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-rw-r--r--compiler/rustc_codegen_ssa/src/mir/block.rs3
-rw-r--r--compiler/rustc_const_eval/src/const_eval/machine.rs16
-rw-r--r--compiler/rustc_hir/src/lang_items.rs2
-rw-r--r--compiler/rustc_middle/src/ty/consts/valtree.rs5
-rw-r--r--compiler/rustc_middle/src/ty/layout.rs175
-rw-r--r--compiler/rustc_mir_transform/src/lib.rs71
-rw-r--r--compiler/rustc_monomorphize/src/collector.rs8
-rw-r--r--compiler/rustc_span/src/symbol.rs3
-rw-r--r--compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs10
-rw-r--r--compiler/rustc_trait_selection/src/traits/on_unimplemented.rs24
-rw-r--r--compiler/rustc_typeck/src/check/fn_ctxt/checks.rs33
-rw-r--r--compiler/rustc_typeck/src/check/op.rs25
-rw-r--r--library/alloc/src/collections/btree/dedup_sorted_iter.rs4
-rw-r--r--library/alloc/src/lib.rs1
-rw-r--r--library/alloc/src/vec/is_zero.rs16
-rw-r--r--library/core/src/char/methods.rs22
-rw-r--r--library/core/src/intrinsics.rs144
-rw-r--r--library/core/src/lib.rs1
-rw-r--r--library/core/src/mem/valid_align.rs2
-rw-r--r--library/core/src/num/f32.rs24
-rw-r--r--library/core/src/num/f64.rs24
-rw-r--r--library/core/src/num/nonzero.rs2
-rw-r--r--library/core/src/ops/try_trait.rs84
-rw-r--r--library/core/src/ptr/const_ptr.rs5
-rw-r--r--library/core/src/ptr/mod.rs8
-rw-r--r--library/core/src/slice/index.rs20
-rw-r--r--library/core/src/slice/mod.rs15
-rw-r--r--library/core/src/slice/raw.rs4
-rw-r--r--library/core/src/str/mod.rs2
-rw-r--r--library/core/src/unicode/unicode_data.rs37
-rw-r--r--library/std/src/alloc.rs5
-rw-r--r--library/std/src/fs.rs2
-rw-r--r--library/std/src/io/stdio.rs41
-rw-r--r--library/std/src/sync/once_lock.rs55
-rw-r--r--library/std/src/sys/hermit/mutex.rs3
-rw-r--r--library/std/src/sys/itron/mutex.rs6
-rw-r--r--library/std/src/sys/sgx/mutex.rs3
-rw-r--r--library/std/src/sys/unix/locks/fuchsia_mutex.rs3
-rw-r--r--library/std/src/sys/unix/locks/futex_mutex.rs3
-rw-r--r--library/std/src/sys/unix/locks/pthread_mutex.rs2
-rw-r--r--library/std/src/sys/unsupported/locks/mutex.rs3
-rw-r--r--library/std/src/sys/windows/locks/mutex.rs2
-rw-r--r--library/std/src/sys_common/remutex.rs46
-rw-r--r--library/std/src/sys_common/remutex/tests.rs37
-rw-r--r--src/ci/docker/host-x86_64/mingw-check/Dockerfile3
-rw-r--r--src/librustdoc/clean/mod.rs13
-rw-r--r--src/librustdoc/clean/types.rs26
-rw-r--r--src/librustdoc/clean/utils.rs34
-rw-r--r--src/librustdoc/fold.rs2
-rw-r--r--src/librustdoc/html/render/print_item.rs3
-rw-r--r--src/librustdoc/html/static/css/rustdoc.css4
-rw-r--r--src/librustdoc/json/conversions.rs14
-rw-r--r--src/librustdoc/visit.rs2
-rw-r--r--src/rustdoc-json-types/lib.rs21
-rw-r--r--src/test/rustdoc-gui/search-input.goml22
-rw-r--r--src/test/rustdoc-json/enums/discriminant/basic.rs12
-rw-r--r--src/test/rustdoc-json/enums/discriminant/expr.rs39
-rw-r--r--src/test/rustdoc-json/enums/discriminant/limits.rs43
-rw-r--r--src/test/rustdoc-json/enums/discriminant/num_underscore_and_suffix.rs15
-rw-r--r--src/test/rustdoc-json/enums/discriminant/only_some_have_discriminant.rs10
-rw-r--r--src/test/ui/consts/const-float-bits-reject-conv.stderr40
-rw-r--r--src/test/ui/intrinsics/const-eval-select-backtrace-std.rs6
-rw-r--r--src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr2
-rw-r--r--src/test/ui/intrinsics/const-eval-select-backtrace.rs18
-rw-r--r--src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr2
-rw-r--r--src/test/ui/intrinsics/const-eval-select-bad.rs12
-rw-r--r--src/test/ui/intrinsics/const-eval-select-bad.stderr79
-rw-r--r--src/test/ui/on-unimplemented/enclosing-scope.rs27
-rw-r--r--src/test/ui/on-unimplemented/enclosing-scope.stderr86
-rw-r--r--src/test/ui/on-unimplemented/parent-label.rs27
-rw-r--r--src/test/ui/on-unimplemented/parent-label.stderr69
-rw-r--r--src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr48
-rw-r--r--src/test/ui/try-trait/bad-interconversion.stderr73
-rw-r--r--src/test/ui/try-trait/option-to-result.stderr24
-rw-r--r--src/test/ui/try-trait/try-on-option-diagnostics.stderr47
-rw-r--r--src/test/ui/try-trait/try-on-option.stderr24
-rw-r--r--src/test/ui/try-trait/try-operator-on-main.stderr30
-rw-r--r--src/test/ui/typeck/assign-non-lval-needs-deref.rs19
-rw-r--r--src/test/ui/typeck/assign-non-lval-needs-deref.stderr16
-rw-r--r--src/tools/unicode-table-generator/src/range_search.rs15
-rw-r--r--src/tools/unicode-table-generator/src/raw_emitter.rs15
81 files changed, 1124 insertions, 819 deletions
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 5c67d3b6431..3154f12a779 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -13,8 +13,7 @@ use rustc_ast as ast;
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_hir::lang_items::LangItem;
 use rustc_index::vec::Idx;
-use rustc_middle::mir::AssertKind;
-use rustc_middle::mir::{self, SwitchTargets};
+use rustc_middle::mir::{self, AssertKind, SwitchTargets};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
 use rustc_middle::ty::{self, Instance, Ty, TypeVisitable};
diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index 9ea9fbe0e0e..6e5c840bdfd 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -35,21 +35,7 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
         // All `#[rustc_do_not_const_check]` functions should be hooked here.
         let def_id = instance.def_id();
 
-        if Some(def_id) == self.tcx.lang_items().const_eval_select() {
-            // redirect to const_eval_select_ct
-            if let Some(const_eval_select) = self.tcx.lang_items().const_eval_select_ct() {
-                return Ok(Some(
-                    ty::Instance::resolve(
-                        *self.tcx,
-                        ty::ParamEnv::reveal_all(),
-                        const_eval_select,
-                        instance.substs,
-                    )
-                    .unwrap()
-                    .unwrap(),
-                ));
-            }
-        } else if Some(def_id) == self.tcx.lang_items().panic_display()
+        if Some(def_id) == self.tcx.lang_items().panic_display()
             || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
         {
             // &str or &&str
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index f19d07d98dc..bc1ea1c4c73 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -269,8 +269,6 @@ language_item_table! {
     DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);
     Oom,                     sym::oom,                 oom,                        Target::Fn,             GenericRequirement::None;
     AllocLayout,             sym::alloc_layout,        alloc_layout,               Target::Struct,         GenericRequirement::None;
-    ConstEvalSelect,         sym::const_eval_select,   const_eval_select,          Target::Fn,             GenericRequirement::Exact(4);
-    ConstConstEvalSelect,    sym::const_eval_select_ct,const_eval_select_ct,       Target::Fn,             GenericRequirement::Exact(4);
 
     Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::Exact(1);
 
diff --git a/compiler/rustc_middle/src/ty/consts/valtree.rs b/compiler/rustc_middle/src/ty/consts/valtree.rs
index 93707bb18ce..a803fca0d5b 100644
--- a/compiler/rustc_middle/src/ty/consts/valtree.rs
+++ b/compiler/rustc_middle/src/ty/consts/valtree.rs
@@ -18,7 +18,7 @@ use rustc_macros::{HashStable, TyDecodable, TyEncodable};
 /// `ValTree` does not have this problem with representation, as it only contains integers or
 /// lists of (nested) `ValTree`.
 pub enum ValTree<'tcx> {
-    /// ZSTs, integers, `bool`, `char` are represented as scalars.
+    /// integers, `bool`, `char` are represented as scalars.
     /// See the `ScalarInt` documentation for how `ScalarInt` guarantees that equal values
     /// of these types have the same representation.
     Leaf(ScalarInt),
@@ -27,8 +27,11 @@ pub enum ValTree<'tcx> {
     // dont use SliceOrStr for now
     /// The fields of any kind of aggregate. Structs, tuples and arrays are represented by
     /// listing their fields' values in order.
+    ///
     /// Enums are represented by storing their discriminant as a field, followed by all
     /// the fields of the variant.
+    ///
+    /// ZST types are represented as an empty slice.
     Branch(&'tcx [ValTree<'tcx>]),
 }
 
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 26b60e4f339..2c587b76f02 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -263,6 +263,7 @@ fn layout_of<'tcx>(
     Ok(layout)
 }
 
+#[derive(Clone, Copy)]
 pub struct LayoutCx<'tcx, C> {
     pub tcx: C,
     pub param_env: ty::ParamEnv<'tcx>,
@@ -3063,6 +3064,93 @@ fn fn_abi_of_instance<'tcx>(
     )
 }
 
+// Handle safe Rust thin and fat pointers.
+pub fn adjust_for_rust_scalar<'tcx>(
+    cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
+    attrs: &mut ArgAttributes,
+    scalar: Scalar,
+    layout: TyAndLayout<'tcx>,
+    offset: Size,
+    is_return: bool,
+) {
+    // Booleans are always a noundef i1 that needs to be zero-extended.
+    if scalar.is_bool() {
+        attrs.ext(ArgExtension::Zext);
+        attrs.set(ArgAttribute::NoUndef);
+        return;
+    }
+
+    // Scalars which have invalid values cannot be undef.
+    if !scalar.is_always_valid(&cx) {
+        attrs.set(ArgAttribute::NoUndef);
+    }
+
+    // Only pointer types handled below.
+    let Scalar::Initialized { value: Pointer, valid_range} = scalar else { return };
+
+    if !valid_range.contains(0) {
+        attrs.set(ArgAttribute::NonNull);
+    }
+
+    if let Some(pointee) = layout.pointee_info_at(&cx, offset) {
+        if let Some(kind) = pointee.safe {
+            attrs.pointee_align = Some(pointee.align);
+
+            // `Box` (`UniqueBorrowed`) are not necessarily dereferenceable
+            // for the entire duration of the function as they can be deallocated
+            // at any time. Same for shared mutable references. If LLVM had a
+            // way to say "dereferenceable on entry" we could use it here.
+            attrs.pointee_size = match kind {
+                PointerKind::UniqueBorrowed
+                | PointerKind::UniqueBorrowedPinned
+                | PointerKind::Frozen => pointee.size,
+                PointerKind::SharedMutable | PointerKind::UniqueOwned => Size::ZERO,
+            };
+
+            // `Box`, `&T`, and `&mut T` cannot be undef.
+            // Note that this only applies to the value of the pointer itself;
+            // this attribute doesn't make it UB for the pointed-to data to be undef.
+            attrs.set(ArgAttribute::NoUndef);
+
+            // The aliasing rules for `Box<T>` are still not decided, but currently we emit
+            // `noalias` for it. This can be turned off using an unstable flag.
+            // See https://github.com/rust-lang/unsafe-code-guidelines/issues/326
+            let noalias_for_box = cx.tcx.sess.opts.unstable_opts.box_noalias.unwrap_or(true);
+
+            // `&mut` pointer parameters never alias other parameters,
+            // or mutable global data
+            //
+            // `&T` where `T` contains no `UnsafeCell<U>` is immutable,
+            // and can be marked as both `readonly` and `noalias`, as
+            // LLVM's definition of `noalias` is based solely on memory
+            // dependencies rather than pointer equality
+            //
+            // Due to past miscompiles in LLVM, we apply a separate NoAliasMutRef attribute
+            // for UniqueBorrowed arguments, so that the codegen backend can decide whether
+            // or not to actually emit the attribute. It can also be controlled with the
+            // `-Zmutable-noalias` debugging option.
+            let no_alias = match kind {
+                PointerKind::SharedMutable
+                | PointerKind::UniqueBorrowed
+                | PointerKind::UniqueBorrowedPinned => false,
+                PointerKind::UniqueOwned => noalias_for_box,
+                PointerKind::Frozen => !is_return,
+            };
+            if no_alias {
+                attrs.set(ArgAttribute::NoAlias);
+            }
+
+            if kind == PointerKind::Frozen && !is_return {
+                attrs.set(ArgAttribute::ReadOnly);
+            }
+
+            if kind == PointerKind::UniqueBorrowed && !is_return {
+                attrs.set(ArgAttribute::NoAliasMutRef);
+            }
+        }
+    }
+}
+
 impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
     // FIXME(eddyb) perhaps group the signature/type-containing (or all of them?)
     // arguments of this method, into a separate `struct`.
@@ -3118,91 +3206,6 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
         use SpecAbi::*;
         let rust_abi = matches!(sig.abi, RustIntrinsic | PlatformIntrinsic | Rust | RustCall);
 
-        // Handle safe Rust thin and fat pointers.
-        let adjust_for_rust_scalar = |attrs: &mut ArgAttributes,
-                                      scalar: Scalar,
-                                      layout: TyAndLayout<'tcx>,
-                                      offset: Size,
-                                      is_return: bool| {
-            // Booleans are always a noundef i1 that needs to be zero-extended.
-            if scalar.is_bool() {
-                attrs.ext(ArgExtension::Zext);
-                attrs.set(ArgAttribute::NoUndef);
-                return;
-            }
-
-            // Scalars which have invalid values cannot be undef.
-            if !scalar.is_always_valid(self) {
-                attrs.set(ArgAttribute::NoUndef);
-            }
-
-            // Only pointer types handled below.
-            let Scalar::Initialized { value: Pointer, valid_range} = scalar else { return };
-
-            if !valid_range.contains(0) {
-                attrs.set(ArgAttribute::NonNull);
-            }
-
-            if let Some(pointee) = layout.pointee_info_at(self, offset) {
-                if let Some(kind) = pointee.safe {
-                    attrs.pointee_align = Some(pointee.align);
-
-                    // `Box` (`UniqueBorrowed`) are not necessarily dereferenceable
-                    // for the entire duration of the function as they can be deallocated
-                    // at any time. Same for shared mutable references. If LLVM had a
-                    // way to say "dereferenceable on entry" we could use it here.
-                    attrs.pointee_size = match kind {
-                        PointerKind::UniqueBorrowed
-                        | PointerKind::UniqueBorrowedPinned
-                        | PointerKind::Frozen => pointee.size,
-                        PointerKind::SharedMutable | PointerKind::UniqueOwned => Size::ZERO,
-                    };
-
-                    // `Box`, `&T`, and `&mut T` cannot be undef.
-                    // Note that this only applies to the value of the pointer itself;
-                    // this attribute doesn't make it UB for the pointed-to data to be undef.
-                    attrs.set(ArgAttribute::NoUndef);
-
-                    // The aliasing rules for `Box<T>` are still not decided, but currently we emit
-                    // `noalias` for it. This can be turned off using an unstable flag.
-                    // See https://github.com/rust-lang/unsafe-code-guidelines/issues/326
-                    let noalias_for_box =
-                        self.tcx().sess.opts.unstable_opts.box_noalias.unwrap_or(true);
-
-                    // `&mut` pointer parameters never alias other parameters,
-                    // or mutable global data
-                    //
-                    // `&T` where `T` contains no `UnsafeCell<U>` is immutable,
-                    // and can be marked as both `readonly` and `noalias`, as
-                    // LLVM's definition of `noalias` is based solely on memory
-                    // dependencies rather than pointer equality
-                    //
-                    // Due to past miscompiles in LLVM, we apply a separate NoAliasMutRef attribute
-                    // for UniqueBorrowed arguments, so that the codegen backend can decide whether
-                    // or not to actually emit the attribute. It can also be controlled with the
-                    // `-Zmutable-noalias` debugging option.
-                    let no_alias = match kind {
-                        PointerKind::SharedMutable
-                        | PointerKind::UniqueBorrowed
-                        | PointerKind::UniqueBorrowedPinned => false,
-                        PointerKind::UniqueOwned => noalias_for_box,
-                        PointerKind::Frozen => !is_return,
-                    };
-                    if no_alias {
-                        attrs.set(ArgAttribute::NoAlias);
-                    }
-
-                    if kind == PointerKind::Frozen && !is_return {
-                        attrs.set(ArgAttribute::ReadOnly);
-                    }
-
-                    if kind == PointerKind::UniqueBorrowed && !is_return {
-                        attrs.set(ArgAttribute::NoAliasMutRef);
-                    }
-                }
-            }
-        };
-
         let arg_of = |ty: Ty<'tcx>, arg_idx: Option<usize>| -> Result<_, FnAbiError<'tcx>> {
             let is_return = arg_idx.is_none();
 
@@ -3218,7 +3221,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
 
             let mut arg = ArgAbi::new(self, layout, |layout, scalar, offset| {
                 let mut attrs = ArgAttributes::new();
-                adjust_for_rust_scalar(&mut attrs, scalar, *layout, offset, is_return);
+                adjust_for_rust_scalar(*self, &mut attrs, scalar, *layout, offset, is_return);
                 attrs
             });
 
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 0b674b38f32..162f7d969b1 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -10,6 +10,7 @@
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
+#![feature(if_let_guard)]
 #![recursion_limit = "256"]
 
 #[macro_use]
@@ -27,10 +28,13 @@ use rustc_hir::intravisit::{self, Visitor};
 use rustc_index::vec::IndexVec;
 use rustc_middle::mir::visit::Visitor as _;
 use rustc_middle::mir::{
-    traversal, AnalysisPhase, Body, ConstQualifs, MirPass, MirPhase, Promoted, RuntimePhase,
+    traversal, AnalysisPhase, Body, ConstQualifs, Constant, LocalDecl, MirPass, MirPhase, Operand,
+    Place, ProjectionElem, Promoted, RuntimePhase, Rvalue, SourceInfo, Statement, StatementKind,
+    TerminatorKind,
 };
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
+use rustc_span::sym;
 
 #[macro_use]
 mod pass_manager;
@@ -140,6 +144,64 @@ pub fn provide(providers: &mut Providers) {
     };
 }
 
+fn remap_mir_for_const_eval_select<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    mut body: Body<'tcx>,
+    context: hir::Constness,
+) -> Body<'tcx> {
+    for bb in body.basic_blocks.as_mut().iter_mut() {
+        let terminator = bb.terminator.as_mut().expect("invalid terminator");
+        match terminator.kind {
+            TerminatorKind::Call {
+                func: Operand::Constant(box Constant { ref literal, .. }),
+                ref mut args,
+                destination,
+                target,
+                cleanup,
+                fn_span,
+                ..
+            } if let ty::FnDef(def_id, _) = *literal.ty().kind()
+                && tcx.item_name(def_id) == sym::const_eval_select
+                && tcx.is_intrinsic(def_id) =>
+            {
+                let [tupled_args, called_in_const, called_at_rt]: [_; 3] = std::mem::take(args).try_into().unwrap();
+                let ty = tupled_args.ty(&body.local_decls, tcx);
+                let fields = ty.tuple_fields();
+                let num_args = fields.len();
+                let func = if context == hir::Constness::Const { called_in_const } else { called_at_rt };
+                let (method, place): (fn(Place<'tcx>) -> Operand<'tcx>, Place<'tcx>) = match tupled_args {
+                    Operand::Constant(_) => {
+                        // there is no good way of extracting a tuple arg from a constant (const generic stuff)
+                        // so we just create a temporary and deconstruct that.
+                        let local = body.local_decls.push(LocalDecl::new(ty, fn_span));
+                        bb.statements.push(Statement {
+                            source_info: SourceInfo::outermost(fn_span),
+                            kind: StatementKind::Assign(Box::new((local.into(), Rvalue::Use(tupled_args.clone())))),
+                        });
+                        (Operand::Move, local.into())
+                    }
+                    Operand::Move(place) => (Operand::Move, place),
+                    Operand::Copy(place) => (Operand::Copy, place),
+                };
+                let place_elems = place.projection;
+                let arguments = (0..num_args).map(|x| {
+                    let mut place_elems = place_elems.to_vec();
+                    place_elems.push(ProjectionElem::Field(x.into(), fields[x]));
+                    let projection = tcx.intern_place_elems(&place_elems);
+                    let place = Place {
+                        local: place.local,
+                        projection,
+                    };
+                    method(place)
+                }).collect();
+                terminator.kind = TerminatorKind::Call { func, args: arguments, destination, target, cleanup, from_hir_call: false, fn_span };
+            }
+            _ => {}
+        }
+    }
+    body
+}
+
 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     let def_id = def_id.expect_local();
     tcx.mir_keys(()).contains(&def_id)
@@ -325,7 +387,9 @@ fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -
         .body_const_context(def.did)
         .expect("mir_for_ctfe should not be used for runtime functions");
 
-    let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
+    let body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
+
+    let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::Const);
 
     match context {
         // Do not const prop functions, either they get executed at runtime or exported to metadata,
@@ -558,8 +622,9 @@ fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
     }
     debug!("about to call mir_drops_elaborated...");
-    let mut body =
+    let body =
         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
+    let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::NotConst);
     debug!("body: {:#?}", body);
     run_optimization_passes(tcx, &mut body);
 
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 4e37da0dedb..be74a9d11e3 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -112,12 +112,6 @@
 //! method in operand position, we treat it as a neighbor of the current
 //! mono item. Calls are just a special case of that.
 //!
-//! #### Closures
-//! In a way, closures are a simple case. Since every closure object needs to be
-//! constructed somewhere, we can reliably discover them by observing
-//! `RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also
-//! true for closures inlined from other crates.
-//!
 //! #### Drop glue
 //! Drop glue mono items are introduced by MIR drop-statements. The
 //! generated mono item will again have drop-glue item neighbors if the
@@ -835,7 +829,7 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
             mir::TerminatorKind::Call { ref func, .. } => {
                 let callee_ty = func.ty(self.body, tcx);
                 let callee_ty = self.monomorphize(callee_ty);
-                visit_fn_use(self.tcx, callee_ty, true, source, &mut self.output);
+                visit_fn_use(self.tcx, callee_ty, true, source, &mut self.output)
             }
             mir::TerminatorKind::Drop { ref place, .. }
             | mir::TerminatorKind::DropAndReplace { ref place, .. } => {
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index c501fba21c6..75b1dfc856a 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -510,7 +510,6 @@ symbols! {
         const_deallocate,
         const_eval_limit,
         const_eval_select,
-        const_eval_select_ct,
         const_evaluatable_checked,
         const_extern_fn,
         const_fn,
@@ -662,7 +661,6 @@ symbols! {
         emit_struct,
         emit_struct_field,
         enable,
-        enclosing_scope,
         encode,
         end,
         env,
@@ -1065,6 +1063,7 @@ symbols! {
         panic_unwind,
         panicking,
         param_attrs,
+        parent_label,
         partial_cmp,
         partial_ord,
         passes,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 8151d2b365d..34b877d3f72 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -349,7 +349,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             message,
                             label,
                             note,
-                            enclosing_scope,
+                            parent_label,
                             append_const_msg,
                         } = self.on_unimplemented_note(trait_ref, &obligation);
                         let have_alt_message = message.is_some() || label.is_some();
@@ -530,7 +530,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
                             err.note(s.as_str());
                         }
-                        if let Some(ref s) = enclosing_scope {
+                        if let Some(ref s) = parent_label {
                             let body = tcx
                                 .hir()
                                 .opt_local_def_id(obligation.cause.body_id)
@@ -539,11 +539,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                                         hir_id: obligation.cause.body_id,
                                     })
                                 });
-
-                            let enclosing_scope_span =
-                                tcx.hir().span_with_body(tcx.hir().local_def_id_to_hir_id(body));
-
-                            err.span_label(enclosing_scope_span, s);
+                            err.span_label(tcx.def_span(body), s);
                         }
 
                         self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
diff --git a/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs
index 3d8840e9e74..4a4f34b7680 100644
--- a/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs
@@ -22,7 +22,7 @@ pub struct OnUnimplementedDirective {
     pub message: Option<OnUnimplementedFormatString>,
     pub label: Option<OnUnimplementedFormatString>,
     pub note: Option<OnUnimplementedFormatString>,
-    pub enclosing_scope: Option<OnUnimplementedFormatString>,
+    pub parent_label: Option<OnUnimplementedFormatString>,
     pub append_const_msg: Option<Option<Symbol>>,
 }
 
@@ -31,7 +31,7 @@ pub struct OnUnimplementedNote {
     pub message: Option<String>,
     pub label: Option<String>,
     pub note: Option<String>,
-    pub enclosing_scope: Option<String>,
+    pub parent_label: Option<String>,
     /// Append a message for `~const Trait` errors. `None` means not requested and
     /// should fallback to a generic message, `Some(None)` suggests using the default
     /// appended message, `Some(Some(s))` suggests use the `s` message instead of the
@@ -74,7 +74,7 @@ impl<'tcx> OnUnimplementedDirective {
         let mut message = None;
         let mut label = None;
         let mut note = None;
-        let mut enclosing_scope = None;
+        let mut parent_label = None;
         let mut subcommands = vec![];
         let mut append_const_msg = None;
 
@@ -94,9 +94,9 @@ impl<'tcx> OnUnimplementedDirective {
                     note = parse_value(note_)?;
                     continue;
                 }
-            } else if item.has_name(sym::enclosing_scope) && enclosing_scope.is_none() {
-                if let Some(enclosing_scope_) = item.value_str() {
-                    enclosing_scope = parse_value(enclosing_scope_)?;
+            } else if item.has_name(sym::parent_label) && parent_label.is_none() {
+                if let Some(parent_label_) = item.value_str() {
+                    parent_label = parse_value(parent_label_)?;
                     continue;
                 }
             } else if item.has_name(sym::on)
@@ -135,7 +135,7 @@ impl<'tcx> OnUnimplementedDirective {
                 message,
                 label,
                 note,
-                enclosing_scope,
+                parent_label,
                 append_const_msg,
             })
         }
@@ -160,7 +160,7 @@ impl<'tcx> OnUnimplementedDirective {
                     attr.span,
                 )?),
                 note: None,
-                enclosing_scope: None,
+                parent_label: None,
                 append_const_msg: None,
             }))
         } else {
@@ -181,7 +181,7 @@ impl<'tcx> OnUnimplementedDirective {
         let mut message = None;
         let mut label = None;
         let mut note = None;
-        let mut enclosing_scope = None;
+        let mut parent_label = None;
         let mut append_const_msg = None;
         info!("evaluate({:?}, trait_ref={:?}, options={:?})", self, trait_ref, options);
 
@@ -217,8 +217,8 @@ impl<'tcx> OnUnimplementedDirective {
                 note = Some(note_.clone());
             }
 
-            if let Some(ref enclosing_scope_) = command.enclosing_scope {
-                enclosing_scope = Some(enclosing_scope_.clone());
+            if let Some(ref parent_label_) = command.parent_label {
+                parent_label = Some(parent_label_.clone());
             }
 
             append_const_msg = command.append_const_msg;
@@ -228,7 +228,7 @@ impl<'tcx> OnUnimplementedDirective {
             label: label.map(|l| l.format(tcx, trait_ref, &options_map)),
             message: message.map(|m| m.format(tcx, trait_ref, &options_map)),
             note: note.map(|n| n.format(tcx, trait_ref, &options_map)),
-            enclosing_scope: enclosing_scope.map(|e_s| e_s.format(tcx, trait_ref, &options_map)),
+            parent_label: parent_label.map(|e_s| e_s.format(tcx, trait_ref, &options_map)),
             append_const_msg,
         }
     }
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs b/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
index ce0e59d0622..d1d27db9131 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
@@ -31,7 +31,7 @@ use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{self, DefIdTree, IsSuggestable, Ty, TypeSuperVisitable, TypeVisitor};
 use rustc_session::Session;
 use rustc_span::symbol::Ident;
-use rustc_span::{self, Span};
+use rustc_span::{self, sym, Span};
 use rustc_trait_selection::traits::{self, ObligationCauseCode, SelectionContext};
 
 use std::iter;
@@ -224,6 +224,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let minimum_input_count = expected_input_tys.len();
         let provided_arg_count = provided_args.len();
 
+        let is_const_eval_select = matches!(fn_def_id, Some(def_id) if
+            self.tcx.def_kind(def_id) == hir::def::DefKind::Fn
+            && self.tcx.is_intrinsic(def_id)
+            && self.tcx.item_name(def_id) == sym::const_eval_select);
+
         // We introduce a helper function to demand that a given argument satisfy a given input
         // This is more complicated than just checking type equality, as arguments could be coerced
         // This version writes those types back so further type checking uses the narrowed types
@@ -259,6 +264,32 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 return Compatibility::Incompatible(coerce_error);
             }
 
+            // Check that second and third argument of `const_eval_select` must be `FnDef`, and additionally that
+            // the second argument must be `const fn`. The first argument must be a tuple, but this is already expressed
+            // in the function signature (`F: FnOnce<ARG>`), so I did not bother to add another check here.
+            //
+            // This check is here because there is currently no way to express a trait bound for `FnDef` types only.
+            if is_const_eval_select && (1..=2).contains(&idx) {
+                if let ty::FnDef(def_id, _) = checked_ty.kind() {
+                    if idx == 1 && !self.tcx.is_const_fn_raw(*def_id) {
+                        self.tcx
+                            .sess
+                            .struct_span_err(provided_arg.span, "this argument must be a `const fn`")
+                            .help("consult the documentation on `const_eval_select` for more information")
+                            .emit();
+                    }
+                } else {
+                    self.tcx
+                        .sess
+                        .struct_span_err(provided_arg.span, "this argument must be a function item")
+                        .note(format!("expected a function item, found {checked_ty}"))
+                        .help(
+                            "consult the documentation on `const_eval_select` for more information",
+                        )
+                        .emit();
+                }
+            }
+
             // 3. Check if the formal type is a supertype of the checked one
             //    and register any such obligations for future type checks
             let supertype_error = self
diff --git a/compiler/rustc_typeck/src/check/op.rs b/compiler/rustc_typeck/src/check/op.rs
index 952086e898f..0d9dbb5bc11 100644
--- a/compiler/rustc_typeck/src/check/op.rs
+++ b/compiler/rustc_typeck/src/check/op.rs
@@ -57,9 +57,28 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     )
                     .is_ok()
                 {
-                    // Suppress this error, since we already emitted
-                    // a deref suggestion in check_overloaded_binop
-                    err.downgrade_to_delayed_bug();
+                    // If LHS += RHS is an error, but *LHS += RHS is successful, then we will have
+                    // emitted a better suggestion during error handling in check_overloaded_binop.
+                    if self
+                        .lookup_op_method(
+                            lhs_ty,
+                            Some(rhs_ty),
+                            Some(rhs),
+                            Op::Binary(op, IsAssign::Yes),
+                            expected,
+                        )
+                        .is_err()
+                    {
+                        err.downgrade_to_delayed_bug();
+                    } else {
+                        // Otherwise, it's valid to suggest dereferencing the LHS here.
+                        err.span_suggestion_verbose(
+                            lhs.span.shrink_to_lo(),
+                            "consider dereferencing the left-hand side of this operation",
+                            "*",
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
                 }
             }
         });
diff --git a/library/alloc/src/collections/btree/dedup_sorted_iter.rs b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
index 60bf83b8387..17ee78045a9 100644
--- a/library/alloc/src/collections/btree/dedup_sorted_iter.rs
+++ b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
@@ -3,7 +3,9 @@ use core::iter::Peekable;
 /// A iterator for deduping the key of a sorted iterator.
 /// When encountering the duplicated key, only the last key-value pair is yielded.
 ///
-/// Used by [`BTreeMap::bulk_build_from_sorted_iter`].
+/// Used by [`BTreeMap::bulk_build_from_sorted_iter`][1].
+///
+/// [1]: crate::collections::BTreeMap::bulk_build_from_sorted_iter
 pub struct DedupSortedIter<K, V, I>
 where
     I: Iterator<Item = (K, V)>,
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index ad6d19bbc68..e5cf9033c86 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -134,6 +134,7 @@
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]
 #![feature(receiver_trait)]
+#![feature(saturating_int_impl)]
 #![feature(set_ptr_value)]
 #![feature(slice_from_ptr_range)]
 #![feature(slice_group_by)]
diff --git a/library/alloc/src/vec/is_zero.rs b/library/alloc/src/vec/is_zero.rs
index 92a32779b8e..2e025c8a4a5 100644
--- a/library/alloc/src/vec/is_zero.rs
+++ b/library/alloc/src/vec/is_zero.rs
@@ -1,3 +1,5 @@
+use core::num::{Saturating, Wrapping};
+
 use crate::boxed::Box;
 
 #[rustc_specialization_trait]
@@ -144,3 +146,17 @@ impl_is_zero_option_of_nonzero!(
     NonZeroUsize,
     NonZeroIsize,
 );
+
+unsafe impl<T: IsZero> IsZero for Wrapping<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
+unsafe impl<T: IsZero> IsZero for Saturating<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index 2433139a592..b7a63b7c675 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -746,10 +746,19 @@ impl char {
     /// assert!(!'中'.is_lowercase());
     /// assert!(!' '.is_lowercase());
     /// ```
+    ///
+    /// In a const context:
+    ///
+    /// ```
+    /// #![feature(const_unicode_case_lookup)]
+    /// const CAPITAL_DELTA_IS_LOWERCASE: bool = 'Δ'.is_lowercase();
+    /// assert!(!CAPITAL_DELTA_IS_LOWERCASE);
+    /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
     #[inline]
-    pub fn is_lowercase(self) -> bool {
+    pub const fn is_lowercase(self) -> bool {
         match self {
             'a'..='z' => true,
             c => c > '\x7f' && unicode::Lowercase(c),
@@ -779,10 +788,19 @@ impl char {
     /// assert!(!'中'.is_uppercase());
     /// assert!(!' '.is_uppercase());
     /// ```
+    ///
+    /// In a const context:
+    ///
+    /// ```
+    /// #![feature(const_unicode_case_lookup)]
+    /// const CAPITAL_DELTA_IS_UPPERCASE: bool = 'Δ'.is_uppercase();
+    /// assert!(CAPITAL_DELTA_IS_UPPERCASE);
+    /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
     #[inline]
-    pub fn is_uppercase(self) -> bool {
+    pub const fn is_uppercase(self) -> bool {
         match self {
             'A'..='Z' => true,
             c => c > '\x7f' && unicode::Uppercase(c),
diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index d610f0a02f4..56f5824efd4 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -54,7 +54,9 @@
 )]
 #![allow(missing_docs)]
 
-use crate::marker::{Destruct, DiscriminantKind};
+#[cfg(bootstrap)]
+use crate::marker::Destruct;
+use crate::marker::DiscriminantKind;
 use crate::mem;
 
 // These imports are used for simplifying intra-doc links
@@ -2085,6 +2087,65 @@ extern "rust-intrinsic" {
     /// `ptr` must point to a vtable.
     /// The intrinsic will return the alignment stored in that vtable.
     pub fn vtable_align(ptr: *const ()) -> usize;
+
+    /// Selects which function to call depending on the context.
+    ///
+    /// If this function is evaluated at compile-time, then a call to this
+    /// intrinsic will be replaced with a call to `called_in_const`. It gets
+    /// replaced with a call to `called_at_rt` otherwise.
+    ///
+    /// # Type Requirements
+    ///
+    /// The two functions must be both function items. They cannot be function
+    /// pointers or closures. The first function must be a `const fn`.
+    ///
+    /// `arg` will be the tupled arguments that will be passed to either one of
+    /// the two functions, therefore, both functions must accept the same type of
+    /// arguments. Both functions must return RET.
+    ///
+    /// # Safety
+    ///
+    /// The two functions must behave observably equivalent. Safe code in other
+    /// crates may assume that calling a `const fn` at compile-time and at run-time
+    /// produces the same result. A function that produces a different result when
+    /// evaluated at run-time, or has any other observable side-effects, is
+    /// *unsound*.
+    ///
+    /// Here is an example of how this could cause a problem:
+    /// ```no_run
+    /// #![feature(const_eval_select)]
+    /// #![feature(core_intrinsics)]
+    /// use std::hint::unreachable_unchecked;
+    /// use std::intrinsics::const_eval_select;
+    ///
+    /// // Crate A
+    /// pub const fn inconsistent() -> i32 {
+    ///     fn runtime() -> i32 { 1 }
+    ///     const fn compiletime() -> i32 { 2 }
+    ///
+    ///     unsafe {
+    //          // âš  This code violates the required equivalence of `compiletime`
+    ///         // and `runtime`.
+    ///         const_eval_select((), compiletime, runtime)
+    ///     }
+    /// }
+    ///
+    /// // Crate B
+    /// const X: i32 = inconsistent();
+    /// let x = inconsistent();
+    /// if x != X { unsafe { unreachable_unchecked(); }}
+    /// ```
+    ///
+    /// This code causes Undefined Behavior when being run, since the
+    /// `unreachable_unchecked` is actually being reached. The bug is in *crate A*,
+    /// which violates the principle that a `const fn` must behave the same at
+    /// compile-time and at run-time. The unsafe code in crate B is fine.
+    #[cfg(not(bootstrap))]
+    #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
+    pub fn const_eval_select<ARG, F, G, RET>(arg: ARG, called_in_const: F, called_at_rt: G) -> RET
+    where
+        G: FnOnce<ARG, Output = RET>,
+        F: FnOnce<ARG, Output = RET>;
 }
 
 // Some functions are defined here because they accidentally got made
@@ -2095,6 +2156,11 @@ extern "rust-intrinsic" {
 /// Check that the preconditions of an unsafe function are followed, if debug_assertions are on,
 /// and only at runtime.
 ///
+/// This macro should be called as `assert_unsafe_precondition!([Generics](name: Type) => Expression)`
+/// where the names specified will be moved into the macro as captured variables, and defines an item
+/// to call `const_eval_select` on. The tokens inside the square brackets are used to denote generics
+/// for the function declaractions and can be omitted if there is no generics.
+///
 /// # Safety
 ///
 /// Invoking this macro is only sound if the following code is already UB when the passed
@@ -2109,18 +2175,21 @@ extern "rust-intrinsic" {
 /// the occasional mistake, and this check should help them figure things out.
 #[allow_internal_unstable(const_eval_select)] // permit this to be called in stably-const fn
 macro_rules! assert_unsafe_precondition {
-    ($e:expr) => {
+    ($([$($tt:tt)*])?($($i:ident:$ty:ty),*$(,)?) => $e:expr) => {
         if cfg!(debug_assertions) {
-            // Use a closure so that we can capture arbitrary expressions from the invocation
-            let runtime = || {
+            // allow non_snake_case to allow capturing const generics
+            #[allow(non_snake_case)]
+            #[inline(always)]
+            fn runtime$(<$($tt)*>)?($($i:$ty),*) {
                 if !$e {
                     // abort instead of panicking to reduce impact on code size
                     ::core::intrinsics::abort();
                 }
-            };
-            const fn comptime() {}
+            }
+            #[allow(non_snake_case)]
+            const fn comptime$(<$($tt)*>)?($(_:$ty),*) {}
 
-            ::core::intrinsics::const_eval_select((), comptime, runtime);
+            ::core::intrinsics::const_eval_select(($($i,)*), comptime, runtime);
         }
     };
 }
@@ -2243,7 +2312,7 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
     // SAFETY: the safety contract for `copy_nonoverlapping` must be
     // upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](src: *const T, dst: *mut T, count: usize) =>
             is_aligned_and_not_null(src)
                 && is_aligned_and_not_null(dst)
                 && is_nonoverlapping(src, dst, count)
@@ -2329,7 +2398,8 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 
     // SAFETY: the safety contract for `copy` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(src) && is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](src: *const T, dst: *mut T) =>
+            is_aligned_and_not_null(src) && is_aligned_and_not_null(dst));
         copy(src, dst, count)
     }
 }
@@ -2397,63 +2467,12 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
 
     // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
         write_bytes(dst, val, count)
     }
 }
 
-/// Selects which function to call depending on the context.
-///
-/// If this function is evaluated at compile-time, then a call to this
-/// intrinsic will be replaced with a call to `called_in_const`. It gets
-/// replaced with a call to `called_at_rt` otherwise.
-///
-/// # Type Requirements
-///
-/// The two functions must be both function items. They cannot be function
-/// pointers or closures.
-///
-/// `arg` will be the arguments that will be passed to either one of the
-/// two functions, therefore, both functions must accept the same type of
-/// arguments. Both functions must return RET.
-///
-/// # Safety
-///
-/// The two functions must behave observably equivalent. Safe code in other
-/// crates may assume that calling a `const fn` at compile-time and at run-time
-/// produces the same result. A function that produces a different result when
-/// evaluated at run-time, or has any other observable side-effects, is
-/// *unsound*.
-///
-/// Here is an example of how this could cause a problem:
-/// ```no_run
-/// #![feature(const_eval_select)]
-/// #![feature(core_intrinsics)]
-/// use std::hint::unreachable_unchecked;
-/// use std::intrinsics::const_eval_select;
-///
-/// // Crate A
-/// pub const fn inconsistent() -> i32 {
-///     fn runtime() -> i32 { 1 }
-///     const fn compiletime() -> i32 { 2 }
-///
-///     unsafe {
-//          // âš  This code violates the required equivalence of `compiletime`
-///         // and `runtime`.
-///         const_eval_select((), compiletime, runtime)
-///     }
-/// }
-///
-/// // Crate B
-/// const X: i32 = inconsistent();
-/// let x = inconsistent();
-/// if x != X { unsafe { unreachable_unchecked(); }}
-/// ```
-///
-/// This code causes Undefined Behavior when being run, since the
-/// `unreachable_unchecked` is actually being reached. The bug is in *crate A*,
-/// which violates the principle that a `const fn` must behave the same at
-/// compile-time and at run-time. The unsafe code in crate B is fine.
+#[cfg(bootstrap)]
 #[unstable(
     feature = "const_eval_select",
     issue = "none",
@@ -2475,6 +2494,7 @@ where
     called_at_rt.call_once(arg)
 }
 
+#[cfg(bootstrap)]
 #[unstable(
     feature = "const_eval_select",
     issue = "none",
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 9d857eb63da..5b1e2045fff 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -143,6 +143,7 @@
 #![feature(const_type_id)]
 #![feature(const_type_name)]
 #![feature(const_default_impls)]
+#![feature(const_unicode_case_lookup)]
 #![feature(const_unsafecell_get_mut)]
 #![feature(core_panic)]
 #![feature(duration_consts_float)]
diff --git a/library/core/src/mem/valid_align.rs b/library/core/src/mem/valid_align.rs
index b9ccc0b4c79..32b2afb72b0 100644
--- a/library/core/src/mem/valid_align.rs
+++ b/library/core/src/mem/valid_align.rs
@@ -28,7 +28,7 @@ impl ValidAlign {
     #[inline]
     pub(crate) const unsafe fn new_unchecked(align: usize) -> Self {
         // SAFETY: Precondition passed to the caller.
-        unsafe { assert_unsafe_precondition!(align.is_power_of_two()) };
+        unsafe { assert_unsafe_precondition!((align: usize) => align.is_power_of_two()) };
 
         // SAFETY: By precondition, this must be a power of two, and
         // our variants encompass all possible powers of two.
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index da41ea53635..c83b928efc1 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -1033,10 +1033,14 @@ impl f32 {
                 }
             }
         }
-        // SAFETY: `u32` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_f32_to_u32 = |rt| unsafe { mem::transmute::<f32, u32>(rt) };
+
+        #[inline(always)] // See https://github.com/rust-lang/compiler-builtins/issues/491
+        fn rt_f32_to_u32(x: f32) -> u32 {
+            // SAFETY: `u32` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute(x) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((self,), ct_f32_to_u32, rt_f32_to_u32) }
     }
@@ -1121,10 +1125,14 @@ impl f32 {
                 }
             }
         }
-        // SAFETY: `u32` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_u32_to_f32 = |rt| unsafe { mem::transmute::<u32, f32>(rt) };
+
+        #[inline(always)] // See https://github.com/rust-lang/compiler-builtins/issues/491
+        fn rt_u32_to_f32(x: u32) -> f32 {
+            // SAFETY: `u32` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute(x) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((v,), ct_u32_to_f32, rt_u32_to_f32) }
     }
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index 631d559df5f..28d23f733de 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -1026,10 +1026,14 @@ impl f64 {
                 }
             }
         }
-        // SAFETY: `u64` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_f64_to_u64 = |rt| unsafe { mem::transmute::<f64, u64>(rt) };
+
+        #[inline(always)] // See https://github.com/rust-lang/compiler-builtins/issues/491
+        fn rt_f64_to_u64(rt: f64) -> u64 {
+            // SAFETY: `u64` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute::<f64, u64>(rt) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
     }
@@ -1119,10 +1123,14 @@ impl f64 {
                 }
             }
         }
-        // SAFETY: `u64` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_u64_to_f64 = |rt| unsafe { mem::transmute::<u64, f64>(rt) };
+
+        #[inline(always)] // See https://github.com/rust-lang/compiler-builtins/issues/491
+        fn rt_u64_to_f64(rt: u64) -> f64 {
+            // SAFETY: `u64` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute::<u64, f64>(rt) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((v,), ct_u64_to_f64, rt_u64_to_f64) }
     }
diff --git a/library/core/src/num/nonzero.rs b/library/core/src/num/nonzero.rs
index 1cf306f2103..532a09736a7 100644
--- a/library/core/src/num/nonzero.rs
+++ b/library/core/src/num/nonzero.rs
@@ -56,7 +56,7 @@ macro_rules! nonzero_integers {
                 pub const unsafe fn new_unchecked(n: $Int) -> Self {
                     // SAFETY: this is guaranteed to be safe by the caller.
                     unsafe {
-                        core::intrinsics::assert_unsafe_precondition!(n != 0);
+                        core::intrinsics::assert_unsafe_precondition!((n: $Int) => n != 0);
                         Self(n)
                     }
                 }
diff --git a/library/core/src/ops/try_trait.rs b/library/core/src/ops/try_trait.rs
index 02f7f62bfe2..10f04134409 100644
--- a/library/core/src/ops/try_trait.rs
+++ b/library/core/src/ops/try_trait.rs
@@ -222,7 +222,87 @@ pub trait Try: FromResidual {
 /// Every `Try` type needs to be recreatable from its own associated
 /// `Residual` type, but can also have additional `FromResidual` implementations
 /// to support interconversion with other `Try` types.
-#[rustc_on_unimplemented(
+#[cfg_attr(not(bootstrap), rustc_on_unimplemented(
+    on(
+        all(
+            from_desugaring = "QuestionMark",
+            _Self = "std::result::Result<T, E>",
+            R = "std::option::Option<std::convert::Infallible>"
+        ),
+        message = "the `?` operator can only be used on `Result`s, not `Option`s, \
+            in {ItemContext} that returns `Result`",
+        label = "use `.ok_or(...)?` to provide an error compatible with `{Self}`",
+        parent_label = "this function returns a `Result`"
+    ),
+    on(
+        all(
+            from_desugaring = "QuestionMark",
+            _Self = "std::result::Result<T, E>",
+        ),
+        // There's a special error message in the trait selection code for
+        // `From` in `?`, so this is not shown for result-in-result errors,
+        // and thus it can be phrased more strongly than `ControlFlow`'s.
+        message = "the `?` operator can only be used on `Result`s \
+            in {ItemContext} that returns `Result`",
+        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
+        parent_label = "this function returns a `Result`"
+    ),
+    on(
+        all(
+            from_desugaring = "QuestionMark",
+            _Self = "std::option::Option<T>",
+            R = "std::result::Result<T, E>",
+        ),
+        message = "the `?` operator can only be used on `Option`s, not `Result`s, \
+            in {ItemContext} that returns `Option`",
+        label = "use `.ok()?` if you want to discard the `{R}` error information",
+        parent_label = "this function returns an `Option`"
+    ),
+    on(
+        all(
+            from_desugaring = "QuestionMark",
+            _Self = "std::option::Option<T>",
+        ),
+        // `Option`-in-`Option` always works, as there's only one possible
+        // residual, so this can also be phrased strongly.
+        message = "the `?` operator can only be used on `Option`s \
+            in {ItemContext} that returns `Option`",
+        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
+        parent_label = "this function returns an `Option`"
+    ),
+    on(
+        all(
+            from_desugaring = "QuestionMark",
+            _Self = "std::ops::ControlFlow<B, C>",
+            R = "std::ops::ControlFlow<B, C>",
+        ),
+        message = "the `?` operator in {ItemContext} that returns `ControlFlow<B, _>` \
+            can only be used on other `ControlFlow<B, _>`s (with the same Break type)",
+        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
+        parent_label = "this function returns a `ControlFlow`",
+        note = "unlike `Result`, there's no `From`-conversion performed for `ControlFlow`"
+    ),
+    on(
+        all(
+            from_desugaring = "QuestionMark",
+            _Self = "std::ops::ControlFlow<B, C>",
+            // `R` is not a `ControlFlow`, as that case was matched previously
+        ),
+        message = "the `?` operator can only be used on `ControlFlow`s \
+            in {ItemContext} that returns `ControlFlow`",
+        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
+        parent_label = "this function returns a `ControlFlow`",
+    ),
+    on(
+        all(from_desugaring = "QuestionMark"),
+        message = "the `?` operator can only be used in {ItemContext} \
+                    that returns `Result` or `Option` \
+                    (or another type that implements `{FromResidual}`)",
+        label = "cannot use the `?` operator in {ItemContext} that returns `{Self}`",
+        parent_label = "this function should return `Result` or `Option` to accept `?`"
+    ),
+))]
+#[cfg_attr(bootstrap, rustc_on_unimplemented(
     on(
         all(
             from_desugaring = "QuestionMark",
@@ -301,7 +381,7 @@ pub trait Try: FromResidual {
         label = "cannot use the `?` operator in {ItemContext} that returns `{Self}`",
         enclosing_scope = "this function should return `Result` or `Option` to accept `?`"
     ),
-)]
+))]
 #[rustc_diagnostic_item = "FromResidual"]
 #[unstable(feature = "try_trait_v2", issue = "84277")]
 pub trait FromResidual<R = <Self as Try>::Residual> {
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index f5c72d79755..80bff74f3e9 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -755,9 +755,12 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        let this = self;
         // SAFETY: The comparison has no side-effects, and the intrinsic
         // does this check internally in the CTFE implementation.
-        unsafe { assert_unsafe_precondition!(self >= origin) };
+        unsafe {
+            assert_unsafe_precondition!([T](this: *const T, origin: *const T) => this >= origin)
+        };
 
         let pointee_size = mem::size_of::<T>();
         assert!(0 < pointee_size && pointee_size <= isize::MAX as usize);
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index 41a2685d361..e976abed774 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -886,7 +886,7 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
     // SAFETY: the caller must guarantee that `x` and `y` are
     // valid for writes and properly aligned.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](x: *mut T, y: *mut T, count: usize) =>
             is_aligned_and_not_null(x)
                 && is_aligned_and_not_null(y)
                 && is_nonoverlapping(x, y, count)
@@ -983,7 +983,7 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
     // and cannot overlap `src` since `dst` must point to a distinct
     // allocated object.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
         mem::swap(&mut *dst, &mut src); // cannot overlap
     }
     src
@@ -1470,7 +1470,7 @@ pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 pub unsafe fn read_volatile<T>(src: *const T) -> T {
     // SAFETY: the caller must uphold the safety contract for `volatile_load`.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(src));
+        assert_unsafe_precondition!([T](src: *const T) => is_aligned_and_not_null(src));
         intrinsics::volatile_load(src)
     }
 }
@@ -1541,7 +1541,7 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
 pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
     // SAFETY: the caller must uphold the safety contract for `volatile_store`.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
         intrinsics::volatile_store(dst, src);
     }
 }
diff --git a/library/core/src/slice/index.rs b/library/core/src/slice/index.rs
index fd7ecf3daf3..3403a5a86f7 100644
--- a/library/core/src/slice/index.rs
+++ b/library/core/src/slice/index.rs
@@ -48,10 +48,12 @@ const fn slice_start_index_len_fail(index: usize, len: usize) -> ! {
 }
 
 // FIXME const-hack
+#[track_caller]
 fn slice_start_index_len_fail_rt(index: usize, len: usize) -> ! {
     panic!("range start index {index} out of range for slice of length {len}");
 }
 
+#[track_caller]
 const fn slice_start_index_len_fail_ct(_: usize, _: usize) -> ! {
     panic!("slice start index is out of range for slice");
 }
@@ -69,10 +71,12 @@ const fn slice_end_index_len_fail(index: usize, len: usize) -> ! {
 }
 
 // FIXME const-hack
+#[track_caller]
 fn slice_end_index_len_fail_rt(index: usize, len: usize) -> ! {
     panic!("range end index {index} out of range for slice of length {len}");
 }
 
+#[track_caller]
 const fn slice_end_index_len_fail_ct(_: usize, _: usize) -> ! {
     panic!("slice end index is out of range for slice");
 }
@@ -88,10 +92,12 @@ const fn slice_index_order_fail(index: usize, end: usize) -> ! {
 }
 
 // FIXME const-hack
+#[track_caller]
 fn slice_index_order_fail_rt(index: usize, end: usize) -> ! {
     panic!("slice index starts at {index} but ends at {end}");
 }
 
+#[track_caller]
 const fn slice_index_order_fail_ct(_: usize, _: usize) -> ! {
     panic!("slice index start is larger than end");
 }
@@ -217,21 +223,23 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
 
     #[inline]
     unsafe fn get_unchecked(self, slice: *const [T]) -> *const T {
+        let this = self;
         // SAFETY: the caller guarantees that `slice` is not dangling, so it
         // cannot be longer than `isize::MAX`. They also guarantee that
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
         // so the call to `add` is safe.
         unsafe {
-            assert_unsafe_precondition!(self < slice.len());
+            assert_unsafe_precondition!([T](this: usize, slice: *const [T]) => this < slice.len());
             slice.as_ptr().add(self)
         }
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut T {
+        let this = self;
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!(self < slice.len());
+            assert_unsafe_precondition!([T](this: usize, slice: *mut [T]) => this < slice.len());
             slice.as_mut_ptr().add(self)
         }
     }
@@ -276,22 +284,26 @@ unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
 
     #[inline]
     unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        let this = ops::Range { start: self.start, end: self.end };
         // SAFETY: the caller guarantees that `slice` is not dangling, so it
         // cannot be longer than `isize::MAX`. They also guarantee that
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
         // so the call to `add` is safe.
 
         unsafe {
-            assert_unsafe_precondition!(self.end >= self.start && self.end <= slice.len());
+            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *const [T]) =>
+            this.end >= this.start && this.end <= slice.len());
             ptr::slice_from_raw_parts(slice.as_ptr().add(self.start), self.end - self.start)
         }
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        let this = ops::Range { start: self.start, end: self.end };
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!(self.end >= self.start && self.end <= slice.len());
+            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *mut [T]) =>
+                this.end >= this.start && this.end <= slice.len());
             ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start), self.end - self.start)
         }
     }
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 1958745b586..6a7150d2986 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -656,10 +656,11 @@ impl<T> [T] {
     #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
     #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
     pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
-        let ptr = self.as_mut_ptr();
+        let this = self;
+        let ptr = this.as_mut_ptr();
         // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
         unsafe {
-            assert_unsafe_precondition!(a < self.len() && b < self.len());
+            assert_unsafe_precondition!([T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len());
             ptr::swap(ptr.add(a), ptr.add(b));
         }
     }
@@ -972,9 +973,10 @@ impl<T> [T] {
     #[inline]
     #[must_use]
     pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
+        let this = self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
+            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
             exact_div(self.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
@@ -1111,10 +1113,11 @@ impl<T> [T] {
     #[inline]
     #[must_use]
     pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
+        let this = &*self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
-            exact_div(self.len(), N)
+            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+            exact_div(this.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
         // a slice of `new_len` many `N` elements chunks.
@@ -1687,7 +1690,7 @@ impl<T> [T] {
         // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
         // is fine.
         unsafe {
-            assert_unsafe_precondition!(mid <= len);
+            assert_unsafe_precondition!((mid: usize, len: usize) => mid <= len);
             (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
         }
     }
diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs
index 107e71ab68b..f1e8bc79bf4 100644
--- a/library/core/src/slice/raw.rs
+++ b/library/core/src/slice/raw.rs
@@ -90,7 +90,7 @@ use crate::ptr;
 pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](data: *const T, len: usize) =>
             is_aligned_and_not_null(data)
                 && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
         );
@@ -134,7 +134,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
 pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](data: *mut T, len: usize) =>
             is_aligned_and_not_null(data)
                 && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
         );
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index 2120bf61d75..f673aa2a44b 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -91,10 +91,12 @@ const fn slice_error_fail(s: &str, begin: usize, end: usize) -> ! {
     }
 }
 
+#[track_caller]
 const fn slice_error_fail_ct(_: &str, _: usize, _: usize) -> ! {
     panic!("failed to slice string");
 }
 
+#[track_caller]
 fn slice_error_fail_rt(s: &str, begin: usize, end: usize) -> ! {
     const MAX_DISPLAY_LENGTH: usize = 256;
     let trunc_len = s.floor_char_boundary(MAX_DISPLAY_LENGTH);
diff --git a/library/core/src/unicode/unicode_data.rs b/library/core/src/unicode/unicode_data.rs
index c1eff3a36e6..7301da2afec 100644
--- a/library/core/src/unicode/unicode_data.rs
+++ b/library/core/src/unicode/unicode_data.rs
@@ -1,7 +1,8 @@
 ///! This file is generated by src/tools/unicode-table-generator; do not edit manually!
 
+#[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
 #[inline(always)]
-fn bitset_search<
+const fn bitset_search<
     const N: usize,
     const CHUNK_SIZE: usize,
     const N1: usize,
@@ -17,14 +18,18 @@ fn bitset_search<
     let bucket_idx = (needle / 64) as usize;
     let chunk_map_idx = bucket_idx / CHUNK_SIZE;
     let chunk_piece = bucket_idx % CHUNK_SIZE;
-    let chunk_idx = if let Some(&v) = chunk_idx_map.get(chunk_map_idx) {
-        v
+    // FIXME: const-hack: Revert to `slice::get` after `const_slice_index`
+    // feature stabilizes.
+    let chunk_idx = if chunk_map_idx < chunk_idx_map.len() {
+        chunk_idx_map[chunk_map_idx]
     } else {
         return false;
     };
     let idx = bitset_chunk_idx[chunk_idx as usize][chunk_piece] as usize;
-    let word = if let Some(word) = bitset_canonical.get(idx) {
-        *word
+    // FIXME: const-hack: Revert to `slice::get` after `const_slice_index`
+    // feature stabilizes.
+    let word = if idx < bitset_canonical.len() {
+        bitset_canonical[idx]
     } else {
         let (real_idx, mapping) = bitset_canonicalized[idx - bitset_canonical.len()];
         let mut word = bitset_canonical[real_idx as usize];
@@ -318,14 +323,14 @@ pub mod grapheme_extend {
 
 #[rustfmt::skip]
 pub mod lowercase {
-    static BITSET_CHUNKS_MAP: [u8; 123] = [
+    const BITSET_CHUNKS_MAP: &'static [u8; 123] = &[
         14, 17, 0, 0, 9, 0, 0, 12, 13, 10, 0, 16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 0, 4, 1, 0, 15, 0, 8, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 18, 0,
         3, 0, 0, 7,
     ];
-    static BITSET_INDEX_CHUNKS: [[u8; 16]; 19] = [
+    const BITSET_INDEX_CHUNKS: &'static [[u8; 16]; 19] = &[
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 59, 0, 0],
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 16, 14, 55, 0],
@@ -346,7 +351,7 @@ pub mod lowercase {
         [16, 49, 2, 20, 66, 9, 57, 0, 0, 0, 0, 0, 0, 0, 0, 0],
         [63, 39, 54, 12, 73, 61, 18, 1, 6, 62, 71, 19, 68, 69, 3, 44],
     ];
-    static BITSET_CANONICAL: [u64; 55] = [
+    const BITSET_CANONICAL: &'static [u64; 55] = &[
         0b0000000000000000000000000000000000000000000000000000000000000000,
         0b1111111111111111110000000000000000000000000011111111111111111111,
         0b1010101010101010101010101010101010101010101010101010100000000010,
@@ -403,13 +408,14 @@ pub mod lowercase {
         0b1110011111111111111111111111111111111111111111110000000000000000,
         0b1110101111000000000000000000000000001111111111111111111111111100,
     ];
-    static BITSET_MAPPING: [(u8, u8); 20] = [
+    const BITSET_MAPPING: &'static [(u8, u8); 20] = &[
         (0, 64), (1, 188), (1, 183), (1, 176), (1, 109), (1, 124), (1, 126), (1, 66), (1, 70),
         (1, 77), (2, 146), (2, 144), (2, 83), (3, 12), (3, 6), (4, 156), (4, 78), (5, 187),
         (6, 132), (7, 93),
     ];
 
-    pub fn lookup(c: char) -> bool {
+    #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
+    pub const fn lookup(c: char) -> bool {
         super::bitset_search(
             c as u32,
             &BITSET_CHUNKS_MAP,
@@ -454,14 +460,14 @@ pub mod n {
 
 #[rustfmt::skip]
 pub mod uppercase {
-    static BITSET_CHUNKS_MAP: [u8; 125] = [
+    const BITSET_CHUNKS_MAP: &'static [u8; 125] = &[
         12, 15, 6, 6, 0, 6, 6, 2, 4, 11, 6, 16, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
         6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 8, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
         6, 6, 6, 5, 6, 14, 6, 10, 6, 6, 1, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
         6, 7, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 13, 6, 6,
         6, 6, 9, 6, 3,
     ];
-    static BITSET_INDEX_CHUNKS: [[u8; 16]; 17] = [
+    const BITSET_INDEX_CHUNKS: &'static [[u8; 16]; 17] = &[
         [43, 43, 5, 34, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 5, 1],
         [43, 43, 5, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43],
         [43, 43, 39, 43, 43, 43, 43, 43, 17, 17, 62, 17, 42, 29, 24, 23],
@@ -480,7 +486,7 @@ pub mod uppercase {
         [57, 19, 2, 18, 10, 47, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43],
         [57, 37, 17, 27, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43],
     ];
-    static BITSET_CANONICAL: [u64; 43] = [
+    const BITSET_CANONICAL: &'static [u64; 43] = &[
         0b0000011111111111111111111111111000000000000000000000000000000000,
         0b0000000000111111111111111111111111111111111111111111111111111111,
         0b0101010101010101010101010101010101010101010101010101010000000001,
@@ -525,13 +531,14 @@ pub mod uppercase {
         0b1111011111111111000000000000000000000000000000000000000000000000,
         0b1111111100000000111111110000000000111111000000001111111100000000,
     ];
-    static BITSET_MAPPING: [(u8, u8); 25] = [
+    const BITSET_MAPPING: &'static [(u8, u8); 25] = &[
         (0, 187), (0, 177), (0, 171), (0, 167), (0, 164), (0, 32), (0, 47), (0, 51), (0, 121),
         (0, 117), (0, 109), (1, 150), (1, 148), (1, 142), (1, 134), (1, 131), (1, 64), (2, 164),
         (2, 146), (2, 20), (3, 146), (3, 140), (3, 134), (4, 178), (4, 171),
     ];
 
-    pub fn lookup(c: char) -> bool {
+    #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
+    pub const fn lookup(c: char) -> bool {
         super::bitset_search(
             c as u32,
             &BITSET_CHUNKS_MAP,
diff --git a/library/std/src/alloc.rs b/library/std/src/alloc.rs
index a05e0db3af7..61c1ff578b2 100644
--- a/library/std/src/alloc.rs
+++ b/library/std/src/alloc.rs
@@ -68,7 +68,10 @@ pub use alloc_crate::alloc::*;
 /// The default memory allocator provided by the operating system.
 ///
 /// This is based on `malloc` on Unix platforms and `HeapAlloc` on Windows,
-/// plus related functions.
+/// plus related functions. However, it is not valid to mix use of the backing
+/// system allocator with `System`, as this implementation may include extra
+/// work, such as to serve alignment requests greater than the alignment
+/// provided directly by the backing system allocator.
 ///
 /// This type implements the `GlobalAlloc` trait and Rust programs by default
 /// work as if they had this definition:
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 28a2c99f7e5..c6c78dc3939 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -19,7 +19,7 @@ use crate::sys::fs as fs_imp;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
 use crate::time::SystemTime;
 
-/// A reference to an open file on the filesystem.
+/// An object providing access to an open file on the filesystem.
 ///
 /// An instance of a `File` can be read and/or written depending on what options
 /// it was opened with. Files also implement [`Seek`] to alter the logical cursor
diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
index 07239746258..dd4ff4952fd 100644
--- a/library/std/src/io/stdio.rs
+++ b/library/std/src/io/stdio.rs
@@ -8,7 +8,6 @@ use crate::io::prelude::*;
 use crate::cell::{Cell, RefCell};
 use crate::fmt;
 use crate::io::{self, BufReader, IoSlice, IoSliceMut, LineWriter, Lines};
-use crate::pin::Pin;
 use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sync::{Arc, Mutex, MutexGuard, OnceLock};
 use crate::sys::stdio;
@@ -526,7 +525,7 @@ pub struct Stdout {
     // FIXME: this should be LineWriter or BufWriter depending on the state of
     //        stdout (tty or not). Note that if this is not line buffered it
     //        should also flush-on-panic or some form of flush-on-abort.
-    inner: Pin<&'static ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>>,
+    inner: &'static ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>,
 }
 
 /// A locked reference to the [`Stdout`] handle.
@@ -603,24 +602,20 @@ static STDOUT: OnceLock<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> = OnceLo
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stdout() -> Stdout {
     Stdout {
-        inner: Pin::static_ref(&STDOUT).get_or_init_pin(
-            || unsafe { ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw()))) },
-            |mutex| unsafe { mutex.init() },
-        ),
+        inner: STDOUT
+            .get_or_init(|| ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw())))),
     }
 }
 
 pub fn cleanup() {
-    if let Some(instance) = STDOUT.get() {
-        // Flush the data and disable buffering during shutdown
-        // by replacing the line writer by one with zero
-        // buffering capacity.
-        // We use try_lock() instead of lock(), because someone
-        // might have leaked a StdoutLock, which would
-        // otherwise cause a deadlock here.
-        if let Some(lock) = Pin::static_ref(instance).try_lock() {
-            *lock.borrow_mut() = LineWriter::with_capacity(0, stdout_raw());
-        }
+    // Flush the data and disable buffering during shutdown
+    // by replacing the line writer by one with zero
+    // buffering capacity.
+    // We use try_lock() instead of lock(), because someone
+    // might have leaked a StdoutLock, which would
+    // otherwise cause a deadlock here.
+    if let Some(lock) = STDOUT.get().and_then(ReentrantMutex::try_lock) {
+        *lock.borrow_mut() = LineWriter::with_capacity(0, stdout_raw());
     }
 }
 
@@ -761,7 +756,7 @@ impl fmt::Debug for StdoutLock<'_> {
 /// standard library or via raw Windows API calls, will fail.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Stderr {
-    inner: Pin<&'static ReentrantMutex<RefCell<StderrRaw>>>,
+    inner: &'static ReentrantMutex<RefCell<StderrRaw>>,
 }
 
 /// A locked reference to the [`Stderr`] handle.
@@ -834,16 +829,12 @@ pub struct StderrLock<'a> {
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn stderr() -> Stderr {
     // Note that unlike `stdout()` we don't use `at_exit` here to register a
-    // destructor. Stderr is not buffered , so there's no need to run a
+    // destructor. Stderr is not buffered, so there's no need to run a
     // destructor for flushing the buffer
-    static INSTANCE: OnceLock<ReentrantMutex<RefCell<StderrRaw>>> = OnceLock::new();
+    static INSTANCE: ReentrantMutex<RefCell<StderrRaw>> =
+        ReentrantMutex::new(RefCell::new(stderr_raw()));
 
-    Stderr {
-        inner: Pin::static_ref(&INSTANCE).get_or_init_pin(
-            || unsafe { ReentrantMutex::new(RefCell::new(stderr_raw())) },
-            |mutex| unsafe { mutex.init() },
-        ),
-    }
+    Stderr { inner: &INSTANCE }
 }
 
 impl Stderr {
diff --git a/library/std/src/sync/once_lock.rs b/library/std/src/sync/once_lock.rs
index 813516040cd..37413ec62a7 100644
--- a/library/std/src/sync/once_lock.rs
+++ b/library/std/src/sync/once_lock.rs
@@ -3,7 +3,6 @@ use crate::fmt;
 use crate::marker::PhantomData;
 use crate::mem::MaybeUninit;
 use crate::panic::{RefUnwindSafe, UnwindSafe};
-use crate::pin::Pin;
 use crate::sync::Once;
 
 /// A synchronization primitive which can be written to only once.
@@ -223,60 +222,6 @@ impl<T> OnceLock<T> {
         Ok(unsafe { self.get_unchecked() })
     }
 
-    /// Internal-only API that gets the contents of the cell, initializing it
-    /// in two steps with `f` and `g` if the cell was empty.
-    ///
-    /// `f` is called to construct the value, which is then moved into the cell
-    /// and given as a (pinned) mutable reference to `g` to finish
-    /// initialization.
-    ///
-    /// This allows `g` to inspect an manipulate the value after it has been
-    /// moved into its final place in the cell, but before the cell is
-    /// considered initialized.
-    ///
-    /// # Panics
-    ///
-    /// If `f` or `g` panics, the panic is propagated to the caller, and the
-    /// cell remains uninitialized.
-    ///
-    /// With the current implementation, if `g` panics, the value from `f` will
-    /// not be dropped. This should probably be fixed if this is ever used for
-    /// a type where this matters.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`. The exact
-    /// outcome is unspecified. Current implementation deadlocks, but this may
-    /// be changed to a panic in the future.
-    pub(crate) fn get_or_init_pin<F, G>(self: Pin<&Self>, f: F, g: G) -> Pin<&T>
-    where
-        F: FnOnce() -> T,
-        G: FnOnce(Pin<&mut T>),
-    {
-        if let Some(value) = self.get_ref().get() {
-            // SAFETY: The inner value was already initialized, and will not be
-            // moved anymore.
-            return unsafe { Pin::new_unchecked(value) };
-        }
-
-        let slot = &self.value;
-
-        // Ignore poisoning from other threads
-        // If another thread panics, then we'll be able to run our closure
-        self.once.call_once_force(|_| {
-            let value = f();
-            // SAFETY: We use the Once (self.once) to guarantee unique access
-            // to the UnsafeCell (slot).
-            let value: &mut T = unsafe { (&mut *slot.get()).write(value) };
-            // SAFETY: The value has been written to its final place in
-            // self.value. We do not to move it anymore, which we promise here
-            // with a Pin<&mut T>.
-            g(unsafe { Pin::new_unchecked(value) });
-        });
-
-        // SAFETY: The inner value has been initialized, and will not be moved
-        // anymore.
-        unsafe { Pin::new_unchecked(self.get_ref().get_unchecked()) }
-    }
-
     /// Consumes the `OnceLock`, returning the wrapped value. Returns
     /// `None` if the cell was empty.
     ///
diff --git a/library/std/src/sys/hermit/mutex.rs b/library/std/src/sys/hermit/mutex.rs
index eb15a04ffcf..e0184eb5baf 100644
--- a/library/std/src/sys/hermit/mutex.rs
+++ b/library/std/src/sys/hermit/mutex.rs
@@ -175,9 +175,6 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn init(&mut self) {}
-
-    #[inline]
     pub unsafe fn lock(&self) {
         loop {
             let mut guard = self.inner.lock();
diff --git a/library/std/src/sys/itron/mutex.rs b/library/std/src/sys/itron/mutex.rs
index 715e94c3b3d..085662e6d44 100644
--- a/library/std/src/sys/itron/mutex.rs
+++ b/library/std/src/sys/itron/mutex.rs
@@ -31,12 +31,6 @@ impl Mutex {
         Mutex { mtx: SpinIdOnceCell::new() }
     }
 
-    pub unsafe fn init(&mut self) {
-        // Initialize `self.mtx` eagerly
-        let id = new_mtx().unwrap_or_else(|e| fail(e, &"acre_mtx"));
-        unsafe { self.mtx.set_unchecked((id, ())) };
-    }
-
     /// Get the inner mutex's ID, which is lazily created.
     fn raw(&self) -> abi::ID {
         match self.mtx.get_or_try_init(|| new_mtx().map(|id| (id, ()))) {
diff --git a/library/std/src/sys/sgx/mutex.rs b/library/std/src/sys/sgx/mutex.rs
index 513cd77fd2a..aa747d56b0d 100644
--- a/library/std/src/sys/sgx/mutex.rs
+++ b/library/std/src/sys/sgx/mutex.rs
@@ -21,9 +21,6 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn init(&mut self) {}
-
-    #[inline]
     pub unsafe fn lock(&self) {
         let mut guard = self.inner.lock();
         if *guard.lock_var() {
diff --git a/library/std/src/sys/unix/locks/fuchsia_mutex.rs b/library/std/src/sys/unix/locks/fuchsia_mutex.rs
index dbb9829bb66..117611ce43f 100644
--- a/library/std/src/sys/unix/locks/fuchsia_mutex.rs
+++ b/library/std/src/sys/unix/locks/fuchsia_mutex.rs
@@ -86,9 +86,6 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn init(&mut self) {}
-
-    #[inline]
     pub unsafe fn try_lock(&self) -> bool {
         let thread_self = zx_thread_self();
         self.futex.compare_exchange(UNLOCKED, to_state(thread_self), Acquire, Relaxed).is_ok()
diff --git a/library/std/src/sys/unix/locks/futex_mutex.rs b/library/std/src/sys/unix/locks/futex_mutex.rs
index 1b5be46c605..33b13dad4d6 100644
--- a/library/std/src/sys/unix/locks/futex_mutex.rs
+++ b/library/std/src/sys/unix/locks/futex_mutex.rs
@@ -20,9 +20,6 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn init(&mut self) {}
-
-    #[inline]
     pub unsafe fn try_lock(&self) -> bool {
         self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_ok()
     }
diff --git a/library/std/src/sys/unix/locks/pthread_mutex.rs b/library/std/src/sys/unix/locks/pthread_mutex.rs
index 98afee69ba6..5964935ddb5 100644
--- a/library/std/src/sys/unix/locks/pthread_mutex.rs
+++ b/library/std/src/sys/unix/locks/pthread_mutex.rs
@@ -52,7 +52,7 @@ impl Mutex {
         Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
     }
     #[inline]
-    pub unsafe fn init(&mut self) {
+    unsafe fn init(&mut self) {
         // Issue #33770
         //
         // A pthread mutex initialized with PTHREAD_MUTEX_INITIALIZER will have
diff --git a/library/std/src/sys/unsupported/locks/mutex.rs b/library/std/src/sys/unsupported/locks/mutex.rs
index d7cb12e0cf9..2be0b34b985 100644
--- a/library/std/src/sys/unsupported/locks/mutex.rs
+++ b/library/std/src/sys/unsupported/locks/mutex.rs
@@ -17,9 +17,6 @@ impl Mutex {
     }
 
     #[inline]
-    pub unsafe fn init(&mut self) {}
-
-    #[inline]
     pub unsafe fn lock(&self) {
         assert_eq!(self.locked.replace(true), false, "cannot recursively acquire mutex");
     }
diff --git a/library/std/src/sys/windows/locks/mutex.rs b/library/std/src/sys/windows/locks/mutex.rs
index f91e8f9f59a..91207f5f466 100644
--- a/library/std/src/sys/windows/locks/mutex.rs
+++ b/library/std/src/sys/windows/locks/mutex.rs
@@ -37,8 +37,6 @@ impl Mutex {
     pub const fn new() -> Mutex {
         Mutex { srwlock: UnsafeCell::new(c::SRWLOCK_INIT) }
     }
-    #[inline]
-    pub unsafe fn init(&mut self) {}
 
     #[inline]
     pub unsafe fn lock(&self) {
diff --git a/library/std/src/sys_common/remutex.rs b/library/std/src/sys_common/remutex.rs
index 8921af311d4..b448ae3a997 100644
--- a/library/std/src/sys_common/remutex.rs
+++ b/library/std/src/sys_common/remutex.rs
@@ -1,13 +1,11 @@
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod tests;
 
+use super::mutex as sys;
 use crate::cell::UnsafeCell;
-use crate::marker::PhantomPinned;
 use crate::ops::Deref;
 use crate::panic::{RefUnwindSafe, UnwindSafe};
-use crate::pin::Pin;
 use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed};
-use crate::sys::locks as sys;
 
 /// A re-entrant mutual exclusion
 ///
@@ -41,11 +39,10 @@ use crate::sys::locks as sys;
 /// synchronization is left to the mutex, making relaxed memory ordering for
 /// the `owner` field fine in all cases.
 pub struct ReentrantMutex<T> {
-    mutex: sys::Mutex,
+    mutex: sys::MovableMutex,
     owner: AtomicUsize,
     lock_count: UnsafeCell<u32>,
     data: T,
-    _pinned: PhantomPinned,
 }
 
 unsafe impl<T: Send> Send for ReentrantMutex<T> {}
@@ -68,39 +65,22 @@ impl<T> RefUnwindSafe for ReentrantMutex<T> {}
 /// guarded data.
 #[must_use = "if unused the ReentrantMutex will immediately unlock"]
 pub struct ReentrantMutexGuard<'a, T: 'a> {
-    lock: Pin<&'a ReentrantMutex<T>>,
+    lock: &'a ReentrantMutex<T>,
 }
 
 impl<T> !Send for ReentrantMutexGuard<'_, T> {}
 
 impl<T> ReentrantMutex<T> {
     /// Creates a new reentrant mutex in an unlocked state.
-    ///
-    /// # Unsafety
-    ///
-    /// This function is unsafe because it is required that `init` is called
-    /// once this mutex is in its final resting place, and only then are the
-    /// lock/unlock methods safe.
-    pub const unsafe fn new(t: T) -> ReentrantMutex<T> {
+    pub const fn new(t: T) -> ReentrantMutex<T> {
         ReentrantMutex {
-            mutex: sys::Mutex::new(),
+            mutex: sys::MovableMutex::new(),
             owner: AtomicUsize::new(0),
             lock_count: UnsafeCell::new(0),
             data: t,
-            _pinned: PhantomPinned,
         }
     }
 
-    /// Initializes this mutex so it's ready for use.
-    ///
-    /// # Unsafety
-    ///
-    /// Unsafe to call more than once, and must be called after this will no
-    /// longer move in memory.
-    pub unsafe fn init(self: Pin<&mut Self>) {
-        self.get_unchecked_mut().mutex.init()
-    }
-
     /// Acquires a mutex, blocking the current thread until it is able to do so.
     ///
     /// This function will block the caller until it is available to acquire the mutex.
@@ -113,15 +93,14 @@ impl<T> ReentrantMutex<T> {
     /// If another user of this mutex panicked while holding the mutex, then
     /// this call will return failure if the mutex would otherwise be
     /// acquired.
-    pub fn lock(self: Pin<&Self>) -> ReentrantMutexGuard<'_, T> {
+    pub fn lock(&self) -> ReentrantMutexGuard<'_, T> {
         let this_thread = current_thread_unique_ptr();
-        // Safety: We only touch lock_count when we own the lock,
-        // and since self is pinned we can safely call the lock() on the mutex.
+        // Safety: We only touch lock_count when we own the lock.
         unsafe {
             if self.owner.load(Relaxed) == this_thread {
                 self.increment_lock_count();
             } else {
-                self.mutex.lock();
+                self.mutex.raw_lock();
                 self.owner.store(this_thread, Relaxed);
                 debug_assert_eq!(*self.lock_count.get(), 0);
                 *self.lock_count.get() = 1;
@@ -142,10 +121,9 @@ impl<T> ReentrantMutex<T> {
     /// If another user of this mutex panicked while holding the mutex, then
     /// this call will return failure if the mutex would otherwise be
     /// acquired.
-    pub fn try_lock(self: Pin<&Self>) -> Option<ReentrantMutexGuard<'_, T>> {
+    pub fn try_lock(&self) -> Option<ReentrantMutexGuard<'_, T>> {
         let this_thread = current_thread_unique_ptr();
-        // Safety: We only touch lock_count when we own the lock,
-        // and since self is pinned we can safely call the try_lock on the mutex.
+        // Safety: We only touch lock_count when we own the lock.
         unsafe {
             if self.owner.load(Relaxed) == this_thread {
                 self.increment_lock_count();
@@ -179,12 +157,12 @@ impl<T> Deref for ReentrantMutexGuard<'_, T> {
 impl<T> Drop for ReentrantMutexGuard<'_, T> {
     #[inline]
     fn drop(&mut self) {
-        // Safety: We own the lock, and the lock is pinned.
+        // Safety: We own the lock.
         unsafe {
             *self.lock.lock_count.get() -= 1;
             if *self.lock.lock_count.get() == 0 {
                 self.lock.owner.store(0, Relaxed);
-                self.lock.mutex.unlock();
+                self.lock.mutex.raw_unlock();
             }
         }
     }
diff --git a/library/std/src/sys_common/remutex/tests.rs b/library/std/src/sys_common/remutex/tests.rs
index 64873b850d3..8e97ce11c34 100644
--- a/library/std/src/sys_common/remutex/tests.rs
+++ b/library/std/src/sys_common/remutex/tests.rs
@@ -1,18 +1,11 @@
-use crate::boxed::Box;
 use crate::cell::RefCell;
-use crate::pin::Pin;
 use crate::sync::Arc;
 use crate::sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
 use crate::thread;
 
 #[test]
 fn smoke() {
-    let m = unsafe {
-        let mut m = Box::pin(ReentrantMutex::new(()));
-        m.as_mut().init();
-        m
-    };
-    let m = m.as_ref();
+    let m = ReentrantMutex::new(());
     {
         let a = m.lock();
         {
@@ -29,20 +22,15 @@ fn smoke() {
 
 #[test]
 fn is_mutex() {
-    let m = unsafe {
-        // FIXME: Simplify this if Arc gets an Arc::get_pin_mut.
-        let mut m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
-        Pin::new_unchecked(Arc::get_mut_unchecked(&mut m)).init();
-        Pin::new_unchecked(m)
-    };
+    let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
     let m2 = m.clone();
-    let lock = m.as_ref().lock();
+    let lock = m.lock();
     let child = thread::spawn(move || {
-        let lock = m2.as_ref().lock();
+        let lock = m2.lock();
         assert_eq!(*lock.borrow(), 4950);
     });
     for i in 0..100 {
-        let lock = m.as_ref().lock();
+        let lock = m.lock();
         *lock.borrow_mut() += i;
     }
     drop(lock);
@@ -51,22 +39,17 @@ fn is_mutex() {
 
 #[test]
 fn trylock_works() {
-    let m = unsafe {
-        // FIXME: Simplify this if Arc gets an Arc::get_pin_mut.
-        let mut m = Arc::new(ReentrantMutex::new(()));
-        Pin::new_unchecked(Arc::get_mut_unchecked(&mut m)).init();
-        Pin::new_unchecked(m)
-    };
+    let m = Arc::new(ReentrantMutex::new(()));
     let m2 = m.clone();
-    let _lock = m.as_ref().try_lock();
-    let _lock2 = m.as_ref().try_lock();
+    let _lock = m.try_lock();
+    let _lock2 = m.try_lock();
     thread::spawn(move || {
-        let lock = m2.as_ref().try_lock();
+        let lock = m2.try_lock();
         assert!(lock.is_none());
     })
     .join()
     .unwrap();
-    let _lock3 = m.as_ref().try_lock();
+    let _lock3 = m.try_lock();
 }
 
 pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);
diff --git a/src/ci/docker/host-x86_64/mingw-check/Dockerfile b/src/ci/docker/host-x86_64/mingw-check/Dockerfile
index c6723d91c8b..52a7776153d 100644
--- a/src/ci/docker/host-x86_64/mingw-check/Dockerfile
+++ b/src/ci/docker/host-x86_64/mingw-check/Dockerfile
@@ -45,7 +45,8 @@ ENV SCRIPT python3 ../x.py --stage 2 test src/tools/expand-yaml-anchors && \
            python3 ../x.py test --stage 0 src/tools/compiletest && \
            python3 ../x.py test --stage 2 src/tools/tidy && \
            python3 ../x.py test --stage 0 core alloc std test proc_macro && \
-           python3 ../x.py doc --stage 0 library/test && \
+           # Build both public and internal documentation.
+           RUSTDOCFLAGS="--document-private-items" python3 ../x.py doc --stage 0 library/test && \
            /scripts/validate-toolstate.sh && \
            /scripts/validate-error-codes.sh && \
            reuse lint && \
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index ebf6c55ee35..be2227f47af 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1786,7 +1786,10 @@ pub(crate) fn clean_visibility(vis: ty::Visibility) -> Visibility {
 
 pub(crate) fn clean_variant_def<'tcx>(variant: &ty::VariantDef, cx: &mut DocContext<'tcx>) -> Item {
     let kind = match variant.ctor_kind {
-        CtorKind::Const => Variant::CLike,
+        CtorKind::Const => Variant::CLike(match variant.discr {
+            ty::VariantDiscr::Explicit(def_id) => Some(Discriminant { expr: None, value: def_id }),
+            ty::VariantDiscr::Relative(_) => None,
+        }),
         CtorKind::Fn => Variant::Tuple(
             variant.fields.iter().map(|field| clean_middle_field(field, cx)).collect(),
         ),
@@ -1803,6 +1806,7 @@ pub(crate) fn clean_variant_def<'tcx>(variant: &ty::VariantDef, cx: &mut DocCont
 
 fn clean_variant_data<'tcx>(
     variant: &hir::VariantData<'tcx>,
+    disr_expr: &Option<hir::AnonConst>,
     cx: &mut DocContext<'tcx>,
 ) -> Variant {
     match variant {
@@ -1813,7 +1817,10 @@ fn clean_variant_data<'tcx>(
         hir::VariantData::Tuple(..) => {
             Variant::Tuple(variant.fields().iter().map(|x| clean_field(x, cx)).collect())
         }
-        hir::VariantData::Unit(..) => Variant::CLike,
+        hir::VariantData::Unit(..) => Variant::CLike(disr_expr.map(|disr| Discriminant {
+            expr: Some(disr.body),
+            value: cx.tcx.hir().local_def_id(disr.hir_id).to_def_id(),
+        })),
     }
 }
 
@@ -1967,7 +1974,7 @@ fn clean_maybe_renamed_item<'tcx>(
 }
 
 fn clean_variant<'tcx>(variant: &hir::Variant<'tcx>, cx: &mut DocContext<'tcx>) -> Item {
-    let kind = VariantItem(clean_variant_data(&variant.data, cx));
+    let kind = VariantItem(clean_variant_data(&variant.data, &variant.disr_expr, cx));
     let what_rustc_thinks =
         Item::from_hir_id_and_parts(variant.id, Some(variant.ident.name), kind, cx);
     // don't show `pub` for variants, which are always public
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index 2808b400a0b..d6bb7c6c4fc 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -2098,7 +2098,7 @@ impl Enum {
 
 #[derive(Clone, Debug)]
 pub(crate) enum Variant {
-    CLike,
+    CLike(Option<Discriminant>),
     Tuple(Vec<Item>),
     Struct(VariantStruct),
 }
@@ -2107,11 +2107,31 @@ impl Variant {
     pub(crate) fn has_stripped_entries(&self) -> Option<bool> {
         match *self {
             Self::Struct(ref struct_) => Some(struct_.has_stripped_entries()),
-            Self::CLike | Self::Tuple(_) => None,
+            Self::CLike(..) | Self::Tuple(_) => None,
         }
     }
 }
 
+#[derive(Clone, Debug)]
+pub(crate) struct Discriminant {
+    // In the case of cross crate re-exports, we don't have the nessesary information
+    // to reconstruct the expression of the discriminant, only the value.
+    pub(super) expr: Option<BodyId>,
+    pub(super) value: DefId,
+}
+
+impl Discriminant {
+    /// Will be `None` in the case of cross-crate reexports, and may be
+    /// simplified
+    pub(crate) fn expr(&self, tcx: TyCtxt<'_>) -> Option<String> {
+        self.expr.map(|body| print_const_expr(tcx, body))
+    }
+    /// Will always be a machine readable number, without underscores or suffixes.
+    pub(crate) fn value(&self, tcx: TyCtxt<'_>) -> String {
+        print_evaluated_const(tcx, self.value, false).unwrap()
+    }
+}
+
 /// Small wrapper around [`rustc_span::Span`] that adds helper methods
 /// and enforces calling [`rustc_span::Span::source_callsite()`].
 #[derive(Copy, Clone, Debug)]
@@ -2338,7 +2358,7 @@ impl ConstantKind {
         match *self {
             ConstantKind::TyConst { .. } | ConstantKind::Anonymous { .. } => None,
             ConstantKind::Extern { def_id } | ConstantKind::Local { def_id, .. } => {
-                print_evaluated_const(tcx, def_id)
+                print_evaluated_const(tcx, def_id, true)
             }
         }
     }
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index ac9ab339616..a9d511ae11e 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -261,7 +261,11 @@ pub(crate) fn print_const(cx: &DocContext<'_>, n: ty::Const<'_>) -> String {
     }
 }
 
-pub(crate) fn print_evaluated_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<String> {
+pub(crate) fn print_evaluated_const(
+    tcx: TyCtxt<'_>,
+    def_id: DefId,
+    underscores_and_type: bool,
+) -> Option<String> {
     tcx.const_eval_poly(def_id).ok().and_then(|val| {
         let ty = tcx.type_of(def_id);
         match (val, ty.kind()) {
@@ -269,7 +273,7 @@ pub(crate) fn print_evaluated_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<St
             (ConstValue::Scalar(_), &ty::Adt(_, _)) => None,
             (ConstValue::Scalar(_), _) => {
                 let const_ = mir::ConstantKind::from_value(val, ty);
-                Some(print_const_with_custom_print_scalar(tcx, const_))
+                Some(print_const_with_custom_print_scalar(tcx, const_, underscores_and_type))
             }
             _ => None,
         }
@@ -302,23 +306,35 @@ fn format_integer_with_underscore_sep(num: &str) -> String {
         .collect()
 }
 
-fn print_const_with_custom_print_scalar(tcx: TyCtxt<'_>, ct: mir::ConstantKind<'_>) -> String {
+fn print_const_with_custom_print_scalar(
+    tcx: TyCtxt<'_>,
+    ct: mir::ConstantKind<'_>,
+    underscores_and_type: bool,
+) -> String {
     // Use a slightly different format for integer types which always shows the actual value.
     // For all other types, fallback to the original `pretty_print_const`.
     match (ct, ct.ty().kind()) {
         (mir::ConstantKind::Val(ConstValue::Scalar(int), _), ty::Uint(ui)) => {
-            format!("{}{}", format_integer_with_underscore_sep(&int.to_string()), ui.name_str())
+            if underscores_and_type {
+                format!("{}{}", format_integer_with_underscore_sep(&int.to_string()), ui.name_str())
+            } else {
+                int.to_string()
+            }
         }
         (mir::ConstantKind::Val(ConstValue::Scalar(int), _), ty::Int(i)) => {
             let ty = tcx.lift(ct.ty()).unwrap();
             let size = tcx.layout_of(ty::ParamEnv::empty().and(ty)).unwrap().size;
             let data = int.assert_bits(size);
             let sign_extended_data = size.sign_extend(data) as i128;
-            format!(
-                "{}{}",
-                format_integer_with_underscore_sep(&sign_extended_data.to_string()),
-                i.name_str()
-            )
+            if underscores_and_type {
+                format!(
+                    "{}{}",
+                    format_integer_with_underscore_sep(&sign_extended_data.to_string()),
+                    i.name_str()
+                )
+            } else {
+                sign_extended_data.to_string()
+            }
         }
         _ => ct.to_string(),
     }
diff --git a/src/librustdoc/fold.rs b/src/librustdoc/fold.rs
index 6b7e67e2ce3..ed702f5c4a9 100644
--- a/src/librustdoc/fold.rs
+++ b/src/librustdoc/fold.rs
@@ -46,7 +46,7 @@ pub(crate) trait DocFolder: Sized {
                     let fields = fields.into_iter().filter_map(|x| self.fold_item(x)).collect();
                     VariantItem(Variant::Tuple(fields))
                 }
-                Variant::CLike => VariantItem(Variant::CLike),
+                Variant::CLike(disr) => VariantItem(Variant::CLike(disr)),
             },
             ExternCrateItem { src: _ }
             | ImportItem(_)
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index d63d4c2d159..cfa4509428f 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -1203,7 +1203,8 @@ fn item_enum(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, e: &clean::
                     let name = v.name.unwrap();
                     match *v.kind {
                         clean::VariantItem(ref var) => match var {
-                            clean::Variant::CLike => write!(w, "{}", name),
+                            // FIXME(#101337): Show discriminant
+                            clean::Variant::CLike(..) => write!(w, "{}", name),
                             clean::Variant::Tuple(ref s) => {
                                 write!(w, "{}(", name);
                                 print_tuple_struct_fields(w, cx, s);
diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index fddff771f1c..3502d97d470 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -1883,10 +1883,6 @@ in storage.js plus the media query with (min-width: 701px)
 		background-color: var(--sidebar-background-color);
 	}
 
-	.source nav:not(.sidebar).sub {
-		margin-left: 32px;
-	}
-
 	.content {
 		margin-left: 0px;
 	}
diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
index 5c0c023c64e..4d009316730 100644
--- a/src/librustdoc/json/conversions.rs
+++ b/src/librustdoc/json/conversions.rs
@@ -662,7 +662,7 @@ impl FromWithTcx<clean::Variant> for Variant {
     fn from_tcx(variant: clean::Variant, tcx: TyCtxt<'_>) -> Self {
         use clean::Variant::*;
         match variant {
-            CLike => Variant::Plain,
+            CLike(disr) => Variant::Plain(disr.map(|disr| disr.into_tcx(tcx))),
             Tuple(fields) => Variant::Tuple(
                 fields
                     .into_iter()
@@ -678,6 +678,18 @@ impl FromWithTcx<clean::Variant> for Variant {
     }
 }
 
+impl FromWithTcx<clean::Discriminant> for Discriminant {
+    fn from_tcx(disr: clean::Discriminant, tcx: TyCtxt<'_>) -> Self {
+        Discriminant {
+            // expr is only none if going throught the inlineing path, which gets
+            // `rustc_middle` types, not `rustc_hir`, but because JSON never inlines
+            // the expr is always some.
+            expr: disr.expr(tcx).unwrap(),
+            value: disr.value(tcx),
+        }
+    }
+}
+
 impl FromWithTcx<clean::Import> for Import {
     fn from_tcx(import: clean::Import, tcx: TyCtxt<'_>) -> Self {
         use clean::ImportKind::*;
diff --git a/src/librustdoc/visit.rs b/src/librustdoc/visit.rs
index 0bb41977c97..c40274394f3 100644
--- a/src/librustdoc/visit.rs
+++ b/src/librustdoc/visit.rs
@@ -20,7 +20,7 @@ pub(crate) trait DocVisitor: Sized {
             VariantItem(i) => match i {
                 Variant::Struct(j) => j.fields.iter().for_each(|x| self.visit_item(x)),
                 Variant::Tuple(fields) => fields.iter().for_each(|x| self.visit_item(x)),
-                Variant::CLike => {}
+                Variant::CLike(_) => {}
             },
             ExternCrateItem { src: _ }
             | ImportItem(_)
diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
index 7dcad66b1f9..d25f68b3743 100644
--- a/src/rustdoc-json-types/lib.rs
+++ b/src/rustdoc-json-types/lib.rs
@@ -9,7 +9,7 @@ use std::path::PathBuf;
 use serde::{Deserialize, Serialize};
 
 /// rustdoc format-version.
-pub const FORMAT_VERSION: u32 = 18;
+pub const FORMAT_VERSION: u32 = 19;
 
 /// A `Crate` is the root of the emitted JSON blob. It contains all type/documentation information
 /// about the language items in the local crate, as well as info about external items to allow
@@ -308,12 +308,29 @@ pub struct Enum {
 #[serde(rename_all = "snake_case")]
 #[serde(tag = "variant_kind", content = "variant_inner")]
 pub enum Variant {
-    Plain,
+    Plain(Option<Discriminant>),
     Tuple(Vec<Type>),
     Struct(Vec<Id>),
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct Discriminant {
+    /// The expression that produced the discriminant.
+    ///
+    /// Unlike `value`, this preserves the original formatting (eg suffixes,
+    /// hexadecimal, and underscores), making it unsuitable to be machine
+    /// interpreted.
+    ///
+    /// In some cases, when the value is to complex, this may be `"{ _ }"`.
+    /// When this occurs is unstable, and may change without notice.
+    pub expr: String,
+    /// The numerical value of the discriminant. Stored as a string due to
+    /// JSON's poor support for large integers, and the fact that it would need
+    /// to store from [`i128::MIN`] to [`u128::MAX`].
+    pub value: String,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum StructType {
     Plain,
diff --git a/src/test/rustdoc-gui/search-input.goml b/src/test/rustdoc-gui/search-input.goml
deleted file mode 100644
index fd61c4f43d1..00000000000
--- a/src/test/rustdoc-gui/search-input.goml
+++ /dev/null
@@ -1,22 +0,0 @@
-// Ensures that the search input border color changes on focus.
-goto: file://|DOC_PATH|/test_docs/index.html
-local-storage: {"rustdoc-use-system-theme": "false", "rustdoc-theme": "dark"}
-reload:
-
-assert-css: (".search-input", {"border-color": "rgb(224, 224, 224)"})
-click: ".search-input"
-assert-css: (".search-input", {"border-color": "rgb(0, 141, 253)"})
-
-local-storage: {"rustdoc-theme": "light"}
-reload:
-
-assert-css: (".search-input", {"border-color": "rgb(224, 224, 224)"})
-click: ".search-input"
-assert-css: (".search-input", {"border-color": "rgb(102, 175, 233)"})
-
-local-storage: {"rustdoc-theme": "ayu"}
-reload:
-
-assert-css: (".search-input", {"border-color": "rgb(92, 103, 115)"})
-click: ".search-input"
-assert-css: (".search-input", {"border-color": "rgb(92, 103, 115)"})
diff --git a/src/test/rustdoc-json/enums/discriminant/basic.rs b/src/test/rustdoc-json/enums/discriminant/basic.rs
new file mode 100644
index 00000000000..8c221615aa7
--- /dev/null
+++ b/src/test/rustdoc-json/enums/discriminant/basic.rs
@@ -0,0 +1,12 @@
+#[repr(i8)]
+pub enum Ordering {
+    // @is "$.index[*][?(@.name=='Less')].inner.variant_inner.expr" '"-1"'
+    // @is "$.index[*][?(@.name=='Less')].inner.variant_inner.value" '"-1"'
+    Less = -1,
+    // @is "$.index[*][?(@.name=='Equal')].inner.variant_inner.expr" '"0"'
+    // @is "$.index[*][?(@.name=='Equal')].inner.variant_inner.value" '"0"'
+    Equal = 0,
+    // @is "$.index[*][?(@.name=='Greater')].inner.variant_inner.expr" '"1"'
+    // @is "$.index[*][?(@.name=='Greater')].inner.variant_inner.value" '"1"'
+    Greater = 1,
+}
diff --git a/src/test/rustdoc-json/enums/discriminant/expr.rs b/src/test/rustdoc-json/enums/discriminant/expr.rs
new file mode 100644
index 00000000000..235b0b47381
--- /dev/null
+++ b/src/test/rustdoc-json/enums/discriminant/expr.rs
@@ -0,0 +1,39 @@
+pub enum Foo {
+    // @is "$.index[*][?(@.name=='Addition')].inner.variant_inner.value" '"0"'
+    // @is "$.index[*][?(@.name=='Addition')].inner.variant_inner.expr" '"{ _ }"'
+    Addition = 0 + 0,
+    // @is "$.index[*][?(@.name=='Bin')].inner.variant_inner.value" '"1"'
+    // @is "$.index[*][?(@.name=='Bin')].inner.variant_inner.expr" '"0b1"'
+    Bin = 0b1,
+    // @is "$.index[*][?(@.name=='Oct')].inner.variant_inner.value" '"2"'
+    // @is "$.index[*][?(@.name=='Oct')].inner.variant_inner.expr" '"0o2"'
+    Oct = 0o2,
+    // @is "$.index[*][?(@.name=='PubConst')].inner.variant_inner.value" '"3"'
+    // @is "$.index[*][?(@.name=='PubConst')].inner.variant_inner.expr" '"THREE"'
+    PubConst = THREE,
+    // @is "$.index[*][?(@.name=='Hex')].inner.variant_inner.value" '"4"'
+    // @is "$.index[*][?(@.name=='Hex')].inner.variant_inner.expr" '"0x4"'
+    Hex = 0x4,
+    // @is "$.index[*][?(@.name=='Cast')].inner.variant_inner.value" '"5"'
+    // @is "$.index[*][?(@.name=='Cast')].inner.variant_inner.expr" '"{ _ }"'
+    Cast = 5 as isize,
+    // @is "$.index[*][?(@.name=='PubCall')].inner.variant_inner.value" '"6"'
+    // @is "$.index[*][?(@.name=='PubCall')].inner.variant_inner.expr" '"{ _ }"'
+    PubCall = six(),
+    // @is "$.index[*][?(@.name=='PrivCall')].inner.variant_inner.value" '"7"'
+    // @is "$.index[*][?(@.name=='PrivCall')].inner.variant_inner.expr" '"{ _ }"'
+    PrivCall = seven(),
+    // @is "$.index[*][?(@.name=='PrivConst')].inner.variant_inner.value" '"8"'
+    // @is "$.index[*][?(@.name=='PrivConst')].inner.variant_inner.expr" '"EIGHT"'
+    PrivConst = EIGHT,
+}
+
+pub const THREE: isize = 3;
+const EIGHT: isize = 8;
+
+pub const fn six() -> isize {
+    6
+}
+const fn seven() -> isize {
+    7
+}
diff --git a/src/test/rustdoc-json/enums/discriminant/limits.rs b/src/test/rustdoc-json/enums/discriminant/limits.rs
new file mode 100644
index 00000000000..8df73d78d23
--- /dev/null
+++ b/src/test/rustdoc-json/enums/discriminant/limits.rs
@@ -0,0 +1,43 @@
+// ignore-tidy-linelength
+#![feature(repr128)]
+#![allow(incomplete_features)]
+
+#[repr(u64)]
+pub enum U64 {
+    // @is "$.index[*][?(@.name=='U64Min')].inner.variant_inner.value" '"0"'
+    // @is "$.index[*][?(@.name=='U64Min')].inner.variant_inner.expr" '"u64::MIN"'
+    U64Min = u64::MIN,
+    // @is "$.index[*][?(@.name=='U64Max')].inner.variant_inner.value" '"18446744073709551615"'
+    // @is "$.index[*][?(@.name=='U64Max')].inner.variant_inner.expr" '"u64::MAX"'
+    U64Max = u64::MAX,
+}
+
+#[repr(i64)]
+pub enum I64 {
+    // @is "$.index[*][?(@.name=='I64Min')].inner.variant_inner.value" '"-9223372036854775808"'
+    // @is "$.index[*][?(@.name=='I64Min')].inner.variant_inner.expr" '"i64::MIN"'
+    I64Min = i64::MIN,
+    // @is "$.index[*][?(@.name=='I64Max')].inner.variant_inner.value" '"9223372036854775807"'
+    // @is "$.index[*][?(@.name=='I64Max')].inner.variant_inner.expr" '"i64::MAX"'
+    I64Max = i64::MAX,
+}
+
+#[repr(u128)]
+pub enum U128 {
+    // @is "$.index[*][?(@.name=='U128Min')].inner.variant_inner.value" '"0"'
+    // @is "$.index[*][?(@.name=='U128Min')].inner.variant_inner.expr" '"u128::MIN"'
+    U128Min = u128::MIN,
+    // @is "$.index[*][?(@.name=='U128Max')].inner.variant_inner.value" '"340282366920938463463374607431768211455"'
+    // @is "$.index[*][?(@.name=='U128Max')].inner.variant_inner.expr" '"u128::MAX"'
+    U128Max = u128::MAX,
+}
+
+#[repr(i128)]
+pub enum I128 {
+    // @is "$.index[*][?(@.name=='I128Min')].inner.variant_inner.value" '"-170141183460469231731687303715884105728"'
+    // @is "$.index[*][?(@.name=='I128Min')].inner.variant_inner.expr" '"i128::MIN"'
+    I128Min = i128::MIN,
+    // @is "$.index[*][?(@.name=='I128Max')].inner.variant_inner.value" '"170141183460469231731687303715884105727"'
+    // @is "$.index[*][?(@.name=='I128Max')].inner.variant_inner.expr" '"i128::MAX"'
+    I128Max = i128::MAX,
+}
diff --git a/src/test/rustdoc-json/enums/discriminant/num_underscore_and_suffix.rs b/src/test/rustdoc-json/enums/discriminant/num_underscore_and_suffix.rs
new file mode 100644
index 00000000000..3417baa0760
--- /dev/null
+++ b/src/test/rustdoc-json/enums/discriminant/num_underscore_and_suffix.rs
@@ -0,0 +1,15 @@
+#[repr(u32)]
+pub enum Foo {
+    // @is "$.index[*][?(@.name=='Basic')].inner.variant_inner.value" '"0"'
+    // @is "$.index[*][?(@.name=='Basic')].inner.variant_inner.expr" '"0"'
+    Basic = 0,
+    // @is "$.index[*][?(@.name=='Suffix')].inner.variant_inner.value" '"10"'
+    // @is "$.index[*][?(@.name=='Suffix')].inner.variant_inner.expr" '"10u32"'
+    Suffix = 10u32,
+    // @is "$.index[*][?(@.name=='Underscore')].inner.variant_inner.value" '"100"'
+    // @is "$.index[*][?(@.name=='Underscore')].inner.variant_inner.expr" '"1_0_0"'
+    Underscore = 1_0_0,
+    // @is "$.index[*][?(@.name=='SuffixUnderscore')].inner.variant_inner.value" '"1000"'
+    // @is "$.index[*][?(@.name=='SuffixUnderscore')].inner.variant_inner.expr" '"1_0_0_0u32"'
+    SuffixUnderscore = 1_0_0_0u32,
+}
diff --git a/src/test/rustdoc-json/enums/discriminant/only_some_have_discriminant.rs b/src/test/rustdoc-json/enums/discriminant/only_some_have_discriminant.rs
new file mode 100644
index 00000000000..6af944a2219
--- /dev/null
+++ b/src/test/rustdoc-json/enums/discriminant/only_some_have_discriminant.rs
@@ -0,0 +1,10 @@
+pub enum Foo {
+    // @is "$.index[*][?(@.name=='Has')].inner.variant_inner" '{"expr":"0", "value":"0"}'
+    Has = 0,
+    // @is "$.index[*][?(@.name=='Doesnt')].inner.variant_inner" null
+    Doesnt,
+    // @is "$.index[*][?(@.name=='AlsoDoesnt')].inner.variant_inner" null
+    AlsoDoesnt,
+    // @is "$.index[*][?(@.name=='AlsoHas')].inner.variant_inner" '{"expr":"44", "value":"44"}'
+    AlsoHas = 44,
+}
diff --git a/src/test/ui/consts/const-float-bits-reject-conv.stderr b/src/test/ui/consts/const-float-bits-reject-conv.stderr
index d6e993a1010..01f2f489564 100644
--- a/src/test/ui/consts/const-float-bits-reject-conv.stderr
+++ b/src/test/ui/consts/const-float-bits-reject-conv.stderr
@@ -10,16 +10,6 @@ LL |                     panic!("const-eval error: cannot use f32::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f32_to_u32, rt_f32_to_u32) }
    |                  -------------------------------------------------------------------- inside `core::f32::<impl f32>::to_bits` at $SRC_DIR/core/src/num/f32.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32} as FnOnce<(f32,)>>::call_once - shim(fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f32,), fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32}, [closure@core::f32::<impl f32>::to_bits::{closure#0}], u32>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:27:30
    |
 LL |     const MASKED_NAN1: u32 = f32::NAN.to_bits() ^ 0x002A_AAAA;
@@ -39,16 +29,6 @@ LL |                     panic!("const-eval error: cannot use f32::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f32_to_u32, rt_f32_to_u32) }
    |                  -------------------------------------------------------------------- inside `core::f32::<impl f32>::to_bits` at $SRC_DIR/core/src/num/f32.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32} as FnOnce<(f32,)>>::call_once - shim(fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f32,), fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32}, [closure@core::f32::<impl f32>::to_bits::{closure#0}], u32>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:28:30
    |
 LL |     const MASKED_NAN2: u32 = f32::NAN.to_bits() ^ 0x0055_5555;
@@ -117,16 +97,6 @@ LL |                     panic!("const-eval error: cannot use f64::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
    |                  -------------------------------------------------------------------- inside `core::f64::<impl f64>::to_bits` at $SRC_DIR/core/src/num/f64.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64} as FnOnce<(f64,)>>::call_once - shim(fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f64,), fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64}, [closure@core::f64::<impl f64>::to_bits::{closure#0}], u64>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:54:30
    |
 LL |     const MASKED_NAN1: u64 = f64::NAN.to_bits() ^ 0x000A_AAAA_AAAA_AAAA;
@@ -146,16 +116,6 @@ LL |                     panic!("const-eval error: cannot use f64::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
    |                  -------------------------------------------------------------------- inside `core::f64::<impl f64>::to_bits` at $SRC_DIR/core/src/num/f64.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64} as FnOnce<(f64,)>>::call_once - shim(fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f64,), fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64}, [closure@core::f64::<impl f64>::to_bits::{closure#0}], u64>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:55:30
    |
 LL |     const MASKED_NAN2: u64 = f64::NAN.to_bits() ^ 0x0005_5555_5555_5555;
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace-std.rs b/src/test/ui/intrinsics/const-eval-select-backtrace-std.rs
new file mode 100644
index 00000000000..29aefe07162
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace-std.rs
@@ -0,0 +1,6 @@
+// See issue #100696.
+// run-fail
+// check-run-results
+fn main() {
+    &""[1..];
+}
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr b/src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr
new file mode 100644
index 00000000000..e53e6034620
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr
@@ -0,0 +1,2 @@
+thread 'main' panicked at 'byte index 1 is out of bounds of ``', $DIR/const-eval-select-backtrace-std.rs:5:6
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace.rs b/src/test/ui/intrinsics/const-eval-select-backtrace.rs
new file mode 100644
index 00000000000..99f0725200c
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace.rs
@@ -0,0 +1,18 @@
+#![feature(core_intrinsics)]
+// See issue #100696.
+// run-fail
+// check-run-results
+
+#[track_caller]
+fn uhoh() {
+    panic!("Aaah!")
+}
+
+const fn c() {}
+
+fn main() {
+    // safety: this is unsound and just used to test
+    unsafe {
+        std::intrinsics::const_eval_select((), c, uhoh);
+    }
+}
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr b/src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr
new file mode 100644
index 00000000000..2fd730ac7a6
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr
@@ -0,0 +1,2 @@
+thread 'main' panicked at 'Aaah!', $DIR/const-eval-select-backtrace.rs:16:9
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
diff --git a/src/test/ui/intrinsics/const-eval-select-bad.rs b/src/test/ui/intrinsics/const-eval-select-bad.rs
index e5640f5ab53..fa14efad7b4 100644
--- a/src/test/ui/intrinsics/const-eval-select-bad.rs
+++ b/src/test/ui/intrinsics/const-eval-select-bad.rs
@@ -5,10 +5,13 @@ use std::intrinsics::const_eval_select;
 
 const fn not_fn_items() {
     const_eval_select((), || {}, || {});
-    //~^ ERROR the trait bound
+    //~^ ERROR this argument must be a function item
+    //~| ERROR this argument must be a function item
     const_eval_select((), 42, 0xDEADBEEF);
-    //~^ ERROR the trait bound
+    //~^ ERROR expected a `FnOnce<()>` closure
     //~| ERROR expected a `FnOnce<()>` closure
+    //~| ERROR this argument must be a function item
+    //~| ERROR this argument must be a function item
 }
 
 const fn foo(n: i32) -> i32 {
@@ -35,4 +38,9 @@ const fn args_ty_mismatch() {
     //~^ ERROR type mismatch
 }
 
+const fn non_const_fn() {
+    const_eval_select((1,), bar, bar);
+    //~^ ERROR this argument must be a `const fn`
+}
+
 fn main() {}
diff --git a/src/test/ui/intrinsics/const-eval-select-bad.stderr b/src/test/ui/intrinsics/const-eval-select-bad.stderr
index 904e83624b3..3720528ad4e 100644
--- a/src/test/ui/intrinsics/const-eval-select-bad.stderr
+++ b/src/test/ui/intrinsics/const-eval-select-bad.stderr
@@ -1,42 +1,57 @@
-error[E0277]: the trait bound `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]: FnOnce<()>` is not satisfied
+error: this argument must be a function item
   --> $DIR/const-eval-select-bad.rs:7:27
    |
 LL |     const_eval_select((), || {}, || {});
-   |     -----------------     ^^^^^ expected an `FnOnce<()>` closure, found `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]`
-   |     |
-   |     required by a bound introduced by this call
+   |                           ^^^^^
    |
-   = help: the trait `~const FnOnce<()>` is not implemented for closure `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]`
-note: the trait `FnOnce<()>` is implemented for `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]`, but that implementation is not `const`
-  --> $DIR/const-eval-select-bad.rs:7:27
+   = note: expected a function item, found [closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]
+   = help: consult the documentation on `const_eval_select` for more information
+
+error: this argument must be a function item
+  --> $DIR/const-eval-select-bad.rs:7:34
    |
 LL |     const_eval_select((), || {}, || {});
-   |                           ^^^^^
-   = note: wrap the `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]` in a closure with no arguments: `|| { /* code */ }`
-note: required by a bound in `const_eval_select`
-  --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
+   |                                  ^^^^^
    |
-LL |     F: ~const FnOnce<ARG, Output = RET>,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+   = note: expected a function item, found [closure@$DIR/const-eval-select-bad.rs:7:34: 7:36]
+   = help: consult the documentation on `const_eval_select` for more information
 
-error[E0277]: the trait bound `{integer}: FnOnce<()>` is not satisfied
-  --> $DIR/const-eval-select-bad.rs:9:27
+error: this argument must be a function item
+  --> $DIR/const-eval-select-bad.rs:10:27
+   |
+LL |     const_eval_select((), 42, 0xDEADBEEF);
+   |                           ^^
+   |
+   = note: expected a function item, found {integer}
+   = help: consult the documentation on `const_eval_select` for more information
+
+error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
+  --> $DIR/const-eval-select-bad.rs:10:27
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
    |     -----------------     ^^ expected an `FnOnce<()>` closure, found `{integer}`
    |     |
    |     required by a bound introduced by this call
    |
-   = help: the trait `~const FnOnce<()>` is not implemented for `{integer}`
+   = help: the trait `FnOnce<()>` is not implemented for `{integer}`
    = note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     F: ~const FnOnce<ARG, Output = RET>,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         F: FnOnce<ARG, Output = RET>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+
+error: this argument must be a function item
+  --> $DIR/const-eval-select-bad.rs:10:31
+   |
+LL |     const_eval_select((), 42, 0xDEADBEEF);
+   |                               ^^^^^^^^^^
+   |
+   = note: expected a function item, found {integer}
+   = help: consult the documentation on `const_eval_select` for more information
 
 error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
-  --> $DIR/const-eval-select-bad.rs:9:31
+  --> $DIR/const-eval-select-bad.rs:10:31
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
    |     -----------------         ^^^^^^^^^^ expected an `FnOnce<()>` closure, found `{integer}`
@@ -48,11 +63,11 @@ LL |     const_eval_select((), 42, 0xDEADBEEF);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     G: FnOnce<ARG, Output = RET> + ~const Destruct,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         G: FnOnce<ARG, Output = RET>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
 
 error[E0271]: expected `fn(i32) -> bool {bar}` to be a fn item that returns `i32`, but it returns `bool`
-  --> $DIR/const-eval-select-bad.rs:29:34
+  --> $DIR/const-eval-select-bad.rs:32:34
    |
 LL |     const_eval_select((1,), foo, bar);
    |     -----------------            ^^^ expected `i32`, found `bool`
@@ -62,11 +77,11 @@ LL |     const_eval_select((1,), foo, bar);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     G: FnOnce<ARG, Output = RET> + ~const Destruct,
-   |                    ^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         G: FnOnce<ARG, Output = RET>,
+   |                        ^^^^^^^^^^^^ required by this bound in `const_eval_select`
 
 error[E0631]: type mismatch in function arguments
-  --> $DIR/const-eval-select-bad.rs:34:32
+  --> $DIR/const-eval-select-bad.rs:37:32
    |
 LL | const fn foo(n: i32) -> i32 {
    | --------------------------- found signature defined here
@@ -81,10 +96,18 @@ LL |     const_eval_select((true,), foo, baz);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     F: ~const FnOnce<ARG, Output = RET>,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         F: FnOnce<ARG, Output = RET>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+
+error: this argument must be a `const fn`
+  --> $DIR/const-eval-select-bad.rs:42:29
+   |
+LL |     const_eval_select((1,), bar, bar);
+   |                             ^^^
+   |
+   = help: consult the documentation on `const_eval_select` for more information
 
-error: aborting due to 5 previous errors
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0271, E0277, E0631.
 For more information about an error, try `rustc --explain E0271`.
diff --git a/src/test/ui/on-unimplemented/enclosing-scope.rs b/src/test/ui/on-unimplemented/enclosing-scope.rs
deleted file mode 100644
index 881bff63f5f..00000000000
--- a/src/test/ui/on-unimplemented/enclosing-scope.rs
+++ /dev/null
@@ -1,27 +0,0 @@
-// Test scope annotations from `enclosing_scope` parameter
-
-#![feature(rustc_attrs)]
-
-#[rustc_on_unimplemented(enclosing_scope="in this scope")]
-trait Trait{}
-
-struct Foo;
-
-fn f<T: Trait>(x: T) {}
-
-fn main() {
-    let x = || {
-        f(Foo{}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
-        let y = || {
-            f(Foo{}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
-        };
-    };
-
-    {
-        {
-            f(Foo{}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
-        }
-    }
-
-    f(Foo{}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
-}
diff --git a/src/test/ui/on-unimplemented/enclosing-scope.stderr b/src/test/ui/on-unimplemented/enclosing-scope.stderr
deleted file mode 100644
index 67759d02a16..00000000000
--- a/src/test/ui/on-unimplemented/enclosing-scope.stderr
+++ /dev/null
@@ -1,86 +0,0 @@
-error[E0277]: the trait bound `Foo: Trait` is not satisfied
-  --> $DIR/enclosing-scope.rs:14:11
-   |
-LL |       let x = || {
-   |  _____________-
-LL | |         f(Foo{});
-   | |         - ^^^^^ the trait `Trait` is not implemented for `Foo`
-   | |         |
-   | |         required by a bound introduced by this call
-LL | |         let y = || {
-LL | |             f(Foo{});
-LL | |         };
-LL | |     };
-   | |_____- in this scope
-   |
-note: required by a bound in `f`
-  --> $DIR/enclosing-scope.rs:10:9
-   |
-LL | fn f<T: Trait>(x: T) {}
-   |         ^^^^^ required by this bound in `f`
-
-error[E0277]: the trait bound `Foo: Trait` is not satisfied
-  --> $DIR/enclosing-scope.rs:16:15
-   |
-LL |           let y = || {
-   |  _________________-
-LL | |             f(Foo{});
-   | |             - ^^^^^ the trait `Trait` is not implemented for `Foo`
-   | |             |
-   | |             required by a bound introduced by this call
-LL | |         };
-   | |_________- in this scope
-   |
-note: required by a bound in `f`
-  --> $DIR/enclosing-scope.rs:10:9
-   |
-LL | fn f<T: Trait>(x: T) {}
-   |         ^^^^^ required by this bound in `f`
-
-error[E0277]: the trait bound `Foo: Trait` is not satisfied
-  --> $DIR/enclosing-scope.rs:22:15
-   |
-LL | / fn main() {
-LL | |     let x = || {
-LL | |         f(Foo{});
-LL | |         let y = || {
-...  |
-LL | |             f(Foo{});
-   | |             - ^^^^^ the trait `Trait` is not implemented for `Foo`
-   | |             |
-   | |             required by a bound introduced by this call
-...  |
-LL | |     f(Foo{});
-LL | | }
-   | |_- in this scope
-   |
-note: required by a bound in `f`
-  --> $DIR/enclosing-scope.rs:10:9
-   |
-LL | fn f<T: Trait>(x: T) {}
-   |         ^^^^^ required by this bound in `f`
-
-error[E0277]: the trait bound `Foo: Trait` is not satisfied
-  --> $DIR/enclosing-scope.rs:26:7
-   |
-LL | / fn main() {
-LL | |     let x = || {
-LL | |         f(Foo{});
-LL | |         let y = || {
-...  |
-LL | |     f(Foo{});
-   | |     - ^^^^^ the trait `Trait` is not implemented for `Foo`
-   | |     |
-   | |     required by a bound introduced by this call
-LL | | }
-   | |_- in this scope
-   |
-note: required by a bound in `f`
-  --> $DIR/enclosing-scope.rs:10:9
-   |
-LL | fn f<T: Trait>(x: T) {}
-   |         ^^^^^ required by this bound in `f`
-
-error: aborting due to 4 previous errors
-
-For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/on-unimplemented/parent-label.rs b/src/test/ui/on-unimplemented/parent-label.rs
new file mode 100644
index 00000000000..b65f6496831
--- /dev/null
+++ b/src/test/ui/on-unimplemented/parent-label.rs
@@ -0,0 +1,27 @@
+// Test scope annotations from `parent_label` parameter
+
+#![feature(rustc_attrs)]
+
+#[rustc_on_unimplemented(parent_label = "in this scope")]
+trait Trait {}
+
+struct Foo;
+
+fn f<T: Trait>(x: T) {}
+
+fn main() {
+    let x = || {
+        f(Foo {}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
+        let y = || {
+            f(Foo {}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
+        };
+    };
+
+    {
+        {
+            f(Foo {}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
+        }
+    }
+
+    f(Foo {}); //~ ERROR the trait bound `Foo: Trait` is not satisfied
+}
diff --git a/src/test/ui/on-unimplemented/parent-label.stderr b/src/test/ui/on-unimplemented/parent-label.stderr
new file mode 100644
index 00000000000..8cd7412fd9d
--- /dev/null
+++ b/src/test/ui/on-unimplemented/parent-label.stderr
@@ -0,0 +1,69 @@
+error[E0277]: the trait bound `Foo: Trait` is not satisfied
+  --> $DIR/parent-label.rs:14:11
+   |
+LL |     let x = || {
+   |             -- in this scope
+LL |         f(Foo {});
+   |         - ^^^^^^ the trait `Trait` is not implemented for `Foo`
+   |         |
+   |         required by a bound introduced by this call
+   |
+note: required by a bound in `f`
+  --> $DIR/parent-label.rs:10:9
+   |
+LL | fn f<T: Trait>(x: T) {}
+   |         ^^^^^ required by this bound in `f`
+
+error[E0277]: the trait bound `Foo: Trait` is not satisfied
+  --> $DIR/parent-label.rs:16:15
+   |
+LL |         let y = || {
+   |                 -- in this scope
+LL |             f(Foo {});
+   |             - ^^^^^^ the trait `Trait` is not implemented for `Foo`
+   |             |
+   |             required by a bound introduced by this call
+   |
+note: required by a bound in `f`
+  --> $DIR/parent-label.rs:10:9
+   |
+LL | fn f<T: Trait>(x: T) {}
+   |         ^^^^^ required by this bound in `f`
+
+error[E0277]: the trait bound `Foo: Trait` is not satisfied
+  --> $DIR/parent-label.rs:22:15
+   |
+LL | fn main() {
+   | --------- in this scope
+...
+LL |             f(Foo {});
+   |             - ^^^^^^ the trait `Trait` is not implemented for `Foo`
+   |             |
+   |             required by a bound introduced by this call
+   |
+note: required by a bound in `f`
+  --> $DIR/parent-label.rs:10:9
+   |
+LL | fn f<T: Trait>(x: T) {}
+   |         ^^^^^ required by this bound in `f`
+
+error[E0277]: the trait bound `Foo: Trait` is not satisfied
+  --> $DIR/parent-label.rs:26:7
+   |
+LL | fn main() {
+   | --------- in this scope
+...
+LL |     f(Foo {});
+   |     - ^^^^^^ the trait `Trait` is not implemented for `Foo`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `f`
+  --> $DIR/parent-label.rs:10:9
+   |
+LL | fn f<T: Trait>(x: T) {}
+   |         ^^^^^ required by this bound in `f`
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr b/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr
index fce0cdfe0d5..bc06fde49e9 100644
--- a/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr
+++ b/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr
@@ -1493,17 +1493,11 @@ LL |     if (let 0 = 0)? {}
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/disallowed-positions.rs:132:19
    |
-LL | / fn nested_within_if_expr() {
-LL | |     if &let 0 = 0 {}
-LL | |
-LL | |
-...  |
-LL | |     if (let 0 = 0)? {}
-   | |                   ^ cannot use the `?` operator in a function that returns `()`
-...  |
-LL | |
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn nested_within_if_expr() {
+   | -------------------------- this function should return `Result` or `Option` to accept `?`
+...
+LL |     if (let 0 = 0)? {}
+   |                   ^ cannot use the `?` operator in a function that returns `()`
    |
    = help: the trait `FromResidual<_>` is not implemented for `()`
 
@@ -1693,17 +1687,11 @@ LL |     while (let 0 = 0)? {}
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/disallowed-positions.rs:224:22
    |
-LL | / fn nested_within_while_expr() {
-LL | |     while &let 0 = 0 {}
-LL | |
-LL | |
-...  |
-LL | |     while (let 0 = 0)? {}
-   | |                      ^ cannot use the `?` operator in a function that returns `()`
-...  |
-LL | |
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn nested_within_while_expr() {
+   | ----------------------------- this function should return `Result` or `Option` to accept `?`
+...
+LL |     while (let 0 = 0)? {}
+   |                      ^ cannot use the `?` operator in a function that returns `()`
    |
    = help: the trait `FromResidual<_>` is not implemented for `()`
 
@@ -1881,17 +1869,11 @@ LL |     (let 0 = 0)?;
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/disallowed-positions.rs:325:16
    |
-LL | / fn outside_if_and_while_expr() {
-LL | |     &let 0 = 0;
-LL | |
-LL | |
-...  |
-LL | |     (let 0 = 0)?;
-   | |                ^ cannot use the `?` operator in a function that returns `()`
-...  |
-LL | |
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn outside_if_and_while_expr() {
+   | ------------------------------ this function should return `Result` or `Option` to accept `?`
+...
+LL |     (let 0 = 0)?;
+   |                ^ cannot use the `?` operator in a function that returns `()`
    |
    = help: the trait `FromResidual<_>` is not implemented for `()`
 
diff --git a/src/test/ui/try-trait/bad-interconversion.stderr b/src/test/ui/try-trait/bad-interconversion.stderr
index 529f5f16c8f..27e6a603acd 100644
--- a/src/test/ui/try-trait/bad-interconversion.stderr
+++ b/src/test/ui/try-trait/bad-interconversion.stderr
@@ -22,13 +22,10 @@ LL |     Ok(Err(123_i32)?)
 error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
   --> $DIR/bad-interconversion.rs:11:12
    |
-LL | / fn option_to_result() -> Result<u64, String> {
-LL | |     Some(3)?;
-   | |            ^ use `.ok_or(...)?` to provide an error compatible with `Result<u64, String>`
-LL | |
-LL | |     Ok(10)
-LL | | }
-   | |_- this function returns a `Result`
+LL | fn option_to_result() -> Result<u64, String> {
+   | -------------------------------------------- this function returns a `Result`
+LL |     Some(3)?;
+   |            ^ use `.ok_or(...)?` to provide an error compatible with `Result<u64, String>`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `Result<u64, String>`
    = help: the following other types implement trait `FromResidual<R>`:
@@ -38,12 +35,10 @@ LL | | }
 error[E0277]: the `?` operator can only be used on `Result`s in a function that returns `Result`
   --> $DIR/bad-interconversion.rs:17:31
    |
-LL | / fn control_flow_to_result() -> Result<u64, String> {
-LL | |     Ok(ControlFlow::Break(123)?)
-   | |                               ^ this `?` produces `ControlFlow<{integer}, Infallible>`, which is incompatible with `Result<u64, String>`
-LL | |
-LL | | }
-   | |_- this function returns a `Result`
+LL | fn control_flow_to_result() -> Result<u64, String> {
+   | -------------------------------------------------- this function returns a `Result`
+LL |     Ok(ControlFlow::Break(123)?)
+   |                               ^ this `?` produces `ControlFlow<{integer}, Infallible>`, which is incompatible with `Result<u64, String>`
    |
    = help: the trait `FromResidual<ControlFlow<{integer}, Infallible>>` is not implemented for `Result<u64, String>`
    = help: the following other types implement trait `FromResidual<R>`:
@@ -53,12 +48,10 @@ LL | | }
 error[E0277]: the `?` operator can only be used on `Option`s, not `Result`s, in a function that returns `Option`
   --> $DIR/bad-interconversion.rs:22:22
    |
-LL | / fn result_to_option() -> Option<u16> {
-LL | |     Some(Err("hello")?)
-   | |                      ^ use `.ok()?` if you want to discard the `Result<Infallible, &str>` error information
-LL | |
-LL | | }
-   | |_- this function returns an `Option`
+LL | fn result_to_option() -> Option<u16> {
+   | ------------------------------------ this function returns an `Option`
+LL |     Some(Err("hello")?)
+   |                      ^ use `.ok()?` if you want to discard the `Result<Infallible, &str>` error information
    |
    = help: the trait `FromResidual<Result<Infallible, &str>>` is not implemented for `Option<u16>`
    = help: the following other types implement trait `FromResidual<R>`:
@@ -68,12 +61,10 @@ LL | | }
 error[E0277]: the `?` operator can only be used on `Option`s in a function that returns `Option`
   --> $DIR/bad-interconversion.rs:27:33
    |
-LL | / fn control_flow_to_option() -> Option<u64> {
-LL | |     Some(ControlFlow::Break(123)?)
-   | |                                 ^ this `?` produces `ControlFlow<{integer}, Infallible>`, which is incompatible with `Option<u64>`
-LL | |
-LL | | }
-   | |_- this function returns an `Option`
+LL | fn control_flow_to_option() -> Option<u64> {
+   | ------------------------------------------ this function returns an `Option`
+LL |     Some(ControlFlow::Break(123)?)
+   |                                 ^ this `?` produces `ControlFlow<{integer}, Infallible>`, which is incompatible with `Option<u64>`
    |
    = help: the trait `FromResidual<ControlFlow<{integer}, Infallible>>` is not implemented for `Option<u64>`
    = help: the following other types implement trait `FromResidual<R>`:
@@ -83,12 +74,10 @@ LL | | }
 error[E0277]: the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
   --> $DIR/bad-interconversion.rs:32:39
    |
-LL | / fn result_to_control_flow() -> ControlFlow<String> {
-LL | |     ControlFlow::Continue(Err("hello")?)
-   | |                                       ^ this `?` produces `Result<Infallible, &str>`, which is incompatible with `ControlFlow<String>`
-LL | |
-LL | | }
-   | |_- this function returns a `ControlFlow`
+LL | fn result_to_control_flow() -> ControlFlow<String> {
+   | -------------------------------------------------- this function returns a `ControlFlow`
+LL |     ControlFlow::Continue(Err("hello")?)
+   |                                       ^ this `?` produces `Result<Infallible, &str>`, which is incompatible with `ControlFlow<String>`
    |
    = help: the trait `FromResidual<Result<Infallible, &str>>` is not implemented for `ControlFlow<String>`
    = help: the trait `FromResidual` is implemented for `ControlFlow<B, C>`
@@ -96,13 +85,10 @@ LL | | }
 error[E0277]: the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
   --> $DIR/bad-interconversion.rs:37:12
    |
-LL | / fn option_to_control_flow() -> ControlFlow<u64> {
-LL | |     Some(3)?;
-   | |            ^ this `?` produces `Option<Infallible>`, which is incompatible with `ControlFlow<u64>`
-LL | |
-LL | |     ControlFlow::Break(10)
-LL | | }
-   | |_- this function returns a `ControlFlow`
+LL | fn option_to_control_flow() -> ControlFlow<u64> {
+   | ----------------------------------------------- this function returns a `ControlFlow`
+LL |     Some(3)?;
+   |            ^ this `?` produces `Option<Infallible>`, which is incompatible with `ControlFlow<u64>`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `ControlFlow<u64>`
    = help: the trait `FromResidual` is implemented for `ControlFlow<B, C>`
@@ -110,13 +96,10 @@ LL | | }
 error[E0277]: the `?` operator in a function that returns `ControlFlow<B, _>` can only be used on other `ControlFlow<B, _>`s (with the same Break type)
   --> $DIR/bad-interconversion.rs:43:29
    |
-LL | / fn control_flow_to_control_flow() -> ControlFlow<i64> {
-LL | |     ControlFlow::Break(4_u8)?;
-   | |                             ^ this `?` produces `ControlFlow<u8, Infallible>`, which is incompatible with `ControlFlow<i64>`
-LL | |
-LL | |     ControlFlow::Continue(())
-LL | | }
-   | |_- this function returns a `ControlFlow`
+LL | fn control_flow_to_control_flow() -> ControlFlow<i64> {
+   | ----------------------------------------------------- this function returns a `ControlFlow`
+LL |     ControlFlow::Break(4_u8)?;
+   |                             ^ this `?` produces `ControlFlow<u8, Infallible>`, which is incompatible with `ControlFlow<i64>`
    |
    = help: the trait `FromResidual<ControlFlow<u8, Infallible>>` is not implemented for `ControlFlow<i64>`
    = note: unlike `Result`, there's no `From`-conversion performed for `ControlFlow`
diff --git a/src/test/ui/try-trait/option-to-result.stderr b/src/test/ui/try-trait/option-to-result.stderr
index ae5c3ad6282..fabc1ff2c76 100644
--- a/src/test/ui/try-trait/option-to-result.stderr
+++ b/src/test/ui/try-trait/option-to-result.stderr
@@ -1,13 +1,11 @@
 error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
   --> $DIR/option-to-result.rs:5:6
    |
-LL | / fn test_result() -> Result<(),()> {
-LL | |     let a:Option<()> = Some(());
-LL | |     a?;
-   | |      ^ use `.ok_or(...)?` to provide an error compatible with `Result<(), ()>`
-LL | |     Ok(())
-LL | | }
-   | |_- this function returns a `Result`
+LL | fn test_result() -> Result<(),()> {
+   | --------------------------------- this function returns a `Result`
+LL |     let a:Option<()> = Some(());
+LL |     a?;
+   |      ^ use `.ok_or(...)?` to provide an error compatible with `Result<(), ()>`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `Result<(), ()>`
    = help: the following other types implement trait `FromResidual<R>`:
@@ -17,13 +15,11 @@ LL | | }
 error[E0277]: the `?` operator can only be used on `Option`s, not `Result`s, in a function that returns `Option`
   --> $DIR/option-to-result.rs:11:6
    |
-LL | / fn test_option() -> Option<i32>{
-LL | |     let a:Result<i32, i32> = Ok(5);
-LL | |     a?;
-   | |      ^ use `.ok()?` if you want to discard the `Result<Infallible, i32>` error information
-LL | |     Some(5)
-LL | | }
-   | |_- this function returns an `Option`
+LL | fn test_option() -> Option<i32>{
+   | ------------------------------- this function returns an `Option`
+LL |     let a:Result<i32, i32> = Ok(5);
+LL |     a?;
+   |      ^ use `.ok()?` if you want to discard the `Result<Infallible, i32>` error information
    |
    = help: the trait `FromResidual<Result<Infallible, i32>>` is not implemented for `Option<i32>`
    = help: the following other types implement trait `FromResidual<R>`:
diff --git a/src/test/ui/try-trait/try-on-option-diagnostics.stderr b/src/test/ui/try-trait/try-on-option-diagnostics.stderr
index a6badd19038..9ee540c79fd 100644
--- a/src/test/ui/try-trait/try-on-option-diagnostics.stderr
+++ b/src/test/ui/try-trait/try-on-option-diagnostics.stderr
@@ -1,51 +1,44 @@
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-on-option-diagnostics.rs:7:6
    |
-LL | / fn a_function() -> u32 {
-LL | |     let x: Option<u32> = None;
-LL | |     x?;
-   | |      ^ cannot use the `?` operator in a function that returns `u32`
-LL | |     22
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn a_function() -> u32 {
+   | ---------------------- this function should return `Result` or `Option` to accept `?`
+LL |     let x: Option<u32> = None;
+LL |     x?;
+   |      ^ cannot use the `?` operator in a function that returns `u32`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `u32`
 
 error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-on-option-diagnostics.rs:14:10
    |
-LL |       let a_closure = || {
-   |  _____________________-
-LL | |         let x: Option<u32> = None;
-LL | |         x?;
-   | |          ^ cannot use the `?` operator in a closure that returns `{integer}`
-LL | |         22
-LL | |     };
-   | |_____- this function should return `Result` or `Option` to accept `?`
+LL |     let a_closure = || {
+   |                     -- this function should return `Result` or `Option` to accept `?`
+LL |         let x: Option<u32> = None;
+LL |         x?;
+   |          ^ cannot use the `?` operator in a closure that returns `{integer}`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `{integer}`
 
 error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-on-option-diagnostics.rs:26:14
    |
-LL | /         fn a_method() {
-LL | |             let x: Option<u32> = None;
-LL | |             x?;
-   | |              ^ cannot use the `?` operator in a method that returns `()`
-LL | |         }
-   | |_________- this function should return `Result` or `Option` to accept `?`
+LL |         fn a_method() {
+   |         ------------- this function should return `Result` or `Option` to accept `?`
+LL |             let x: Option<u32> = None;
+LL |             x?;
+   |              ^ cannot use the `?` operator in a method that returns `()`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `()`
 
 error[E0277]: the `?` operator can only be used in a trait method that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-on-option-diagnostics.rs:39:14
    |
-LL | /         fn a_trait_method() {
-LL | |             let x: Option<u32> = None;
-LL | |             x?;
-   | |              ^ cannot use the `?` operator in a trait method that returns `()`
-LL | |         }
-   | |_________- this function should return `Result` or `Option` to accept `?`
+LL |         fn a_trait_method() {
+   |         ------------------- this function should return `Result` or `Option` to accept `?`
+LL |             let x: Option<u32> = None;
+LL |             x?;
+   |              ^ cannot use the `?` operator in a trait method that returns `()`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `()`
 
diff --git a/src/test/ui/try-trait/try-on-option.stderr b/src/test/ui/try-trait/try-on-option.stderr
index ba85a7cada2..fad6a1fe823 100644
--- a/src/test/ui/try-trait/try-on-option.stderr
+++ b/src/test/ui/try-trait/try-on-option.stderr
@@ -1,13 +1,11 @@
 error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
   --> $DIR/try-on-option.rs:5:6
    |
-LL | / fn foo() -> Result<u32, ()> {
-LL | |     let x: Option<u32> = None;
-LL | |     x?;
-   | |      ^ use `.ok_or(...)?` to provide an error compatible with `Result<u32, ()>`
-LL | |     Ok(22)
-LL | | }
-   | |_- this function returns a `Result`
+LL | fn foo() -> Result<u32, ()> {
+   | --------------------------- this function returns a `Result`
+LL |     let x: Option<u32> = None;
+LL |     x?;
+   |      ^ use `.ok_or(...)?` to provide an error compatible with `Result<u32, ()>`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `Result<u32, ()>`
    = help: the following other types implement trait `FromResidual<R>`:
@@ -17,13 +15,11 @@ LL | | }
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-on-option.rs:11:6
    |
-LL | / fn bar() -> u32 {
-LL | |     let x: Option<u32> = None;
-LL | |     x?;
-   | |      ^ cannot use the `?` operator in a function that returns `u32`
-LL | |     22
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn bar() -> u32 {
+   | --------------- this function should return `Result` or `Option` to accept `?`
+LL |     let x: Option<u32> = None;
+LL |     x?;
+   |      ^ cannot use the `?` operator in a function that returns `u32`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `u32`
 
diff --git a/src/test/ui/try-trait/try-operator-on-main.stderr b/src/test/ui/try-trait/try-operator-on-main.stderr
index ad55f40b5b6..7cd38e0cf95 100644
--- a/src/test/ui/try-trait/try-operator-on-main.stderr
+++ b/src/test/ui/try-trait/try-operator-on-main.stderr
@@ -1,15 +1,11 @@
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-operator-on-main.rs:7:31
    |
-LL | / fn main() {
-LL | |     // error for a `Try` type on a non-`Try` fn
-LL | |     std::fs::File::open("foo")?;
-   | |                               ^ cannot use the `?` operator in a function that returns `()`
-LL | |
-...  |
-LL | |     try_trait_generic::<()>();
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn main() {
+   | --------- this function should return `Result` or `Option` to accept `?`
+LL |     // error for a `Try` type on a non-`Try` fn
+LL |     std::fs::File::open("foo")?;
+   |                               ^ cannot use the `?` operator in a function that returns `()`
    |
    = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
 
@@ -24,17 +20,11 @@ LL |     ()?;
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
   --> $DIR/try-operator-on-main.rs:10:7
    |
-LL | / fn main() {
-LL | |     // error for a `Try` type on a non-`Try` fn
-LL | |     std::fs::File::open("foo")?;
-LL | |
-LL | |     // a non-`Try` type on a non-`Try` fn
-LL | |     ()?;
-   | |       ^ cannot use the `?` operator in a function that returns `()`
-...  |
-LL | |     try_trait_generic::<()>();
-LL | | }
-   | |_- this function should return `Result` or `Option` to accept `?`
+LL | fn main() {
+   | --------- this function should return `Result` or `Option` to accept `?`
+...
+LL |     ()?;
+   |       ^ cannot use the `?` operator in a function that returns `()`
    |
    = help: the trait `FromResidual<_>` is not implemented for `()`
 
diff --git a/src/test/ui/typeck/assign-non-lval-needs-deref.rs b/src/test/ui/typeck/assign-non-lval-needs-deref.rs
new file mode 100644
index 00000000000..c979d76b4f4
--- /dev/null
+++ b/src/test/ui/typeck/assign-non-lval-needs-deref.rs
@@ -0,0 +1,19 @@
+// issue #101376
+
+use std::ops::AddAssign;
+struct Foo;
+
+impl AddAssign<()> for Foo {
+    fn add_assign(&mut self, _: ()) {}
+}
+
+impl AddAssign<()> for &mut Foo {
+    fn add_assign(&mut self, _: ()) {}
+}
+
+fn main() {
+    (&mut Foo) += ();
+    //~^ ERROR invalid left-hand side of assignment
+    //~| NOTE cannot assign to this expression
+    //~| HELP consider dereferencing the left-hand side of this operation
+}
diff --git a/src/test/ui/typeck/assign-non-lval-needs-deref.stderr b/src/test/ui/typeck/assign-non-lval-needs-deref.stderr
new file mode 100644
index 00000000000..ee83b145321
--- /dev/null
+++ b/src/test/ui/typeck/assign-non-lval-needs-deref.stderr
@@ -0,0 +1,16 @@
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/assign-non-lval-needs-deref.rs:15:16
+   |
+LL |     (&mut Foo) += ();
+   |     ---------- ^^
+   |     |
+   |     cannot assign to this expression
+   |
+help: consider dereferencing the left-hand side of this operation
+   |
+LL |     *(&mut Foo) += ();
+   |     +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0067`.
diff --git a/src/tools/unicode-table-generator/src/range_search.rs b/src/tools/unicode-table-generator/src/range_search.rs
index 39b47ce703f..3a5b869f72f 100644
--- a/src/tools/unicode-table-generator/src/range_search.rs
+++ b/src/tools/unicode-table-generator/src/range_search.rs
@@ -1,5 +1,6 @@
+#[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
 #[inline(always)]
-fn bitset_search<
+const fn bitset_search<
     const N: usize,
     const CHUNK_SIZE: usize,
     const N1: usize,
@@ -15,14 +16,18 @@ fn bitset_search<
     let bucket_idx = (needle / 64) as usize;
     let chunk_map_idx = bucket_idx / CHUNK_SIZE;
     let chunk_piece = bucket_idx % CHUNK_SIZE;
-    let chunk_idx = if let Some(&v) = chunk_idx_map.get(chunk_map_idx) {
-        v
+    // FIXME: const-hack: Revert to `slice::get` after `const_slice_index`
+    // feature stabilizes.
+    let chunk_idx = if chunk_map_idx < chunk_idx_map.len() {
+        chunk_idx_map[chunk_map_idx]
     } else {
         return false;
     };
     let idx = bitset_chunk_idx[chunk_idx as usize][chunk_piece] as usize;
-    let word = if let Some(word) = bitset_canonical.get(idx) {
-        *word
+    // FIXME: const-hack: Revert to `slice::get` after `const_slice_index`
+    // feature stabilizes.
+    let word = if idx < bitset_canonical.len() {
+        bitset_canonical[idx]
     } else {
         let (real_idx, mapping) = bitset_canonicalized[idx - bitset_canonical.len()];
         let mut word = bitset_canonical[real_idx as usize];
diff --git a/src/tools/unicode-table-generator/src/raw_emitter.rs b/src/tools/unicode-table-generator/src/raw_emitter.rs
index 13eed7b1099..890ff986c2b 100644
--- a/src/tools/unicode-table-generator/src/raw_emitter.rs
+++ b/src/tools/unicode-table-generator/src/raw_emitter.rs
@@ -76,7 +76,7 @@ impl RawEmitter {
 
         writeln!(
             &mut self.file,
-            "static BITSET_CANONICAL: [u64; {}] = [{}];",
+            "const BITSET_CANONICAL: &'static [u64; {}] = &[{}];",
             canonicalized.canonical_words.len(),
             fmt_list(canonicalized.canonical_words.iter().map(|v| Bits(*v))),
         )
@@ -84,7 +84,7 @@ impl RawEmitter {
         self.bytes_used += 8 * canonicalized.canonical_words.len();
         writeln!(
             &mut self.file,
-            "static BITSET_MAPPING: [(u8, u8); {}] = [{}];",
+            "const BITSET_MAPPING: &'static [(u8, u8); {}] = &[{}];",
             canonicalized.canonicalized_words.len(),
             fmt_list(&canonicalized.canonicalized_words),
         )
@@ -96,7 +96,12 @@ impl RawEmitter {
 
         self.blank_line();
 
-        writeln!(&mut self.file, "pub fn lookup(c: char) -> bool {{").unwrap();
+        writeln!(
+            &mut self.file,
+            r#"#[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]"#
+        )
+        .unwrap();
+        writeln!(&mut self.file, "pub const fn lookup(c: char) -> bool {{").unwrap();
         writeln!(&mut self.file, "    super::bitset_search(",).unwrap();
         writeln!(&mut self.file, "        c as u32,").unwrap();
         writeln!(&mut self.file, "        &BITSET_CHUNKS_MAP,").unwrap();
@@ -130,7 +135,7 @@ impl RawEmitter {
 
         writeln!(
             &mut self.file,
-            "static BITSET_CHUNKS_MAP: [u8; {}] = [{}];",
+            "const BITSET_CHUNKS_MAP: &'static [u8; {}] = &[{}];",
             chunk_indices.len(),
             fmt_list(&chunk_indices),
         )
@@ -138,7 +143,7 @@ impl RawEmitter {
         self.bytes_used += chunk_indices.len();
         writeln!(
             &mut self.file,
-            "static BITSET_INDEX_CHUNKS: [[u8; {}]; {}] = [{}];",
+            "const BITSET_INDEX_CHUNKS: &'static [[u8; {}]; {}] = &[{}];",
             chunk_length,
             chunks.len(),
             fmt_list(chunks.iter()),