (cleanup): {
+          resume;
++     }
++ 
++     bb30 (cleanup): {
++         drop(_6) -> [return: bb26, unwind terminate(cleanup)];
++     }
++ 
++     bb31 (cleanup): {
++         switchInt(_12) -> [0: bb26, otherwise: bb30];
+      }
+  }
+  
diff --git a/tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-unwind.diff b/tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-unwind.diff
new file mode 100644
index 00000000000..c7df2bb2207
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f_with_arg.ElaborateDrops.panic-unwind.diff
@@ -0,0 +1,184 @@
+- // MIR for `f_with_arg` before ElaborateDrops
++ // MIR for `f_with_arg` after ElaborateDrops
+  
+  fn f_with_arg(_1: String, _2: String) -> () {
+      debug _arg1 => _1;
+      debug _arg2 => _2;
+      let mut _0: ();
+      let mut _3: !;
+      let _4: std::string::String;
+      let _8: ();
+      let mut _9: std::string::String;
+      let mut _10: std::string::String;
+      let mut _11: std::string::String;
++     let mut _12: bool;
+      scope 1 {
+          debug _a => _4;
+          let _5: i32;
+          scope 2 {
+              debug _b => _5;
+              let _6: std::string::String;
+              scope 3 {
+                  debug _c => _6;
+                  let _7: std::string::String;
+                  scope 4 {
+                      debug _d => _7;
+                  }
+              }
+          }
+      }
+  
+      bb0: {
++         _12 = const false;
+          StorageLive(_4);
+          _4 = String::new() -> [return: bb1, unwind: bb27];
+      }
+  
+      bb1: {
+          StorageLive(_5);
+          _5 = const 12_i32;
+          StorageLive(_6);
+          _6 = String::new() -> [return: bb2, unwind: bb26];
+      }
+  
+      bb2: {
++         _12 = const true;
+          StorageLive(_7);
+          _7 = String::new() -> [return: bb3, unwind: bb25];
+      }
+  
+      bb3: {
+          StorageLive(_8);
+          StorageLive(_9);
++         _12 = const false;
+          _9 = move _6;
+          _8 = std::mem::drop::<String>(move _9) -> [return: bb4, unwind: bb23];
+      }
+  
+      bb4: {
+          StorageDead(_9);
+          StorageDead(_8);
+          StorageLive(_10);
+          _10 = String::new() -> [return: bb5, unwind: bb24];
+      }
+  
+      bb5: {
+          StorageLive(_11);
+          _11 = String::new() -> [return: bb6, unwind: bb22];
+      }
+  
+      bb6: {
+          drop(_7) -> [return: bb7, unwind: bb20];
+      }
+  
+      bb7: {
+          StorageDead(_7);
+-         drop(_6) -> [return: bb8, unwind: bb18];
++         goto -> bb8;
+      }
+  
+      bb8: {
++         _12 = const false;
+          StorageDead(_6);
+          StorageDead(_5);
+          drop(_4) -> [return: bb9, unwind: bb16];
+      }
+  
+      bb9: {
+          StorageDead(_4);
+          drop(_2) -> [return: bb10, unwind: bb14];
+      }
+  
+      bb10: {
+          drop(_1) -> [return: bb11, unwind: bb12];
+      }
+  
+      bb11: {
+          tailcall g_with_arg(Spanned { node: move _10, span: $DIR/tail_call_drops.rs:36:23: 36:36 (#0) }, Spanned { node: move _11, span: $DIR/tail_call_drops.rs:36:38: 36:51 (#0) });
+      }
+  
+      bb12 (cleanup): {
+          drop(_10) -> [return: bb13, unwind terminate(cleanup)];
+      }
+  
+      bb13 (cleanup): {
+          drop(_11) -> [return: bb29, unwind terminate(cleanup)];
+      }
+  
+      bb14 (cleanup): {
+          drop(_10) -> [return: bb15, unwind terminate(cleanup)];
+      }
+  
+      bb15 (cleanup): {
+          drop(_11) -> [return: bb28, unwind terminate(cleanup)];
+      }
+  
+      bb16 (cleanup): {
+          drop(_10) -> [return: bb17, unwind terminate(cleanup)];
+      }
+  
+      bb17 (cleanup): {
+          drop(_11) -> [return: bb27, unwind terminate(cleanup)];
+      }
+  
+      bb18 (cleanup): {
+-         drop(_10) -> [return: bb19, unwind terminate(cleanup)];
++         goto -> bb19;
+      }
+  
+      bb19 (cleanup): {
+-         drop(_11) -> [return: bb26, unwind terminate(cleanup)];
++         goto -> bb26;
+      }
+  
+      bb20 (cleanup): {
+          drop(_10) -> [return: bb21, unwind terminate(cleanup)];
+      }
+  
+      bb21 (cleanup): {
+          drop(_11) -> [return: bb25, unwind terminate(cleanup)];
+      }
+  
+      bb22 (cleanup): {
+          drop(_10) -> [return: bb24, unwind terminate(cleanup)];
+      }
+  
+      bb23 (cleanup): {
+-         drop(_9) -> [return: bb24, unwind terminate(cleanup)];
++         goto -> bb24;
+      }
+  
+      bb24 (cleanup): {
+          drop(_7) -> [return: bb25, unwind terminate(cleanup)];
+      }
+  
+      bb25 (cleanup): {
+-         drop(_6) -> [return: bb26, unwind terminate(cleanup)];
++         goto -> bb31;
+      }
+  
+      bb26 (cleanup): {
+          drop(_4) -> [return: bb27, unwind terminate(cleanup)];
+      }
+  
+      bb27 (cleanup): {
+          drop(_2) -> [return: bb28, unwind terminate(cleanup)];
+      }
+  
+      bb28 (cleanup): {
+          drop(_1) -> [return: bb29, unwind terminate(cleanup)];
+      }
+  
+      bb29 (cleanup): {
+          resume;
++     }
++ 
++     bb30 (cleanup): {
++         drop(_6) -> [return: bb26, unwind terminate(cleanup)];
++     }
++ 
++     bb31 (cleanup): {
++         switchInt(_12) -> [0: bb26, otherwise: bb30];
+      }
+  }
+  
diff --git a/tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-abort.mir b/tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-abort.mir
new file mode 100644
index 00000000000..744f1989acc
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-abort.mir
@@ -0,0 +1,202 @@
+// MIR for `f_with_arg` after built
+
+fn f_with_arg(_1: String, _2: String) -> () {
+    debug _arg1 => _1;
+    debug _arg2 => _2;
+    let mut _0: ();
+    let mut _3: !;
+    let _4: std::string::String;
+    let _8: ();
+    let mut _9: std::string::String;
+    let mut _10: std::string::String;
+    let mut _11: std::string::String;
+    scope 1 {
+        debug _a => _4;
+        let _5: i32;
+        scope 2 {
+            debug _b => _5;
+            let _6: std::string::String;
+            scope 3 {
+                debug _c => _6;
+                let _7: std::string::String;
+                scope 4 {
+                    debug _d => _7;
+                }
+            }
+        }
+    }
+
+    bb0: {
+        StorageLive(_4);
+        _4 = String::new() -> [return: bb1, unwind: bb34];
+    }
+
+    bb1: {
+        FakeRead(ForLet(None), _4);
+        StorageLive(_5);
+        _5 = const 12_i32;
+        FakeRead(ForLet(None), _5);
+        StorageLive(_6);
+        _6 = String::new() -> [return: bb2, unwind: bb33];
+    }
+
+    bb2: {
+        FakeRead(ForLet(None), _6);
+        StorageLive(_7);
+        _7 = String::new() -> [return: bb3, unwind: bb32];
+    }
+
+    bb3: {
+        FakeRead(ForLet(None), _7);
+        StorageLive(_8);
+        StorageLive(_9);
+        _9 = move _6;
+        _8 = std::mem::drop::<String>(move _9) -> [return: bb4, unwind: bb30];
+    }
+
+    bb4: {
+        StorageDead(_9);
+        StorageDead(_8);
+        StorageLive(_10);
+        _10 = String::new() -> [return: bb5, unwind: bb31];
+    }
+
+    bb5: {
+        StorageLive(_11);
+        _11 = String::new() -> [return: bb6, unwind: bb29];
+    }
+
+    bb6: {
+        drop(_7) -> [return: bb7, unwind: bb27];
+    }
+
+    bb7: {
+        StorageDead(_7);
+        drop(_6) -> [return: bb8, unwind: bb25];
+    }
+
+    bb8: {
+        StorageDead(_6);
+        StorageDead(_5);
+        drop(_4) -> [return: bb9, unwind: bb23];
+    }
+
+    bb9: {
+        StorageDead(_4);
+        drop(_2) -> [return: bb10, unwind: bb21];
+    }
+
+    bb10: {
+        drop(_1) -> [return: bb11, unwind: bb19];
+    }
+
+    bb11: {
+        tailcall g_with_arg(Spanned { node: move _10, span: $DIR/tail_call_drops.rs:36:23: 36:36 (#0) }, Spanned { node: move _11, span: $DIR/tail_call_drops.rs:36:38: 36:51 (#0) });
+    }
+
+    bb12: {
+        StorageDead(_11);
+        StorageDead(_10);
+        drop(_7) -> [return: bb13, unwind: bb32];
+    }
+
+    bb13: {
+        StorageDead(_7);
+        drop(_6) -> [return: bb14, unwind: bb33];
+    }
+
+    bb14: {
+        StorageDead(_6);
+        StorageDead(_5);
+        drop(_4) -> [return: bb15, unwind: bb34];
+    }
+
+    bb15: {
+        StorageDead(_4);
+        unreachable;
+    }
+
+    bb16: {
+        drop(_2) -> [return: bb17, unwind: bb35];
+    }
+
+    bb17: {
+        drop(_1) -> [return: bb18, unwind: bb36];
+    }
+
+    bb18: {
+        return;
+    }
+
+    bb19 (cleanup): {
+        drop(_10) -> [return: bb20, unwind terminate(cleanup)];
+    }
+
+    bb20 (cleanup): {
+        drop(_11) -> [return: bb36, unwind terminate(cleanup)];
+    }
+
+    bb21 (cleanup): {
+        drop(_10) -> [return: bb22, unwind terminate(cleanup)];
+    }
+
+    bb22 (cleanup): {
+        drop(_11) -> [return: bb35, unwind terminate(cleanup)];
+    }
+
+    bb23 (cleanup): {
+        drop(_10) -> [return: bb24, unwind terminate(cleanup)];
+    }
+
+    bb24 (cleanup): {
+        drop(_11) -> [return: bb34, unwind terminate(cleanup)];
+    }
+
+    bb25 (cleanup): {
+        drop(_10) -> [return: bb26, unwind terminate(cleanup)];
+    }
+
+    bb26 (cleanup): {
+        drop(_11) -> [return: bb33, unwind terminate(cleanup)];
+    }
+
+    bb27 (cleanup): {
+        drop(_10) -> [return: bb28, unwind terminate(cleanup)];
+    }
+
+    bb28 (cleanup): {
+        drop(_11) -> [return: bb32, unwind terminate(cleanup)];
+    }
+
+    bb29 (cleanup): {
+        drop(_10) -> [return: bb31, unwind terminate(cleanup)];
+    }
+
+    bb30 (cleanup): {
+        drop(_9) -> [return: bb31, unwind terminate(cleanup)];
+    }
+
+    bb31 (cleanup): {
+        drop(_7) -> [return: bb32, unwind terminate(cleanup)];
+    }
+
+    bb32 (cleanup): {
+        drop(_6) -> [return: bb33, unwind terminate(cleanup)];
+    }
+
+    bb33 (cleanup): {
+        drop(_4) -> [return: bb34, unwind terminate(cleanup)];
+    }
+
+    bb34 (cleanup): {
+        drop(_2) -> [return: bb35, unwind terminate(cleanup)];
+    }
+
+    bb35 (cleanup): {
+        drop(_1) -> [return: bb36, unwind terminate(cleanup)];
+    }
+
+    bb36 (cleanup): {
+        resume;
+    }
+}
diff --git a/tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-unwind.mir b/tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-unwind.mir
new file mode 100644
index 00000000000..744f1989acc
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.f_with_arg.built.after.panic-unwind.mir
@@ -0,0 +1,202 @@
+// MIR for `f_with_arg` after built
+
+fn f_with_arg(_1: String, _2: String) -> () {
+    debug _arg1 => _1;
+    debug _arg2 => _2;
+    let mut _0: ();
+    let mut _3: !;
+    let _4: std::string::String;
+    let _8: ();
+    let mut _9: std::string::String;
+    let mut _10: std::string::String;
+    let mut _11: std::string::String;
+    scope 1 {
+        debug _a => _4;
+        let _5: i32;
+        scope 2 {
+            debug _b => _5;
+            let _6: std::string::String;
+            scope 3 {
+                debug _c => _6;
+                let _7: std::string::String;
+                scope 4 {
+                    debug _d => _7;
+                }
+            }
+        }
+    }
+
+    bb0: {
+        StorageLive(_4);
+        _4 = String::new() -> [return: bb1, unwind: bb34];
+    }
+
+    bb1: {
+        FakeRead(ForLet(None), _4);
+        StorageLive(_5);
+        _5 = const 12_i32;
+        FakeRead(ForLet(None), _5);
+        StorageLive(_6);
+        _6 = String::new() -> [return: bb2, unwind: bb33];
+    }
+
+    bb2: {
+        FakeRead(ForLet(None), _6);
+        StorageLive(_7);
+        _7 = String::new() -> [return: bb3, unwind: bb32];
+    }
+
+    bb3: {
+        FakeRead(ForLet(None), _7);
+        StorageLive(_8);
+        StorageLive(_9);
+        _9 = move _6;
+        _8 = std::mem::drop::<String>(move _9) -> [return: bb4, unwind: bb30];
+    }
+
+    bb4: {
+        StorageDead(_9);
+        StorageDead(_8);
+        StorageLive(_10);
+        _10 = String::new() -> [return: bb5, unwind: bb31];
+    }
+
+    bb5: {
+        StorageLive(_11);
+        _11 = String::new() -> [return: bb6, unwind: bb29];
+    }
+
+    bb6: {
+        drop(_7) -> [return: bb7, unwind: bb27];
+    }
+
+    bb7: {
+        StorageDead(_7);
+        drop(_6) -> [return: bb8, unwind: bb25];
+    }
+
+    bb8: {
+        StorageDead(_6);
+        StorageDead(_5);
+        drop(_4) -> [return: bb9, unwind: bb23];
+    }
+
+    bb9: {
+        StorageDead(_4);
+        drop(_2) -> [return: bb10, unwind: bb21];
+    }
+
+    bb10: {
+        drop(_1) -> [return: bb11, unwind: bb19];
+    }
+
+    bb11: {
+        tailcall g_with_arg(Spanned { node: move _10, span: $DIR/tail_call_drops.rs:36:23: 36:36 (#0) }, Spanned { node: move _11, span: $DIR/tail_call_drops.rs:36:38: 36:51 (#0) });
+    }
+
+    bb12: {
+        StorageDead(_11);
+        StorageDead(_10);
+        drop(_7) -> [return: bb13, unwind: bb32];
+    }
+
+    bb13: {
+        StorageDead(_7);
+        drop(_6) -> [return: bb14, unwind: bb33];
+    }
+
+    bb14: {
+        StorageDead(_6);
+        StorageDead(_5);
+        drop(_4) -> [return: bb15, unwind: bb34];
+    }
+
+    bb15: {
+        StorageDead(_4);
+        unreachable;
+    }
+
+    bb16: {
+        drop(_2) -> [return: bb17, unwind: bb35];
+    }
+
+    bb17: {
+        drop(_1) -> [return: bb18, unwind: bb36];
+    }
+
+    bb18: {
+        return;
+    }
+
+    bb19 (cleanup): {
+        drop(_10) -> [return: bb20, unwind terminate(cleanup)];
+    }
+
+    bb20 (cleanup): {
+        drop(_11) -> [return: bb36, unwind terminate(cleanup)];
+    }
+
+    bb21 (cleanup): {
+        drop(_10) -> [return: bb22, unwind terminate(cleanup)];
+    }
+
+    bb22 (cleanup): {
+        drop(_11) -> [return: bb35, unwind terminate(cleanup)];
+    }
+
+    bb23 (cleanup): {
+        drop(_10) -> [return: bb24, unwind terminate(cleanup)];
+    }
+
+    bb24 (cleanup): {
+        drop(_11) -> [return: bb34, unwind terminate(cleanup)];
+    }
+
+    bb25 (cleanup): {
+        drop(_10) -> [return: bb26, unwind terminate(cleanup)];
+    }
+
+    bb26 (cleanup): {
+        drop(_11) -> [return: bb33, unwind terminate(cleanup)];
+    }
+
+    bb27 (cleanup): {
+        drop(_10) -> [return: bb28, unwind terminate(cleanup)];
+    }
+
+    bb28 (cleanup): {
+        drop(_11) -> [return: bb32, unwind terminate(cleanup)];
+    }
+
+    bb29 (cleanup): {
+        drop(_10) -> [return: bb31, unwind terminate(cleanup)];
+    }
+
+    bb30 (cleanup): {
+        drop(_9) -> [return: bb31, unwind terminate(cleanup)];
+    }
+
+    bb31 (cleanup): {
+        drop(_7) -> [return: bb32, unwind terminate(cleanup)];
+    }
+
+    bb32 (cleanup): {
+        drop(_6) -> [return: bb33, unwind terminate(cleanup)];
+    }
+
+    bb33 (cleanup): {
+        drop(_4) -> [return: bb34, unwind terminate(cleanup)];
+    }
+
+    bb34 (cleanup): {
+        drop(_2) -> [return: bb35, unwind terminate(cleanup)];
+    }
+
+    bb35 (cleanup): {
+        drop(_1) -> [return: bb36, unwind terminate(cleanup)];
+    }
+
+    bb36 (cleanup): {
+        resume;
+    }
+}
diff --git a/tests/mir-opt/tail_call_drops.rs b/tests/mir-opt/tail_call_drops.rs
new file mode 100644
index 00000000000..56f4852a95f
--- /dev/null
+++ b/tests/mir-opt/tail_call_drops.rs
@@ -0,0 +1,41 @@
+// skip-filecheck
+// EMIT_MIR_FOR_EACH_PANIC_STRATEGY
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+// EMIT_MIR tail_call_drops.f.built.after.mir
+//   Expected result:
+//   drop(_d) -> drop(_c) -> drop(_a) -> tailcall g()
+//
+// EMIT_MIR tail_call_drops.f.ElaborateDrops.diff
+//   Expected result:
+//   drop(_d) ->             drop(_a) -> tailcall g()
+fn f() {
+    let _a = String::new();
+    let _b = 12;
+    let _c = String::new();
+    let _d = String::new();
+
+    drop(_c);
+
+    become g();
+}
+
+fn g() {}
+
+// EMIT_MIR tail_call_drops.f_with_arg.built.after.mir
+// EMIT_MIR tail_call_drops.f_with_arg.ElaborateDrops.diff
+fn f_with_arg(_arg1: String, _arg2: String) {
+    let _a = String::new();
+    let _b = 12;
+    let _c = String::new();
+    let _d = String::new();
+
+    drop(_c);
+
+    become g_with_arg(String::new(), String::new());
+}
+
+fn g_with_arg(_arg1: String, _arg2: String) {}
+
+fn main() {}
diff --git a/tests/pretty/issue-4264.pp b/tests/pretty/issue-4264.pp
index 018ccf82dae..fa958d9f1e8 100644
--- a/tests/pretty/issue-4264.pp
+++ b/tests/pretty/issue-4264.pp
@@ -29,16 +29,17 @@ fn bar() ({
 
 
 
-    ({
-        let res =
-            ((::alloc::fmt::format as
-                    for<'a> fn(Arguments<'a>) -> String {format})(((format_arguments::new_const
-                        as
-                        fn(&[&'static str; 1]) -> Arguments<'_> {Arguments::<'_>::new_const::<1>})((&([("test"
-                                    as &str)] as [&str; 1]) as &[&str; 1])) as Arguments<'_>))
-                as String);
-        (res as String)
-    } as String);
+    ((::alloc::__export::must_use as
+            fn(String) -> String {must_use::<String>})(({
+            let res =
+                ((::alloc::fmt::format as
+                        for<'a> fn(Arguments<'a>) -> String {format})(((format_arguments::new_const
+                            as
+                            fn(&[&'static str; 1]) -> Arguments<'_> {Arguments::<'_>::new_const::<1>})((&([("test"
+                                        as &str)] as [&str; 1]) as &[&str; 1])) as Arguments<'_>))
+                    as String);
+            (res as String)
+        } as String)) as String);
 } as ())
 type Foo = [i32; (3 as usize)];
 struct Bar {
diff --git a/tests/run-make/emit-path-unhashed/Makefile b/tests/run-make/emit-path-unhashed/Makefile
deleted file mode 100644
index 611f8578140..00000000000
--- a/tests/run-make/emit-path-unhashed/Makefile
+++ /dev/null
@@ -1,37 +0,0 @@
-include ../tools.mk
-
-OUT=$(TMPDIR)/emit
-
-# --emit KIND=PATH should not affect crate hash vs --emit KIND
-all: $(OUT)/a/libfoo.rlib $(OUT)/b/libfoo.rlib $(OUT)/c/libfoo.rlib \
-		$(TMPDIR)/libfoo.rlib
-	$(RUSTC) -Zls=root $(TMPDIR)/libfoo.rlib > $(TMPDIR)/base.txt
-	$(RUSTC) -Zls=root $(OUT)/a/libfoo.rlib > $(TMPDIR)/a.txt
-	$(RUSTC) -Zls=root $(OUT)/b/libfoo.rlib > $(TMPDIR)/b.txt
-	$(RUSTC) -Zls=root $(OUT)/c/libfoo.rlib > $(TMPDIR)/c.txt
-
-	diff $(TMPDIR)/base.txt $(TMPDIR)/a.txt
-	diff $(TMPDIR)/base.txt $(TMPDIR)/b.txt
-
-	# Different KIND parameters do affect hash.
-	# diff exits 1 on difference, 2 on trouble
-	diff $(TMPDIR)/base.txt $(TMPDIR)/c.txt ; test "$$?" -eq 1
-
-# Default output name
-$(TMPDIR)/libfoo.rlib: foo.rs
-	$(RUSTC) --emit link foo.rs
-
-# Output named with -o
-$(OUT)/a/libfoo.rlib: foo.rs
-	mkdir -p $(OUT)/a
-	$(RUSTC) --emit link -o $@ foo.rs
-
-# Output named with KIND=PATH
-$(OUT)/b/libfoo.rlib: foo.rs
-	mkdir -p $(OUT)/b
-	$(RUSTC) --emit link=$@ foo.rs
-
-# Output multiple kinds
-$(OUT)/c/libfoo.rlib: foo.rs
-	mkdir -p $(OUT)/c
-	$(RUSTC) --emit link=$@,metadata foo.rs
diff --git a/tests/run-make/emit-path-unhashed/rmake.rs b/tests/run-make/emit-path-unhashed/rmake.rs
new file mode 100644
index 00000000000..ce56c197588
--- /dev/null
+++ b/tests/run-make/emit-path-unhashed/rmake.rs
@@ -0,0 +1,34 @@
+// Specifying how rustc outputs a file can be done in different ways, such as
+// the output flag or the KIND=NAME syntax. However, some of these methods used
+// to result in different hashes on output files even though they yielded the
+// exact same result otherwise. This was fixed in #86045, and this test checks
+// that the hash is only modified when the output is made different, such as by
+// adding a new output type (in this test, metadata).
+// See https://github.com/rust-lang/rust/issues/86044
+
+use run_make_support::{diff, fs_wrapper, rustc};
+
+fn main() {
+    fs_wrapper::create_dir("emit");
+    fs_wrapper::create_dir("emit/a");
+    fs_wrapper::create_dir("emit/b");
+    fs_wrapper::create_dir("emit/c");
+    // The default output name.
+    rustc().emit("link").input("foo.rs").run();
+    // The output is named with the output flag.
+    rustc().emit("link").output("emit/a/libfoo.rlib").input("foo.rs").run();
+    // The output is named with link=NAME.
+    rustc().emit("link=emit/b/libfoo.rlib").input("foo.rs").run();
+    // The output is named with link=NAME, with an additional kind tacked on.
+    rustc().emit("link=emit/c/libfoo.rlib,metadata").input("foo.rs").run();
+
+    let base = rustc().arg("-Zls=root").input("libfoo.rlib").run().stdout_utf8();
+    let a = rustc().arg("-Zls=root").input("emit/a/libfoo.rlib").run().stdout_utf8();
+    let b = rustc().arg("-Zls=root").input("emit/b/libfoo.rlib").run().stdout_utf8();
+    let c = rustc().arg("-Zls=root").input("emit/c/libfoo.rlib").run().stdout_utf8();
+    // Both the output flag and link=NAME methods do not modify the hash of the output file.
+    diff().expected_text("base", &base).actual_text("a", a).run();
+    diff().expected_text("base", &base).actual_text("b", b).run();
+    // However, having multiple types of outputs does modify the hash.
+    diff().expected_text("base", &base).actual_text("c", c).run_fail();
+}
diff --git a/tests/run-make/emit-shared-files/Makefile b/tests/run-make/emit-shared-files/Makefile
deleted file mode 100644
index 27c72b00368..00000000000
--- a/tests/run-make/emit-shared-files/Makefile
+++ /dev/null
@@ -1,46 +0,0 @@
-include ../tools.mk
-
-INVOCATION_ONLY = $(TMPDIR)/invocation-only
-TOOLCHAIN_ONLY = $(TMPDIR)/toolchain-only
-ALL_SHARED = $(TMPDIR)/all-shared
-
-all: invocation-only toolchain-only all-shared
-
-invocation-only:
-	$(RUSTDOC) -Z unstable-options --emit=invocation-specific --output $(INVOCATION_ONLY) --resource-suffix=-xxx --theme y.css --extend-css z.css x.rs
-	[ -e $(INVOCATION_ONLY)/search-index-xxx.js ]
-	[ -e $(INVOCATION_ONLY)/settings.html ]
-	[ -e $(INVOCATION_ONLY)/x/all.html ]
-	[ -e $(INVOCATION_ONLY)/x/index.html ]
-	[ -e $(INVOCATION_ONLY)/theme-xxx.css ] # generated from z.css
-	! [ -e $(INVOCATION_ONLY)/storage-xxx.js ]
-	! [ -e $(INVOCATION_ONLY)/SourceSerif4-It.ttf.woff2 ]
-
-	# FIXME: this probably shouldn't have a suffix
-	[ -e $(INVOCATION_ONLY)/y-xxx.css ]
-	# FIXME: this is technically incorrect (see `write_shared`)
-	! [ -e $(INVOCATION_ONLY)/main-xxx.js ]
-
-toolchain-only:
-	$(RUSTDOC) -Z unstable-options --emit=toolchain-shared-resources --output $(TOOLCHAIN_ONLY) --resource-suffix=-xxx --extend-css z.css x.rs
-	[ -e $(TOOLCHAIN_ONLY)/static.files/storage-*.js ]
-	[ -e $(TOOLCHAIN_ONLY)/static.files/SourceSerif4-It-*.ttf.woff2 ]
-	! [ -e $(TOOLCHAIN_ONLY)/search-index-xxx.js ]
-	! [ -e $(TOOLCHAIN_ONLY)/x/index.html ]
-	! [ -e $(TOOLCHAIN_ONLY)/theme.css ]
-
-	[ -e $(TOOLCHAIN_ONLY)/static.files/main-*.js ]
-	! [ -e $(TOOLCHAIN_ONLY)/y-xxx.css ]
-
-all-shared:
-	$(RUSTDOC) -Z unstable-options --emit=toolchain-shared-resources,unversioned-shared-resources --output $(ALL_SHARED) --resource-suffix=-xxx --extend-css z.css x.rs
-	[ -e $(ALL_SHARED)/static.files/storage-*.js ]
-	[ -e $(ALL_SHARED)/static.files/SourceSerif4-It-*.ttf.woff2 ]
-	! [ -e $(ALL_SHARED)/search-index-xxx.js ]
-	! [ -e $(ALL_SHARED)/settings.html ]
-	! [ -e $(ALL_SHARED)/x ]
-	! [ -e $(ALL_SHARED)/src ]
-	! [ -e $(ALL_SHARED)/theme.css ]
-
-	[ -e $(ALL_SHARED)/static.files/main-*.js ]
-	! [ -e $(ALL_SHARED)/y-xxx.css ]
diff --git a/tests/run-make/emit-shared-files/rmake.rs b/tests/run-make/emit-shared-files/rmake.rs
new file mode 100644
index 00000000000..33c12310246
--- /dev/null
+++ b/tests/run-make/emit-shared-files/rmake.rs
@@ -0,0 +1,102 @@
+// This test checks the functionality of one of rustdoc's unstable options,
+// the ability to specify emit restrictions with `--emit`.
+// `invocation-only` should only emit crate-specific files.
+// `toolchain-only` should only emit toolchain-specific files.
+// `all-shared` should only emit files that can be shared between crates.
+// See https://github.com/rust-lang/rust/pull/83478
+
+use run_make_support::{has_extension, has_prefix, rustdoc, shallow_find_files};
+use std::path::Path;
+
+fn main() {
+    rustdoc()
+        .arg("-Zunstable-options")
+        .arg("--emit=invocation-specific")
+        .output("invocation-only")
+        .arg("--resource-suffix=-xxx")
+        .args(&["--theme", "y.css"])
+        .args(&["--extend-css", "z.css"])
+        .input("x.rs")
+        .run();
+    assert!(Path::new("invocation-only/search-index-xxx.js").exists());
+    assert!(Path::new("invocation-only/settings.html").exists());
+    assert!(Path::new("invocation-only/x/all.html").exists());
+    assert!(Path::new("invocation-only/x/index.html").exists());
+    assert!(Path::new("invocation-only/theme-xxx.css").exists()); // generated from z.css
+    assert!(!Path::new("invocation-only/storage-xxx.js").exists());
+    assert!(!Path::new("invocation-only/SourceSerif4-It.ttf.woff2").exists());
+    // FIXME: this probably shouldn't have a suffix
+    assert!(Path::new("invocation-only/y-xxx.css").exists());
+    // FIXME: this is technically incorrect (see `write_shared`)
+    assert!(!Path::new("invocation-only/main-xxx.js").exists());
+
+    rustdoc()
+        .arg("-Zunstable-options")
+        .arg("--emit=toolchain-shared-resources")
+        .output("toolchain-only")
+        .arg("--resource-suffix=-xxx")
+        .args(&["--extend-css", "z.css"])
+        .input("x.rs")
+        .run();
+    assert_eq!(
+        shallow_find_files("toolchain-only/static.files", |path| {
+            has_prefix(path, "storage-") && has_extension(path, "js")
+        })
+        .len(),
+        1
+    );
+    assert_eq!(
+        shallow_find_files("toolchain-only/static.files", |path| {
+            has_prefix(path, "SourceSerif4-It-") && has_extension(path, "woff2")
+        })
+        .len(),
+        1
+    );
+    assert_eq!(
+        shallow_find_files("toolchain-only/static.files", |path| {
+            has_prefix(path, "main-") && has_extension(path, "js")
+        })
+        .len(),
+        1
+    );
+    assert!(!Path::new("toolchain-only/search-index-xxx.js").exists());
+    assert!(!Path::new("toolchain-only/x/index.html").exists());
+    assert!(!Path::new("toolchain-only/theme.css").exists());
+    assert!(!Path::new("toolchain-only/y-xxx.css").exists());
+
+    rustdoc()
+        .arg("-Zunstable-options")
+        .arg("--emit=toolchain-shared-resources,unversioned-shared-resources")
+        .output("all-shared")
+        .arg("--resource-suffix=-xxx")
+        .args(&["--extend-css", "z.css"])
+        .input("x.rs")
+        .run();
+    assert_eq!(
+        shallow_find_files("all-shared/static.files", |path| {
+            has_prefix(path, "storage-") && has_extension(path, "js")
+        })
+        .len(),
+        1
+    );
+    assert_eq!(
+        shallow_find_files("all-shared/static.files", |path| {
+            has_prefix(path, "SourceSerif4-It-") && has_extension(path, "woff2")
+        })
+        .len(),
+        1
+    );
+    assert!(!Path::new("all-shared/search-index-xxx.js").exists());
+    assert!(!Path::new("all-shared/settings.html").exists());
+    assert!(!Path::new("all-shared/x").exists());
+    assert!(!Path::new("all-shared/src").exists());
+    assert!(!Path::new("all-shared/theme.css").exists());
+    assert_eq!(
+        shallow_find_files("all-shared/static.files", |path| {
+            has_prefix(path, "main-") && has_extension(path, "js")
+        })
+        .len(),
+        1
+    );
+    assert!(!Path::new("all-shared/y-xxx.css").exists());
+}
diff --git a/tests/run-make/intrinsic-unreachable/Makefile b/tests/run-make/intrinsic-unreachable/Makefile
deleted file mode 100644
index ff9cc57098c..00000000000
--- a/tests/run-make/intrinsic-unreachable/Makefile
+++ /dev/null
@@ -1,12 +0,0 @@
-include ../tools.mk
-
-# needs-asm-support
-# ignore-windows-msvc
-#
-# Because of Windows exception handling, the code is not necessarily any shorter.
-# https://github.com/llvm-mirror/llvm/commit/64b2297786f7fd6f5fa24cdd4db0298fbf211466
-
-all:
-	$(RUSTC) -O --emit asm exit-ret.rs
-	$(RUSTC) -O --emit asm exit-unreachable.rs
-	test `wc -l < $(TMPDIR)/exit-unreachable.s` -lt `wc -l < $(TMPDIR)/exit-ret.s`
diff --git a/tests/run-make/intrinsic-unreachable/rmake.rs b/tests/run-make/intrinsic-unreachable/rmake.rs
new file mode 100644
index 00000000000..7e78c8288b8
--- /dev/null
+++ b/tests/run-make/intrinsic-unreachable/rmake.rs
@@ -0,0 +1,20 @@
+// intrinsics::unreachable tells the compiler that a certain point in the code
+// is not reachable by any means, which enables some useful optimizations.
+// In this test, exit-unreachable contains this instruction and exit-ret does not,
+// which means the emitted artifacts should be shorter in length.
+// See https://github.com/rust-lang/rust/pull/16970
+
+//@ needs-asm-support
+//@ ignore-windows
+// Reason: Because of Windows exception handling, the code is not necessarily any shorter.
+
+use run_make_support::{fs_wrapper, rustc};
+
+fn main() {
+    rustc().opt().emit("asm").input("exit-ret.rs").run();
+    rustc().opt().emit("asm").input("exit-unreachable.rs").run();
+    assert!(
+        fs_wrapper::read_to_string("exit-unreachable.s").lines().count()
+            < fs_wrapper::read_to_string("exit-ret.s").lines().count()
+    );
+}
diff --git a/tests/run-make/issue-37839/Makefile b/tests/run-make/issue-37839/Makefile
deleted file mode 100644
index 6bad27b7bdc..00000000000
--- a/tests/run-make/issue-37839/Makefile
+++ /dev/null
@@ -1,7 +0,0 @@
-# ignore-cross-compile
-include ../tools.mk
-
-all:
-	$(RUSTC) a.rs && $(RUSTC) b.rs
-	$(BARE_RUSTC) c.rs -L dependency=$(TMPDIR) --extern b=$(TMPDIR)/libb.rlib \
-		--out-dir=$(TMPDIR)
diff --git a/tests/run-make/llvm-ident/rmake.rs b/tests/run-make/llvm-ident/rmake.rs
index 6934a4b36d0..9699d0579f6 100644
--- a/tests/run-make/llvm-ident/rmake.rs
+++ b/tests/run-make/llvm-ident/rmake.rs
@@ -2,9 +2,9 @@
 //@ ignore-cross-compile
 
 use run_make_support::llvm::llvm_bin_dir;
-use run_make_support::{cmd, env_var, llvm_filecheck, read_dir, rustc, source_root};
-
-use std::ffi::OsStr;
+use run_make_support::{
+    cmd, env_var, has_extension, llvm_filecheck, rustc, shallow_find_files, source_root,
+};
 
 fn main() {
     // `-Ccodegen-units=16 -Copt-level=2` is used here to trigger thin LTO
@@ -22,20 +22,14 @@ fn main() {
 
     // `llvm-dis` is used here since `--emit=llvm-ir` does not emit LLVM IR
     // for temporary outputs.
-    let mut files = Vec::new();
-    read_dir(".", |path| {
-        if path.is_file() && path.extension().is_some_and(|ext| ext == OsStr::new("bc")) {
-            files.push(path.to_path_buf());
-        }
-    });
+    let files = shallow_find_files(".", |path| has_extension(path, "bc"));
     cmd(llvm_bin_dir().join("llvm-dis")).args(files).run();
 
     // Check LLVM IR files (including temporary outputs) have `!llvm.ident`
     // named metadata, reusing the related codegen test.
     let llvm_ident_path = source_root().join("tests/codegen/llvm-ident.rs");
-    read_dir(".", |path| {
-        if path.is_file() && path.extension().is_some_and(|ext| ext == OsStr::new("ll")) {
-            llvm_filecheck().input_file(path).arg(&llvm_ident_path).run();
-        }
-    });
+    let files = shallow_find_files(".", |path| has_extension(path, "ll"));
+    for file in files {
+        llvm_filecheck().input_file(file).arg(&llvm_ident_path).run();
+    }
 }
diff --git a/tests/run-make/output-type-permutations/rmake.rs b/tests/run-make/output-type-permutations/rmake.rs
index 30036dc7eea..1d1637a744e 100644
--- a/tests/run-make/output-type-permutations/rmake.rs
+++ b/tests/run-make/output-type-permutations/rmake.rs
@@ -17,9 +17,8 @@ use std::path::PathBuf;
 // `rustc_invocation`: the rustc command being tested
 // Any unexpected output files not listed in `must_exist` or `can_exist` will cause a failure.
 fn assert_expected_output_files(expectations: Expectations, rustc_invocation: impl Fn()) {
-    let must_exist = expectations.expected_files;
-    let can_exist = expectations.allowed_files;
-    let dir = expectations.test_dir;
+    let Expectations { expected_files: must_exist, allowed_files: can_exist, test_dir: dir } =
+        expectations;
 
     fs_wrapper::create_dir(&dir);
     rustc_invocation();
diff --git a/tests/run-make/pass-linker-flags-flavor/Makefile b/tests/run-make/pass-linker-flags-flavor/Makefile
deleted file mode 100644
index 1bb05d0f974..00000000000
--- a/tests/run-make/pass-linker-flags-flavor/Makefile
+++ /dev/null
@@ -1,11 +0,0 @@
-# only-linux
-
-include ../tools.mk
-
-all:
-	$(RUSTC) empty.rs -Z unstable-options -C linker-flavor=gnu-cc -l static=l1 -l link-arg=a1 -l static=l2 -l link-arg=a2 -l dylib=d1 -l link-arg=a3 --print link-args | $(CGREP) -e 'l1.*-Wl,a1.*l2.*-Wl,a2.*d1.*-Wl,a3'
-	$(RUSTC) empty.rs -Z unstable-options -C linker-flavor=gnu-cc -l static=l1 -l link-arg:+verbatim=a1 -l static=l2 -l link-arg=a2 -l dylib=d1 -l link-arg=a3 --print link-args | $(CGREP) -e 'l1.*"a1".*l2.*-Wl,a2.*d1.*-Wl,a3'
-	$(RUSTC) empty.rs -Z unstable-options -C linker-flavor=ld -l static=l1 -l link-arg=a1 -l static=l2 -l link-arg=a2 -l dylib=d1 -l link-arg=a3 --print link-args | $(CGREP) -e 'l1.*"a1".*l2.*"a2".*d1.*"a3"'
-	$(RUSTC) attribute.rs -Z unstable-options -C linker-flavor=gnu-cc --print link-args | $(CGREP) -e 'l1.*-Wl,a1.*l2.*-Wl,a2.*d1.*-Wl,a3'
-	$(RUSTC) --cfg 'feature="verbatim"' attribute.rs -Z unstable-options -C linker-flavor=gnu-cc --print link-args | $(CGREP) -e 'l1.*"a1".*l2.*-Wl,a2.*d1.*-Wl,a3'
-	$(RUSTC) attribute.rs -C linker-flavor=ld --print link-args | $(CGREP) -e 'l1.*"a1".*l2.*"a2".*d1.*"a3"'
diff --git a/tests/run-make/pass-linker-flags-flavor/rmake.rs b/tests/run-make/pass-linker-flags-flavor/rmake.rs
new file mode 100644
index 00000000000..e36d68cc884
--- /dev/null
+++ b/tests/run-make/pass-linker-flags-flavor/rmake.rs
@@ -0,0 +1,84 @@
+// Setting the linker flavor as a C compiler should cause the output of the -l flags to be
+// prefixed by -Wl, except when a flag is requested to be verbatim. A bare linker (ld) should
+// never cause prefixes to appear in the output. This test checks this ruleset twice, once with
+// explicit flags and then with those flags passed inside the rust source code.
+// See https://github.com/rust-lang/rust/pull/118202
+
+//@ only-linux
+// Reason: the `gnu-cc` linker is only available on linux
+
+use run_make_support::{regex, rustc};
+
+fn main() {
+    let out_gnu = rustc()
+        .input("empty.rs")
+        .linker_flavor("gnu-cc")
+        .arg("-Zunstable-options")
+        .arg("-lstatic=l1")
+        .arg("-llink-arg=a1")
+        .arg("-lstatic=l2")
+        .arg("-llink-arg=a2")
+        .arg("-ldylib=d1")
+        .arg("-llink-arg=a3")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out_gnu_verbatim = rustc()
+        .input("empty.rs")
+        .linker_flavor("gnu-cc")
+        .arg("-Zunstable-options")
+        .arg("-lstatic=l1")
+        .arg("-llink-arg:+verbatim=a1")
+        .arg("-lstatic=l2")
+        .arg("-llink-arg=a2")
+        .arg("-ldylib=d1")
+        .arg("-llink-arg=a3")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out_ld = rustc()
+        .input("empty.rs")
+        .linker_flavor("ld")
+        .arg("-Zunstable-options")
+        .arg("-lstatic=l1")
+        .arg("-llink-arg=a1")
+        .arg("-lstatic=l2")
+        .arg("-llink-arg=a2")
+        .arg("-ldylib=d1")
+        .arg("-llink-arg=a3")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out_att_gnu = rustc()
+        .arg("-Zunstable-options")
+        .linker_flavor("gnu-cc")
+        .input("attribute.rs")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out_att_gnu_verbatim = rustc()
+        .cfg(r#"feature="verbatim""#)
+        .arg("-Zunstable-options")
+        .linker_flavor("gnu-cc")
+        .input("attribute.rs")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out_att_ld = rustc()
+        .linker_flavor("ld")
+        .input("attribute.rs")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+
+    let no_verbatim = regex::Regex::new("l1.*-Wl,a1.*l2.*-Wl,a2.*d1.*-Wl,a3").unwrap();
+    let one_verbatim = regex::Regex::new(r#"l1.*"a1".*l2.*-Wl,a2.*d1.*-Wl,a3"#).unwrap();
+    let ld = regex::Regex::new(r#"l1.*"a1".*l2.*"a2".*d1.*"a3""#).unwrap();
+
+    assert!(no_verbatim.is_match(&out_gnu));
+    assert!(no_verbatim.is_match(&out_att_gnu));
+    assert!(one_verbatim.is_match(&out_gnu_verbatim));
+    assert!(one_verbatim.is_match(&out_att_gnu_verbatim));
+    assert!(ld.is_match(&out_ld));
+    assert!(ld.is_match(&out_att_ld));
+}
diff --git a/tests/run-make/pass-linker-flags-from-dep/Makefile b/tests/run-make/pass-linker-flags-from-dep/Makefile
deleted file mode 100644
index 48b3b26ce81..00000000000
--- a/tests/run-make/pass-linker-flags-from-dep/Makefile
+++ /dev/null
@@ -1,12 +0,0 @@
-include ../tools.mk
-
-all:
-	# Build deps
-	$(RUSTC) native_dep_1.rs --crate-type=staticlib
-	$(RUSTC) native_dep_2.rs --crate-type=staticlib
-	$(RUSTC) rust_dep_flag.rs -l static:-bundle=native_dep_1 -l link-arg=some_flag -l static:-bundle=native_dep_2 --crate-type=lib -Z unstable-options
-	$(RUSTC) rust_dep_attr.rs --crate-type=lib
-
-	# Check sequence of linker args
-	$(RUSTC) main.rs --extern lib=$(TMPDIR)/librust_dep_flag.rlib --crate-type=bin --print link-args | $(CGREP) -e 'native_dep_1.*some_flag.*native_dep_2'
-	$(RUSTC) main.rs --extern lib=$(TMPDIR)/librust_dep_attr.rlib --crate-type=bin --print link-args | $(CGREP) -e 'native_dep_1.*some_flag.*native_dep_2'
diff --git a/tests/run-make/pass-linker-flags-from-dep/rmake.rs b/tests/run-make/pass-linker-flags-from-dep/rmake.rs
new file mode 100644
index 00000000000..4b8e0486e14
--- /dev/null
+++ b/tests/run-make/pass-linker-flags-from-dep/rmake.rs
@@ -0,0 +1,43 @@
+// A similar test to pass-linker-flags, testing that the `-l link-arg` flag
+// respects the order relative to other `-l` flags, but this time, the flags
+// are passed on the compilation of a dependency. This test checks that the
+// downstream compiled binary contains the linker arguments of the dependency,
+// and in the correct order.
+// See https://github.com/rust-lang/rust/issues/99427
+
+use run_make_support::{regex, rust_lib_name, rustc};
+
+fn main() {
+    // Build dependencies
+    rustc().input("native_dep_1.rs").crate_type("staticlib").run();
+    rustc().input("native_dep_2.rs").crate_type("staticlib").run();
+    rustc()
+        .input("rust_dep_flag.rs")
+        .arg("-lstatic:-bundle=native_dep_1")
+        .arg("-llink-arg=some_flag")
+        .arg("-lstatic:-bundle=native_dep_2")
+        .crate_type("lib")
+        .arg("-Zunstable-options")
+        .run();
+    rustc().input("rust_dep_attr.rs").crate_type("lib").run();
+
+    // Check sequence of linker arguments
+    let out_flag = rustc()
+        .input("main.rs")
+        .extern_("lib", rust_lib_name("rust_dep_flag"))
+        .crate_type("bin")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out_attr = rustc()
+        .input("main.rs")
+        .extern_("lib", rust_lib_name("rust_dep_attr"))
+        .crate_type("bin")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+
+    let re = regex::Regex::new("native_dep_1.*some_flag.*native_dep_2").unwrap();
+    assert!(re.is_match(&out_flag));
+    assert!(re.is_match(&out_attr));
+}
diff --git a/tests/run-make/pass-linker-flags/Makefile b/tests/run-make/pass-linker-flags/Makefile
deleted file mode 100644
index 226943e93bd..00000000000
--- a/tests/run-make/pass-linker-flags/Makefile
+++ /dev/null
@@ -1,5 +0,0 @@
-include ../tools.mk
-
-all:
-	$(RUSTC) empty.rs -Z unstable-options -l static=l1 -l link-arg=a1 -l static=l2 -l link-arg=a2 -l dylib=d1 -l link-arg=a3 --print link-args | $(CGREP) -e 'l1.*a1.*l2.*a2.*d1.*a3'
-	$(RUSTC) attribute.rs --print link-args | $(CGREP) -e 'l1.*a1.*l2.*a2.*d1.*a3'
diff --git a/tests/run-make/pass-linker-flags/rmake.rs b/tests/run-make/pass-linker-flags/rmake.rs
new file mode 100644
index 00000000000..de69567a6e6
--- /dev/null
+++ b/tests/run-make/pass-linker-flags/rmake.rs
@@ -0,0 +1,28 @@
+// This test checks the proper function of `-l link-arg=NAME`, which, unlike
+// -C link-arg, is supposed to guarantee that the order relative to other -l
+// options will be respected. In this test, compilation fails (because none of the
+// link arguments like `a1` exist), but it is still checked if the output contains the
+// link arguments in the exact order they were passed in. `attribute.rs` is a variant
+// of the test where the flags are defined in the rust file itself.
+// See https://github.com/rust-lang/rust/issues/99427
+
+use run_make_support::{regex, rustc};
+
+fn main() {
+    let out = rustc()
+        .input("empty.rs")
+        .arg("-Zunstable-options")
+        .arg("-lstatic=l1")
+        .arg("-llink-arg=a1")
+        .arg("-lstatic=l2")
+        .arg("-llink-arg=a2")
+        .arg("-ldylib=d1")
+        .arg("-llink-arg=a3")
+        .print("link-args")
+        .run_unchecked()
+        .stdout_utf8();
+    let out2 = rustc().input("attribute.rs").print("link-args").run_unchecked().stdout_utf8();
+    let re = regex::Regex::new("l1.*a1.*l2.*a2.*d1.*a3").unwrap();
+    assert!(re.is_match(&out));
+    assert!(re.is_match(&out2));
+}
diff --git a/tests/run-make/issue-37839/a.rs b/tests/run-make/proc-macro-three-crates/a.rs
index b5dffac3ff6..b5dffac3ff6 100644
--- a/tests/run-make/issue-37839/a.rs
+++ b/tests/run-make/proc-macro-three-crates/a.rs
diff --git a/tests/run-make/issue-37839/b.rs b/tests/run-make/proc-macro-three-crates/b.rs
index 067f47c1b7a..067f47c1b7a 100644
--- a/tests/run-make/issue-37839/b.rs
+++ b/tests/run-make/proc-macro-three-crates/b.rs
diff --git a/tests/run-make/issue-37839/c.rs b/tests/run-make/proc-macro-three-crates/c.rs
index 4c7ce01b6a0..4c7ce01b6a0 100644
--- a/tests/run-make/issue-37839/c.rs
+++ b/tests/run-make/proc-macro-three-crates/c.rs
diff --git a/tests/run-make/proc-macro-three-crates/rmake.rs b/tests/run-make/proc-macro-three-crates/rmake.rs
new file mode 100644
index 00000000000..d3735540fdd
--- /dev/null
+++ b/tests/run-make/proc-macro-three-crates/rmake.rs
@@ -0,0 +1,20 @@
+// A compiler bug caused the following issue:
+// If a crate A depends on crate B, and crate B
+// depends on crate C, and crate C contains a procedural
+// macro, compiling crate A would fail.
+// This was fixed in #37846, and this test checks
+// that this bug does not make a resurgence.
+
+use run_make_support::{bare_rustc, cwd, rust_lib_name, rustc};
+
+fn main() {
+    rustc().input("a.rs").run();
+    rustc().input("b.rs").run();
+    let curr_dir = cwd().display().to_string();
+    bare_rustc()
+        .input("c.rs")
+        .arg(format!("-Ldependency={curr_dir}"))
+        .extern_("b", cwd().join(rust_lib_name("b")))
+        .out_dir(cwd())
+        .run();
+}
diff --git a/tests/run-make/sepcomp-cci-copies/Makefile b/tests/run-make/sepcomp-cci-copies/Makefile
deleted file mode 100644
index df289d0b0b1..00000000000
--- a/tests/run-make/sepcomp-cci-copies/Makefile
+++ /dev/null
@@ -1,12 +0,0 @@
-include ../tools.mk
-
-# Check that cross-crate inlined items are inlined in all compilation units
-# that refer to them, and not in any other compilation units.
-# Note that we have to pass `-C codegen-units=6` because up to two CGUs may be
-# created for each source module (see `rustc_const_eval::monomorphize::partitioning`).
-
-all:
-	$(RUSTC) cci_lib.rs
-	$(RUSTC) foo.rs --emit=llvm-ir -C codegen-units=6 \
-		-Z inline-in-all-cgus
-	[ "$$(cat "$(TMPDIR)"/foo.*.ll | grep -c define\ .*cci_fn)" -eq "2" ]
diff --git a/tests/run-make/sepcomp-cci-copies/rmake.rs b/tests/run-make/sepcomp-cci-copies/rmake.rs
new file mode 100644
index 00000000000..612a73977fe
--- /dev/null
+++ b/tests/run-make/sepcomp-cci-copies/rmake.rs
@@ -0,0 +1,17 @@
+// Check that cross-crate inlined items are inlined in all compilation units
+// that refer to them, and not in any other compilation units.
+// Note that we have to pass `-C codegen-units=6` because up to two CGUs may be
+// created for each source module (see `rustc_const_eval::monomorphize::partitioning`).
+// See https://github.com/rust-lang/rust/pull/16367
+
+use run_make_support::{
+    count_regex_matches_in_files_with_extension, cwd, fs_wrapper, has_extension, regex, rustc,
+    shallow_find_files,
+};
+
+fn main() {
+    rustc().input("cci_lib.rs").run();
+    rustc().input("foo.rs").emit("llvm-ir").codegen_units(6).arg("-Zinline-in-all-cgus").run();
+    let re = regex::Regex::new(r#"define\ .*cci_fn"#).unwrap();
+    assert_eq!(count_regex_matches_in_files_with_extension(&re, "ll"), 2);
+}
diff --git a/tests/run-make/sepcomp-inlining/Makefile b/tests/run-make/sepcomp-inlining/Makefile
deleted file mode 100644
index 327aeb75e5e..00000000000
--- a/tests/run-make/sepcomp-inlining/Makefile
+++ /dev/null
@@ -1,15 +0,0 @@
-include ../tools.mk
-
-# Test that #[inline] functions still get inlined across compilation unit
-# boundaries. Compilation should produce three IR files, but only the two
-# compilation units that have a usage of the #[inline] function should
-# contain a definition. Also, the non-#[inline] function should be defined
-# in only one compilation unit.
-
-all:
-	$(RUSTC) foo.rs --emit=llvm-ir -C codegen-units=3 \
-		-Z inline-in-all-cgus
-	[ "$$(cat "$(TMPDIR)"/foo.*.ll | grep -c define\ i32\ .*inlined)" -eq "0" ]
-	[ "$$(cat "$(TMPDIR)"/foo.*.ll | grep -c define\ internal\ i32\ .*inlined)" -eq "2" ]
-	[ "$$(cat "$(TMPDIR)"/foo.*.ll | grep -c define\ hidden\ i32\ .*normal)" -eq "1" ]
-	[ "$$(cat "$(TMPDIR)"/foo.*.ll | grep -c declare\ hidden\ i32\ .*normal)" -eq "2" ]
diff --git a/tests/run-make/sepcomp-inlining/rmake.rs b/tests/run-make/sepcomp-inlining/rmake.rs
new file mode 100644
index 00000000000..de7551b9a51
--- /dev/null
+++ b/tests/run-make/sepcomp-inlining/rmake.rs
@@ -0,0 +1,23 @@
+// Test that #[inline] functions still get inlined across compilation unit
+// boundaries. Compilation should produce three IR files, but only the two
+// compilation units that have a usage of the #[inline] function should
+// contain a definition. Also, the non-#[inline] function should be defined
+// in only one compilation unit.
+// See https://github.com/rust-lang/rust/pull/16367
+
+use run_make_support::{
+    count_regex_matches_in_files_with_extension, cwd, fs_wrapper, has_extension, regex, rustc,
+    shallow_find_files,
+};
+
+fn main() {
+    rustc().input("foo.rs").emit("llvm-ir").codegen_units(3).arg("-Zinline-in-all-cgus").run();
+    let re = regex::Regex::new(r#"define\ i32\ .*inlined"#).unwrap();
+    assert_eq!(count_regex_matches_in_files_with_extension(&re, "ll"), 0);
+    let re = regex::Regex::new(r#"define\ internal\ .*inlined"#).unwrap();
+    assert_eq!(count_regex_matches_in_files_with_extension(&re, "ll"), 2);
+    let re = regex::Regex::new(r#"define\ hidden\ i32\ .*normal"#).unwrap();
+    assert_eq!(count_regex_matches_in_files_with_extension(&re, "ll"), 1);
+    let re = regex::Regex::new(r#"declare\ hidden\ i32\ .*normal"#).unwrap();
+    assert_eq!(count_regex_matches_in_files_with_extension(&re, "ll"), 2);
+}
diff --git a/tests/run-make/sepcomp-separate/Makefile b/tests/run-make/sepcomp-separate/Makefile
deleted file mode 100644
index 62cf54a88fb..00000000000
--- a/tests/run-make/sepcomp-separate/Makefile
+++ /dev/null
@@ -1,9 +0,0 @@
-include ../tools.mk
-
-# Test that separate compilation actually puts code into separate compilation
-# units.  `foo.rs` defines `magic_fn` in three different modules, which should
-# wind up in three different compilation units.
-
-all:
-	$(RUSTC) foo.rs --emit=llvm-ir -C codegen-units=3
-	[ "$$(cat "$(TMPDIR)"/foo.*.ll | grep -c define\ .*magic_fn)" -eq "3" ]
diff --git a/tests/run-make/sepcomp-separate/rmake.rs b/tests/run-make/sepcomp-separate/rmake.rs
new file mode 100644
index 00000000000..6f1d22424b5
--- /dev/null
+++ b/tests/run-make/sepcomp-separate/rmake.rs
@@ -0,0 +1,15 @@
+// Test that separate compilation actually puts code into separate compilation
+// units.  `foo.rs` defines `magic_fn` in three different modules, which should
+// wind up in three different compilation units.
+// See https://github.com/rust-lang/rust/pull/16367
+
+use run_make_support::{
+    count_regex_matches_in_files_with_extension, cwd, fs_wrapper, has_extension, regex, rustc,
+    shallow_find_files,
+};
+
+fn main() {
+    rustc().input("foo.rs").emit("llvm-ir").codegen_units(3).run();
+    let re = regex::Regex::new(r#"define\ .*magic_fn"#).unwrap();
+    assert_eq!(count_regex_matches_in_files_with_extension(&re, "ll"), 3);
+}
diff --git a/tests/run-make/target-cpu-native/Makefile b/tests/run-make/target-cpu-native/Makefile
deleted file mode 100644
index eb3ca1e13aa..00000000000
--- a/tests/run-make/target-cpu-native/Makefile
+++ /dev/null
@@ -1,20 +0,0 @@
-include ../tools.mk
-
-# only-linux
-# only-x86_64
-#
-# I *really* don't want to deal with a cross-platform way to compare file sizes,
-# tests in `make` sort of are awful
-
-all: $(TMPDIR)/out.log
-	# Make sure no warnings about "unknown CPU `native`" were emitted
-	if [ "$$(wc -c $(TMPDIR)/out.log | cut -d' ' -f 1)" = "0" ]; then \
-	  echo no warnings generated; \
-	else \
-	  exit 1; \
-	fi
-
-
-$(TMPDIR)/out.log:
-	$(RUSTC) foo.rs -C target-cpu=native 2>&1 | tee $(TMPDIR)/out.log
-	$(call RUN,foo)
diff --git a/tests/run-make/target-cpu-native/rmake.rs b/tests/run-make/target-cpu-native/rmake.rs
new file mode 100644
index 00000000000..fd5fb6193fe
--- /dev/null
+++ b/tests/run-make/target-cpu-native/rmake.rs
@@ -0,0 +1,14 @@
+// target-cpu is a codegen flag that generates code for the processor of the host machine
+// running the compilation. This test is a sanity test that this flag does not cause any
+// warnings when used, and that binaries produced by it can also be successfully executed.
+// See https://github.com/rust-lang/rust/pull/23238
+
+use run_make_support::{run, rustc};
+
+fn main() {
+    let out = rustc().input("foo.rs").arg("-Ctarget-cpu=native").run().stderr_utf8();
+    run("foo");
+    // There should be zero warnings emitted - the bug would cause "unknown CPU `native`"
+    // to be printed out.
+    assert!(out.is_empty());
+}
diff --git a/tests/run-make/target-specs/Makefile b/tests/run-make/target-specs/Makefile
deleted file mode 100644
index 161b6602185..00000000000
--- a/tests/run-make/target-specs/Makefile
+++ /dev/null
@@ -1,12 +0,0 @@
-include ../tools.mk
-all:
-	$(RUSTC) foo.rs --target=my-awesome-platform.json --crate-type=lib --emit=asm
-	$(CGREP) -v morestack < $(TMPDIR)/foo.s
-	$(RUSTC) foo.rs --target=my-invalid-platform.json 2>&1 | $(CGREP) "Error loading target specification"
-	$(RUSTC) foo.rs --target=my-incomplete-platform.json 2>&1 | $(CGREP) 'Field llvm-target'
-	RUST_TARGET_PATH=. $(RUSTC) foo.rs --target=my-awesome-platform --crate-type=lib --emit=asm
-	RUST_TARGET_PATH=. $(RUSTC) foo.rs --target=my-x86_64-unknown-linux-gnu-platform --crate-type=lib --emit=asm
-	$(RUSTC) -Z unstable-options --target=my-awesome-platform.json --print target-spec-json > $(TMPDIR)/test-platform.json && $(RUSTC) -Z unstable-options --target=$(TMPDIR)/test-platform.json --print target-spec-json | diff -q $(TMPDIR)/test-platform.json -
-	$(RUSTC) foo.rs --target=definitely-not-builtin-target 2>&1 | $(CGREP) 'may not set is_builtin'
-	$(RUSTC) foo.rs --target=endianness-mismatch 2>&1 | $(CGREP) '"data-layout" claims architecture is little-endian'
-	$(RUSTC) foo.rs --target=mismatching-data-layout --crate-type=lib 2>&1 | $(CGREP) 'data-layout for target'
diff --git a/tests/run-make/target-specs/rmake.rs b/tests/run-make/target-specs/rmake.rs
new file mode 100644
index 00000000000..d2b5f650838
--- /dev/null
+++ b/tests/run-make/target-specs/rmake.rs
@@ -0,0 +1,71 @@
+// Target-specific compilation in rustc used to have case-by-case peculiarities in 2014,
+// with the compiler having redundant target types and unspecific names. An overarching rework
+// in #16156 changed the way the target flag functions, and this test attempts compilation
+// with the target flag's bundle of new features to check that compilation either succeeds while
+// using them correctly, or fails with the right error message when using them improperly.
+// See https://github.com/rust-lang/rust/pull/16156
+
+use run_make_support::{diff, fs_wrapper, rustc};
+
+fn main() {
+    rustc().input("foo.rs").target("my-awesome-platform.json").crate_type("lib").emit("asm").run();
+    assert!(!fs_wrapper::read_to_string("foo.s").contains("morestack"));
+    rustc()
+        .input("foo.rs")
+        .target("my-invalid-platform.json")
+        .run_fail()
+        .assert_stderr_contains("Error loading target specification");
+    rustc()
+        .input("foo.rs")
+        .target("my-incomplete-platform.json")
+        .run_fail()
+        .assert_stderr_contains("Field llvm-target");
+    rustc()
+        .env("RUST_TARGET_PATH", ".")
+        .input("foo.rs")
+        .target("my-awesome-platform")
+        .crate_type("lib")
+        .emit("asm")
+        .run();
+    rustc()
+        .env("RUST_TARGET_PATH", ".")
+        .input("foo.rs")
+        .target("my-x86_64-unknown-linux-gnu-platform")
+        .crate_type("lib")
+        .emit("asm")
+        .run();
+    let test_platform = rustc()
+        .arg("-Zunstable-options")
+        .target("my-awesome-platform.json")
+        .print("target-spec-json")
+        .run()
+        .stdout_utf8();
+    fs_wrapper::create_file("test-platform.json");
+    fs_wrapper::write("test-platform.json", test_platform.as_bytes());
+    let test_platform_2 = rustc()
+        .arg("-Zunstable-options")
+        .target("test-platform.json")
+        .print("target-spec-json")
+        .run()
+        .stdout_utf8();
+    diff()
+        .expected_file("test-platform.json")
+        .actual_text("test-platform-2", test_platform_2)
+        .run();
+    rustc()
+        .input("foo.rs")
+        .target("definitely-not-builtin-target")
+        .run_fail()
+        .assert_stderr_contains("may not set is_builtin");
+    rustc()
+        .input("foo.rs")
+        .target("endianness-mismatch")
+        .run_fail()
+        .assert_stderr_contains(r#""data-layout" claims architecture is little-endian"#);
+    rustc()
+        .input("foo.rs")
+        .target("mismatching-data-layout")
+        .crate_type("lib")
+        .run_fail()
+        .assert_stderr_contains("data-layout for target");
+}
diff --git a/tests/run-make/target-without-atomic-cas/Makefile b/tests/run-make/target-without-atomic-cas/Makefile
deleted file mode 100644
index 451f03d66cd..00000000000
--- a/tests/run-make/target-without-atomic-cas/Makefile
+++ /dev/null
@@ -1,5 +0,0 @@
-include ../tools.mk
-
-# The target used below doesn't support atomic CAS operations. Verify that's the case
-all:
-	$(RUSTC) --print cfg --target thumbv6m-none-eabi | $(CGREP) -v 'target_has_atomic="ptr"'
diff --git a/tests/run-make/target-without-atomic-cas/rmake.rs b/tests/run-make/target-without-atomic-cas/rmake.rs
new file mode 100644
index 00000000000..c8782b6d1a5
--- /dev/null
+++ b/tests/run-make/target-without-atomic-cas/rmake.rs
@@ -0,0 +1,16 @@
+// ARM Cortex-M are a class of processors supported by the rust compiler. However,
+// they cannot support any atomic features, such as Arc. This test simply prints
+// the configuration details of one Cortex target, and checks that the compiler
+// does not falsely list atomic support.
+// See https://github.com/rust-lang/rust/pull/36874
+
+use run_make_support::rustc;
+
+// The target used below doesn't support atomic CAS operations. Verify that's the case
+fn main() {
+    rustc()
+        .print("cfg")
+        .target("thumbv6m-none-eabi")
+        .run()
+        .assert_stdout_not_contains(r#"target_has_atomic="ptr""#);
+}
diff --git a/tests/run-make/track-path-dep-info/Makefile b/tests/run-make/track-path-dep-info/Makefile
deleted file mode 100644
index 0d6c9b1d2f0..00000000000
--- a/tests/run-make/track-path-dep-info/Makefile
+++ /dev/null
@@ -1,13 +0,0 @@
-include ../tools.mk
-
-# FIXME(eddyb) provide `HOST_RUSTC` and `TARGET_RUSTC`
-# instead of hardcoding them everywhere they're needed.
-ifeq ($(IS_MUSL_HOST),1)
-ADDITIONAL_ARGS := $(RUSTFLAGS)
-endif
-
-all:
-	# Proc macro
-	$(BARE_RUSTC) $(ADDITIONAL_ARGS) --out-dir $(TMPDIR) macro_def.rs
-	EXISTING_PROC_MACRO_ENV=1 $(RUSTC) --emit dep-info macro_use.rs
-	$(CGREP) "emojis.txt:" < $(TMPDIR)/macro_use.d
diff --git a/tests/run-make/track-path-dep-info/rmake.rs b/tests/run-make/track-path-dep-info/rmake.rs
new file mode 100644
index 00000000000..f108dc66051
--- /dev/null
+++ b/tests/run-make/track-path-dep-info/rmake.rs
@@ -0,0 +1,13 @@
+// This test checks the functionality of `tracked_path::path`, a procedural macro
+// feature that adds a dependency to another file inside the procmacro. In this case,
+// the text file is added through this method, and the test checks that the compilation
+// output successfully added the file as a dependency.
+// See https://github.com/rust-lang/rust/pull/84029
+
+use run_make_support::{fs_wrapper, rustc};
+
+fn main() {
+    rustc().input("macro_def.rs").run();
+    rustc().env("EXISTING_PROC_MACRO_ENV", "1").emit("dep-info").input("macro_use.rs").run();
+    assert!(fs_wrapper::read_to_string("macro_use.d").contains("emojis.txt:"));
+}
diff --git a/tests/run-make/track-pgo-dep-info/Makefile b/tests/run-make/track-pgo-dep-info/Makefile
deleted file mode 100644
index 3afe3662fa7..00000000000
--- a/tests/run-make/track-pgo-dep-info/Makefile
+++ /dev/null
@@ -1,25 +0,0 @@
-# needs-profiler-support
-
-include ../tools.mk
-
-# FIXME(eddyb) provide `HOST_RUSTC` and `TARGET_RUSTC`
-# instead of hardcoding them everywhere they're needed.
-ifeq ($(IS_MUSL_HOST),1)
-ADDITIONAL_ARGS := $(RUSTFLAGS)
-endif
-
-all:
-	# Generate PGO profiles
-	$(BARE_RUSTC) $(ADDITIONAL_ARGS) -Cprofile-generate=$(TMPDIR)/profiles --out-dir $(TMPDIR) main.rs
-	$(TMPDIR)/main
-
-	# Merge profiles
-	"$(LLVM_BIN_DIR)/llvm-profdata" merge \
-		-o "$(TMPDIR)/merged.profdata" \
-		"$(TMPDIR)/profiles" || exit 1
-
-	# Use the profile
-	$(RUSTC) -Cprofile-use=$(TMPDIR)/merged.profdata --emit dep-info main.rs
-
-	# Check that profile file is in depinfo
-	$(CGREP) "merged.profdata" < $(TMPDIR)/main.d
diff --git a/tests/run-make/track-pgo-dep-info/rmake.rs b/tests/run-make/track-pgo-dep-info/rmake.rs
new file mode 100644
index 00000000000..acfe05cf8ea
--- /dev/null
+++ b/tests/run-make/track-pgo-dep-info/rmake.rs
@@ -0,0 +1,23 @@
+// Emitting dep-info files used to not have any mention of PGO profiles used
+// in compilation, which meant these profiles could be changed without consequence.
+// After changing this in #100801, this test checks that the profile data is successfully
+// included in dep-info emit files.
+// See https://github.com/rust-lang/rust/pull/100801
+
+//@ ignore-cross-compile
+// Reason: the binary is executed
+//@ needs-profiler-support
+
+use run_make_support::{fs_wrapper, llvm_profdata, run, rustc};
+
+fn main() {
+    // Generate the profile-guided-optimization (PGO) profiles
+    rustc().profile_generate("profiles").input("main.rs").run();
+    // Merge the profiles
+    run("main");
+    llvm_profdata().merge().output("merged.profdata").input("profiles").run();
+    // Use the profiles in compilation
+    rustc().profile_use("merged.profdata").emit("dep-info").input("main.rs").run();
+    // Check that the profile file is in the dep-info emit file
+    assert!(fs_wrapper::read_to_string("main.d").contains("merged.profdata"));
+}
diff --git a/tests/rustdoc-json/trait_alias.rs b/tests/rustdoc-json/trait_alias.rs
new file mode 100644
index 00000000000..dc930550ef1
--- /dev/null
+++ b/tests/rustdoc-json/trait_alias.rs
@@ -0,0 +1,18 @@
+// ignore-tidy-linelength
+#![feature(trait_alias)]
+
+// @set StrLike = "$.index[*][?(@.name=='StrLike')].id"
+// @is "$.index[*][?(@.name=='StrLike')].visibility" \"public\"
+// @has "$.index[*][?(@.name=='StrLike')].inner.trait_alias"
+// @is "$.index[*][?(@.name=='StrLike')].span.filename" $FILE
+pub trait StrLike = AsRef<str>;
+
+// @is "$.index[*][?(@.name=='f')].inner.function.decl.output.impl_trait[0].trait_bound.trait.id" $StrLike
+pub fn f() -> impl StrLike {
+    "heya"
+}
+
+// @!is "$.index[*][?(@.name=='g')].inner.function.decl.output.impl_trait[0].trait_bound.trait.id" $StrLike
+pub fn g() -> impl AsRef<str> {
+    "heya"
+}
diff --git a/tests/rustdoc-json/type_alias.rs b/tests/rustdoc-json/type_alias.rs
new file mode 100644
index 00000000000..7a938c50ba0
--- /dev/null
+++ b/tests/rustdoc-json/type_alias.rs
@@ -0,0 +1,15 @@
+// @set IntVec = "$.index[*][?(@.name=='IntVec')].id"
+// @is "$.index[*][?(@.name=='IntVec')].visibility" \"public\"
+// @has "$.index[*][?(@.name=='IntVec')].inner.type_alias"
+// @is "$.index[*][?(@.name=='IntVec')].span.filename" $FILE
+pub type IntVec = Vec<u32>;
+
+// @is "$.index[*][?(@.name=='f')].inner.function.decl.output.resolved_path.id" $IntVec
+pub fn f() -> IntVec {
+    vec![0; 32]
+}
+
+// @!is "$.index[*][?(@.name=='g')].inner.function.decl.output.resolved_path.id" $IntVec
+pub fn g() -> Vec<u32> {
+    vec![0; 32]
+}
diff --git a/tests/ui/async-await/async-closures/signature-inference-from-two-part-bound.rs b/tests/ui/async-await/async-closures/signature-inference-from-two-part-bound.rs
new file mode 100644
index 00000000000..0e2d1ef1208
--- /dev/null
+++ b/tests/ui/async-await/async-closures/signature-inference-from-two-part-bound.rs
@@ -0,0 +1,27 @@
+//@ edition: 2021
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+#![feature(async_closure)]
+
+use std::future::Future;
+use std::any::Any;
+
+struct Struct;
+impl Struct {
+    fn method(&self) {}
+}
+
+fn fake_async_closure<F, Fut>(_: F)
+where
+    F: Fn(Struct) -> Fut,
+    Fut: Future<Output = ()>,
+{}
+
+fn main() {
+    fake_async_closure(async |s| {
+        s.method();
+    })
+}
diff --git a/tests/ui/cast/cast-rfc0401-vtable-kinds.rs b/tests/ui/cast/cast-rfc0401-vtable-kinds.rs
index 0d8f92f013f..5704a33cc87 100644
--- a/tests/ui/cast/cast-rfc0401-vtable-kinds.rs
+++ b/tests/ui/cast/cast-rfc0401-vtable-kinds.rs
@@ -4,25 +4,12 @@
 
 #![feature(unsized_tuple_coercion)]
 
-trait Foo<T> {
-    fn foo(&self, _: T) -> u32 { 42 }
-}
-
 trait Bar { //~ WARN trait `Bar` is never used
     fn bar(&self) { println!("Bar!"); }
 }
 
-impl<T> Foo<T> for () {}
-impl Foo<u32> for u32 { fn foo(&self, _: u32) -> u32 { self+43 } }
 impl Bar for () {}
 
-unsafe fn round_trip_and_call<'a>(t: *const (dyn Foo<u32>+'a)) -> u32 {
-    let foo_e : *const dyn Foo<u32> = t as *const _;
-    let r_1 = foo_e as *mut dyn Foo<u32>;
-
-    (&*r_1).foo(0)
-}
-
 #[repr(C)]
 struct FooS<T:?Sized>(T);
 #[repr(C)]
@@ -38,11 +25,6 @@ fn tuple_i32_to_u32<T:?Sized>(u: *const (i32, T)) -> *const (u32, T) {
 
 
 fn main() {
-    let x = 4u32;
-    let y : &dyn Foo<u32> = &x;
-    let fl = unsafe { round_trip_and_call(y as *const dyn Foo<u32>) };
-    assert_eq!(fl, (43+4));
-
     let s = FooS([0,1,2]);
     let u: &FooS<[u32]> = &s;
     let u: *const FooS<[u32]> = u;
diff --git a/tests/ui/cast/cast-rfc0401-vtable-kinds.stderr b/tests/ui/cast/cast-rfc0401-vtable-kinds.stderr
index 952687e98d0..4f57e2e7df7 100644
--- a/tests/ui/cast/cast-rfc0401-vtable-kinds.stderr
+++ b/tests/ui/cast/cast-rfc0401-vtable-kinds.stderr
@@ -1,5 +1,5 @@
 warning: trait `Bar` is never used
-  --> $DIR/cast-rfc0401-vtable-kinds.rs:11:7
+  --> $DIR/cast-rfc0401-vtable-kinds.rs:7:7
    |
 LL | trait Bar {
    |       ^^^
diff --git a/tests/ui/cast/ptr-to-trait-obj-add-auto.rs b/tests/ui/cast/ptr-to-trait-obj-add-auto.rs
new file mode 100644
index 00000000000..46e72ea0877
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-add-auto.rs
@@ -0,0 +1,18 @@
+//@ check-pass
+
+trait Trait<'a> {}
+
+fn add_auto<'a>(x: *mut dyn Trait<'a>) -> *mut (dyn Trait<'a> + Send) {
+    x as _
+    //~^ warning: adding an auto trait `Send` to a trait object in a pointer cast may cause UB later on
+    //~| warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+}
+
+// (to test diagnostic list formatting)
+fn add_multiple_auto<'a>(x: *mut dyn Trait<'a>) -> *mut (dyn Trait<'a> + Send + Sync + Unpin) {
+    x as _
+    //~^ warning: adding auto traits `Send`, `Sync`, and `Unpin` to a trait object in a pointer cast may cause UB later on
+    //~| warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+}
+
+fn main() {}
diff --git a/tests/ui/cast/ptr-to-trait-obj-add-auto.stderr b/tests/ui/cast/ptr-to-trait-obj-add-auto.stderr
new file mode 100644
index 00000000000..e5ef8bf76b4
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-add-auto.stderr
@@ -0,0 +1,43 @@
+warning: adding an auto trait `Send` to a trait object in a pointer cast may cause UB later on
+  --> $DIR/ptr-to-trait-obj-add-auto.rs:6:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #127323 <https://github.com/rust-lang/rust/issues/127323>
+   = note: `#[warn(ptr_cast_add_auto_to_object)]` on by default
+
+warning: adding auto traits `Send`, `Sync`, and `Unpin` to a trait object in a pointer cast may cause UB later on
+  --> $DIR/ptr-to-trait-obj-add-auto.rs:13:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #127323 <https://github.com/rust-lang/rust/issues/127323>
+
+warning: 2 warnings emitted
+
+Future incompatibility report: Future breakage diagnostic:
+warning: adding an auto trait `Send` to a trait object in a pointer cast may cause UB later on
+  --> $DIR/ptr-to-trait-obj-add-auto.rs:6:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #127323 <https://github.com/rust-lang/rust/issues/127323>
+   = note: `#[warn(ptr_cast_add_auto_to_object)]` on by default
+
+Future breakage diagnostic:
+warning: adding auto traits `Send`, `Sync`, and `Unpin` to a trait object in a pointer cast may cause UB later on
+  --> $DIR/ptr-to-trait-obj-add-auto.rs:13:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #127323 <https://github.com/rust-lang/rust/issues/127323>
+   = note: `#[warn(ptr_cast_add_auto_to_object)]` on by default
+
diff --git a/tests/ui/cast/ptr-to-trait-obj-add-super-auto.rs b/tests/ui/cast/ptr-to-trait-obj-add-super-auto.rs
new file mode 100644
index 00000000000..ac8108d8ec4
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-add-super-auto.rs
@@ -0,0 +1,9 @@
+//@ check-pass
+
+trait Trait: Send {}
+impl Trait for () {}
+
+fn main() {
+    // This is OK: `Trait` has `Send` super trait.
+    &() as *const dyn Trait as *const (dyn Trait + Send);
+}
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-args.rs b/tests/ui/cast/ptr-to-trait-obj-different-args.rs
new file mode 100644
index 00000000000..c6038cfe864
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-args.rs
@@ -0,0 +1,37 @@
+//@ check-fail
+//
+// issue: <https://github.com/rust-lang/rust/issues/120222>
+
+trait A {}
+impl<T> A for T {}
+trait B {}
+impl<T> B for T {}
+
+trait Trait<G> {}
+struct X;
+impl<T> Trait<X> for T {}
+struct Y;
+impl<T> Trait<Y> for T {}
+
+fn main() {
+    let a: *const dyn A = &();
+    let b: *const dyn B = a as _; //~ error: casting `*const dyn A` as `*const dyn B` is invalid
+
+    let x: *const dyn Trait<X> = &();
+    let y: *const dyn Trait<Y> = x as _; //~ error: mismatched types
+
+    _ = (b, y);
+}
+
+fn generic<T>(x: *const dyn Trait<X>, t: *const dyn Trait<T>) {
+    let _: *const dyn Trait<T> = x as _; //~ error: mismatched types
+    let _: *const dyn Trait<X> = t as _; //~ error: mismatched types
+}
+
+trait Assocked {
+    type Assoc: ?Sized;
+}
+
+fn change_assoc(x: *mut dyn Assocked<Assoc = u8>) -> *mut dyn Assocked<Assoc = u32> {
+    x as _ //~ error: mismatched types
+}
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-args.stderr b/tests/ui/cast/ptr-to-trait-obj-different-args.stderr
new file mode 100644
index 00000000000..b04289ae747
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-args.stderr
@@ -0,0 +1,53 @@
+error[E0606]: casting `*const dyn A` as `*const dyn B` is invalid
+  --> $DIR/ptr-to-trait-obj-different-args.rs:18:27
+   |
+LL |     let b: *const dyn B = a as _;
+   |                           ^^^^^^
+   |
+   = note: vtable kinds may not match
+
+error[E0308]: mismatched types
+  --> $DIR/ptr-to-trait-obj-different-args.rs:21:34
+   |
+LL |     let y: *const dyn Trait<Y> = x as _;
+   |                                  ^^^^^^ expected `X`, found `Y`
+   |
+   = note: expected trait object `dyn Trait<X>`
+              found trait object `dyn Trait<Y>`
+
+error[E0308]: mismatched types
+  --> $DIR/ptr-to-trait-obj-different-args.rs:27:34
+   |
+LL | fn generic<T>(x: *const dyn Trait<X>, t: *const dyn Trait<T>) {
+   |            - found this type parameter
+LL |     let _: *const dyn Trait<T> = x as _;
+   |                                  ^^^^^^ expected `X`, found type parameter `T`
+   |
+   = note: expected trait object `dyn Trait<X>`
+              found trait object `dyn Trait<T>`
+
+error[E0308]: mismatched types
+  --> $DIR/ptr-to-trait-obj-different-args.rs:28:34
+   |
+LL | fn generic<T>(x: *const dyn Trait<X>, t: *const dyn Trait<T>) {
+   |            - expected this type parameter
+LL |     let _: *const dyn Trait<T> = x as _;
+LL |     let _: *const dyn Trait<X> = t as _;
+   |                                  ^^^^^^ expected type parameter `T`, found `X`
+   |
+   = note: expected trait object `dyn Trait<T>`
+              found trait object `dyn Trait<X>`
+
+error[E0308]: mismatched types
+  --> $DIR/ptr-to-trait-obj-different-args.rs:36:5
+   |
+LL |     x as _
+   |     ^^^^^^ expected `u8`, found `u32`
+   |
+   = note: expected trait object `dyn Assocked<Assoc = u8>`
+              found trait object `dyn Assocked<Assoc = u32>`
+
+error: aborting due to 5 previous errors
+
+Some errors have detailed explanations: E0308, E0606.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-id-trait.rs b/tests/ui/cast/ptr-to-trait-obj-different-regions-id-trait.rs
new file mode 100644
index 00000000000..cdd55e24392
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-id-trait.rs
@@ -0,0 +1,27 @@
+//@ check-fail
+//
+// Make sure we can't trick the compiler by using a projection.
+
+trait Cat<'a> {}
+impl Cat<'_> for () {}
+
+trait Id {
+    type Id: ?Sized;
+}
+impl<T: ?Sized> Id for T {
+    type Id = T;
+}
+
+struct S<T: ?Sized> {
+    tail: <T as Id>::Id,
+}
+
+fn m<'a>() {
+    let unsend: *const dyn Cat<'a> = &();
+    let _send = unsend as *const S<dyn Cat<'static>>;
+    //~^ error: lifetime may not live long enough
+}
+
+fn main() {
+    m();
+}
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-id-trait.stderr b/tests/ui/cast/ptr-to-trait-obj-different-regions-id-trait.stderr
new file mode 100644
index 00000000000..d1d598e603f
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-id-trait.stderr
@@ -0,0 +1,15 @@
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-id-trait.rs:21:17
+   |
+LL | fn m<'a>() {
+   |      -- lifetime `'a` defined here
+LL |     let unsend: *const dyn Cat<'a> = &();
+LL |     let _send = unsend as *const S<dyn Cat<'static>>;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
+   |
+   = note: requirement occurs because of the type `S<dyn Cat<'_>>`, which makes the generic argument `dyn Cat<'_>` invariant
+   = note: the struct `S<T>` is invariant over the parameter `T`
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-lt-ext.rs b/tests/ui/cast/ptr-to-trait-obj-different-regions-lt-ext.rs
new file mode 100644
index 00000000000..96345de01c9
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-lt-ext.rs
@@ -0,0 +1,31 @@
+//@ check-fail
+//
+// issue: <https://github.com/rust-lang/rust/issues/120217>
+
+#![feature(arbitrary_self_types)]
+
+trait Static<'a> {
+    fn proof(self: *const Self, s: &'a str) -> &'static str;
+}
+
+fn bad_cast<'a>(x: *const dyn Static<'static>) -> *const dyn Static<'a> {
+    x as _ //~ error: lifetime may not live long enough
+}
+
+impl Static<'static> for () {
+    fn proof(self: *const Self, s: &'static str) -> &'static str {
+        s
+    }
+}
+
+fn extend_lifetime(s: &str) -> &'static str {
+    bad_cast(&()).proof(s)
+}
+
+fn main() {
+    let s = String::from("Hello World");
+    let slice = extend_lifetime(&s);
+    println!("Now it exists: {slice}");
+    drop(s);
+    println!("Now it’s gone: {slice}");
+}
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-lt-ext.stderr b/tests/ui/cast/ptr-to-trait-obj-different-regions-lt-ext.stderr
new file mode 100644
index 00000000000..b7319e3356b
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-lt-ext.stderr
@@ -0,0 +1,10 @@
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-lt-ext.rs:12:5
+   |
+LL | fn bad_cast<'a>(x: *const dyn Static<'static>) -> *const dyn Static<'a> {
+   |             -- lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.rs b/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.rs
new file mode 100644
index 00000000000..01c347bfae5
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.rs
@@ -0,0 +1,37 @@
+//@ check-fail
+
+trait Trait<'a> {}
+
+fn change_lt<'a, 'b>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+    x as _ //~ error: lifetime may not live long enough
+           //~| error: lifetime may not live long enough
+}
+
+fn change_lt_ab<'a: 'b, 'b>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+    x as _ //~ error: lifetime may not live long enough
+}
+
+fn change_lt_ba<'a, 'b: 'a>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+    x as _ //~ error: lifetime may not live long enough
+}
+
+trait Assocked {
+    type Assoc: ?Sized;
+}
+
+fn change_assoc_0<'a, 'b>(
+    x: *mut dyn Assocked<Assoc = dyn Send + 'a>,
+) -> *mut dyn Assocked<Assoc = dyn Send + 'b> {
+    x as _ //~ error: lifetime may not live long enough
+           //~| error: lifetime may not live long enough
+}
+
+fn change_assoc_1<'a, 'b>(
+    x: *mut dyn Assocked<Assoc = dyn Trait<'a>>,
+) -> *mut dyn Assocked<Assoc = dyn Trait<'b>> {
+    x as _ //~ error: lifetime may not live long enough
+           //~| error: lifetime may not live long enough
+}
+
+
+fn main() {}
diff --git a/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr b/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr
new file mode 100644
index 00000000000..7044e4dec1f
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-different-regions-misc.stderr
@@ -0,0 +1,136 @@
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:6:5
+   |
+LL | fn change_lt<'a, 'b>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+   |              --  -- lifetime `'b` defined here
+   |              |
+   |              lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
+   |
+   = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable pointer to `dyn Trait<'_>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:6:5
+   |
+LL | fn change_lt<'a, 'b>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+   |              --  -- lifetime `'b` defined here
+   |              |
+   |              lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+   |
+   = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to `dyn Trait<'_>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+help: `'b` and `'a` must be the same: replace one with the other
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:11:5
+   |
+LL | fn change_lt_ab<'a: 'b, 'b>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+   |                 --      -- lifetime `'b` defined here
+   |                 |
+   |                 lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
+   |
+   = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable pointer to `dyn Trait<'_>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:15:5
+   |
+LL | fn change_lt_ba<'a, 'b: 'a>(x: *mut dyn Trait<'a>) -> *mut dyn Trait<'b> {
+   |                 --  -- lifetime `'b` defined here
+   |                 |
+   |                 lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+   |
+   = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to `dyn Trait<'_>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:25:5
+   |
+LL | fn change_assoc_0<'a, 'b>(
+   |                   --  -- lifetime `'b` defined here
+   |                   |
+   |                   lifetime `'a` defined here
+...
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
+   |
+   = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable pointer to `dyn Assocked<Assoc = dyn Send>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:25:5
+   |
+LL | fn change_assoc_0<'a, 'b>(
+   |                   --  -- lifetime `'b` defined here
+   |                   |
+   |                   lifetime `'a` defined here
+...
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+   |
+   = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to `dyn Assocked<Assoc = dyn Send>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+help: `'b` and `'a` must be the same: replace one with the other
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:32:5
+   |
+LL | fn change_assoc_1<'a, 'b>(
+   |                   --  -- lifetime `'b` defined here
+   |                   |
+   |                   lifetime `'a` defined here
+...
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
+   |
+   = help: consider adding the following bound: `'b: 'a`
+   = note: requirement occurs because of a mutable pointer to `dyn Assocked<Assoc = dyn Trait<'_>>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-trait-obj-different-regions-misc.rs:32:5
+   |
+LL | fn change_assoc_1<'a, 'b>(
+   |                   --  -- lifetime `'b` defined here
+   |                   |
+   |                   lifetime `'a` defined here
+...
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+   |
+   = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to `dyn Assocked<Assoc = dyn Trait<'_>>`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+help: `'b` and `'a` must be the same: replace one with the other
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 8 previous errors
+
diff --git a/tests/ui/cast/ptr-to-trait-obj-ok.rs b/tests/ui/cast/ptr-to-trait-obj-ok.rs
new file mode 100644
index 00000000000..656c99c58dc
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-ok.rs
@@ -0,0 +1,17 @@
+//@ check-pass
+
+trait Trait<'a> {}
+
+fn remove_auto<'a>(x: *mut (dyn Trait<'a> + Send)) -> *mut dyn Trait<'a> {
+    x as _
+}
+
+fn cast_inherent_lt<'a, 'b>(x: *mut (dyn Trait<'static> + 'a)) -> *mut (dyn Trait<'static> + 'b) {
+    x as _
+}
+
+fn unprincipled<'a, 'b>(x: *mut (dyn Send + 'a)) -> *mut (dyn Sync + 'b) {
+    x as _
+}
+
+fn main() {}
diff --git a/tests/ui/cast/ptr-to-trait-obj-wrap-upcast.rs b/tests/ui/cast/ptr-to-trait-obj-wrap-upcast.rs
new file mode 100644
index 00000000000..ff2c4cacfb1
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-wrap-upcast.rs
@@ -0,0 +1,14 @@
+trait Super {}
+trait Sub: Super {}
+
+struct Wrapper<T: ?Sized>(T);
+
+// This cast should not compile.
+// Upcasting can't work here, because we are also changing the type (`Wrapper`),
+// and reinterpreting would be confusing/surprising.
+// See <https://github.com/rust-lang/rust/pull/120248#discussion_r1487739518>
+fn cast(ptr: *const dyn Sub) -> *const Wrapper<dyn Super> {
+    ptr as _ //~ error: casting `*const (dyn Sub + 'static)` as `*const Wrapper<dyn Super>` is invalid
+}
+
+fn main() {}
diff --git a/tests/ui/cast/ptr-to-trait-obj-wrap-upcast.stderr b/tests/ui/cast/ptr-to-trait-obj-wrap-upcast.stderr
new file mode 100644
index 00000000000..38c8ba96bc5
--- /dev/null
+++ b/tests/ui/cast/ptr-to-trait-obj-wrap-upcast.stderr
@@ -0,0 +1,11 @@
+error[E0606]: casting `*const (dyn Sub + 'static)` as `*const Wrapper<dyn Super>` is invalid
+  --> $DIR/ptr-to-trait-obj-wrap-upcast.rs:11:5
+   |
+LL |     ptr as _
+   |     ^^^^^^^^
+   |
+   = note: vtable kinds may not match
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0606`.
diff --git a/tests/ui/deriving/deriving-in-fn.rs b/tests/ui/deriving/deriving-in-fn.rs
index 72da2148350..13f3d39597c 100644
--- a/tests/ui/deriving/deriving-in-fn.rs
+++ b/tests/ui/deriving/deriving-in-fn.rs
@@ -9,5 +9,5 @@ pub fn main() {
     }
 
     let f = Foo { foo: 10 };
-    format!("{:?}", f);
+    let _ = format!("{:?}", f);
 }
diff --git a/tests/ui/explicit-tail-calls/constck.rs b/tests/ui/explicit-tail-calls/constck.rs
new file mode 100644
index 00000000000..938f15f12c0
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/constck.rs
@@ -0,0 +1,22 @@
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+const fn f() {
+    if false {
+        become not_const();
+        //~^ error: cannot call non-const fn `not_const` in constant functions
+    }
+}
+
+const fn g((): ()) {
+    if false {
+        become yes_const(not_const());
+        //~^ error: cannot call non-const fn `not_const` in constant functions
+    }
+}
+
+fn not_const() {}
+
+const fn yes_const((): ()) {}
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/constck.stderr b/tests/ui/explicit-tail-calls/constck.stderr
new file mode 100644
index 00000000000..d9967c45fa0
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/constck.stderr
@@ -0,0 +1,19 @@
+error[E0015]: cannot call non-const fn `not_const` in constant functions
+  --> $DIR/constck.rs:6:16
+   |
+LL |         become not_const();
+   |                ^^^^^^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+
+error[E0015]: cannot call non-const fn `not_const` in constant functions
+  --> $DIR/constck.rs:13:26
+   |
+LL |         become yes_const(not_const());
+   |                          ^^^^^^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0015`.
diff --git a/tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.rs b/tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.rs
new file mode 100644
index 00000000000..5a105ee4eb5
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.rs
@@ -0,0 +1,14 @@
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+pub const fn test(_: &Type) {
+    const fn takes_borrow(_: &Type) {}
+
+    let local = Type;
+    become takes_borrow(&local);
+    //~^ error: `local` does not live long enough
+}
+
+struct Type;
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.stderr b/tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.stderr
new file mode 100644
index 00000000000..75fb13c378c
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-arg-bad-borrow.stderr
@@ -0,0 +1,14 @@
+error[E0597]: `local` does not live long enough
+  --> $DIR/ctfe-arg-bad-borrow.rs:8:25
+   |
+LL |     let local = Type;
+   |         ----- binding `local` declared here
+LL |     become takes_borrow(&local);
+   |                         ^^^^^^ borrowed value does not live long enough
+LL |
+LL | }
+   | - `local` dropped here while still borrowed
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0597`.
diff --git a/tests/ui/explicit-tail-calls/ctfe-arg-good-borrow.rs b/tests/ui/explicit-tail-calls/ctfe-arg-good-borrow.rs
new file mode 100644
index 00000000000..50bf6c946ca
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-arg-good-borrow.rs
@@ -0,0 +1,13 @@
+//@ check-pass
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+pub const fn test(x: &Type) {
+    const fn takes_borrow(_: &Type) {}
+
+    become takes_borrow(x);
+}
+
+pub struct Type;
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/ctfe-arg-move.rs b/tests/ui/explicit-tail-calls/ctfe-arg-move.rs
new file mode 100644
index 00000000000..88ff3a4a5ad
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-arg-move.rs
@@ -0,0 +1,15 @@
+//@ check-pass
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+pub const fn test(s: String) -> String {
+    const fn takes_string(s: String) -> String {
+        s
+    }
+
+    become takes_string(s);
+}
+
+struct Type;
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/ctfe-collatz-multi-rec.rs b/tests/ui/explicit-tail-calls/ctfe-collatz-multi-rec.rs
new file mode 100644
index 00000000000..86041b66960
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-collatz-multi-rec.rs
@@ -0,0 +1,43 @@
+//@ run-pass
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+/// A very unnecessarily complicated "implementation" of the Collatz conjecture.
+/// Returns the number of steps to reach `1`.
+///
+/// This is just a test for tail calls, which involves multiple functions calling each other.
+///
+/// Panics if `x == 0`.
+const fn collatz(x: u32) -> u32 {
+    assert!(x > 0);
+
+    const fn switch(x: u32, steps: u32) -> u32 {
+        match x {
+            1 => steps,
+            _ if x & 1 == 0 => become div2(x, steps + 1),
+            _ => become mul3plus1(x, steps + 1),
+        }
+    }
+
+    const fn div2(x: u32, steps: u32) -> u32 {
+        become switch(x >> 1, steps)
+    }
+
+    const fn mul3plus1(x: u32, steps: u32) -> u32 {
+        become switch(3 * x + 1, steps)
+    }
+
+    switch(x, 0)
+}
+
+const ASSERTS: () = {
+    assert!(collatz(1) == 0);
+    assert!(collatz(2) == 1);
+    assert!(collatz(3) == 7);
+    assert!(collatz(4) == 2);
+    assert!(collatz(6171) == 261);
+};
+
+fn main() {
+    let _ = ASSERTS;
+}
diff --git a/tests/ui/explicit-tail-calls/ctfe-id-unlimited.return.stderr b/tests/ui/explicit-tail-calls/ctfe-id-unlimited.return.stderr
new file mode 100644
index 00000000000..4a1e50b4111
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-id-unlimited.return.stderr
@@ -0,0 +1,36 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ctfe-id-unlimited.rs:17:42
+   |
+LL |             #[cfg(r#return)] _ => return inner(acc + 1, n - 1),
+   |                                          ^^^^^^^^^^^^^^^^^^^^^ reached the configured maximum number of stack frames
+   |
+note: inside `inner`
+  --> $DIR/ctfe-id-unlimited.rs:17:42
+   |
+LL |             #[cfg(r#return)] _ => return inner(acc + 1, n - 1),
+   |                                          ^^^^^^^^^^^^^^^^^^^^^
+note: [... 125 additional calls inside `inner` ...]
+  --> $DIR/ctfe-id-unlimited.rs:17:42
+   |
+LL |             #[cfg(r#return)] _ => return inner(acc + 1, n - 1),
+   |                                          ^^^^^^^^^^^^^^^^^^^^^
+note: inside `rec_id`
+  --> $DIR/ctfe-id-unlimited.rs:22:5
+   |
+LL |     inner(0, n)
+   |     ^^^^^^^^^^^
+note: inside `ID_ED`
+  --> $DIR/ctfe-id-unlimited.rs:29:20
+   |
+LL | const ID_ED: u32 = rec_id(ORIGINAL);
+   |                    ^^^^^^^^^^^^^^^^
+
+note: erroneous constant encountered
+  --> $DIR/ctfe-id-unlimited.rs:31:40
+   |
+LL | const ASSERT: () = assert!(ORIGINAL == ID_ED);
+   |                                        ^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/explicit-tail-calls/ctfe-id-unlimited.rs b/tests/ui/explicit-tail-calls/ctfe-id-unlimited.rs
new file mode 100644
index 00000000000..54e68b2b7f7
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-id-unlimited.rs
@@ -0,0 +1,35 @@
+//@ revisions: become return
+//@ [become] run-pass
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+// This is an identity function (`|x| x`), but implemented using recursion.
+// Each step we increment accumulator and decrement the number.
+//
+// With normal calls this fails compilation because of the recursion limit,
+// but with tail calls/`become` we don't grow the stack/spend recursion limit
+// so this should compile.
+const fn rec_id(n: u32) -> u32 {
+    const fn inner(acc: u32, n: u32) -> u32 {
+        match n {
+            0 => acc,
+            #[cfg(r#become)] _ => become inner(acc + 1, n - 1),
+            #[cfg(r#return)] _ => return inner(acc + 1, n - 1),
+            //[return]~^ error: evaluation of constant value failed
+        }
+    }
+
+    inner(0, n)
+}
+
+// Some relatively big number that is higher than recursion limit
+const ORIGINAL: u32 = 12345;
+// Original number, but with identity function applied
+// (this is the same, but requires execution of the recursion)
+const ID_ED: u32 = rec_id(ORIGINAL);
+// Assert to make absolutely sure the computation actually happens
+const ASSERT: () = assert!(ORIGINAL == ID_ED);
+
+fn main() {
+    let _ = ASSERT;
+}
diff --git a/tests/ui/explicit-tail-calls/ctfe-tail-call-panic.rs b/tests/ui/explicit-tail-calls/ctfe-tail-call-panic.rs
new file mode 100644
index 00000000000..3d69cde2989
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-tail-call-panic.rs
@@ -0,0 +1,19 @@
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+pub const fn f() {
+    become g();
+}
+
+const fn g() {
+    panic!()
+    //~^ error: evaluation of constant value failed
+    //~| note: in this expansion of panic!
+    //~| note: inside `g`
+    //~| note: in this expansion of panic!
+}
+
+const _: () = f();
+//~^ note: inside `_`
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/ctfe-tail-call-panic.stderr b/tests/ui/explicit-tail-calls/ctfe-tail-call-panic.stderr
new file mode 100644
index 00000000000..8c070512105
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ctfe-tail-call-panic.stderr
@@ -0,0 +1,21 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ctfe-tail-call-panic.rs:9:5
+   |
+LL |     panic!()
+   |     ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/ctfe-tail-call-panic.rs:9:5
+   |
+note: inside `g`
+  --> $DIR/ctfe-tail-call-panic.rs:9:5
+   |
+LL |     panic!()
+   |     ^^^^^^^^
+note: inside `_`
+  --> $DIR/ctfe-tail-call-panic.rs:16:15
+   |
+LL | const _: () = f();
+   |               ^^^
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/explicit-tail-calls/drop-order.rs b/tests/ui/explicit-tail-calls/drop-order.rs
new file mode 100644
index 00000000000..e20730446ec
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/drop-order.rs
@@ -0,0 +1,70 @@
+// FIXME(explicit_tail_calls): enable this test once rustc_codegen_ssa supports tail calls
+//@ ignore-test: tail calls are not implemented in rustc_codegen_ssa yet, so this causes 🧊
+//@ run-pass
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+use std::cell::RefCell;
+
+fn main() {
+    let tail_counter = Default::default();
+    tail_recursive(0, &tail_counter);
+    assert_eq!(tail_counter.into_inner(), (0..128).collect::<Vec<u8>>());
+
+    let simply_counter = Default::default();
+    simply_recursive(0, &simply_counter);
+    assert_eq!(simply_counter.into_inner(), (0..128).rev().collect::<Vec<u8>>());
+
+    let scope_counter = Default::default();
+    out_of_inner_scope(&scope_counter);
+    assert_eq!(scope_counter.into_inner(), (0..8).collect::<Vec<u8>>());
+}
+
+fn tail_recursive(n: u8, order: &RefCell<Vec<u8>>) {
+    if n >= 128 {
+        return;
+    }
+
+    let _local = DropCounter(n, order);
+
+    become tail_recursive(n + 1, order)
+}
+
+fn simply_recursive(n: u8, order: &RefCell<Vec<u8>>) {
+    if n >= 128 {
+        return;
+    }
+
+    let _local = DropCounter(n, order);
+
+    return simply_recursive(n + 1, order);
+}
+
+fn out_of_inner_scope(order: &RefCell<Vec<u8>>) {
+    fn inner(order: &RefCell<Vec<u8>>) {
+        let _7 = DropCounter(7, order);
+        let _6 = DropCounter(6, order);
+    }
+
+    let _5 = DropCounter(5, order);
+    let _4 = DropCounter(4, order);
+
+    if true {
+        let _3 = DropCounter(3, order);
+        let _2 = DropCounter(2, order);
+        loop {
+            let _1 = DropCounter(1, order);
+            let _0 = DropCounter(0, order);
+
+            become inner(order);
+        }
+    }
+}
+
+struct DropCounter<'a>(u8, &'a RefCell<Vec<u8>>);
+
+impl Drop for DropCounter<'_> {
+    #[track_caller]
+    fn drop(&mut self) {
+        self.1.borrow_mut().push(self.0);
+    }
+}
diff --git a/tests/ui/explicit-tail-calls/return-mismatches.rs b/tests/ui/explicit-tail-calls/return-mismatches.rs
index 8094a192913..935a1a1d28b 100644
--- a/tests/ui/explicit-tail-calls/return-mismatches.rs
+++ b/tests/ui/explicit-tail-calls/return-mismatches.rs
@@ -13,7 +13,7 @@ fn _f1() {
     become _g1(); //~ error: mismatched types
 }
 
-fn _g1() -> ! { //~ WARN: cannot return without recursing
+fn _g1() -> ! {
     become _g1();
 }
 
diff --git a/tests/ui/explicit-tail-calls/return-mismatches.stderr b/tests/ui/explicit-tail-calls/return-mismatches.stderr
index 31c7a46ded9..1dcc35797c1 100644
--- a/tests/ui/explicit-tail-calls/return-mismatches.stderr
+++ b/tests/ui/explicit-tail-calls/return-mismatches.stderr
@@ -22,17 +22,6 @@ error[E0308]: mismatched types
 LL |     become _g2();
    |     ^^^^^^^^^^^^ expected `u32`, found `u16`
 
-warning: function cannot return without recursing
-  --> $DIR/return-mismatches.rs:16:1
-   |
-LL | fn _g1() -> ! {
-   | ^^^^^^^^^^^^^ cannot return without recursing
-LL |     become _g1();
-   |            ----- recursive call site
-   |
-   = help: a `loop` may express intention better if this is on purpose
-   = note: `#[warn(unconditional_recursion)]` on by default
-
-error: aborting due to 3 previous errors; 1 warning emitted
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/explicit-tail-calls/unsafeck.rs b/tests/ui/explicit-tail-calls/unsafeck.rs
new file mode 100644
index 00000000000..872a70ca3a0
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/unsafeck.rs
@@ -0,0 +1,11 @@
+#![allow(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+const fn f() {
+    become dangerous();
+    //~^ error: call to unsafe function `dangerous` is unsafe and requires unsafe function or block
+}
+
+const unsafe fn dangerous() {}
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/unsafeck.stderr b/tests/ui/explicit-tail-calls/unsafeck.stderr
new file mode 100644
index 00000000000..25b8967e17b
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/unsafeck.stderr
@@ -0,0 +1,11 @@
+error[E0133]: call to unsafe function `dangerous` is unsafe and requires unsafe function or block
+  --> $DIR/unsafeck.rs:5:12
+   |
+LL |     become dangerous();
+   |            ^^^^^^^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0133`.
diff --git a/tests/ui/fmt/struct-field-as-captured-argument.fixed b/tests/ui/fmt/struct-field-as-captured-argument.fixed
index e13af744ec8..0da40737354 100644
--- a/tests/ui/fmt/struct-field-as-captured-argument.fixed
+++ b/tests/ui/fmt/struct-field-as-captured-argument.fixed
@@ -8,11 +8,11 @@ struct Foo {
 fn main() {
     let foo = Foo { field: 0 };
     let bar = 3;
-    format!("{0}", foo.field); //~ ERROR invalid format string: field access isn't supported
-    format!("{1} {} {bar}", "aa", foo.field); //~ ERROR invalid format string: field access isn't supported
-    format!("{2} {} {1} {bar}", "aa", "bb", foo.field); //~ ERROR invalid format string: field access isn't supported
-    format!("{1} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{1:?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{1:#?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{1:.3} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{0}", foo.field); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1} {} {bar}", "aa", foo.field); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{2} {} {1} {bar}", "aa", "bb", foo.field); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1:?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1:#?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1:.3} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
 }
diff --git a/tests/ui/fmt/struct-field-as-captured-argument.rs b/tests/ui/fmt/struct-field-as-captured-argument.rs
index 6a875a85848..325b4e3a218 100644
--- a/tests/ui/fmt/struct-field-as-captured-argument.rs
+++ b/tests/ui/fmt/struct-field-as-captured-argument.rs
@@ -8,11 +8,11 @@ struct Foo {
 fn main() {
     let foo = Foo { field: 0 };
     let bar = 3;
-    format!("{foo.field}"); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field} {} {bar}", "aa"); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field} {} {1} {bar}", "aa", "bb"); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field:?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field:#?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field:.3} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field}"); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field} {} {bar}", "aa"); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field} {} {1} {bar}", "aa", "bb"); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field:?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field:#?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field:.3} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
 }
diff --git a/tests/ui/fmt/struct-field-as-captured-argument.stderr b/tests/ui/fmt/struct-field-as-captured-argument.stderr
index 7ea8b4068f2..4ef022cecb0 100644
--- a/tests/ui/fmt/struct-field-as-captured-argument.stderr
+++ b/tests/ui/fmt/struct-field-as-captured-argument.stderr
@@ -1,79 +1,79 @@
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:11:15
+  --> $DIR/struct-field-as-captured-argument.rs:11:23
    |
-LL |     format!("{foo.field}");
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field}");
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{0}", foo.field);
-   |               ~  +++++++++++
+LL |     let _ = format!("{0}", foo.field);
+   |                       ~  +++++++++++
 
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:12:15
+  --> $DIR/struct-field-as-captured-argument.rs:12:23
    |
-LL |     format!("{foo.field} {} {bar}", "aa");
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field} {} {bar}", "aa");
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{1} {} {bar}", "aa", foo.field);
-   |               ~                 +++++++++++
+LL |     let _ = format!("{1} {} {bar}", "aa", foo.field);
+   |                       ~                 +++++++++++
 
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:13:15
+  --> $DIR/struct-field-as-captured-argument.rs:13:23
    |
-LL |     format!("{foo.field} {} {1} {bar}", "aa", "bb");
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field} {} {1} {bar}", "aa", "bb");
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{2} {} {1} {bar}", "aa", "bb", foo.field);
-   |               ~                           +++++++++++
+LL |     let _ = format!("{2} {} {1} {bar}", "aa", "bb", foo.field);
+   |                       ~                           +++++++++++
 
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:14:15
+  --> $DIR/struct-field-as-captured-argument.rs:14:23
    |
-LL |     format!("{foo.field} {} {baz}", "aa", baz = 3);
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field} {} {baz}", "aa", baz = 3);
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{1} {} {baz}", "aa", foo.field, baz = 3);
-   |               ~                 +++++++++++
+LL |     let _ = format!("{1} {} {baz}", "aa", foo.field, baz = 3);
+   |                       ~                 +++++++++++
 
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:15:15
+  --> $DIR/struct-field-as-captured-argument.rs:15:23
    |
-LL |     format!("{foo.field:?} {} {baz}", "aa", baz = 3);
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field:?} {} {baz}", "aa", baz = 3);
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{1:?} {} {baz}", "aa", foo.field, baz = 3);
-   |               ~                   +++++++++++
+LL |     let _ = format!("{1:?} {} {baz}", "aa", foo.field, baz = 3);
+   |                       ~                   +++++++++++
 
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:16:15
+  --> $DIR/struct-field-as-captured-argument.rs:16:23
    |
-LL |     format!("{foo.field:#?} {} {baz}", "aa", baz = 3);
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field:#?} {} {baz}", "aa", baz = 3);
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{1:#?} {} {baz}", "aa", foo.field, baz = 3);
-   |               ~                    +++++++++++
+LL |     let _ = format!("{1:#?} {} {baz}", "aa", foo.field, baz = 3);
+   |                       ~                    +++++++++++
 
 error: invalid format string: field access isn't supported
-  --> $DIR/struct-field-as-captured-argument.rs:17:15
+  --> $DIR/struct-field-as-captured-argument.rs:17:23
    |
-LL |     format!("{foo.field:.3} {} {baz}", "aa", baz = 3);
-   |               ^^^^^^^^^ not supported in format string
+LL |     let _ = format!("{foo.field:.3} {} {baz}", "aa", baz = 3);
+   |                       ^^^^^^^^^ not supported in format string
    |
 help: consider using a positional formatting argument instead
    |
-LL |     format!("{1:.3} {} {baz}", "aa", foo.field, baz = 3);
-   |               ~                    +++++++++++
+LL |     let _ = format!("{1:.3} {} {baz}", "aa", foo.field, baz = 3);
+   |                       ~                    +++++++++++
 
 error: aborting due to 7 previous errors
 
diff --git a/tests/ui/generic-associated-types/assume-gat-normalization-for-nested-goals.next.stderr b/tests/ui/generic-associated-types/assume-gat-normalization-for-nested-goals.next.stderr
index 9b5d84b5b09..c5c4f2c4d23 100644
--- a/tests/ui/generic-associated-types/assume-gat-normalization-for-nested-goals.next.stderr
+++ b/tests/ui/generic-associated-types/assume-gat-normalization-for-nested-goals.next.stderr
@@ -1,4 +1,4 @@
-error[E0277]: the trait bound `i32: Baz<Self>` is not satisfied
+error[E0277]: the trait bound `<Self as Foo>::Bar<()>: Eq<i32>` is not satisfied
   --> $DIR/assume-gat-normalization-for-nested-goals.rs:9:30
    |
 LL |     type Bar<T>: Baz<Self> = i32;
diff --git a/tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.current.stderr b/tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.current.stderr
new file mode 100644
index 00000000000..d71c1768a6a
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.current.stderr
@@ -0,0 +1,173 @@
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:5
+   |
+LL | /     fn autobatch<F>(self) -> impl Trait
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     where
+LL | |         F: Callback<Self::CallbackArg>,
+   | |_______________________________________^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:30
+   |
+LL |     fn autobatch<F>(self) -> impl Trait
+   |                              ^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+note: required by a bound in `<Sender as ChannelSender>::autobatch`
+  --> $DIR/false-positive-predicate-entailment-error.rs:43:12
+   |
+LL |     fn autobatch<F>(self) -> impl Trait
+   |        --------- required by a bound in this associated function
+...
+LL |         F: Callback<Self::CallbackArg>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `<Sender as ChannelSender>::autobatch`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:5
+   |
+LL | /     fn autobatch<F>(self) -> impl Trait
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     where
+LL | |         F: Callback<Self::CallbackArg>,
+   | |_______________________________________^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: Callback<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:43:12
+   |
+LL |         F: Callback<Self::CallbackArg>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+note: the requirement `F: Callback<i32>` appears on the `impl`'s method `autobatch` but not on the corresponding trait's method
+  --> $DIR/false-positive-predicate-entailment-error.rs:25:8
+   |
+LL | trait ChannelSender {
+   |       ------------- in this trait
+...
+LL |     fn autobatch<F>(self) -> impl Trait
+   |        ^^^^^^^^^ this trait's method doesn't have the requirement `F: Callback<i32>`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:30
+   |
+LL |     fn autobatch<F>(self) -> impl Trait
+   |                              ^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+
+error[E0277]: the trait bound `F: Callback<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:27:12
+   |
+LL |         F: Callback<Self::CallbackArg>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:5
+   |
+LL | /     fn autobatch<F>(self) -> impl Trait
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     where
+LL | |         F: Callback<Self::CallbackArg>,
+   | |_______________________________________^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:43:12
+   |
+LL |         F: Callback<Self::CallbackArg>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`
+   |
+note: required by a bound in `Callback`
+  --> $DIR/false-positive-predicate-entailment-error.rs:10:20
+   |
+LL | trait Callback<A>: MyFn<A, Output = Self::Ret> {
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Callback`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.rs b/tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.rs
new file mode 100644
index 00000000000..59fdeab9e0a
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.rs
@@ -0,0 +1,51 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+trait MyFn<T> {
+    type Output;
+}
+
+trait Callback<A>: MyFn<A, Output = Self::Ret> {
+    type Ret;
+}
+
+impl<A, F: MyFn<A>> Callback<A> for F {
+    type Ret = F::Output;
+}
+
+struct Thing;
+trait Trait {}
+impl Trait for Thing {}
+
+trait ChannelSender {
+    type CallbackArg;
+
+    fn autobatch<F>(self) -> impl Trait
+    where
+        F: Callback<Self::CallbackArg>;
+        //[current]~^ ERROR the trait bound `F: Callback<i32>` is not satisfied
+}
+
+struct Sender;
+
+impl ChannelSender for Sender {
+    type CallbackArg = i32;
+
+    fn autobatch<F>(self) -> impl Trait
+    //[current]~^ ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    where
+        F: Callback<Self::CallbackArg>,
+        //[current]~^ ERROR the trait bound `F: Callback<i32>` is not satisfied
+        //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    {
+        Thing
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/nested_impl_trait.rs b/tests/ui/impl-trait/nested_impl_trait.rs
index 502b2af2bc6..760102794c3 100644
--- a/tests/ui/impl-trait/nested_impl_trait.rs
+++ b/tests/ui/impl-trait/nested_impl_trait.rs
@@ -5,7 +5,7 @@ fn fine(x: impl Into<u32>) -> impl Into<u32> { x }
 
 fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
 //~^ ERROR nested `impl Trait` is not allowed
-//~| ERROR the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+//~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
 
 fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
 //~^ ERROR nested `impl Trait` is not allowed
@@ -18,7 +18,7 @@ struct X;
 impl X {
     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
     //~^ ERROR nested `impl Trait` is not allowed
-    //~| ERROR the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+    //~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
 }
 
 fn allowed_in_assoc_type() -> impl Iterator<Item=impl Fn()> {
diff --git a/tests/ui/impl-trait/nested_impl_trait.stderr b/tests/ui/impl-trait/nested_impl_trait.stderr
index a53312e5c0b..83d1347aff4 100644
--- a/tests/ui/impl-trait/nested_impl_trait.stderr
+++ b/tests/ui/impl-trait/nested_impl_trait.stderr
@@ -42,7 +42,7 @@ LL | fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
    |
    = note: `impl Trait` is only allowed in arguments and return types of functions and methods
 
-error[E0277]: the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
   --> $DIR/nested_impl_trait.rs:6:46
    |
 LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
@@ -51,7 +51,7 @@ LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
    = help: the trait `Into<U>` is implemented for `T`
    = note: required for `impl Into<u32>` to implement `Into<impl Debug>`
 
-error[E0277]: the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
   --> $DIR/nested_impl_trait.rs:19:34
    |
 LL |     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
diff --git a/tests/ui/intrinsics/not-overridden.rs b/tests/ui/intrinsics/not-overridden.rs
index a53071e304d..93b408331b8 100644
--- a/tests/ui/intrinsics/not-overridden.rs
+++ b/tests/ui/intrinsics/not-overridden.rs
@@ -1,6 +1,6 @@
 //! Check that intrinsics that do not get overridden, but are marked as such,
 //! cause an error instead of silently invoking the body.
-#![feature(rustc_attrs/* , effects*/)] // FIXME(effects)
+#![feature(rustc_attrs)]
 //@ build-fail
 //@ failure-status:101
 //@ normalize-stderr-test ".*note: .*\n\n" -> ""
diff --git a/tests/ui/intrinsics/safe-intrinsic-mismatch.effects.stderr b/tests/ui/intrinsics/safe-intrinsic-mismatch.effects.stderr
new file mode 100644
index 00000000000..d9a4960feec
--- /dev/null
+++ b/tests/ui/intrinsics/safe-intrinsic-mismatch.effects.stderr
@@ -0,0 +1,52 @@
+error: using `#![feature(effects)]` without enabling next trait solver globally
+   |
+   = note: the next trait solver must be enabled globally for the effects feature to work correctly
+   = help: use `-Znext-solver` to enable
+
+error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `size_of`
+  --> $DIR/safe-intrinsic-mismatch.rs:11:5
+   |
+LL |     fn size_of<T>() -> usize;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `size_of`
+  --> $DIR/safe-intrinsic-mismatch.rs:11:5
+   |
+LL |     fn size_of<T>() -> usize;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `assume`
+  --> $DIR/safe-intrinsic-mismatch.rs:16:1
+   |
+LL | const fn assume(_b: bool) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0308]: intrinsic has wrong type
+  --> $DIR/safe-intrinsic-mismatch.rs:16:16
+   |
+LL | const fn assume(_b: bool) {}
+   |                ^ expected unsafe fn, found safe fn
+   |
+   = note: expected signature `unsafe fn(_)`
+              found signature `fn(_)`
+
+error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `const_deallocate`
+  --> $DIR/safe-intrinsic-mismatch.rs:20:1
+   |
+LL | const fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0308]: intrinsic has wrong type
+  --> $DIR/safe-intrinsic-mismatch.rs:20:26
+   |
+LL | const fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
+   |                          ^ expected unsafe fn, found safe fn
+   |
+   = note: expected signature `unsafe fn(_, _, _)`
+              found signature `fn(_, _, _)`
+
+error: aborting due to 7 previous errors
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/intrinsics/safe-intrinsic-mismatch.rs b/tests/ui/intrinsics/safe-intrinsic-mismatch.rs
index c116ba7a62e..af563e996c1 100644
--- a/tests/ui/intrinsics/safe-intrinsic-mismatch.rs
+++ b/tests/ui/intrinsics/safe-intrinsic-mismatch.rs
@@ -1,6 +1,11 @@
+//@ revisions: stock effects
 #![feature(intrinsics)]
 #![feature(rustc_attrs)]
-// FIXME(effects) do this with revisions #![feature(effects)]
+// as effects insert a const generic param to const intrinsics,
+// check here that it doesn't report a const param mismatch either
+// enabling or disabling effects.
+#![cfg_attr(effects, feature(effects))]
+#![allow(incomplete_features)]
 
 extern "rust-intrinsic" {
     fn size_of<T>() -> usize; //~ ERROR intrinsic safety mismatch
diff --git a/tests/ui/intrinsics/safe-intrinsic-mismatch.stderr b/tests/ui/intrinsics/safe-intrinsic-mismatch.stock.stderr
index 7f37e0f8211..6864c0f36de 100644
--- a/tests/ui/intrinsics/safe-intrinsic-mismatch.stderr
+++ b/tests/ui/intrinsics/safe-intrinsic-mismatch.stock.stderr
@@ -1,11 +1,11 @@
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `size_of`
-  --> $DIR/safe-intrinsic-mismatch.rs:6:5
+  --> $DIR/safe-intrinsic-mismatch.rs:11:5
    |
 LL |     fn size_of<T>() -> usize;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `size_of`
-  --> $DIR/safe-intrinsic-mismatch.rs:6:5
+  --> $DIR/safe-intrinsic-mismatch.rs:11:5
    |
 LL |     fn size_of<T>() -> usize;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -13,13 +13,13 @@ LL |     fn size_of<T>() -> usize;
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `assume`
-  --> $DIR/safe-intrinsic-mismatch.rs:11:1
+  --> $DIR/safe-intrinsic-mismatch.rs:16:1
    |
 LL | const fn assume(_b: bool) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: intrinsic has wrong type
-  --> $DIR/safe-intrinsic-mismatch.rs:11:16
+  --> $DIR/safe-intrinsic-mismatch.rs:16:16
    |
 LL | const fn assume(_b: bool) {}
    |                ^ expected unsafe fn, found safe fn
@@ -28,13 +28,13 @@ LL | const fn assume(_b: bool) {}
               found signature `fn(_)`
 
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `const_deallocate`
-  --> $DIR/safe-intrinsic-mismatch.rs:15:1
+  --> $DIR/safe-intrinsic-mismatch.rs:20:1
    |
 LL | const fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: intrinsic has wrong type
-  --> $DIR/safe-intrinsic-mismatch.rs:15:26
+  --> $DIR/safe-intrinsic-mismatch.rs:20:26
    |
 LL | const fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
    |                          ^ expected unsafe fn, found safe fn
diff --git a/tests/ui/issues/issue-20676.rs b/tests/ui/issues/issue-20676.rs
index b3319950b42..2059365c7d6 100644
--- a/tests/ui/issues/issue-20676.rs
+++ b/tests/ui/issues/issue-20676.rs
@@ -8,5 +8,5 @@ use std::fmt;
 
 fn main() {
     let a: &dyn fmt::Debug = &1;
-    format!("{:?}", a);
+    let _ = format!("{:?}", a);
 }
diff --git a/tests/ui/lint/lint-unconditional-recursion-tail-calls.rs b/tests/ui/lint/lint-unconditional-recursion-tail-calls.rs
new file mode 100644
index 00000000000..c94bf032579
--- /dev/null
+++ b/tests/ui/lint/lint-unconditional-recursion-tail-calls.rs
@@ -0,0 +1,24 @@
+#![allow(incomplete_features, dead_code)]
+#![deny(unconditional_recursion)] //~ note: the lint level is defined here
+#![feature(explicit_tail_calls)]
+
+fn f(x: bool) {
+    //~^ error: function cannot return without recursing
+    //~| note: cannot return without recursing
+    if x {
+        become f(!x)
+    } else {
+        f(!x) //~ note: recursive call site
+    }
+}
+
+// This should *not* lint, tail-recursive functions which never return is a reasonable thing
+fn g(x: bool) {
+    if x {
+        become g(!x)
+    } else {
+        become g(!x)
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/lint/lint-unconditional-recursion-tail-calls.stderr b/tests/ui/lint/lint-unconditional-recursion-tail-calls.stderr
new file mode 100644
index 00000000000..52f9740d027
--- /dev/null
+++ b/tests/ui/lint/lint-unconditional-recursion-tail-calls.stderr
@@ -0,0 +1,18 @@
+error: function cannot return without recursing
+  --> $DIR/lint-unconditional-recursion-tail-calls.rs:5:1
+   |
+LL | fn f(x: bool) {
+   | ^^^^^^^^^^^^^ cannot return without recursing
+...
+LL |         f(!x)
+   |         ----- recursive call site
+   |
+   = help: a `loop` may express intention better if this is on purpose
+note: the lint level is defined here
+  --> $DIR/lint-unconditional-recursion-tail-calls.rs:2:9
+   |
+LL | #![deny(unconditional_recursion)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/macros/macro-metavar-expr-concat/allowed-operations.rs b/tests/ui/macros/macro-metavar-expr-concat/allowed-operations.rs
index e44eeffb01b..1acefa314aa 100644
--- a/tests/ui/macros/macro-metavar-expr-concat/allowed-operations.rs
+++ b/tests/ui/macros/macro-metavar-expr-concat/allowed-operations.rs
@@ -37,6 +37,16 @@ macro_rules! without_dollar_sign_is_an_ident {
     };
 }
 
+macro_rules! literals {
+    ($ident:ident) => {{
+        let ${concat(_a, "_b")}: () = ();
+        let ${concat("_b", _a)}: () = ();
+
+        let ${concat($ident, "_b")}: () = ();
+        let ${concat("_b", $ident)}: () = ();
+    }};
+}
+
 fn main() {
     create_things!(behold);
     behold_separated_idents_in_a_fn();
@@ -55,4 +65,6 @@ fn main() {
     without_dollar_sign_is_an_ident!(_123);
     assert_eq!(VARident, 1);
     assert_eq!(VAR_123, 2);
+
+    literals!(_hello);
 }
diff --git a/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.rs b/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.rs
index f72b9baca89..b1cb2141cc4 100644
--- a/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.rs
+++ b/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.rs
@@ -26,14 +26,14 @@ macro_rules! idents_11 {
 macro_rules! no_params {
     () => {
         let ${concat(r#abc, abc)}: () = ();
-        //~^ ERROR `${concat(..)}` currently does not support raw identifiers
+        //~^ ERROR expected identifier or string literal
         //~| ERROR expected pattern, found `$`
 
         let ${concat(abc, r#abc)}: () = ();
-        //~^ ERROR `${concat(..)}` currently does not support raw identifiers
+        //~^ ERROR expected identifier or string literal
 
         let ${concat(r#abc, r#abc)}: () = ();
-        //~^ ERROR `${concat(..)}` currently does not support raw identifiers
+        //~^ ERROR expected identifier or string literal
     };
 }
 
diff --git a/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.stderr b/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.stderr
index dd525cf0801..4e11e20acc5 100644
--- a/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.stderr
+++ b/tests/ui/macros/macro-metavar-expr-concat/raw-identifiers.stderr
@@ -1,16 +1,16 @@
-error: `${concat(..)}` currently does not support raw identifiers
+error: expected identifier or string literal
   --> $DIR/raw-identifiers.rs:28:22
    |
 LL |         let ${concat(r#abc, abc)}: () = ();
    |                      ^^^^^
 
-error: `${concat(..)}` currently does not support raw identifiers
+error: expected identifier or string literal
   --> $DIR/raw-identifiers.rs:32:27
    |
 LL |         let ${concat(abc, r#abc)}: () = ();
    |                           ^^^^^
 
-error: `${concat(..)}` currently does not support raw identifiers
+error: expected identifier or string literal
   --> $DIR/raw-identifiers.rs:35:22
    |
 LL |         let ${concat(r#abc, r#abc)}: () = ();
diff --git a/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.rs b/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.rs
index bf47442ea76..b2845c8d1c1 100644
--- a/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.rs
+++ b/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.rs
@@ -11,9 +11,6 @@ macro_rules! wrong_concat_declarations {
         ${concat(aaaa,)}
         //~^ ERROR expected identifier
 
-        ${concat(aaaa, 1)}
-        //~^ ERROR expected identifier
-
         ${concat(_, aaaa)}
 
         ${concat(aaaa aaaa)}
@@ -30,9 +27,6 @@ macro_rules! wrong_concat_declarations {
 
         ${concat($ex, aaaa,)}
         //~^ ERROR expected identifier
-
-        ${concat($ex, aaaa, 123)}
-        //~^ ERROR expected identifier
     };
 }
 
@@ -43,8 +37,80 @@ macro_rules! dollar_sign_without_referenced_ident {
     };
 }
 
+macro_rules! starting_number {
+    ($ident:ident) => {{
+        let ${concat("1", $ident)}: () = ();
+        //~^ ERROR `${concat(..)}` is not generating a valid identifier
+    }};
+}
+
+macro_rules! starting_valid_unicode {
+    ($ident:ident) => {{
+        let ${concat("Ý", $ident)}: () = ();
+    }};
+}
+
+macro_rules! starting_invalid_unicode {
+    ($ident:ident) => {{
+        let ${concat("\u{00BD}", $ident)}: () = ();
+        //~^ ERROR `${concat(..)}` is not generating a valid identifier
+    }};
+}
+
+macro_rules! ending_number {
+    ($ident:ident) => {{
+        let ${concat($ident, "1")}: () = ();
+    }};
+}
+
+macro_rules! ending_valid_unicode {
+    ($ident:ident) => {{
+        let ${concat($ident, "Ý")}: () = ();
+    }};
+}
+
+macro_rules! ending_invalid_unicode {
+    ($ident:ident) => {{
+        let ${concat($ident, "\u{00BD}")}: () = ();
+        //~^ ERROR `${concat(..)}` is not generating a valid identifier
+    }};
+}
+
+macro_rules! empty {
+    () => {{
+        let ${concat("", "")}: () = ();
+        //~^ ERROR `${concat(..)}` is not generating a valid identifier
+    }};
+}
+
+macro_rules! unsupported_literals {
+    ($ident:ident) => {{
+        let ${concat(_a, 'b')}: () = ();
+        //~^ ERROR expected identifier or string literal
+        //~| ERROR expected pattern
+        let ${concat(_a, 1)}: () = ();
+        //~^ ERROR expected identifier or string literal
+
+        let ${concat($ident, 'b')}: () = ();
+        //~^ ERROR expected identifier or string literal
+        let ${concat($ident, 1)}: () = ();
+        //~^ ERROR expected identifier or string literal
+    }};
+}
+
 fn main() {
     wrong_concat_declarations!(1);
 
     dollar_sign_without_referenced_ident!(VAR);
+
+    starting_number!(_abc);
+    starting_valid_unicode!(_abc);
+    starting_invalid_unicode!(_abc);
+
+    ending_number!(_abc);
+    ending_valid_unicode!(_abc);
+    ending_invalid_unicode!(_abc);
+    unsupported_literals!(_abc);
+
+    empty!();
 }
diff --git a/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.stderr b/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.stderr
index b216a86d59a..2fe5842b39e 100644
--- a/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.stderr
+++ b/tests/ui/macros/macro-metavar-expr-concat/syntax-errors.stderr
@@ -1,4 +1,4 @@
-error: expected identifier
+error: expected identifier or string literal
   --> $DIR/syntax-errors.rs:5:10
    |
 LL |         ${concat()}
@@ -10,59 +10,126 @@ error: `concat` must have at least two elements
 LL |         ${concat(aaaa)}
    |           ^^^^^^
 
-error: expected identifier
+error: expected identifier or string literal
   --> $DIR/syntax-errors.rs:11:10
    |
 LL |         ${concat(aaaa,)}
    |          ^^^^^^^^^^^^^^^
 
-error: expected identifier, found `1`
-  --> $DIR/syntax-errors.rs:14:24
-   |
-LL |         ${concat(aaaa, 1)}
-   |                        ^ help: try removing `1`
-
 error: expected comma
-  --> $DIR/syntax-errors.rs:19:10
+  --> $DIR/syntax-errors.rs:16:10
    |
 LL |         ${concat(aaaa aaaa)}
    |          ^^^^^^^^^^^^^^^^^^^
 
 error: `concat` must have at least two elements
-  --> $DIR/syntax-errors.rs:22:11
+  --> $DIR/syntax-errors.rs:19:11
    |
 LL |         ${concat($ex)}
    |           ^^^^^^
 
 error: expected comma
-  --> $DIR/syntax-errors.rs:28:10
+  --> $DIR/syntax-errors.rs:25:10
    |
 LL |         ${concat($ex, aaaa 123)}
    |          ^^^^^^^^^^^^^^^^^^^^^^^
 
-error: expected identifier
-  --> $DIR/syntax-errors.rs:31:10
+error: expected identifier or string literal
+  --> $DIR/syntax-errors.rs:28:10
    |
 LL |         ${concat($ex, aaaa,)}
    |          ^^^^^^^^^^^^^^^^^^^^
 
-error: expected identifier, found `123`
-  --> $DIR/syntax-errors.rs:34:29
+error: expected identifier or string literal
+  --> $DIR/syntax-errors.rs:88:26
    |
-LL |         ${concat($ex, aaaa, 123)}
-   |                             ^^^ help: try removing `123`
+LL |         let ${concat(_a, 'b')}: () = ();
+   |                          ^^^
+
+error: expected identifier or string literal
+  --> $DIR/syntax-errors.rs:91:26
+   |
+LL |         let ${concat(_a, 1)}: () = ();
+   |                          ^
+
+error: expected identifier or string literal
+  --> $DIR/syntax-errors.rs:94:30
+   |
+LL |         let ${concat($ident, 'b')}: () = ();
+   |                              ^^^
+
+error: expected identifier or string literal
+  --> $DIR/syntax-errors.rs:96:30
+   |
+LL |         let ${concat($ident, 1)}: () = ();
+   |                              ^
 
 error: `${concat(..)}` currently only accepts identifiers or meta-variables as parameters
-  --> $DIR/syntax-errors.rs:25:19
+  --> $DIR/syntax-errors.rs:22:19
    |
 LL |         ${concat($ex, aaaa)}
    |                   ^^
 
 error: variable `foo` is not recognized in meta-variable expression
-  --> $DIR/syntax-errors.rs:41:30
+  --> $DIR/syntax-errors.rs:35:30
    |
 LL |         const ${concat(FOO, $foo)}: i32 = 2;
    |                              ^^^
 
-error: aborting due to 11 previous errors
+error: `${concat(..)}` is not generating a valid identifier
+  --> $DIR/syntax-errors.rs:42:14
+   |
+LL |         let ${concat("1", $ident)}: () = ();
+   |              ^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     starting_number!(_abc);
+   |     ---------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `starting_number` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: `${concat(..)}` is not generating a valid identifier
+  --> $DIR/syntax-errors.rs:55:14
+   |
+LL |         let ${concat("\u{00BD}", $ident)}: () = ();
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     starting_invalid_unicode!(_abc);
+   |     ------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `starting_invalid_unicode` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: `${concat(..)}` is not generating a valid identifier
+  --> $DIR/syntax-errors.rs:74:14
+   |
+LL |         let ${concat($ident, "\u{00BD}")}: () = ();
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     ending_invalid_unicode!(_abc);
+   |     ----------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `ending_invalid_unicode` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected pattern, found `$`
+  --> $DIR/syntax-errors.rs:88:13
+   |
+LL |         let ${concat(_a, 'b')}: () = ();
+   |             ^ expected pattern
+...
+LL |     unsupported_literals!(_abc);
+   |     --------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `unsupported_literals` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: `${concat(..)}` is not generating a valid identifier
+  --> $DIR/syntax-errors.rs:81:14
+   |
+LL |         let ${concat("", "")}: () = ();
+   |              ^^^^^^^^^^^^^^^^
+...
+LL |     empty!();
+   |     -------- in this macro invocation
+   |
+   = note: this error originates in the macro `empty` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 18 previous errors
 
diff --git a/tests/ui/macros/macro-metavar-expr-concat/unicode-expansion.rs b/tests/ui/macros/macro-metavar-expr-concat/unicode-expansion.rs
new file mode 100644
index 00000000000..b2cfb211e2d
--- /dev/null
+++ b/tests/ui/macros/macro-metavar-expr-concat/unicode-expansion.rs
@@ -0,0 +1,14 @@
+//@ run-pass
+
+#![feature(macro_metavar_expr_concat)]
+
+macro_rules! turn_to_page {
+    ($ident:ident) => {
+        const ${concat("Ḧ", $ident)}: i32 = 394;
+    };
+}
+
+fn main() {
+    turn_to_page!(P);
+    assert_eq!(ḦP, 394);
+}
diff --git a/tests/ui/macros/out-of-scope-calls-false-positives.rs b/tests/ui/macros/out-of-scope-calls-false-positives.rs
new file mode 100644
index 00000000000..8d696c177e4
--- /dev/null
+++ b/tests/ui/macros/out-of-scope-calls-false-positives.rs
@@ -0,0 +1,10 @@
+//@ check-pass
+//@ needs-asm-support
+
+macro_rules! mac { () => { "" } }
+macro_rules! mac2 { () => { "auxiliary/issue-40469.rs" } }
+
+std::arch::global_asm!(mac!()); // OK
+include!(mac2!()); // OK
+
+fn main() {}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr b/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr
index 8e4ba192d79..2c44ad2e0a4 100644
--- a/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr
+++ b/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr
@@ -190,7 +190,7 @@ error: unrecognized meta-variable expression
 LL |     ( $( $i:ident ),* ) => { ${ aaaaaaaaaaaaaa(i) } };
    |                                 ^^^^^^^^^^^^^^ help: supported expressions are count, ignore, index and len
 
-error: expected identifier
+error: expected identifier or string literal
   --> $DIR/syntax-errors.rs:118:33
    |
 LL |     ( $( $i:ident ),* ) => { ${ {} } };
diff --git a/tests/ui/mir/alignment/misaligned-constant-gvn.rs b/tests/ui/mir/alignment/misaligned-constant-gvn.rs
new file mode 100644
index 00000000000..363d5c0ed34
--- /dev/null
+++ b/tests/ui/mir/alignment/misaligned-constant-gvn.rs
@@ -0,0 +1,8 @@
+//@ build-pass
+//@ compile-flags: -Zmir-opt-level=0 -Zmir-enable-passes=+GVN
+
+fn main() {
+    let variant: Option<u32> = None;
+    let transmuted: u64 = unsafe { std::mem::transmute(variant) };
+    println!("{transmuted}");
+}
diff --git a/tests/ui/mismatched_types/cast-rfc0401.rs b/tests/ui/mismatched_types/cast-rfc0401.rs
index 57222f45947..b2ff5b4a0c0 100644
--- a/tests/ui/mismatched_types/cast-rfc0401.rs
+++ b/tests/ui/mismatched_types/cast-rfc0401.rs
@@ -66,7 +66,7 @@ fn main()
 
     let cf: *const dyn Foo = &0;
     let _ = cf as *const [u16]; //~ ERROR is invalid
-    let _ = cf as *const dyn Bar; //~ ERROR is invalid
+    let _ = cf as *const dyn Bar; //~ ERROR casting `*const dyn Foo` as `*const dyn Bar` is invalid
 
     vec![0.0].iter().map(|s| s as f32).collect::<Vec<f32>>(); //~ ERROR is invalid
 }
diff --git a/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.stderr b/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2015.stderr
index fbd92f8f662..a75039b8237 100644
--- a/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.stderr
+++ b/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2015.stderr
@@ -1,5 +1,5 @@
 warning: never type fallback affects this call to an `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:8:18
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:13:18
    |
 LL |         unsafe { mem::zeroed() }
    |                  ^^^^^^^^^^^^^
@@ -10,7 +10,7 @@ LL |         unsafe { mem::zeroed() }
    = note: `#[warn(never_type_fallback_flowing_into_unsafe)]` on by default
 
 warning: never type fallback affects this call to an `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:23:13
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:30:13
    |
 LL |             core::mem::transmute(Zst)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -20,7 +20,7 @@ LL |             core::mem::transmute(Zst)
    = help: specify the type explicitly
 
 warning: never type fallback affects this union access
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:39:18
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:47:18
    |
 LL |         unsafe { Union { a: () }.b }
    |                  ^^^^^^^^^^^^^^^^^
@@ -30,7 +30,7 @@ LL |         unsafe { Union { a: () }.b }
    = help: specify the type explicitly
 
 warning: never type fallback affects this raw pointer dereference
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:49:18
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:58:18
    |
 LL |         unsafe { *ptr::from_ref(&()).cast() }
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -40,7 +40,7 @@ LL |         unsafe { *ptr::from_ref(&()).cast() }
    = help: specify the type explicitly
 
 warning: never type fallback affects this call to an `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:67:18
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:79:18
    |
 LL |         unsafe { internally_create(x) }
    |                  ^^^^^^^^^^^^^^^^^^^^
@@ -50,7 +50,7 @@ LL |         unsafe { internally_create(x) }
    = help: specify the type explicitly
 
 warning: never type fallback affects this call to an `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:83:18
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:97:18
    |
 LL |         unsafe { zeroed() }
    |                  ^^^^^^^^
@@ -60,7 +60,7 @@ LL |         unsafe { zeroed() }
    = help: specify the type explicitly
 
 warning: never type fallback affects this `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:79:22
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:92:22
    |
 LL |         let zeroed = mem::zeroed;
    |                      ^^^^^^^^^^^
@@ -70,7 +70,7 @@ LL |         let zeroed = mem::zeroed;
    = help: specify the type explicitly
 
 warning: never type fallback affects this `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:98:17
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:115:17
    |
 LL |         let f = internally_create;
    |                 ^^^^^^^^^^^^^^^^^
@@ -80,7 +80,7 @@ LL |         let f = internally_create;
    = help: specify the type explicitly
 
 warning: never type fallback affects this call to an `unsafe` method
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:122:13
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:140:13
    |
 LL |             S(marker::PhantomData).create_out_of_thin_air()
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -90,7 +90,7 @@ LL |             S(marker::PhantomData).create_out_of_thin_air()
    = help: specify the type explicitly
 
 warning: never type fallback affects this call to an `unsafe` function
-  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:139:19
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:158:19
    |
 LL |             match send_message::<_ /* ?0 */>() {
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2024.stderr b/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2024.stderr
new file mode 100644
index 00000000000..4138e9f8c86
--- /dev/null
+++ b/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2024.stderr
@@ -0,0 +1,116 @@
+error: never type fallback affects this call to an `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:13:18
+   |
+LL |         unsafe { mem::zeroed() }
+   |                  ^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+   = note: `#[deny(never_type_fallback_flowing_into_unsafe)]` on by default
+
+error: never type fallback affects this call to an `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:30:13
+   |
+LL |             core::mem::transmute(Zst)
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this union access
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:47:18
+   |
+LL |         unsafe { Union { a: () }.b }
+   |                  ^^^^^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this raw pointer dereference
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:58:18
+   |
+LL |         unsafe { *ptr::from_ref(&()).cast() }
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this call to an `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:79:18
+   |
+LL |         unsafe { internally_create(x) }
+   |                  ^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this call to an `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:97:18
+   |
+LL |         unsafe { zeroed() }
+   |                  ^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:92:22
+   |
+LL |         let zeroed = mem::zeroed;
+   |                      ^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:115:17
+   |
+LL |         let f = internally_create;
+   |                 ^^^^^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this call to an `unsafe` method
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:140:13
+   |
+LL |             S(marker::PhantomData).create_out_of_thin_air()
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+
+error: never type fallback affects this call to an `unsafe` function
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:158:19
+   |
+LL |             match send_message::<_ /* ?0 */>() {
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |         msg_send!();
+   |         ----------- in this macro invocation
+   |
+   = warning: this will change its meaning in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the type explicitly
+   = note: this error originates in the macro `msg_send` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: the type `!` does not permit zero-initialization
+  --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:13:18
+   |
+LL |         unsafe { mem::zeroed() }
+   |                  ^^^^^^^^^^^^^ this code causes undefined behavior when executed
+   |
+   = note: the `!` type has no valid value
+   = note: `#[warn(invalid_value)]` on by default
+
+error: aborting due to 10 previous errors; 1 warning emitted
+
diff --git a/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.rs b/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.rs
index d65bfee843e..c96f4dda3f8 100644
--- a/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.rs
+++ b/tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.rs
@@ -1,4 +1,9 @@
-//@ check-pass
+//@ revisions: e2015 e2024
+//@[e2015] check-pass
+//@[e2024] check-fail
+//@[e2024] edition:2024
+//@[e2024] compile-flags: -Zunstable-options
+
 use std::{marker, mem, ptr};
 
 fn main() {}
@@ -6,8 +11,10 @@ fn main() {}
 fn _zero() {
     if false {
         unsafe { mem::zeroed() }
-        //~^ warn: never type fallback affects this call to an `unsafe` function
+        //[e2015]~^ warn: never type fallback affects this call to an `unsafe` function
+        //[e2024]~^^ error: never type fallback affects this call to an `unsafe` function
         //~| warn: this will change its meaning in a future release!
+        //[e2024]~| warning: the type `!` does not permit zero-initialization
     } else {
         return;
     };
@@ -21,7 +28,8 @@ fn _trans() {
         unsafe {
             struct Zst;
             core::mem::transmute(Zst)
-            //~^ warn: never type fallback affects this call to an `unsafe` function
+            //[e2015]~^ warn: never type fallback affects this call to an `unsafe` function
+            //[e2024]~^^ error: never type fallback affects this call to an `unsafe` function
             //~| warn: this will change its meaning in a future release!
         }
     } else {
@@ -37,7 +45,8 @@ fn _union() {
         }
 
         unsafe { Union { a: () }.b }
-        //~^ warn: never type fallback affects this union access
+        //[e2015]~^ warn: never type fallback affects this union access
+        //[e2024]~^^ error: never type fallback affects this union access
         //~| warn: this will change its meaning in a future release!
     } else {
         return;
@@ -47,7 +56,8 @@ fn _union() {
 fn _deref() {
     if false {
         unsafe { *ptr::from_ref(&()).cast() }
-        //~^ warn: never type fallback affects this raw pointer dereference
+        //[e2015]~^ warn: never type fallback affects this raw pointer dereference
+        //[e2024]~^^ error: never type fallback affects this raw pointer dereference
         //~| warn: this will change its meaning in a future release!
     } else {
         return;
@@ -57,7 +67,9 @@ fn _deref() {
 fn _only_generics() {
     if false {
         unsafe fn internally_create<T>(_: Option<T>) {
-            let _ = mem::zeroed::<T>();
+            unsafe {
+                let _ = mem::zeroed::<T>();
+            }
         }
 
         // We need the option (and unwrap later) to call a function in a way,
@@ -65,7 +77,8 @@ fn _only_generics() {
         let x = None;
 
         unsafe { internally_create(x) }
-        //~^ warn: never type fallback affects this call to an `unsafe` function
+        //[e2015]~^ warn: never type fallback affects this call to an `unsafe` function
+        //[e2024]~^^ error: never type fallback affects this call to an `unsafe` function
         //~| warn: this will change its meaning in a future release!
 
         x.unwrap()
@@ -77,11 +90,13 @@ fn _only_generics() {
 fn _stored_function() {
     if false {
         let zeroed = mem::zeroed;
-        //~^ warn: never type fallback affects this `unsafe` function
+        //[e2015]~^ warn: never type fallback affects this `unsafe` function
+        //[e2024]~^^ error: never type fallback affects this `unsafe` function
         //~| warn: this will change its meaning in a future release!
 
         unsafe { zeroed() }
-        //~^ warn: never type fallback affects this call to an `unsafe` function
+        //[e2015]~^ warn: never type fallback affects this call to an `unsafe` function
+        //[e2024]~^^ error: never type fallback affects this call to an `unsafe` function
         //~| warn: this will change its meaning in a future release!
     } else {
         return;
@@ -91,12 +106,15 @@ fn _stored_function() {
 fn _only_generics_stored_function() {
     if false {
         unsafe fn internally_create<T>(_: Option<T>) {
-            let _ = mem::zeroed::<T>();
+            unsafe {
+                let _ = mem::zeroed::<T>();
+            }
         }
 
         let x = None;
         let f = internally_create;
-        //~^ warn: never type fallback affects this `unsafe` function
+        //[e2015]~^ warn: never type fallback affects this `unsafe` function
+        //[e2024]~^^ error: never type fallback affects this `unsafe` function
         //~| warn: this will change its meaning in a future release!
 
         unsafe { f(x) }
@@ -120,7 +138,8 @@ fn _method() {
     if false {
         unsafe {
             S(marker::PhantomData).create_out_of_thin_air()
-            //~^ warn: never type fallback affects this call to an `unsafe` method
+            //[e2015]~^ warn: never type fallback affects this call to an `unsafe` method
+            //[e2024]~^^ error: never type fallback affects this call to an `unsafe` method
             //~| warn: this will change its meaning in a future release!
         }
     } else {
@@ -137,7 +156,8 @@ fn _objc() {
     macro_rules! msg_send {
         () => {
             match send_message::<_ /* ?0 */>() {
-                //~^ warn: never type fallback affects this call to an `unsafe` function
+                //[e2015]~^ warn: never type fallback affects this call to an `unsafe` function
+                //[e2024]~^^ error: never type fallback affects this call to an `unsafe` function
                 //~| warn: this will change its meaning in a future release!
                 Ok(x) => x,
                 Err(_) => loop {},
diff --git a/tests/ui/parser/bad-let-else-statement.rs b/tests/ui/parser/bad-let-else-statement.rs
index ff6619cbc98..3ede26dbcd0 100644
--- a/tests/ui/parser/bad-let-else-statement.rs
+++ b/tests/ui/parser/bad-let-else-statement.rs
@@ -147,14 +147,14 @@ fn o() -> Result<(), ()> {
     };
 }
 
-fn p() {
-    let 0 = become {
-        ()
-    } else {
-        //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
-        return;
-    };
-}
+// fn p() { // FIXME(explicit_tail_calls): this currently trips an assertion...
+//     let 0 = become {
+//         ()
+//     } else {
+//         // ~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
+//         return;
+//     };
+// }
 
 fn q() {
     let foo = |x: i32| {
diff --git a/tests/ui/parser/bad-let-else-statement.stderr b/tests/ui/parser/bad-let-else-statement.stderr
index 0bf6a346dfb..79d722bb7ac 100644
--- a/tests/ui/parser/bad-let-else-statement.stderr
+++ b/tests/ui/parser/bad-let-else-statement.stderr
@@ -204,19 +204,6 @@ LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:153:5
-   |
-LL |     } else {
-   |     ^
-   |
-help: wrap the expression in parentheses
-   |
-LL ~     let 0 = become ({
-LL |         ()
-LL ~     }) else {
-   |
-
-error: right curly brace `}` before `else` in a `let...else` statement not allowed
   --> $DIR/bad-let-else-statement.rs:163:5
    |
 LL |     } else {
@@ -325,5 +312,5 @@ LL | |     } else {
    = note: this pattern will always match, so the `else` clause is useless
    = help: consider removing the `else` clause
 
-error: aborting due to 20 previous errors; 5 warnings emitted
+error: aborting due to 19 previous errors; 5 warnings emitted
 
diff --git a/tests/ui/resolve/field-and-method-in-self-not-available-in-assoc-fn.stderr b/tests/ui/resolve/field-and-method-in-self-not-available-in-assoc-fn.stderr
index 3c44c1c249c..2f624f24804 100644
--- a/tests/ui/resolve/field-and-method-in-self-not-available-in-assoc-fn.stderr
+++ b/tests/ui/resolve/field-and-method-in-self-not-available-in-assoc-fn.stderr
@@ -2,7 +2,7 @@ error[E0425]: cannot find value `field` in this scope
   --> $DIR/field-and-method-in-self-not-available-in-assoc-fn.rs:11:9
    |
 LL |     field: u32,
-   |     ---------- a field by that name exists in `Self`
+   |     ----- a field by that name exists in `Self`
 ...
 LL |     fn field(&self) -> u32 {
    |        ----- a method by that name is available on `Self` here
@@ -14,7 +14,7 @@ error[E0425]: cannot find value `field` in this scope
   --> $DIR/field-and-method-in-self-not-available-in-assoc-fn.rs:12:15
    |
 LL |     field: u32,
-   |     ---------- a field by that name exists in `Self`
+   |     ----- a field by that name exists in `Self`
 ...
 LL |     fn field(&self) -> u32 {
    |        ----- a method by that name is available on `Self` here
diff --git a/tests/ui/resolve/issue-2356.stderr b/tests/ui/resolve/issue-2356.stderr
index 5f75ae98870..74a2c9268a2 100644
--- a/tests/ui/resolve/issue-2356.stderr
+++ b/tests/ui/resolve/issue-2356.stderr
@@ -2,7 +2,7 @@ error[E0425]: cannot find value `whiskers` in this scope
   --> $DIR/issue-2356.rs:39:5
    |
 LL |   whiskers: isize,
-   |   --------------- a field by that name exists in `Self`
+   |   -------- a field by that name exists in `Self`
 ...
 LL |     whiskers -= other;
    |     ^^^^^^^^
@@ -35,7 +35,7 @@ error[E0425]: cannot find value `whiskers` in this scope
   --> $DIR/issue-2356.rs:84:5
    |
 LL |   whiskers: isize,
-   |   --------------- a field by that name exists in `Self`
+   |   -------- a field by that name exists in `Self`
 ...
 LL |     whiskers = 4;
    |     ^^^^^^^^
diff --git a/tests/ui/resolve/issue-60057.stderr b/tests/ui/resolve/issue-60057.stderr
index a2ab8644353..8737cf77001 100644
--- a/tests/ui/resolve/issue-60057.stderr
+++ b/tests/ui/resolve/issue-60057.stderr
@@ -2,7 +2,7 @@ error[E0425]: cannot find value `banana` in this scope
   --> $DIR/issue-60057.rs:8:21
    |
 LL |     banana: u8,
-   |     ---------- a field by that name exists in `Self`
+   |     ------ a field by that name exists in `Self`
 ...
 LL |             banana: banana
    |                     ^^^^^^
diff --git a/tests/ui/resolve/typo-suggestion-for-variable-with-name-similar-to-struct-field.stderr b/tests/ui/resolve/typo-suggestion-for-variable-with-name-similar-to-struct-field.stderr
index 0306c8af87d..5662021a2d5 100644
--- a/tests/ui/resolve/typo-suggestion-for-variable-with-name-similar-to-struct-field.stderr
+++ b/tests/ui/resolve/typo-suggestion-for-variable-with-name-similar-to-struct-field.stderr
@@ -2,7 +2,7 @@ error[E0425]: cannot find value `config` in this scope
   --> $DIR/typo-suggestion-for-variable-with-name-similar-to-struct-field.rs:7:16
    |
 LL |     config: String,
-   |     -------------- a field by that name exists in `Self`
+   |     ------ a field by that name exists in `Self`
 ...
 LL |         Self { config }
    |                ^^^^^^ help: a local variable with a similar name exists: `cofig`
@@ -11,7 +11,7 @@ error[E0425]: cannot find value `config` in this scope
   --> $DIR/typo-suggestion-for-variable-with-name-similar-to-struct-field.rs:11:20
    |
 LL |     config: String,
-   |     -------------- a field by that name exists in `Self`
+   |     ------ a field by that name exists in `Self`
 ...
 LL |         println!("{config}");
    |                    ^^^^^^ help: a local variable with a similar name exists: `cofig`
diff --git a/tests/ui/resolve/unresolved_static_type_field.stderr b/tests/ui/resolve/unresolved_static_type_field.stderr
index e3de0a3fb74..f039eef2e06 100644
--- a/tests/ui/resolve/unresolved_static_type_field.stderr
+++ b/tests/ui/resolve/unresolved_static_type_field.stderr
@@ -2,7 +2,7 @@ error[E0425]: cannot find value `cx` in this scope
   --> $DIR/unresolved_static_type_field.rs:9:11
    |
 LL |     cx: bool,
-   |     -------- a field by that name exists in `Self`
+   |     -- a field by that name exists in `Self`
 ...
 LL |         f(cx);
    |           ^^
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
index af88a73b4d6..63c353c7d66 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
@@ -1,12 +1,16 @@
 //@ known-bug: #110395
+//@ failure-status: 101
+//@ normalize-stderr-test ".*note: .*\n\n" -> ""
+//@ normalize-stderr-test "thread 'rustc' panicked.*:\n.*\n" -> ""
+//@ rustc-env:RUST_BACKTRACE=0
 // FIXME(effects) check-pass
-// FIXME(effects) fix intrinsics const parameter counting
+//@ compile-flags: -Znext-solver
 
 #![crate_type = "lib"]
 #![feature(no_core, lang_items, unboxed_closures, auto_traits, intrinsics, rustc_attrs, staged_api)]
-#![feature(fundamental)]
+#![feature(fundamental, marker_trait_attr)]
 #![feature(const_trait_impl, effects, const_mut_refs)]
-#![allow(internal_features)]
+#![allow(internal_features, incomplete_features)]
 #![no_std]
 #![no_core]
 #![stable(feature = "minicore", since = "1.0.0")]
@@ -532,3 +536,35 @@ fn test_const_eval_select() {
 
     const_eval_select((), const_fn, rt_fn);
 }
+
+mod effects {
+    use super::Sized;
+
+    #[lang = "EffectsNoRuntime"]
+    pub struct NoRuntime;
+    #[lang = "EffectsMaybe"]
+    pub struct Maybe;
+    #[lang = "EffectsRuntime"]
+    pub struct Runtime;
+
+    #[lang = "EffectsCompat"]
+    pub trait Compat<#[rustc_runtime] const RUNTIME: bool> {}
+
+    impl Compat<false> for NoRuntime {}
+    impl Compat<true> for Runtime {}
+    impl<#[rustc_runtime] const RUNTIME: bool> Compat<RUNTIME> for Maybe {}
+
+    #[lang = "EffectsTyCompat"]
+    #[marker]
+    pub trait TyCompat<T: ?Sized> {}
+
+    impl<T: ?Sized> TyCompat<T> for T {}
+    impl<T: ?Sized> TyCompat<T> for Maybe {}
+    impl<T: ?Sized> TyCompat<Maybe> for T {}
+
+    #[lang = "EffectsIntersection"]
+    pub trait Intersection {
+        #[lang = "EffectsIntersectionOutput"]
+        type Output: ?Sized;
+    }
+}
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr
index 1963332b856..823ab69df9c 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr
@@ -1,17 +1,13 @@
-warning: the feature `effects` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/minicore.rs:8:30
-   |
-LL | #![feature(const_trait_impl, effects, const_mut_refs)]
-   |                              ^^^^^^^
-   |
-   = note: see issue #102090 <https://github.com/rust-lang/rust/issues/102090> for more information
-   = note: `#[warn(incomplete_features)]` on by default
+error: the compiler unexpectedly panicked. this is a bug.
 
-error: requires `EffectsCompat` lang_item
-  --> $DIR/minicore.rs:455:9
-   |
-LL | impl<T: Clone> Clone for RefCell<T> {
-   |         ^^^^^
+query stack during panic:
+#0 [check_well_formed] checking that `<impl at $DIR/minicore.rs:459:1: 459:36>` is well-formed
+#1 [check_mod_type_wf] checking that types are well-formed in top-level module
+end of query stack
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: the compiler unexpectedly panicked. this is a bug.
 
+query stack during panic:
+#0 [check_well_formed] checking that `drop` is well-formed
+#1 [check_mod_type_wf] checking that types are well-formed in top-level module
+end of query stack
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.nn.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.nn.stderr
deleted file mode 100644
index 03536dca1e8..00000000000
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.nn.stderr
+++ /dev/null
@@ -1,12 +0,0 @@
-error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Index>::Output`
-  --> $DIR/issue-100222.rs:34:12
-   |
-LL |     fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
-   |            ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
-   |
-   = note:      expected unit type `()`
-           found mutable reference `&mut <() as Index>::Output`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.ny.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.ny.stderr
deleted file mode 100644
index 6a70a503606..00000000000
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.ny.stderr
+++ /dev/null
@@ -1,12 +0,0 @@
-error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Index>::Output`
-  --> $DIR/issue-100222.rs:25:12
-   |
-LL |     fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
-   |            ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
-   |
-   = note:      expected unit type `()`
-           found mutable reference `&mut <() as Index>::Output`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.rs b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.rs
index 7949772a2b4..47f9fc664ce 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.rs
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.rs
@@ -1,6 +1,7 @@
 //@ revisions: nn ny yn yy
-//@ known-bug: #110395
 //@ compile-flags: -Znext-solver
+//@ check-pass
+
 #![allow(incomplete_features)]
 #![feature(const_trait_impl, effects, associated_type_defaults, const_mut_refs)]
 
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yn.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yn.stderr
deleted file mode 100644
index 03536dca1e8..00000000000
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yn.stderr
+++ /dev/null
@@ -1,12 +0,0 @@
-error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Index>::Output`
-  --> $DIR/issue-100222.rs:34:12
-   |
-LL |     fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
-   |            ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
-   |
-   = note:      expected unit type `()`
-           found mutable reference `&mut <() as Index>::Output`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yy.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yy.stderr
deleted file mode 100644
index 6a70a503606..00000000000
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yy.stderr
+++ /dev/null
@@ -1,12 +0,0 @@
-error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Index>::Output`
-  --> $DIR/issue-100222.rs:25:12
-   |
-LL |     fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
-   |            ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
-   |
-   = note:      expected unit type `()`
-           found mutable reference `&mut <() as Index>::Output`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.fixed b/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.fixed
index e072c476c6b..4e562193f0d 100644
--- a/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.fixed
+++ b/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.fixed
@@ -3,9 +3,9 @@
 
 trait Trait {}
 
-fn assert_send(ptr: *mut dyn Trait) -> *mut (dyn Trait + Send) {
+fn assert_send() -> *mut (dyn Trait + Send) {
     //~^ ERROR incorrect parentheses around trait bounds
-    ptr as _
+    loop {}
 }
 
 fn foo2(_: &(dyn Trait + Send)) {}
diff --git a/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.rs b/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.rs
index 88995141426..4a00059400c 100644
--- a/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.rs
+++ b/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.rs
@@ -3,9 +3,9 @@
 
 trait Trait {}
 
-fn assert_send(ptr: *mut dyn Trait) -> *mut dyn (Trait + Send) {
+fn assert_send() -> *mut dyn (Trait + Send) {
     //~^ ERROR incorrect parentheses around trait bounds
-    ptr as _
+    loop {}
 }
 
 fn foo2(_: &dyn (Trait + Send)) {}
diff --git a/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.stderr b/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.stderr
index 2d1abe91a1e..c67557fa14f 100644
--- a/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.stderr
+++ b/tests/ui/suggestions/issue-114797-bad-parentheses-dyn-trait.stderr
@@ -1,13 +1,13 @@
 error: incorrect parentheses around trait bounds
-  --> $DIR/issue-114797-bad-parentheses-dyn-trait.rs:6:49
+  --> $DIR/issue-114797-bad-parentheses-dyn-trait.rs:6:30
    |
-LL | fn assert_send(ptr: *mut dyn Trait) -> *mut dyn (Trait + Send) {
-   |                                                 ^            ^
+LL | fn assert_send() -> *mut dyn (Trait + Send) {
+   |                              ^            ^
    |
 help: fix the parentheses
    |
-LL - fn assert_send(ptr: *mut dyn Trait) -> *mut dyn (Trait + Send) {
-LL + fn assert_send(ptr: *mut dyn Trait) -> *mut (dyn Trait + Send) {
+LL - fn assert_send() -> *mut dyn (Trait + Send) {
+LL + fn assert_send() -> *mut (dyn Trait + Send) {
    |
 
 error: incorrect parentheses around trait bounds
diff --git a/tests/ui/traits/next-solver/auto-with-drop_tracking_mir.fail.stderr b/tests/ui/traits/next-solver/auto-with-drop_tracking_mir.fail.stderr
index e0b23bd8110..c2029a5a1c8 100644
--- a/tests/ui/traits/next-solver/auto-with-drop_tracking_mir.fail.stderr
+++ b/tests/ui/traits/next-solver/auto-with-drop_tracking_mir.fail.stderr
@@ -17,10 +17,6 @@ note: required by a bound in `is_send`
    |
 LL |     fn is_send(_: impl Send) {}
    |                        ^^^^ required by this bound in `is_send`
-help: consider dereferencing here
-   |
-LL |     is_send(*foo());
-   |             +
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/traits/next-solver/typeck/receiver-self-ty-check-eq.rs b/tests/ui/traits/next-solver/typeck/receiver-self-ty-check-eq.rs
new file mode 100644
index 00000000000..f8c8a17b7e5
--- /dev/null
+++ b/tests/ui/traits/next-solver/typeck/receiver-self-ty-check-eq.rs
@@ -0,0 +1,23 @@
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// Fixes a regression in `receiver_is_valid` in wfcheck where we were using
+// `InferCtxt::can_eq` instead of processing alias-relate goals, leading to false
+// positives, not deref'ing enough steps to check the receiver is valid.
+
+trait Mirror {
+    type Mirror: ?Sized;
+}
+impl<T: ?Sized> Mirror for T {
+    type Mirror = T;
+}
+
+trait Foo {
+    fn foo(&self) {}
+}
+
+impl Foo for <() as Mirror>::Mirror {
+    fn foo(&self) {}
+}
+
+fn main() {}
diff --git a/tests/ui/traits/upcast_soundness_bug.rs b/tests/ui/traits/upcast_soundness_bug.rs
index 95b48cdf379..5eaa58f7efe 100644
--- a/tests/ui/traits/upcast_soundness_bug.rs
+++ b/tests/ui/traits/upcast_soundness_bug.rs
@@ -1,7 +1,8 @@
 #![feature(trait_upcasting)]
-//@ known-bug: #120222
-//@ check-pass
-//! This will segfault at runtime.
+//@ check-fail
+//
+// issue: <https://github.com/rust-lang/rust/pull/120222>
+//! This would segfault at runtime.
 
 pub trait SupSupA {
     fn method(&self) {}
@@ -56,6 +57,7 @@ pub fn user2() -> &'static dyn Trait<u8, u16> {
 fn main() {
     let p: *const dyn Trait<u8, u8> = &();
     let p = p as *const dyn Trait<u8, u16>; // <- this is bad!
+    //~^ error: mismatched types
     let p = p as *const dyn Super<u16>; // <- this upcast accesses improper vtable entry
     // accessing from L__unnamed_2 the position for the 'Super<u16> vtable (pointer)',
     // thus reading 'null pointer for missing_method'
diff --git a/tests/ui/traits/upcast_soundness_bug.stderr b/tests/ui/traits/upcast_soundness_bug.stderr
new file mode 100644
index 00000000000..5864abcdb41
--- /dev/null
+++ b/tests/ui/traits/upcast_soundness_bug.stderr
@@ -0,0 +1,13 @@
+error[E0308]: mismatched types
+  --> $DIR/upcast_soundness_bug.rs:59:13
+   |
+LL |     let p = p as *const dyn Trait<u8, u16>; // <- this is bad!
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u8`, found `u16`
+   |
+   = note: expected trait object `dyn Trait<u8, u8>`
+              found trait object `dyn Trait<u8, u16>`
+   = help: `dyn Trait<u8, u16>` implements `Trait` so you could box the found value and coerce it to the trait object `Box<dyn Trait>`, you will have to change the expected type as well
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/type-alias-impl-trait/method_resolution3.current.stderr b/tests/ui/type-alias-impl-trait/method_resolution3.current.stderr
index e992d059daf..09efd7a9e7e 100644
--- a/tests/ui/type-alias-impl-trait/method_resolution3.current.stderr
+++ b/tests/ui/type-alias-impl-trait/method_resolution3.current.stderr
@@ -8,7 +8,7 @@ LL |     fn bar(self: Bar<u32>) {
    = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error[E0307]: invalid `self` parameter type: `&Bar<u32>`
-  --> $DIR/method_resolution3.rs:21:18
+  --> $DIR/method_resolution3.rs:20:18
    |
 LL |     fn baz(self: &Bar<u32>) {
    |                  ^^^^^^^^^
diff --git a/tests/ui/type-alias-impl-trait/method_resolution3.next.stderr b/tests/ui/type-alias-impl-trait/method_resolution3.next.stderr
index 9272017cdf5..09efd7a9e7e 100644
--- a/tests/ui/type-alias-impl-trait/method_resolution3.next.stderr
+++ b/tests/ui/type-alias-impl-trait/method_resolution3.next.stderr
@@ -1,15 +1,21 @@
-error[E0271]: type mismatch resolving `Foo == u32`
+error[E0307]: invalid `self` parameter type: `Bar<u32>`
   --> $DIR/method_resolution3.rs:16:18
    |
 LL |     fn bar(self: Bar<u32>) {
-   |                  ^^^^^^^^ types differ
+   |                  ^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
-error[E0271]: type mismatch resolving `Foo == u32`
-  --> $DIR/method_resolution3.rs:21:18
+error[E0307]: invalid `self` parameter type: `&Bar<u32>`
+  --> $DIR/method_resolution3.rs:20:18
    |
 LL |     fn baz(self: &Bar<u32>) {
-   |                  ^^^^^^^^^ types differ
+   |                  ^^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0307`.
diff --git a/tests/ui/type-alias-impl-trait/method_resolution3.rs b/tests/ui/type-alias-impl-trait/method_resolution3.rs
index 447f3144b82..0e6176bfe03 100644
--- a/tests/ui/type-alias-impl-trait/method_resolution3.rs
+++ b/tests/ui/type-alias-impl-trait/method_resolution3.rs
@@ -14,13 +14,11 @@ struct Bar<T>(T);
 
 impl Bar<Foo> {
     fn bar(self: Bar<u32>) {
-        //[current]~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `Foo == u32`
+        //~^ ERROR: invalid `self` parameter
         self.foo()
     }
     fn baz(self: &Bar<u32>) {
-        //[current]~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `Foo == u32`
+        //~^ ERROR: invalid `self` parameter
         self.foo()
     }
 }
diff --git a/tests/ui/type-alias-impl-trait/method_resolution4.current.stderr b/tests/ui/type-alias-impl-trait/method_resolution4.current.stderr
index 3a2ca18f890..8ffdb21f251 100644
--- a/tests/ui/type-alias-impl-trait/method_resolution4.current.stderr
+++ b/tests/ui/type-alias-impl-trait/method_resolution4.current.stderr
@@ -8,7 +8,7 @@ LL |     fn foo(self: Bar<Foo>) {
    = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error[E0307]: invalid `self` parameter type: `&Bar<Foo>`
-  --> $DIR/method_resolution4.rs:32:20
+  --> $DIR/method_resolution4.rs:31:20
    |
 LL |     fn foomp(self: &Bar<Foo>) {
    |                    ^^^^^^^^^
diff --git a/tests/ui/type-alias-impl-trait/method_resolution4.next.stderr b/tests/ui/type-alias-impl-trait/method_resolution4.next.stderr
index 33ed2800ebe..8ffdb21f251 100644
--- a/tests/ui/type-alias-impl-trait/method_resolution4.next.stderr
+++ b/tests/ui/type-alias-impl-trait/method_resolution4.next.stderr
@@ -1,15 +1,21 @@
-error[E0271]: type mismatch resolving `u32 == Foo`
+error[E0307]: invalid `self` parameter type: `Bar<Foo>`
   --> $DIR/method_resolution4.rs:27:18
    |
 LL |     fn foo(self: Bar<Foo>) {
-   |                  ^^^^^^^^ types differ
+   |                  ^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
-error[E0271]: type mismatch resolving `u32 == Foo`
-  --> $DIR/method_resolution4.rs:32:20
+error[E0307]: invalid `self` parameter type: `&Bar<Foo>`
+  --> $DIR/method_resolution4.rs:31:20
    |
 LL |     fn foomp(self: &Bar<Foo>) {
-   |                    ^^^^^^^^^ types differ
+   |                    ^^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0307`.
diff --git a/tests/ui/type-alias-impl-trait/method_resolution4.rs b/tests/ui/type-alias-impl-trait/method_resolution4.rs
index 42ed04b3c30..f33b4e473ae 100644
--- a/tests/ui/type-alias-impl-trait/method_resolution4.rs
+++ b/tests/ui/type-alias-impl-trait/method_resolution4.rs
@@ -25,13 +25,11 @@ impl Bar<Foo> {
 
 impl Bar<u32> {
     fn foo(self: Bar<Foo>) {
-        //[current]~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `u32 == Foo`
+        //~^ ERROR: invalid `self` parameter
         self.bar()
     }
     fn foomp(self: &Bar<Foo>) {
-        //[current]~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `u32 == Foo`
+        //~^ ERROR: invalid `self` parameter
         self.bar()
     }
 }
diff --git a/tests/ui/typeck/ice-with-expr-not-struct-127332.rs b/tests/ui/typeck/ice-with-expr-not-struct-127332.rs
new file mode 100644
index 00000000000..f3ea360e7e9
--- /dev/null
+++ b/tests/ui/typeck/ice-with-expr-not-struct-127332.rs
@@ -0,0 +1,15 @@
+// Regression test for ICE #127332
+
+// Tests that we do not ICE when a with expr is
+// not a struct but something else like an enum
+
+fn main() {
+    let x = || {
+        enum Foo {
+            A { x: u32 },
+        }
+        let orig = Foo::A { x: 5 };
+        Foo::A { x: 6, ..orig };
+        //~^ ERROR functional record update syntax requires a struct
+    };
+}
diff --git a/tests/ui/typeck/ice-with-expr-not-struct-127332.stderr b/tests/ui/typeck/ice-with-expr-not-struct-127332.stderr
new file mode 100644
index 00000000000..446f49e8639
--- /dev/null
+++ b/tests/ui/typeck/ice-with-expr-not-struct-127332.stderr
@@ -0,0 +1,9 @@
+error[E0436]: functional record update syntax requires a struct
+  --> $DIR/ice-with-expr-not-struct-127332.rs:12:26
+   |
+LL |         Foo::A { x: 6, ..orig };
+   |                          ^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0436`.