Merge from rustc

90 files changed, 2426 insertions, 524 deletions

diff --git a/Cargo.lock b/Cargo.lock
index f03b033db6f..10889139e8d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4260,7 +4260,6 @@ dependencies = [
  "rustc_serialize",
  "rustc_type_ir",
  "rustc_type_ir_macros",
- "smallvec",
  "tracing",
 ]
 
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index 509b24dd703..4706744f353 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -769,12 +769,9 @@ pub(crate) unsafe fn codegen(
             }
         }
 
-        // Two things to note:
-        // - If object files are just LLVM bitcode we write bitcode, copy it to
-        //   the .o file, and delete the bitcode if it wasn't otherwise
-        //   requested.
-        // - If we don't have the integrated assembler then we need to emit
-        //   asm from LLVM and use `gcc` to create the object file.
+        // Note that if object files are just LLVM bitcode we write bitcode,
+        // copy it to the .o file, and delete the bitcode if it wasn't
+        // otherwise requested.
 
         let bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
         let bc_summary_out =
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 8b666c9100f..20be2144609 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -28,8 +28,8 @@ use std::io::{self, IsTerminal, Read, Write};
 use std::panic::{self, PanicHookInfo, catch_unwind};
 use std::path::{Path, PathBuf};
 use std::process::{self, Command, Stdio};
+use std::sync::OnceLock;
 use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, OnceLock};
 use std::time::{Instant, SystemTime};
 use std::{env, str};
 
@@ -60,7 +60,6 @@ use rustc_session::lint::{Lint, LintId};
 use rustc_session::output::collect_crate_types;
 use rustc_session::{EarlyDiagCtxt, Session, config, filesearch};
 use rustc_span::FileName;
-use rustc_span::source_map::FileLoader;
 use rustc_target::json::ToJson;
 use rustc_target::spec::{Target, TargetTuple};
 use time::OffsetDateTime;
@@ -208,84 +207,7 @@ pub fn diagnostics_registry() -> Registry {
 }
 
 /// This is the primary entry point for rustc.
-pub struct RunCompiler<'a> {
-    at_args: &'a [String],
-    callbacks: &'a mut (dyn Callbacks + Send),
-    file_loader: Option<Box<dyn FileLoader + Send + Sync>>,
-    make_codegen_backend:
-        Option<Box<dyn FnOnce(&config::Options) -> Box<dyn CodegenBackend> + Send>>,
-    using_internal_features: Arc<std::sync::atomic::AtomicBool>,
-}
-
-impl<'a> RunCompiler<'a> {
-    pub fn new(at_args: &'a [String], callbacks: &'a mut (dyn Callbacks + Send)) -> Self {
-        Self {
-            at_args,
-            callbacks,
-            file_loader: None,
-            make_codegen_backend: None,
-            using_internal_features: Arc::default(),
-        }
-    }
-
-    /// Set a custom codegen backend.
-    ///
-    /// Has no uses within this repository, but is used by bjorn3 for "the
-    /// hotswapping branch of cg_clif" for "setting the codegen backend from a
-    /// custom driver where the custom codegen backend has arbitrary data."
-    /// (See #102759.)
-    pub fn set_make_codegen_backend(
-        &mut self,
-        make_codegen_backend: Option<
-            Box<dyn FnOnce(&config::Options) -> Box<dyn CodegenBackend> + Send>,
-        >,
-    ) -> &mut Self {
-        self.make_codegen_backend = make_codegen_backend;
-        self
-    }
-
-    /// Load files from sources other than the file system.
-    ///
-    /// Has no uses within this repository, but may be used in the future by
-    /// bjorn3 for "hooking rust-analyzer's VFS into rustc at some point for
-    /// running rustc without having to save". (See #102759.)
-    pub fn set_file_loader(
-        &mut self,
-        file_loader: Option<Box<dyn FileLoader + Send + Sync>>,
-    ) -> &mut Self {
-        self.file_loader = file_loader;
-        self
-    }
-
-    /// Set the session-global flag that checks whether internal features have been used,
-    /// suppressing the message about submitting an issue in ICEs when enabled.
-    #[must_use]
-    pub fn set_using_internal_features(mut self, using_internal_features: Arc<AtomicBool>) -> Self {
-        self.using_internal_features = using_internal_features;
-        self
-    }
-
-    /// Parse args and run the compiler.
-    pub fn run(self) {
-        run_compiler(
-            self.at_args,
-            self.callbacks,
-            self.file_loader,
-            self.make_codegen_backend,
-            self.using_internal_features,
-        );
-    }
-}
-
-fn run_compiler(
-    at_args: &[String],
-    callbacks: &mut (dyn Callbacks + Send),
-    file_loader: Option<Box<dyn FileLoader + Send + Sync>>,
-    make_codegen_backend: Option<
-        Box<dyn FnOnce(&config::Options) -> Box<dyn CodegenBackend> + Send>,
-    >,
-    using_internal_features: Arc<std::sync::atomic::AtomicBool>,
-) {
+pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send)) {
     let mut default_early_dcx = EarlyDiagCtxt::new(ErrorOutputType::default());
 
     // Throw away the first argument, the name of the binary.
@@ -322,16 +244,16 @@ fn run_compiler(
         output_file: ofile,
         output_dir: odir,
         ice_file,
-        file_loader,
+        file_loader: None,
         locale_resources: DEFAULT_LOCALE_RESOURCES.to_vec(),
         lint_caps: Default::default(),
         psess_created: None,
         hash_untracked_state: None,
         register_lints: None,
         override_queries: None,
-        make_codegen_backend,
+        make_codegen_backend: None,
         registry: diagnostics_registry(),
-        using_internal_features,
+        using_internal_features: &USING_INTERNAL_FEATURES,
         expanded_args: args,
     };
 
@@ -1350,6 +1272,8 @@ fn ice_path_with_config(config: Option<&UnstableOptions>) -> &'static Option<Pat
     })
 }
 
+pub static USING_INTERNAL_FEATURES: AtomicBool = AtomicBool::new(false);
+
 /// Installs a panic hook that will print the ICE message on unexpected panics.
 ///
 /// The hook is intended to be useable even by external tools. You can pass a custom
@@ -1360,15 +1284,8 @@ fn ice_path_with_config(config: Option<&UnstableOptions>) -> &'static Option<Pat
 /// If you have no extra info to report, pass the empty closure `|_| ()` as the argument to
 /// extra_info.
 ///
-/// Returns a flag that can be set to disable the note for submitting a bug. This can be passed to
-/// [`RunCompiler::set_using_internal_features`] to let macro expansion set it when encountering
-/// internal features.
-///
 /// A custom rustc driver can skip calling this to set up a custom ICE hook.
-pub fn install_ice_hook(
-    bug_report_url: &'static str,
-    extra_info: fn(&DiagCtxt),
-) -> Arc<AtomicBool> {
+pub fn install_ice_hook(bug_report_url: &'static str, extra_info: fn(&DiagCtxt)) {
     // If the user has not explicitly overridden "RUST_BACKTRACE", then produce
     // full backtraces. When a compiler ICE happens, we want to gather
     // as much information as possible to present in the issue opened
@@ -1385,8 +1302,6 @@ pub fn install_ice_hook(
         }
     }
 
-    let using_internal_features = Arc::new(std::sync::atomic::AtomicBool::default());
-    let using_internal_features_hook = Arc::clone(&using_internal_features);
     panic::update_hook(Box::new(
         move |default_hook: &(dyn Fn(&PanicHookInfo<'_>) + Send + Sync + 'static),
               info: &PanicHookInfo<'_>| {
@@ -1438,11 +1353,9 @@ pub fn install_ice_hook(
             }
 
             // Print the ICE message
-            report_ice(info, bug_report_url, extra_info, &using_internal_features_hook);
+            report_ice(info, bug_report_url, extra_info, &USING_INTERNAL_FEATURES);
         },
     ));
-
-    using_internal_features
 }
 
 /// Prints the ICE message, including query stack, but without backtrace.
@@ -1583,13 +1496,11 @@ pub fn main() -> ! {
     init_rustc_env_logger(&early_dcx);
     signal_handler::install();
     let mut callbacks = TimePassesCallbacks::default();
-    let using_internal_features = install_ice_hook(DEFAULT_BUG_REPORT_URL, |_| ());
+    install_ice_hook(DEFAULT_BUG_REPORT_URL, |_| ());
     install_ctrlc_handler();
 
     let exit_code = catch_with_exit_code(|| {
-        RunCompiler::new(&args::raw_args(&early_dcx)?, &mut callbacks)
-            .set_using_internal_features(using_internal_features)
-            .run();
+        run_compiler(&args::raw_args(&early_dcx)?, &mut callbacks);
         Ok(())
     });
 
diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs
index 3c25f4a8b7c..47abba1cc29 100644
--- a/compiler/rustc_hir_typeck/src/coercion.rs
+++ b/compiler/rustc_hir_typeck/src/coercion.rs
@@ -461,9 +461,17 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         // to the target type), since that should be the least
         // confusing.
         let Some(InferOk { value: ty, mut obligations }) = found else {
-            let err = first_error.expect("coerce_borrowed_pointer had no error");
-            debug!("coerce_borrowed_pointer: failed with err = {:?}", err);
-            return Err(err);
+            if let Some(first_error) = first_error {
+                debug!("coerce_borrowed_pointer: failed with err = {:?}", first_error);
+                return Err(first_error);
+            } else {
+                // This may happen in the new trait solver since autoderef requires
+                // the pointee to be structurally normalizable, or else it'll just bail.
+                // So when we have a type like `&<not well formed>`, then we get no
+                // autoderef steps (even though there should be at least one). That means
+                // we get no type mismatches, since the loop above just exits early.
+                return Err(TypeError::Mismatch);
+            }
         };
 
         if ty == a && mt_a.mutbl.is_not() && autoderef.step_count() == 1 {
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 308d669cf35..2113345eda3 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -1,6 +1,5 @@
 use std::path::PathBuf;
 use std::result;
-use std::sync::Arc;
 
 use rustc_ast::{LitKind, MetaItemKind, token};
 use rustc_codegen_ssa::traits::CodegenBackend;
@@ -309,6 +308,11 @@ pub struct Config {
     pub output_dir: Option<PathBuf>,
     pub output_file: Option<OutFileName>,
     pub ice_file: Option<PathBuf>,
+    /// Load files from sources other than the file system.
+    ///
+    /// Has no uses within this repository, but may be used in the future by
+    /// bjorn3 for "hooking rust-analyzer's VFS into rustc at some point for
+    /// running rustc without having to save". (See #102759.)
     pub file_loader: Option<Box<dyn FileLoader + Send + Sync>>,
     /// The list of fluent resources, used for lints declared with
     /// [`Diagnostic`](rustc_errors::Diagnostic) and [`LintDiagnostic`](rustc_errors::LintDiagnostic).
@@ -337,6 +341,11 @@ pub struct Config {
     pub override_queries: Option<fn(&Session, &mut Providers)>,
 
     /// This is a callback from the driver that is called to create a codegen backend.
+    ///
+    /// Has no uses within this repository, but is used by bjorn3 for "the
+    /// hotswapping branch of cg_clif" for "setting the codegen backend from a
+    /// custom driver where the custom codegen backend has arbitrary data."
+    /// (See #102759.)
     pub make_codegen_backend:
         Option<Box<dyn FnOnce(&config::Options) -> Box<dyn CodegenBackend> + Send>>,
 
@@ -346,8 +355,7 @@ pub struct Config {
     /// The inner atomic value is set to true when a feature marked as `internal` is
     /// enabled. Makes it so that "please report a bug" is hidden, as ICEs with
     /// internal features are wontfix, and they are usually the cause of the ICEs.
-    /// None signifies that this is not tracked.
-    pub using_internal_features: Arc<std::sync::atomic::AtomicBool>,
+    pub using_internal_features: &'static std::sync::atomic::AtomicBool,
 
     /// All commandline args used to invoke the compiler, with @file args fully expanded.
     /// This will only be used within debug info, e.g. in the pdb file on windows
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index d7370c1ff53..74d02ac2227 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -2,7 +2,7 @@
 use std::collections::{BTreeMap, BTreeSet};
 use std::num::NonZero;
 use std::path::{Path, PathBuf};
-use std::sync::Arc;
+use std::sync::atomic::AtomicBool;
 
 use rustc_data_structures::profiling::TimePassesFormat;
 use rustc_errors::emitter::HumanReadableErrorType;
@@ -62,6 +62,8 @@ where
             temps_dir,
         };
 
+        static USING_INTERNAL_FEATURES: AtomicBool = AtomicBool::new(false);
+
         let sess = build_session(
             early_dcx,
             sessopts,
@@ -74,7 +76,7 @@ where
             sysroot,
             "",
             None,
-            Arc::default(),
+            &USING_INTERNAL_FEATURES,
             Default::default(),
         );
         let cfg = parse_cfg(sess.dcx(), matches.opt_strs("cfg"));
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index 14f0787de3e..64c8f00cc83 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -972,6 +972,8 @@ lint_unused_result = unused result of type `{$ty}`
 
 lint_use_let_underscore_ignore_suggestion = use `let _ = ...` to ignore the expression or result
 
+lint_uses_power_alignment = repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+
 lint_variant_size_differences =
     enum variant is more than three times larger ({$largest} bytes) than the next largest
 
diff --git a/compiler/rustc_lint/src/if_let_rescope.rs b/compiler/rustc_lint/src/if_let_rescope.rs
index 259ea908fc6..b5a6159bd0a 100644
--- a/compiler/rustc_lint/src/if_let_rescope.rs
+++ b/compiler/rustc_lint/src/if_let_rescope.rs
@@ -9,7 +9,7 @@ use rustc_errors::{
 use rustc_hir::{self as hir, HirIdSet};
 use rustc_macros::LintDiagnostic;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::lint::{FutureIncompatibilityReason, Level};
+use rustc_session::lint::{FutureIncompatibilityReason, LintId};
 use rustc_session::{declare_lint, impl_lint_pass};
 use rustc_span::Span;
 use rustc_span::edition::Edition;
@@ -245,12 +245,12 @@ impl_lint_pass!(
 
 impl<'tcx> LateLintPass<'tcx> for IfLetRescope {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
-        if expr.span.edition().at_least_rust_2024() {
-            return;
-        }
-        if let (Level::Allow, _) = cx.tcx.lint_level_at_node(IF_LET_RESCOPE, expr.hir_id) {
+        if expr.span.edition().at_least_rust_2024()
+            || cx.tcx.lints_that_dont_need_to_run(()).contains(&LintId::of(IF_LET_RESCOPE))
+        {
             return;
         }
+
         if let hir::ExprKind::Loop(block, _label, hir::LoopSource::While, _span) = expr.kind
             && let Some(value) = block.expr
             && let hir::ExprKind::If(cond, _conseq, _alt) = value.kind
@@ -290,7 +290,6 @@ struct IfLetRescopeLint {
     rewrite: Option<IfLetRescopeRewrite>,
 }
 
-// #[derive(Subdiagnostic)]
 struct IfLetRescopeRewrite {
     match_heads: Vec<SingleArmMatchBegin>,
     consequent_heads: Vec<ConsequentRewrite>,
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index fea3d67ffeb..2f610802ff5 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -1695,6 +1695,10 @@ pub(crate) struct OverflowingLiteral<'a> {
 }
 
 #[derive(LintDiagnostic)]
+#[diag(lint_uses_power_alignment)]
+pub(crate) struct UsesPowerAlignment;
+
+#[derive(LintDiagnostic)]
 #[diag(lint_unused_comparisons)]
 pub(crate) struct UnusedComparisons;
 
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index 3bd27a224e7..0757e6840c6 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -1,14 +1,15 @@
 use std::iter;
 use std::ops::ControlFlow;
 
-use rustc_abi::{BackendRepr, ExternAbi, TagEncoding, Variants, WrappingRange};
+use rustc_abi::{BackendRepr, ExternAbi, TagEncoding, VariantIdx, Variants, WrappingRange};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::DiagMessage;
 use rustc_hir::{Expr, ExprKind, LangItem};
 use rustc_middle::bug;
 use rustc_middle::ty::layout::{LayoutOf, SizeSkeleton};
 use rustc_middle::ty::{
-    self, AdtKind, GenericArgsRef, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
+    self, Adt, AdtKind, GenericArgsRef, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
+    TypeVisitableExt,
 };
 use rustc_session::{declare_lint, declare_lint_pass, impl_lint_pass};
 use rustc_span::def_id::LocalDefId;
@@ -23,7 +24,7 @@ use crate::lints::{
     AmbiguousWidePointerComparisonsAddrSuggestion, AtomicOrderingFence, AtomicOrderingLoad,
     AtomicOrderingStore, ImproperCTypes, InvalidAtomicOrderingDiag, InvalidNanComparisons,
     InvalidNanComparisonsSuggestion, UnpredictableFunctionPointerComparisons,
-    UnpredictableFunctionPointerComparisonsSuggestion, UnusedComparisons,
+    UnpredictableFunctionPointerComparisonsSuggestion, UnusedComparisons, UsesPowerAlignment,
     VariantSizeDifferencesDiag,
 };
 use crate::{LateContext, LateLintPass, LintContext, fluent_generated as fluent};
@@ -727,7 +728,60 @@ declare_lint! {
     "proper use of libc types in foreign item definitions"
 }
 
-declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
+declare_lint! {
+    /// The `uses_power_alignment` lint detects specific `repr(C)`
+    /// aggregates on AIX.
+    /// In its platform C ABI, AIX uses the "power" (as in PowerPC) alignment
+    /// rule (detailed in https://www.ibm.com/docs/en/xl-c-and-cpp-aix/16.1?topic=data-using-alignment-modes#alignment),
+    /// which can also be set for XLC by `#pragma align(power)` or
+    /// `-qalign=power`. Aggregates with a floating-point type as the
+    /// recursively first field (as in "at offset 0") modify the layout of
+    /// *subsequent* fields of the associated structs to use an alignment value
+    /// where the floating-point type is aligned on a 4-byte boundary.
+    ///
+    /// The power alignment rule for structs needed for C compatibility is
+    /// unimplementable within `repr(C)` in the compiler without building in
+    /// handling of references to packed fields and infectious nested layouts,
+    /// so a warning is produced in these situations.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,ignore (fails on non-powerpc64-ibm-aix)
+    /// #[repr(C)]
+    /// pub struct Floats {
+    ///     a: f64,
+    ///     b: u8,
+    ///     c: f64,
+    /// }
+    /// ```
+    ///
+    /// This will produce:
+    ///
+    /// ```text
+    /// warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    ///  --> <source>:5:3
+    ///   |
+    /// 5 |   c: f64,
+    ///   |   ^^^^^^
+    ///   |
+    ///   = note: `#[warn(uses_power_alignment)]` on by default
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// The power alignment rule specifies that the above struct has the
+    /// following alignment:
+    ///  - offset_of!(Floats, a) == 0
+    ///  - offset_of!(Floats, b) == 8
+    ///  - offset_of!(Floats, c) == 12
+    /// However, rust currently aligns `c` at offset_of!(Floats, c) == 16.
+    /// Thus, a warning should be produced for the above struct in this case.
+    USES_POWER_ALIGNMENT,
+    Warn,
+    "Structs do not follow the power alignment rule under repr(C)"
+}
+
+declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS, USES_POWER_ALIGNMENT]);
 
 #[derive(Clone, Copy)]
 pub(crate) enum CItemKind {
@@ -1539,6 +1593,71 @@ impl ImproperCTypesDefinitions {
             vis.check_type_for_ffi_and_report_errors(span, fn_ptr_ty, true, false);
         }
     }
+
+    fn check_arg_for_power_alignment<'tcx>(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        ty: Ty<'tcx>,
+    ) -> bool {
+        // Structs (under repr(C)) follow the power alignment rule if:
+        //   - the first field of the struct is a floating-point type that
+        //     is greater than 4-bytes, or
+        //   - the first field of the struct is an aggregate whose
+        //     recursively first field is a floating-point type greater than
+        //     4 bytes.
+        if cx.tcx.sess.target.os != "aix" {
+            return false;
+        }
+        if ty.is_floating_point() && ty.primitive_size(cx.tcx).bytes() > 4 {
+            return true;
+        } else if let Adt(adt_def, _) = ty.kind()
+            && adt_def.is_struct()
+        {
+            let struct_variant = adt_def.variant(VariantIdx::ZERO);
+            // Within a nested struct, all fields are examined to correctly
+            // report if any fields after the nested struct within the
+            // original struct are misaligned.
+            for struct_field in &struct_variant.fields {
+                let field_ty = cx.tcx.type_of(struct_field.did).instantiate_identity();
+                if self.check_arg_for_power_alignment(cx, field_ty) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    fn check_struct_for_power_alignment<'tcx>(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        item: &'tcx hir::Item<'tcx>,
+    ) {
+        let adt_def = cx.tcx.adt_def(item.owner_id.to_def_id());
+        if adt_def.repr().c()
+            && !adt_def.repr().packed()
+            && cx.tcx.sess.target.os == "aix"
+            && !adt_def.all_fields().next().is_none()
+        {
+            let struct_variant_data = item.expect_struct().0;
+            for (index, ..) in struct_variant_data.fields().iter().enumerate() {
+                // Struct fields (after the first field) are checked for the
+                // power alignment rule, as fields after the first are likely
+                // to be the fields that are misaligned.
+                if index != 0 {
+                    let first_field_def = struct_variant_data.fields()[index];
+                    let def_id = first_field_def.def_id;
+                    let ty = cx.tcx.type_of(def_id).instantiate_identity();
+                    if self.check_arg_for_power_alignment(cx, ty) {
+                        cx.emit_span_lint(
+                            USES_POWER_ALIGNMENT,
+                            first_field_def.span,
+                            UsesPowerAlignment,
+                        );
+                    }
+                }
+            }
+        }
+    }
 }
 
 /// `ImproperCTypesDefinitions` checks items outside of foreign items (e.g. stuff that isn't in
@@ -1562,8 +1681,13 @@ impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
             }
             // See `check_fn`..
             hir::ItemKind::Fn { .. } => {}
+            // Structs are checked based on if they follow the power alignment
+            // rule (under repr(C)).
+            hir::ItemKind::Struct(..) => {
+                self.check_struct_for_power_alignment(cx, item);
+            }
             // See `check_field_def`..
-            hir::ItemKind::Union(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) => {}
+            hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
             // Doesn't define something that can contain a external type to be checked.
             hir::ItemKind::Impl(..)
             | hir::ItemKind::TraitAlias(..)
diff --git a/compiler/rustc_middle/src/query/arena_cached.rs b/compiler/rustc_middle/src/query/arena_cached.rs
new file mode 100644
index 00000000000..ec6e466ff68
--- /dev/null
+++ b/compiler/rustc_middle/src/query/arena_cached.rs
@@ -0,0 +1,47 @@
+/// Helper trait that allows `arena_cache` queries to return `Option<&T>`
+/// instead of `&Option<T>`, and avoid allocating `None` in the arena.
+///
+/// An arena-cached query must be declared to return a type that implements
+/// this trait, i.e. either `&'tcx T` or `Option<&'tcx T>`. This trait then
+/// determines the types returned by the provider and stored in the arena,
+/// and provides a function to bridge between the three types.
+pub trait ArenaCached<'tcx>: Sized {
+    /// Type that is returned by the query provider.
+    type Provided;
+    /// Type that is stored in the arena.
+    type Allocated: 'tcx;
+
+    /// Takes a provided value, and allocates it in the arena (if appropriate)
+    /// with the help of the given `arena_alloc` closure.
+    fn alloc_in_arena(
+        arena_alloc: impl Fn(Self::Allocated) -> &'tcx Self::Allocated,
+        value: Self::Provided,
+    ) -> Self;
+}
+
+impl<'tcx, T> ArenaCached<'tcx> for &'tcx T {
+    type Provided = T;
+    type Allocated = T;
+
+    fn alloc_in_arena(
+        arena_alloc: impl Fn(Self::Allocated) -> &'tcx Self::Allocated,
+        value: Self::Provided,
+    ) -> Self {
+        // Just allocate in the arena normally.
+        arena_alloc(value)
+    }
+}
+
+impl<'tcx, T> ArenaCached<'tcx> for Option<&'tcx T> {
+    type Provided = Option<T>;
+    /// The provide value is `Option<T>`, but we only store `T` in the arena.
+    type Allocated = T;
+
+    fn alloc_in_arena(
+        arena_alloc: impl Fn(Self::Allocated) -> &'tcx Self::Allocated,
+        value: Self::Provided,
+    ) -> Self {
+        // Don't store None in the arena, and wrap the allocated reference in Some.
+        value.map(arena_alloc)
+    }
+}
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 65e93c3a1cc..05ded71dbeb 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -7,7 +7,6 @@
 #![allow(unused_parens)]
 
 use std::mem;
-use std::ops::Deref;
 use std::path::PathBuf;
 use std::sync::Arc;
 
@@ -85,6 +84,7 @@ use crate::ty::{
 };
 use crate::{dep_graph, mir, thir};
 
+mod arena_cached;
 pub mod erase;
 mod keys;
 pub use keys::{AsLocalKey, Key, LocalCrate};
@@ -586,7 +586,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query mir_coroutine_witnesses(key: DefId) -> &'tcx Option<mir::CoroutineLayout<'tcx>> {
+    query mir_coroutine_witnesses(key: DefId) -> Option<&'tcx mir::CoroutineLayout<'tcx>> {
         arena_cache
         desc { |tcx| "coroutine witness types for `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
@@ -2415,7 +2415,7 @@ rustc_queries! {
     /// because the `ty::Ty`-based wfcheck is always run.
     query diagnostic_hir_wf_check(
         key: (ty::Predicate<'tcx>, WellFormedLoc)
-    ) -> &'tcx Option<ObligationCause<'tcx>> {
+    ) -> Option<&'tcx ObligationCause<'tcx>> {
         arena_cache
         eval_always
         no_hash
diff --git a/compiler/rustc_middle/src/query/plumbing.rs b/compiler/rustc_middle/src/query/plumbing.rs
index 2cb6f6d8c6e..1c157f33a81 100644
--- a/compiler/rustc_middle/src/query/plumbing.rs
+++ b/compiler/rustc_middle/src/query/plumbing.rs
@@ -289,10 +289,10 @@ macro_rules! define_callbacks {
 
                 /// This type alias specifies the type returned from query providers and the type
                 /// used for decoding. For regular queries this is the declared returned type `V`,
-                /// but `arena_cache` will use `<V as Deref>::Target` instead.
+                /// but `arena_cache` will use `<V as ArenaCached>::Provided` instead.
                 pub type ProvidedValue<'tcx> = query_if_arena!(
                     [$($modifiers)*]
-                    (<$V as Deref>::Target)
+                    (<$V as $crate::query::arena_cached::ArenaCached<'tcx>>::Provided)
                     ($V)
                 );
 
@@ -307,10 +307,18 @@ macro_rules! define_callbacks {
                 ) -> Erase<Value<'tcx>> {
                     erase(query_if_arena!([$($modifiers)*]
                         {
-                            if mem::needs_drop::<ProvidedValue<'tcx>>() {
-                                &*_tcx.query_system.arenas.$name.alloc(value)
+                            use $crate::query::arena_cached::ArenaCached;
+
+                            if mem::needs_drop::<<$V as ArenaCached<'tcx>>::Allocated>() {
+                                <$V as ArenaCached>::alloc_in_arena(
+                                    |v| _tcx.query_system.arenas.$name.alloc(v),
+                                    value,
+                                )
                             } else {
-                                &*_tcx.arena.dropless.alloc(value)
+                                <$V as ArenaCached>::alloc_in_arena(
+                                    |v| _tcx.arena.dropless.alloc(v),
+                                    value,
+                                )
                             }
                         }
                         (value)
@@ -354,7 +362,7 @@ macro_rules! define_callbacks {
 
         pub struct QueryArenas<'tcx> {
             $($(#[$attr])* pub $name: query_if_arena!([$($modifiers)*]
-                (TypedArena<<$V as Deref>::Target>)
+                (TypedArena<<$V as $crate::query::arena_cached::ArenaCached<'tcx>>::Allocated>)
                 ()
             ),)*
         }
diff --git a/compiler/rustc_next_trait_solver/Cargo.toml b/compiler/rustc_next_trait_solver/Cargo.toml
index f9168112216..451c215566b 100644
--- a/compiler/rustc_next_trait_solver/Cargo.toml
+++ b/compiler/rustc_next_trait_solver/Cargo.toml
@@ -13,7 +13,6 @@ rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
 rustc_type_ir = { path = "../rustc_type_ir", default-features = false }
 rustc_type_ir_macros = { path = "../rustc_type_ir_macros" }
-smallvec = "1.8.1"
 tracing = "0.1"
 # tidy-alphabetical-end
 
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index 4faa243c02a..513fc9355c8 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -8,7 +8,6 @@ use rustc_type_ir::lang_items::TraitSolverLangItem;
 use rustc_type_ir::solve::CanonicalResponse;
 use rustc_type_ir::visit::TypeVisitableExt as _;
 use rustc_type_ir::{self as ty, Interner, TraitPredicate, TypingMode, Upcast as _, elaborate};
-use smallvec::SmallVec;
 use tracing::{instrument, trace};
 
 use crate::delegate::SolverDelegate;
@@ -1199,33 +1198,42 @@ where
         // nested requirements, over all others. This is a fix for #53123 and
         // prevents where-bounds from accidentally extending the lifetime of a
         // variable.
-        if candidates
-            .iter()
-            .any(|c| matches!(c.source, CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial)))
-        {
-            let trivial_builtin_impls: SmallVec<[_; 1]> = candidates
-                .iter()
-                .filter(|c| {
-                    matches!(c.source, CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial))
-                })
-                .map(|c| c.result)
-                .collect();
+        let mut trivial_builtin_impls = candidates.iter().filter(|c| {
+            matches!(c.source, CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial))
+        });
+        if let Some(candidate) = trivial_builtin_impls.next() {
             // There should only ever be a single trivial builtin candidate
             // as they would otherwise overlap.
-            assert_eq!(trivial_builtin_impls.len(), 1);
-            return if let Some(response) = self.try_merge_responses(&trivial_builtin_impls) {
-                Ok((response, Some(TraitGoalProvenVia::Misc)))
-            } else {
-                Ok((self.bail_with_ambiguity(&trivial_builtin_impls), None))
-            };
+            assert!(trivial_builtin_impls.next().is_none());
+            return Ok((candidate.result, Some(TraitGoalProvenVia::Misc)));
         }
 
         // If there are non-global where-bounds, prefer where-bounds
         // (including global ones) over everything else.
         let has_non_global_where_bounds = candidates.iter().any(|c| match c.source {
             CandidateSource::ParamEnv(idx) => {
-                let where_bound = goal.param_env.caller_bounds().get(idx);
-                where_bound.has_bound_vars() || !where_bound.is_global()
+                let where_bound = goal.param_env.caller_bounds().get(idx).unwrap();
+                let ty::ClauseKind::Trait(trait_pred) = where_bound.kind().skip_binder() else {
+                    unreachable!("expected trait-bound: {where_bound:?}");
+                };
+
+                if trait_pred.has_bound_vars() || !trait_pred.is_global() {
+                    return true;
+                }
+
+                // We don't consider a trait-bound global if it has a projection bound.
+                //
+                // See ui/traits/next-solver/normalization-shadowing/global-trait-with-project.rs
+                // for an example where this is necessary.
+                for p in goal.param_env.caller_bounds().iter() {
+                    if let ty::ClauseKind::Projection(proj) = p.kind().skip_binder() {
+                        if proj.projection_term.trait_ref(self.cx()) == trait_pred.trait_ref {
+                            return true;
+                        }
+                    }
+                }
+
+                false
             }
             _ => false,
         });
diff --git a/compiler/rustc_parse_format/src/lib.rs b/compiler/rustc_parse_format/src/lib.rs
index 9eb335cb34c..5418f054beb 100644
--- a/compiler/rustc_parse_format/src/lib.rs
+++ b/compiler/rustc_parse_format/src/lib.rs
@@ -514,13 +514,7 @@ impl<'a> Parser<'a> {
 
     /// Consumes all whitespace characters until the first non-whitespace character
     fn ws(&mut self) {
-        while let Some(&(_, c)) = self.cur.peek() {
-            if c.is_whitespace() {
-                self.cur.next();
-            } else {
-                break;
-            }
-        }
+        while let Some(_) = self.cur.next_if(|&(_, c)| c.is_whitespace()) {}
     }
 
     /// Parses all of a string which is to be considered a "raw literal" in a
@@ -545,7 +539,7 @@ impl<'a> Parser<'a> {
                 }
             }
         }
-        &self.input[start..self.input.len()]
+        &self.input[start..]
     }
 
     /// Parses an `Argument` structure, or what's contained within braces inside the format string.
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 60f1154dc6d..10f1ce376ef 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -189,7 +189,7 @@ pub struct Session {
     /// enabled. Makes it so that "please report a bug" is hidden, as ICEs with
     /// internal features are wontfix, and they are usually the cause of the ICEs.
     /// None signifies that this is not tracked.
-    pub using_internal_features: Arc<AtomicBool>,
+    pub using_internal_features: &'static AtomicBool,
 
     /// All commandline args used to invoke the compiler, with @file args fully expanded.
     /// This will only be used within debug info, e.g. in the pdb file on windows
@@ -966,7 +966,7 @@ pub fn build_session(
     sysroot: PathBuf,
     cfg_version: &'static str,
     ice_file: Option<PathBuf>,
-    using_internal_features: Arc<AtomicBool>,
+    using_internal_features: &'static AtomicBool,
     expanded_args: Vec<String>,
 ) -> Session {
     // FIXME: This is not general enough to make the warning lint completely override
diff --git a/compiler/rustc_smir/src/rustc_internal/mod.rs b/compiler/rustc_smir/src/rustc_internal/mod.rs
index dc63ea1999e..ad38ea228bf 100644
--- a/compiler/rustc_smir/src/rustc_internal/mod.rs
+++ b/compiler/rustc_smir/src/rustc_internal/mod.rs
@@ -316,7 +316,7 @@ macro_rules! optional {
 #[doc(hidden)]
 macro_rules! run_driver {
     ($args:expr, $callback:expr $(, $with_tcx:ident)?) => {{
-        use rustc_driver::{Callbacks, Compilation, RunCompiler};
+        use rustc_driver::{Callbacks, Compilation, run_compiler};
         use rustc_middle::ty::TyCtxt;
         use rustc_interface::interface;
         use stable_mir::CompilerError;
@@ -347,7 +347,7 @@ macro_rules! run_driver {
             /// Runs the compiler against given target and tests it with `test_function`
             pub fn run(&mut self) -> Result<C, CompilerError<B>> {
                 let compiler_result = rustc_driver::catch_fatal_errors(|| -> interface::Result::<()> {
-                    RunCompiler::new(&self.args.clone(), self).run();
+                    run_compiler(&self.args.clone(), self);
                     Ok(())
                 });
                 match (compiler_result, self.result.take()) {
diff --git a/compiler/rustc_target/src/spec/base/windows_gnu.rs b/compiler/rustc_target/src/spec/base/windows_gnu.rs
index e975102e238..d8b6ae8cf32 100644
--- a/compiler/rustc_target/src/spec/base/windows_gnu.rs
+++ b/compiler/rustc_target/src/spec/base/windows_gnu.rs
@@ -97,9 +97,9 @@ pub(crate) fn opts() -> TargetOptions {
         emit_debug_gdb_scripts: false,
         requires_uwtable: true,
         eh_frame_header: false,
+        debuginfo_kind: DebuginfoKind::Dwarf,
         // FIXME(davidtwco): Support Split DWARF on Windows GNU - may require LLVM changes to
         // output DWO, despite using DWARF, doesn't use ELF..
-        debuginfo_kind: DebuginfoKind::Pdb,
         supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
         ..Default::default()
     }
diff --git a/compiler/rustc_target/src/spec/base/windows_gnullvm.rs b/compiler/rustc_target/src/spec/base/windows_gnullvm.rs
index 4f370ec8bd0..86e52117dbf 100644
--- a/compiler/rustc_target/src/spec/base/windows_gnullvm.rs
+++ b/compiler/rustc_target/src/spec/base/windows_gnullvm.rs
@@ -44,9 +44,9 @@ pub(crate) fn opts() -> TargetOptions {
         has_thread_local: true,
         crt_static_allows_dylibs: true,
         crt_static_respected: true,
+        debuginfo_kind: DebuginfoKind::Dwarf,
         // FIXME(davidtwco): Support Split DWARF on Windows GNU - may require LLVM changes to
         // output DWO, despite using DWARF, doesn't use ELF..
-        debuginfo_kind: DebuginfoKind::Pdb,
         supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
         ..Default::default()
     }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
index 36270e0da78..21124cf20e5 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
@@ -167,6 +167,18 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             exp_span, exp_found.expected, exp_found.found,
         );
 
+        match self.tcx.coroutine_kind(cause.body_id) {
+            Some(hir::CoroutineKind::Desugared(
+                hir::CoroutineDesugaring::Async | hir::CoroutineDesugaring::AsyncGen,
+                _,
+            )) => (),
+            None
+            | Some(
+                hir::CoroutineKind::Coroutine(_)
+                | hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _),
+            ) => return,
+        }
+
         if let ObligationCauseCode::CompareImplItem { .. } = cause.code() {
             return;
         }
diff --git a/library/alloc/src/bstr.rs b/library/alloc/src/bstr.rs
new file mode 100644
index 00000000000..61e61019b50
--- /dev/null
+++ b/library/alloc/src/bstr.rs
@@ -0,0 +1,702 @@
+//! The `ByteStr` and `ByteString` types and trait implementations.
+
+// This could be more fine-grained.
+#![cfg(not(no_global_oom_handling))]
+
+use core::borrow::{Borrow, BorrowMut};
+#[unstable(feature = "bstr", issue = "134915")]
+pub use core::bstr::ByteStr;
+use core::bstr::{impl_partial_eq, impl_partial_eq_n, impl_partial_eq_ord};
+use core::cmp::Ordering;
+use core::ops::{
+    Deref, DerefMut, DerefPure, Index, IndexMut, Range, RangeFrom, RangeFull, RangeInclusive,
+    RangeTo, RangeToInclusive,
+};
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+use core::str::FromStr;
+use core::{fmt, hash};
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+use crate::borrow::{Cow, ToOwned};
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+use crate::boxed::Box;
+#[cfg(not(no_rc))]
+use crate::rc::Rc;
+use crate::string::String;
+#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
+use crate::sync::Arc;
+use crate::vec::Vec;
+
+/// A wrapper for `Vec<u8>` representing a human-readable string that's conventionally, but not
+/// always, UTF-8.
+///
+/// Unlike `String`, this type permits non-UTF-8 contents, making it suitable for user input,
+/// non-native filenames (as `Path` only supports native filenames), and other applications that
+/// need to round-trip whatever data the user provides.
+///
+/// A `ByteString` owns its contents and can grow and shrink, like a `Vec` or `String`. For a
+/// borrowed byte string, see [`ByteStr`](../../std/bstr/struct.ByteStr.html).
+///
+/// `ByteString` implements `Deref` to `&Vec<u8>`, so all methods available on `&Vec<u8>` are
+/// available on `ByteString`. Similarly, `ByteString` implements `DerefMut` to `&mut Vec<u8>`,
+/// so you can modify a `ByteString` using any method available on `&mut Vec<u8>`.
+///
+/// The `Debug` and `Display` implementations for `ByteString` are the same as those for `ByteStr`,
+/// showing invalid UTF-8 as hex escapes or the Unicode replacement character, respectively.
+#[unstable(feature = "bstr", issue = "134915")]
+#[repr(transparent)]
+#[derive(Clone)]
+#[doc(alias = "BString")]
+pub struct ByteString(pub Vec<u8>);
+
+impl ByteString {
+    #[inline]
+    pub(crate) fn as_bytes(&self) -> &[u8] {
+        &self.0
+    }
+
+    #[inline]
+    pub(crate) fn as_bytestr(&self) -> &ByteStr {
+        ByteStr::new(&self.0)
+    }
+
+    #[inline]
+    pub(crate) fn as_mut_bytestr(&mut self) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Deref for ByteString {
+    type Target = Vec<u8>;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl DerefMut for ByteString {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl DerefPure for ByteString {}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl fmt::Debug for ByteString {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(self.as_bytestr(), f)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl fmt::Display for ByteString {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self.as_bytestr(), f)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsRef<[u8]> for ByteString {
+    #[inline]
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsRef<ByteStr> for ByteString {
+    #[inline]
+    fn as_ref(&self) -> &ByteStr {
+        self.as_bytestr()
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsMut<[u8]> for ByteString {
+    #[inline]
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsMut<ByteStr> for ByteString {
+    #[inline]
+    fn as_mut(&mut self) -> &mut ByteStr {
+        self.as_mut_bytestr()
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Borrow<[u8]> for ByteString {
+    #[inline]
+    fn borrow(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Borrow<ByteStr> for ByteString {
+    #[inline]
+    fn borrow(&self) -> &ByteStr {
+        self.as_bytestr()
+    }
+}
+
+// `impl Borrow<ByteStr> for Vec<u8>` omitted to avoid inference failures
+// `impl Borrow<ByteStr> for String` omitted to avoid inference failures
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl BorrowMut<[u8]> for ByteString {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl BorrowMut<ByteStr> for ByteString {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut ByteStr {
+        self.as_mut_bytestr()
+    }
+}
+
+// `impl BorrowMut<ByteStr> for Vec<u8>` omitted to avoid inference failures
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Default for ByteString {
+    fn default() -> Self {
+        ByteString(Vec::new())
+    }
+}
+
+// Omitted due to inference failures
+//
+// #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a, const N: usize> From<&'a [u8; N]> for ByteString {
+//     #[inline]
+//     fn from(s: &'a [u8; N]) -> Self {
+//         ByteString(s.as_slice().to_vec())
+//     }
+// }
+//
+// #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<const N: usize> From<[u8; N]> for ByteString {
+//     #[inline]
+//     fn from(s: [u8; N]) -> Self {
+//         ByteString(s.as_slice().to_vec())
+//     }
+// }
+//
+// #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a> From<&'a [u8]> for ByteString {
+//     #[inline]
+//     fn from(s: &'a [u8]) -> Self {
+//         ByteString(s.to_vec())
+//     }
+// }
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl From<Vec<u8>> for ByteString {
+//     #[inline]
+//     fn from(s: Vec<u8>) -> Self {
+//         ByteString(s)
+//     }
+// }
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl From<ByteString> for Vec<u8> {
+    #[inline]
+    fn from(s: ByteString) -> Self {
+        s.0
+    }
+}
+
+// Omitted due to inference failures
+//
+// #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a> From<&'a str> for ByteString {
+//     #[inline]
+//     fn from(s: &'a str) -> Self {
+//         ByteString(s.as_bytes().to_vec())
+//     }
+// }
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl From<String> for ByteString {
+//     #[inline]
+//     fn from(s: String) -> Self {
+//         ByteString(s.into_bytes())
+//     }
+// }
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> From<&'a ByteStr> for ByteString {
+    #[inline]
+    fn from(s: &'a ByteStr) -> Self {
+        ByteString(s.0.to_vec())
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> From<ByteString> for Cow<'a, ByteStr> {
+    #[inline]
+    fn from(s: ByteString) -> Self {
+        Cow::Owned(s)
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> From<&'a ByteString> for Cow<'a, ByteStr> {
+    #[inline]
+    fn from(s: &'a ByteString) -> Self {
+        Cow::Borrowed(s.as_bytestr())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl FromIterator<char> for ByteString {
+    #[inline]
+    fn from_iter<T: IntoIterator<Item = char>>(iter: T) -> Self {
+        ByteString(iter.into_iter().collect::<String>().into_bytes())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl FromIterator<u8> for ByteString {
+    #[inline]
+    fn from_iter<T: IntoIterator<Item = u8>>(iter: T) -> Self {
+        ByteString(iter.into_iter().collect())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> FromIterator<&'a str> for ByteString {
+    #[inline]
+    fn from_iter<T: IntoIterator<Item = &'a str>>(iter: T) -> Self {
+        ByteString(iter.into_iter().collect::<String>().into_bytes())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> FromIterator<&'a [u8]> for ByteString {
+    #[inline]
+    fn from_iter<T: IntoIterator<Item = &'a [u8]>>(iter: T) -> Self {
+        let mut buf = Vec::new();
+        for b in iter {
+            buf.extend_from_slice(b);
+        }
+        ByteString(buf)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> FromIterator<&'a ByteStr> for ByteString {
+    #[inline]
+    fn from_iter<T: IntoIterator<Item = &'a ByteStr>>(iter: T) -> Self {
+        let mut buf = Vec::new();
+        for b in iter {
+            buf.extend_from_slice(&b.0);
+        }
+        ByteString(buf)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl FromIterator<ByteString> for ByteString {
+    #[inline]
+    fn from_iter<T: IntoIterator<Item = ByteString>>(iter: T) -> Self {
+        let mut buf = Vec::new();
+        for mut b in iter {
+            buf.append(&mut b.0);
+        }
+        ByteString(buf)
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl FromStr for ByteString {
+    type Err = core::convert::Infallible;
+
+    #[inline]
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(ByteString(s.as_bytes().to_vec()))
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<usize> for ByteString {
+    type Output = u8;
+
+    #[inline]
+    fn index(&self, idx: usize) -> &u8 {
+        &self.0[idx]
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeFull> for ByteString {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, _: RangeFull) -> &ByteStr {
+        self.as_bytestr()
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<Range<usize>> for ByteString {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: Range<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeInclusive<usize>> for ByteString {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeInclusive<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeFrom<usize>> for ByteString {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeFrom<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeTo<usize>> for ByteString {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeTo<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeToInclusive<usize>> for ByteString {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeToInclusive<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<usize> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, idx: usize) -> &mut u8 {
+        &mut self.0[idx]
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeFull> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, _: RangeFull) -> &mut ByteStr {
+        self.as_mut_bytestr()
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<Range<usize>> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, r: Range<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeInclusive<usize>> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, r: RangeInclusive<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeFrom<usize>> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, r: RangeFrom<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeTo<usize>> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, r: RangeTo<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeToInclusive<usize>> for ByteString {
+    #[inline]
+    fn index_mut(&mut self, r: RangeToInclusive<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl hash::Hash for ByteString {
+    #[inline]
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        self.0.hash(state);
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Eq for ByteString {}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl PartialEq for ByteString {
+    #[inline]
+    fn eq(&self, other: &ByteString) -> bool {
+        self.0 == other.0
+    }
+}
+
+macro_rules! impl_partial_eq_ord_cow {
+    ($lhs:ty, $rhs:ty) => {
+        #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<'a> PartialEq<$rhs> for $lhs {
+            #[inline]
+            fn eq(&self, other: &$rhs) -> bool {
+                let other: &[u8] = (&**other).as_ref();
+                PartialEq::eq(self.as_bytes(), other)
+            }
+        }
+
+        #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<'a> PartialEq<$lhs> for $rhs {
+            #[inline]
+            fn eq(&self, other: &$lhs) -> bool {
+                let this: &[u8] = (&**self).as_ref();
+                PartialEq::eq(this, other.as_bytes())
+            }
+        }
+
+        #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<'a> PartialOrd<$rhs> for $lhs {
+            #[inline]
+            fn partial_cmp(&self, other: &$rhs) -> Option<Ordering> {
+                let other: &[u8] = (&**other).as_ref();
+                PartialOrd::partial_cmp(self.as_bytes(), other)
+            }
+        }
+
+        #[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<'a> PartialOrd<$lhs> for $rhs {
+            #[inline]
+            fn partial_cmp(&self, other: &$lhs) -> Option<Ordering> {
+                let this: &[u8] = (&**self).as_ref();
+                PartialOrd::partial_cmp(this, other.as_bytes())
+            }
+        }
+    };
+}
+
+// PartialOrd with `Vec<u8>` omitted to avoid inference failures
+impl_partial_eq!(ByteString, Vec<u8>);
+// PartialOrd with `[u8]` omitted to avoid inference failures
+impl_partial_eq!(ByteString, [u8]);
+// PartialOrd with `&[u8]` omitted to avoid inference failures
+impl_partial_eq!(ByteString, &[u8]);
+// PartialOrd with `String` omitted to avoid inference failures
+impl_partial_eq!(ByteString, String);
+// PartialOrd with `str` omitted to avoid inference failures
+impl_partial_eq!(ByteString, str);
+// PartialOrd with `&str` omitted to avoid inference failures
+impl_partial_eq!(ByteString, &str);
+impl_partial_eq_ord!(ByteString, ByteStr);
+impl_partial_eq_ord!(ByteString, &ByteStr);
+// PartialOrd with `[u8; N]` omitted to avoid inference failures
+impl_partial_eq_n!(ByteString, [u8; N]);
+// PartialOrd with `&[u8; N]` omitted to avoid inference failures
+impl_partial_eq_n!(ByteString, &[u8; N]);
+impl_partial_eq_ord_cow!(ByteString, Cow<'_, ByteStr>);
+impl_partial_eq_ord_cow!(ByteString, Cow<'_, str>);
+impl_partial_eq_ord_cow!(ByteString, Cow<'_, [u8]>);
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Ord for ByteString {
+    #[inline]
+    fn cmp(&self, other: &ByteString) -> Ordering {
+        Ord::cmp(&self.0, &other.0)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl PartialOrd for ByteString {
+    #[inline]
+    fn partial_cmp(&self, other: &ByteString) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&self.0, &other.0)
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl ToOwned for ByteStr {
+    type Owned = ByteString;
+
+    #[inline]
+    fn to_owned(&self) -> ByteString {
+        ByteString(self.0.to_vec())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl TryFrom<ByteString> for String {
+    type Error = crate::string::FromUtf8Error;
+
+    #[inline]
+    fn try_from(s: ByteString) -> Result<Self, Self::Error> {
+        String::from_utf8(s.0)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> TryFrom<&'a ByteString> for &'a str {
+    type Error = crate::str::Utf8Error;
+
+    #[inline]
+    fn try_from(s: &'a ByteString) -> Result<Self, Self::Error> {
+        crate::str::from_utf8(s.0.as_slice())
+    }
+}
+
+// Additional impls for `ByteStr` that require types from `alloc`:
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl Clone for Box<ByteStr> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Self::from(Box::<[u8]>::from(&self.0))
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> From<&'a ByteStr> for Cow<'a, ByteStr> {
+    #[inline]
+    fn from(s: &'a ByteStr) -> Self {
+        Cow::Borrowed(s)
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl From<Box<[u8]>> for Box<ByteStr> {
+    #[inline]
+    fn from(s: Box<[u8]>) -> Box<ByteStr> {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`.
+        unsafe { Box::from_raw(Box::into_raw(s) as _) }
+    }
+}
+
+#[cfg(not(test))] // https://github.com/rust-lang/rust/issues/135100
+#[unstable(feature = "bstr", issue = "134915")]
+impl From<Box<ByteStr>> for Box<[u8]> {
+    #[inline]
+    fn from(s: Box<ByteStr>) -> Box<[u8]> {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`.
+        unsafe { Box::from_raw(Box::into_raw(s) as _) }
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+#[cfg(not(no_rc))]
+impl From<Rc<[u8]>> for Rc<ByteStr> {
+    #[inline]
+    fn from(s: Rc<[u8]>) -> Rc<ByteStr> {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`.
+        unsafe { Rc::from_raw(Rc::into_raw(s) as _) }
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+#[cfg(not(no_rc))]
+impl From<Rc<ByteStr>> for Rc<[u8]> {
+    #[inline]
+    fn from(s: Rc<ByteStr>) -> Rc<[u8]> {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`.
+        unsafe { Rc::from_raw(Rc::into_raw(s) as _) }
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
+impl From<Arc<[u8]>> for Arc<ByteStr> {
+    #[inline]
+    fn from(s: Arc<[u8]>) -> Arc<ByteStr> {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`.
+        unsafe { Arc::from_raw(Arc::into_raw(s) as _) }
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
+impl From<Arc<ByteStr>> for Arc<[u8]> {
+    #[inline]
+    fn from(s: Arc<ByteStr>) -> Arc<[u8]> {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`.
+        unsafe { Arc::from_raw(Arc::into_raw(s) as _) }
+    }
+}
+
+// PartialOrd with `Vec<u8>` omitted to avoid inference failures
+impl_partial_eq!(ByteStr, Vec<u8>);
+// PartialOrd with `String` omitted to avoid inference failures
+impl_partial_eq!(ByteStr, String);
+impl_partial_eq_ord_cow!(&'a ByteStr, Cow<'a, ByteStr>);
+impl_partial_eq_ord_cow!(&'a ByteStr, Cow<'a, str>);
+impl_partial_eq_ord_cow!(&'a ByteStr, Cow<'a, [u8]>);
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> TryFrom<&'a ByteStr> for String {
+    type Error = core::str::Utf8Error;
+
+    #[inline]
+    fn try_from(s: &'a ByteStr) -> Result<Self, Self::Error> {
+        Ok(core::str::from_utf8(&s.0)?.into())
+    }
+}
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 9660023d694..041f80c1f2c 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -1442,20 +1442,20 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     ///
     /// let mut set = BTreeSet::from([1, 2, 3, 4]);
     ///
-    /// let mut cursor = unsafe { set.upper_bound_mut(Bound::Included(&3)) };
+    /// let mut cursor = set.upper_bound_mut(Bound::Included(&3));
     /// assert_eq!(cursor.peek_prev(), Some(&3));
     /// assert_eq!(cursor.peek_next(), Some(&4));
     ///
-    /// let mut cursor = unsafe { set.upper_bound_mut(Bound::Excluded(&3)) };
+    /// let mut cursor = set.upper_bound_mut(Bound::Excluded(&3));
     /// assert_eq!(cursor.peek_prev(), Some(&2));
     /// assert_eq!(cursor.peek_next(), Some(&3));
     ///
-    /// let mut cursor = unsafe { set.upper_bound_mut(Bound::Unbounded) };
+    /// let mut cursor = set.upper_bound_mut(Bound::Unbounded);
     /// assert_eq!(cursor.peek_prev(), Some(&4));
     /// assert_eq!(cursor.peek_next(), None);
     /// ```
     #[unstable(feature = "btree_cursors", issue = "107540")]
-    pub unsafe fn upper_bound_mut<Q: ?Sized>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, T, A>
+    pub fn upper_bound_mut<Q: ?Sized>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, T, A>
     where
         T: Borrow<Q> + Ord,
         Q: Ord,
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index b4f08debc93..28e4217e303 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -102,6 +102,8 @@
 #![feature(async_fn_traits)]
 #![feature(async_iterator)]
 #![feature(box_uninit_write)]
+#![feature(bstr)]
+#![feature(bstr_internals)]
 #![feature(clone_to_uninit)]
 #![feature(coerce_unsized)]
 #![feature(const_eval_select)]
@@ -228,6 +230,8 @@ mod boxed {
     pub use std::boxed::Box;
 }
 pub mod borrow;
+#[unstable(feature = "bstr", issue = "134915")]
+pub mod bstr;
 pub mod collections;
 #[cfg(all(not(no_rc), not(no_sync), not(no_global_oom_handling)))]
 pub mod ffi;
diff --git a/library/core/src/bstr.rs b/library/core/src/bstr.rs
new file mode 100644
index 00000000000..74e07f3d242
--- /dev/null
+++ b/library/core/src/bstr.rs
@@ -0,0 +1,581 @@
+//! The `ByteStr` type and trait implementations.
+
+use crate::borrow::{Borrow, BorrowMut};
+use crate::cmp::Ordering;
+use crate::ops::{
+    Deref, DerefMut, DerefPure, Index, IndexMut, Range, RangeFrom, RangeFull, RangeInclusive,
+    RangeTo, RangeToInclusive,
+};
+use crate::{fmt, hash};
+
+/// A wrapper for `&[u8]` representing a human-readable string that's conventionally, but not
+/// always, UTF-8.
+///
+/// Unlike `&str`, this type permits non-UTF-8 contents, making it suitable for user input,
+/// non-native filenames (as `Path` only supports native filenames), and other applications that
+/// need to round-trip whatever data the user provides.
+///
+/// For an owned, growable byte string buffer, use
+/// [`ByteString`](../../std/bstr/struct.ByteString.html).
+///
+/// `ByteStr` implements `Deref` to `[u8]`, so all methods available on `[u8]` are available on
+/// `ByteStr`.
+///
+/// # Representation
+///
+/// A `&ByteStr` has the same representation as a `&str`. That is, a `&ByteStr` is a wide pointer
+/// which includes a pointer to some bytes and a length.
+///
+/// # Trait implementations
+///
+/// The `ByteStr` type has a number of trait implementations, and in particular, defines equality
+/// and comparisons between `&ByteStr`, `&str`, and `&[u8]`, for convenience.
+///
+/// The `Debug` implementation for `ByteStr` shows its bytes as a normal string, with invalid UTF-8
+/// presented as hex escape sequences.
+///
+/// The `Display` implementation behaves as if the `ByteStr` were first lossily converted to a
+/// `str`, with invalid UTF-8 presented as the Unicode replacement character: �
+///
+#[unstable(feature = "bstr", issue = "134915")]
+#[repr(transparent)]
+#[doc(alias = "BStr")]
+pub struct ByteStr(pub [u8]);
+
+impl ByteStr {
+    /// Creates a `ByteStr` slice from anything that can be converted to a byte slice.
+    ///
+    /// This is a zero-cost conversion.
+    ///
+    /// # Example
+    ///
+    /// You can create a `ByteStr` from a byte array, a byte slice or a string slice:
+    ///
+    /// ```
+    /// # #![feature(bstr)]
+    /// # use std::bstr::ByteStr;
+    /// let a = ByteStr::new(b"abc");
+    /// let b = ByteStr::new(&b"abc"[..]);
+    /// let c = ByteStr::new("abc");
+    ///
+    /// assert_eq!(a, b);
+    /// assert_eq!(a, c);
+    /// ```
+    #[inline]
+    #[unstable(feature = "bstr", issue = "134915")]
+    pub fn new<B: ?Sized + AsRef<[u8]>>(bytes: &B) -> &Self {
+        ByteStr::from_bytes(bytes.as_ref())
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "bstr_internals", issue = "none")]
+    #[inline]
+    pub fn from_bytes(slice: &[u8]) -> &Self {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`, so we can turn a reference to
+        // the wrapped type into a reference to the wrapper type.
+        unsafe { &*(slice as *const [u8] as *const Self) }
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "bstr_internals", issue = "none")]
+    #[inline]
+    pub fn from_bytes_mut(slice: &mut [u8]) -> &mut Self {
+        // SAFETY: `ByteStr` is a transparent wrapper around `[u8]`, so we can turn a reference to
+        // the wrapped type into a reference to the wrapper type.
+        unsafe { &mut *(slice as *mut [u8] as *mut Self) }
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "bstr_internals", issue = "none")]
+    #[inline]
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Deref for ByteStr {
+    type Target = [u8];
+
+    #[inline]
+    fn deref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl DerefMut for ByteStr {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl DerefPure for ByteStr {}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl fmt::Debug for ByteStr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "\"")?;
+        for chunk in self.utf8_chunks() {
+            for c in chunk.valid().chars() {
+                match c {
+                    '\0' => write!(f, "\\0")?,
+                    '\x01'..='\x7f' => write!(f, "{}", (c as u8).escape_ascii())?,
+                    _ => write!(f, "{}", c.escape_debug())?,
+                }
+            }
+            write!(f, "{}", chunk.invalid().escape_ascii())?;
+        }
+        write!(f, "\"")?;
+        Ok(())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl fmt::Display for ByteStr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fn fmt_nopad(this: &ByteStr, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            for chunk in this.utf8_chunks() {
+                f.write_str(chunk.valid())?;
+                if !chunk.invalid().is_empty() {
+                    f.write_str("\u{FFFD}")?;
+                }
+            }
+            Ok(())
+        }
+
+        let Some(align) = f.align() else {
+            return fmt_nopad(self, f);
+        };
+        let nchars: usize = self
+            .utf8_chunks()
+            .map(|chunk| chunk.valid().len() + if chunk.invalid().is_empty() { 0 } else { 1 })
+            .sum();
+        let padding = f.width().unwrap_or(0).saturating_sub(nchars);
+        let fill = f.fill();
+        let (lpad, rpad) = match align {
+            fmt::Alignment::Left => (0, padding),
+            fmt::Alignment::Right => (padding, 0),
+            fmt::Alignment::Center => {
+                let half = padding / 2;
+                (half, half + padding % 2)
+            }
+        };
+        for _ in 0..lpad {
+            write!(f, "{fill}")?;
+        }
+        fmt_nopad(self, f)?;
+        for _ in 0..rpad {
+            write!(f, "{fill}")?;
+        }
+
+        Ok(())
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsRef<[u8]> for ByteStr {
+    #[inline]
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsRef<ByteStr> for ByteStr {
+    #[inline]
+    fn as_ref(&self) -> &ByteStr {
+        self
+    }
+}
+
+// `impl AsRef<ByteStr> for [u8]` omitted to avoid widespread inference failures
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsRef<ByteStr> for str {
+    #[inline]
+    fn as_ref(&self) -> &ByteStr {
+        ByteStr::new(self)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl AsMut<[u8]> for ByteStr {
+    #[inline]
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
+// `impl AsMut<ByteStr> for [u8]` omitted to avoid widespread inference failures
+
+// `impl Borrow<ByteStr> for [u8]` omitted to avoid widespread inference failures
+
+// `impl Borrow<ByteStr> for str` omitted to avoid widespread inference failures
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Borrow<[u8]> for ByteStr {
+    #[inline]
+    fn borrow(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+// `impl BorrowMut<ByteStr> for [u8]` omitted to avoid widespread inference failures
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl BorrowMut<[u8]> for ByteStr {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> Default for &'a ByteStr {
+    fn default() -> Self {
+        ByteStr::from_bytes(b"")
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> Default for &'a mut ByteStr {
+    fn default() -> Self {
+        ByteStr::from_bytes_mut(&mut [])
+    }
+}
+
+// Omitted due to inference failures
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a, const N: usize> From<&'a [u8; N]> for &'a ByteStr {
+//     #[inline]
+//     fn from(s: &'a [u8; N]) -> Self {
+//         ByteStr::from_bytes(s)
+//     }
+// }
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a> From<&'a [u8]> for &'a ByteStr {
+//     #[inline]
+//     fn from(s: &'a [u8]) -> Self {
+//         ByteStr::from_bytes(s)
+//     }
+// }
+
+// Omitted due to slice-from-array-issue-113238:
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a> From<&'a ByteStr> for &'a [u8] {
+//     #[inline]
+//     fn from(s: &'a ByteStr) -> Self {
+//         &s.0
+//     }
+// }
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a> From<&'a mut ByteStr> for &'a mut [u8] {
+//     #[inline]
+//     fn from(s: &'a mut ByteStr) -> Self {
+//         &mut s.0
+//     }
+// }
+
+// Omitted due to inference failures
+//
+// #[unstable(feature = "bstr", issue = "134915")]
+// impl<'a> From<&'a str> for &'a ByteStr {
+//     #[inline]
+//     fn from(s: &'a str) -> Self {
+//         ByteStr::from_bytes(s.as_bytes())
+//     }
+// }
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl hash::Hash for ByteStr {
+    #[inline]
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        self.0.hash(state);
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<usize> for ByteStr {
+    type Output = u8;
+
+    #[inline]
+    fn index(&self, idx: usize) -> &u8 {
+        &self.0[idx]
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeFull> for ByteStr {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, _: RangeFull) -> &ByteStr {
+        self
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<Range<usize>> for ByteStr {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: Range<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeInclusive<usize>> for ByteStr {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeInclusive<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeFrom<usize>> for ByteStr {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeFrom<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeTo<usize>> for ByteStr {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeTo<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Index<RangeToInclusive<usize>> for ByteStr {
+    type Output = ByteStr;
+
+    #[inline]
+    fn index(&self, r: RangeToInclusive<usize>) -> &ByteStr {
+        ByteStr::from_bytes(&self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<usize> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, idx: usize) -> &mut u8 {
+        &mut self.0[idx]
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeFull> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, _: RangeFull) -> &mut ByteStr {
+        self
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<Range<usize>> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, r: Range<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeInclusive<usize>> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, r: RangeInclusive<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeFrom<usize>> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, r: RangeFrom<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeTo<usize>> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, r: RangeTo<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl IndexMut<RangeToInclusive<usize>> for ByteStr {
+    #[inline]
+    fn index_mut(&mut self, r: RangeToInclusive<usize>) -> &mut ByteStr {
+        ByteStr::from_bytes_mut(&mut self.0[r])
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Eq for ByteStr {}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl PartialEq<ByteStr> for ByteStr {
+    #[inline]
+    fn eq(&self, other: &ByteStr) -> bool {
+        &self.0 == &other.0
+    }
+}
+
+#[doc(hidden)]
+#[macro_export]
+#[unstable(feature = "bstr_internals", issue = "none")]
+macro_rules! impl_partial_eq {
+    ($lhs:ty, $rhs:ty) => {
+        #[allow(unused_lifetimes)]
+        impl<'a> PartialEq<$rhs> for $lhs {
+            #[inline]
+            fn eq(&self, other: &$rhs) -> bool {
+                let other: &[u8] = other.as_ref();
+                PartialEq::eq(self.as_bytes(), other)
+            }
+        }
+
+        #[allow(unused_lifetimes)]
+        impl<'a> PartialEq<$lhs> for $rhs {
+            #[inline]
+            fn eq(&self, other: &$lhs) -> bool {
+                let this: &[u8] = self.as_ref();
+                PartialEq::eq(this, other.as_bytes())
+            }
+        }
+    };
+}
+
+#[doc(hidden)]
+#[unstable(feature = "bstr_internals", issue = "none")]
+pub use impl_partial_eq;
+
+#[doc(hidden)]
+#[macro_export]
+#[unstable(feature = "bstr_internals", issue = "none")]
+macro_rules! impl_partial_eq_ord {
+    ($lhs:ty, $rhs:ty) => {
+        $crate::bstr::impl_partial_eq!($lhs, $rhs);
+
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<'a> PartialOrd<$rhs> for $lhs {
+            #[inline]
+            fn partial_cmp(&self, other: &$rhs) -> Option<Ordering> {
+                let other: &[u8] = other.as_ref();
+                PartialOrd::partial_cmp(self.as_bytes(), other)
+            }
+        }
+
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<'a> PartialOrd<$lhs> for $rhs {
+            #[inline]
+            fn partial_cmp(&self, other: &$lhs) -> Option<Ordering> {
+                let this: &[u8] = self.as_ref();
+                PartialOrd::partial_cmp(this, other.as_bytes())
+            }
+        }
+    };
+}
+
+#[doc(hidden)]
+#[unstable(feature = "bstr_internals", issue = "none")]
+pub use impl_partial_eq_ord;
+
+#[doc(hidden)]
+#[macro_export]
+#[unstable(feature = "bstr_internals", issue = "none")]
+macro_rules! impl_partial_eq_n {
+    ($lhs:ty, $rhs:ty) => {
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<const N: usize> PartialEq<$rhs> for $lhs {
+            #[inline]
+            fn eq(&self, other: &$rhs) -> bool {
+                let other: &[u8] = other.as_ref();
+                PartialEq::eq(self.as_bytes(), other)
+            }
+        }
+
+        #[allow(unused_lifetimes)]
+        #[unstable(feature = "bstr", issue = "134915")]
+        impl<const N: usize> PartialEq<$lhs> for $rhs {
+            #[inline]
+            fn eq(&self, other: &$lhs) -> bool {
+                let this: &[u8] = self.as_ref();
+                PartialEq::eq(this, other.as_bytes())
+            }
+        }
+    };
+}
+
+#[doc(hidden)]
+#[unstable(feature = "bstr_internals", issue = "none")]
+pub use impl_partial_eq_n;
+
+// PartialOrd with `[u8]` omitted to avoid inference failures
+impl_partial_eq!(ByteStr, [u8]);
+// PartialOrd with `&[u8]` omitted to avoid inference failures
+impl_partial_eq!(ByteStr, &[u8]);
+// PartialOrd with `str` omitted to avoid inference failures
+impl_partial_eq!(ByteStr, str);
+// PartialOrd with `&str` omitted to avoid inference failures
+impl_partial_eq!(ByteStr, &str);
+// PartialOrd with `[u8; N]` omitted to avoid inference failures
+impl_partial_eq_n!(ByteStr, [u8; N]);
+// PartialOrd with `[u8; N]` omitted to avoid inference failures
+impl_partial_eq_n!(ByteStr, &[u8; N]);
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl Ord for ByteStr {
+    #[inline]
+    fn cmp(&self, other: &ByteStr) -> Ordering {
+        Ord::cmp(&self.0, &other.0)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl PartialOrd for ByteStr {
+    #[inline]
+    fn partial_cmp(&self, other: &ByteStr) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&self.0, &other.0)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> TryFrom<&'a ByteStr> for &'a str {
+    type Error = crate::str::Utf8Error;
+
+    #[inline]
+    fn try_from(s: &'a ByteStr) -> Result<Self, Self::Error> {
+        crate::str::from_utf8(&s.0)
+    }
+}
+
+#[unstable(feature = "bstr", issue = "134915")]
+impl<'a> TryFrom<&'a mut ByteStr> for &'a mut str {
+    type Error = crate::str::Utf8Error;
+
+    #[inline]
+    fn try_from(s: &'a mut ByteStr) -> Result<Self, Self::Error> {
+        crate::str::from_utf8_mut(&mut s.0)
+    }
+}
diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs
index ec1aed53eaf..00300328b64 100644
--- a/library/core/src/clone.rs
+++ b/library/core/src/clone.rs
@@ -311,6 +311,16 @@ unsafe impl CloneToUninit for crate::ffi::CStr {
     }
 }
 
+#[unstable(feature = "bstr", issue = "134915")]
+unsafe impl CloneToUninit for crate::bstr::ByteStr {
+    #[inline]
+    #[cfg_attr(debug_assertions, track_caller)]
+    unsafe fn clone_to_uninit(&self, dst: *mut u8) {
+        // SAFETY: ByteStr is a `#[repr(transparent)]` wrapper around `[u8]`
+        unsafe { self.as_bytes().clone_to_uninit(dst) }
+    }
+}
+
 /// Implementations of `Clone` for primitive types.
 ///
 /// Implementations that cannot be described in Rust
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
index a033b8bd305..a1bf3a4d7a7 100644
--- a/library/core/src/fmt/mod.rs
+++ b/library/core/src/fmt/mod.rs
@@ -288,7 +288,7 @@ pub enum DebugAsHex {
 ///
 /// `FormattingOptions` is a [`Formatter`] without an attached [`Write`] trait.
 /// It is mainly used to construct `Formatter` instances.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 #[unstable(feature = "formatting_options", issue = "118117")]
 pub struct FormattingOptions {
     flags: u32,
@@ -508,6 +508,15 @@ impl FormattingOptions {
     }
 }
 
+#[unstable(feature = "formatting_options", issue = "118117")]
+impl Default for FormattingOptions {
+    /// Same as [`FormattingOptions::new()`].
+    fn default() -> Self {
+        // The `#[derive(Default)]` implementation would set `fill` to `\0` instead of space.
+        Self::new()
+    }
+}
+
 /// Configuration for formatting.
 ///
 /// A `Formatter` represents various options related to formatting. Users do not
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index f58eab3b1b1..01ed3cc69a2 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -111,6 +111,8 @@
 #![feature(array_ptr_get)]
 #![feature(asm_experimental_arch)]
 #![feature(bigint_helper_methods)]
+#![feature(bstr)]
+#![feature(bstr_internals)]
 #![feature(const_carrying_mul_add)]
 #![feature(const_eval_select)]
 #![feature(core_intrinsics)]
@@ -336,6 +338,8 @@ pub mod ascii;
 pub mod asserting;
 #[unstable(feature = "async_iterator", issue = "79024")]
 pub mod async_iter;
+#[unstable(feature = "bstr", issue = "134915")]
+pub mod bstr;
 pub mod cell;
 pub mod char;
 pub mod ffi;
diff --git a/library/core/tests/bstr.rs b/library/core/tests/bstr.rs
new file mode 100644
index 00000000000..5fecd0a4084
--- /dev/null
+++ b/library/core/tests/bstr.rs
@@ -0,0 +1,54 @@
+#![feature(bstr)]
+
+use core::ByteStr;
+
+#[test]
+fn test_debug() {
+    assert_eq!(
+        r#""\0\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x11\x12\r\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f \x7f\x80\x81\xfe\xff""#,
+        format!("{:?}", ByteStr::new(b"\0\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x11\x12\r\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f \x7f\x80\x81\xfe\xff")),
+    );
+}
+
+#[test]
+fn test_display() {
+    let b1 = ByteStr::new("abc");
+    let b2 = ByteStr::new(b"\xf0\x28\x8c\xbc");
+
+    assert_eq!(&format!("{b1}"), "abc");
+    assert_eq!(&format!("{b2}"), "�(��");
+
+    assert_eq!(&format!("{b1:<7}!"), "abc    !");
+    assert_eq!(&format!("{b1:>7}!"), "    abc!");
+    assert_eq!(&format!("{b1:^7}!"), "  abc  !");
+    assert_eq!(&format!("{b1:^6}!"), " abc  !");
+    assert_eq!(&format!("{b1:-<7}!"), "abc----!");
+    assert_eq!(&format!("{b1:->7}!"), "----abc!");
+    assert_eq!(&format!("{b1:-^7}!"), "--abc--!");
+    assert_eq!(&format!("{b1:-^6}!"), "-abc--!");
+
+    assert_eq!(&format!("{b2:<7}!"), "�(��   !");
+    assert_eq!(&format!("{b2:>7}!"), "   �(��!");
+    assert_eq!(&format!("{b2:^7}!"), " �(��  !");
+    assert_eq!(&format!("{b2:^6}!"), " �(�� !");
+    assert_eq!(&format!("{b2:-<7}!"), "�(��---!");
+    assert_eq!(&format!("{b2:->7}!"), "---�(��!");
+    assert_eq!(&format!("{b2:-^7}!"), "-�(��--!");
+    assert_eq!(&format!("{b2:-^6}!"), "-�(��-!");
+
+    assert_eq!(&format!("{b1:<2}!"), "abc!");
+    assert_eq!(&format!("{b1:>2}!"), "abc!");
+    assert_eq!(&format!("{b1:^2}!"), "abc!");
+    assert_eq!(&format!("{b1:-<2}!"), "abc!");
+    assert_eq!(&format!("{b1:->2}!"), "abc!");
+    assert_eq!(&format!("{b1:-^2}!"), "abc!");
+
+    assert_eq!(&format!("{b2:<3}!"), "�(��!");
+    assert_eq!(&format!("{b2:>3}!"), "�(��!");
+    assert_eq!(&format!("{b2:^3}!"), "�(��!");
+    assert_eq!(&format!("{b2:^2}!"), "�(��!");
+    assert_eq!(&format!("{b2:-<3}!"), "�(��!");
+    assert_eq!(&format!("{b2:->3}!"), "�(��!");
+    assert_eq!(&format!("{b2:-^3}!"), "�(��!");
+    assert_eq!(&format!("{b2:-^2}!"), "�(��!");
+}
diff --git a/library/core/tests/fmt/mod.rs b/library/core/tests/fmt/mod.rs
index 2c93a9bc80d..025c69c4f62 100644
--- a/library/core/tests/fmt/mod.rs
+++ b/library/core/tests/fmt/mod.rs
@@ -52,6 +52,12 @@ fn test_maybe_uninit_short() {
 }
 
 #[test]
+fn formatting_options_ctor() {
+    use core::fmt::FormattingOptions;
+    assert_eq!(FormattingOptions::new(), FormattingOptions::default());
+}
+
+#[test]
 fn formatting_options_flags() {
     use core::fmt::*;
     for sign in [None, Some(Sign::Plus), Some(Sign::Minus)] {
diff --git a/library/std/src/bstr.rs b/library/std/src/bstr.rs
new file mode 100644
index 00000000000..dd491771628
--- /dev/null
+++ b/library/std/src/bstr.rs
@@ -0,0 +1,4 @@
+//! The `ByteStr` and `ByteString` types and trait implementations.
+
+#[unstable(feature = "bstr", issue = "134915")]
+pub use alloc::bstr::{ByteStr, ByteString};
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 39f234e4ba6..acb3a0578e5 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -320,6 +320,8 @@
 // Library features (core):
 // tidy-alphabetical-start
 #![feature(array_chunks)]
+#![feature(bstr)]
+#![feature(bstr_internals)]
 #![feature(c_str_module)]
 #![feature(char_internals)]
 #![feature(clone_to_uninit)]
@@ -581,6 +583,8 @@ pub mod f64;
 pub mod thread;
 pub mod ascii;
 pub mod backtrace;
+#[unstable(feature = "bstr", issue = "134915")]
+pub mod bstr;
 pub mod collections;
 pub mod env;
 pub mod error;
diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index cf55fff4078..3cf25373b89 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -1338,7 +1338,7 @@ impl Step for CrtBeginEnd {
             .file(crtbegin_src)
             .file(crtend_src);
 
-        // Those flags are defined in src/llvm-project/compiler-rt/lib/crt/CMakeLists.txt
+        // Those flags are defined in src/llvm-project/compiler-rt/lib/builtins/CMakeLists.txt
         // Currently only consumer of those objects is musl, which use .init_array/.fini_array
         // instead of .ctors/.dtors
         cfg.flag("-std=c11")
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index 9f3e4d9cc89..0d3ab6ad97d 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -87,7 +87,7 @@ impl Step for CrateBootstrap {
             &[],
         );
         let crate_name = path.rsplit_once('/').unwrap().1;
-        run_cargo_test(cargo, &[], &[], crate_name, crate_name, compiler, bootstrap_host, builder);
+        run_cargo_test(cargo, &[], &[], crate_name, crate_name, bootstrap_host, builder);
     }
 }
 
@@ -143,7 +143,6 @@ You can skip linkcheck with --skip src/tools/linkchecker"
             &[],
             "linkchecker",
             "linkchecker self tests",
-            compiler,
             bootstrap_host,
             builder,
         );
@@ -312,7 +311,7 @@ impl Step for Cargo {
         );
 
         // NOTE: can't use `run_cargo_test` because we need to overwrite `PATH`
-        let mut cargo = prepare_cargo_test(cargo, &[], &[], "cargo", compiler, self.host, builder);
+        let mut cargo = prepare_cargo_test(cargo, &[], &[], "cargo", self.host, builder);
 
         // Don't run cross-compile tests, we may not have cross-compiled libstd libs
         // available.
@@ -397,7 +396,7 @@ impl Step for RustAnalyzer {
         cargo.env("SKIP_SLOW_TESTS", "1");
 
         cargo.add_rustc_lib_path(builder);
-        run_cargo_test(cargo, &[], &[], "rust-analyzer", "rust-analyzer", compiler, host, builder);
+        run_cargo_test(cargo, &[], &[], "rust-analyzer", "rust-analyzer", host, builder);
     }
 }
 
@@ -445,7 +444,7 @@ impl Step for Rustfmt {
 
         cargo.add_rustc_lib_path(builder);
 
-        run_cargo_test(cargo, &[], &[], "rustfmt", "rustfmt", compiler, host, builder);
+        run_cargo_test(cargo, &[], &[], "rustfmt", "rustfmt", host, builder);
     }
 }
 
@@ -565,7 +564,7 @@ impl Step for Miri {
 
         // We can NOT use `run_cargo_test` since Miri's integration tests do not use the usual test
         // harness and therefore do not understand the flags added by `add_flags_and_try_run_test`.
-        let mut cargo = prepare_cargo_test(cargo, &[], &[], "miri", host_compiler, host, builder);
+        let mut cargo = prepare_cargo_test(cargo, &[], &[], "miri", host, builder);
 
         // miri tests need to know about the stage sysroot
         cargo.env("MIRI_SYSROOT", &miri_sysroot);
@@ -713,16 +712,7 @@ impl Step for CompiletestTest {
             &[],
         );
         cargo.allow_features("test");
-        run_cargo_test(
-            cargo,
-            &[],
-            &[],
-            "compiletest",
-            "compiletest self test",
-            compiler,
-            host,
-            builder,
-        );
+        run_cargo_test(cargo, &[], &[], "compiletest", "compiletest self test", host, builder);
     }
 }
 
@@ -769,7 +759,7 @@ impl Step for Clippy {
         cargo.env("HOST_LIBS", host_libs);
 
         cargo.add_rustc_lib_path(builder);
-        let cargo = prepare_cargo_test(cargo, &[], &[], "clippy", compiler, host, builder);
+        let cargo = prepare_cargo_test(cargo, &[], &[], "clippy", host, builder);
 
         let _guard = builder.msg_sysroot_tool(Kind::Test, compiler.stage, "clippy", host, host);
 
@@ -1294,7 +1284,6 @@ impl Step for CrateRunMakeSupport {
             &[],
             "run-make-support",
             "run-make-support self test",
-            compiler,
             host,
             builder,
         );
@@ -1334,16 +1323,7 @@ impl Step for CrateBuildHelper {
             &[],
         );
         cargo.allow_features("test");
-        run_cargo_test(
-            cargo,
-            &[],
-            &[],
-            "build_helper",
-            "build_helper self test",
-            compiler,
-            host,
-            builder,
-        );
+        run_cargo_test(cargo, &[], &[], "build_helper", "build_helper self test", host, builder);
     }
 }
 
@@ -2540,19 +2520,17 @@ impl Step for CrateLibrustc {
 /// Given a `cargo test` subcommand, add the appropriate flags and run it.
 ///
 /// Returns whether the test succeeded.
-#[allow(clippy::too_many_arguments)] // FIXME: reduce the number of args and remove this.
 fn run_cargo_test<'a>(
-    cargo: impl Into<BootstrapCommand>,
+    cargo: builder::Cargo,
     libtest_args: &[&str],
     crates: &[String],
     primary_crate: &str,
     description: impl Into<Option<&'a str>>,
-    compiler: Compiler,
     target: TargetSelection,
     builder: &Builder<'_>,
 ) -> bool {
-    let mut cargo =
-        prepare_cargo_test(cargo, libtest_args, crates, primary_crate, compiler, target, builder);
+    let compiler = cargo.compiler();
+    let mut cargo = prepare_cargo_test(cargo, libtest_args, crates, primary_crate, target, builder);
     let _time = helpers::timeit(builder);
     let _group = description.into().and_then(|what| {
         builder.msg_sysroot_tool(Kind::Test, compiler.stage, what, compiler.host, target)
@@ -2573,15 +2551,15 @@ fn run_cargo_test<'a>(
 
 /// Given a `cargo test` subcommand, pass it the appropriate test flags given a `builder`.
 fn prepare_cargo_test(
-    cargo: impl Into<BootstrapCommand>,
+    cargo: builder::Cargo,
     libtest_args: &[&str],
     crates: &[String],
     primary_crate: &str,
-    compiler: Compiler,
     target: TargetSelection,
     builder: &Builder<'_>,
 ) -> BootstrapCommand {
-    let mut cargo = cargo.into();
+    let compiler = cargo.compiler();
+    let mut cargo: BootstrapCommand = cargo.into();
 
     // Propagate `--bless` if it has not already been set/unset
     // Any tools that want to use this should bless if `RUSTC_BLESS` is set to
@@ -2793,7 +2771,6 @@ impl Step for Crate {
             &self.crates,
             &self.crates[0],
             &*crate_description(&self.crates),
-            compiler,
             target,
             builder,
         );
@@ -2895,7 +2872,6 @@ impl Step for CrateRustdoc {
             &["rustdoc:0.0.0".to_string()],
             "rustdoc",
             "rustdoc",
-            compiler,
             target,
             builder,
         );
@@ -2956,7 +2932,6 @@ impl Step for CrateRustdocJsonTypes {
             &["rustdoc-json-types".to_string()],
             "rustdoc-json-types",
             "rustdoc-json-types",
-            compiler,
             target,
             builder,
         );
@@ -3113,23 +3088,25 @@ impl Step for Bootstrap {
         // Use `python -m unittest` manually if you want to pass arguments.
         check_bootstrap.delay_failure().run(builder);
 
-        let mut cmd = command(&builder.initial_cargo);
-        cmd.arg("test")
-            .current_dir(builder.src.join("src/bootstrap"))
-            .env("RUSTFLAGS", "--cfg test -Cdebuginfo=2")
+        let mut cargo = tool::prepare_tool_cargo(
+            builder,
+            compiler,
+            Mode::ToolBootstrap,
+            host,
+            Kind::Test,
+            "src/bootstrap",
+            SourceType::InTree,
+            &[],
+        );
+
+        cargo
+            .rustflag("-Cdebuginfo=2")
             .env("CARGO_TARGET_DIR", builder.out.join("bootstrap"))
-            .env("RUSTC_BOOTSTRAP", "1")
-            .env("RUSTDOC", builder.rustdoc(compiler))
-            .env("RUSTC", &builder.initial_rustc);
-        if let Some(flags) = option_env!("RUSTFLAGS") {
-            // Use the same rustc flags for testing as for "normal" compilation,
-            // so that Cargo doesn’t recompile the entire dependency graph every time:
-            // https://github.com/rust-lang/rust/issues/49215
-            cmd.env("RUSTFLAGS", flags);
-        }
+            .env("RUSTC_BOOTSTRAP", "1");
+
         // bootstrap tests are racy on directory creation so just run them one at a time.
         // Since there's not many this shouldn't be a problem.
-        run_cargo_test(cmd, &["--test-threads=1"], &[], "bootstrap", None, compiler, host, builder);
+        run_cargo_test(cargo, &["--test-threads=1"], &[], "bootstrap", None, host, builder);
     }
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -3254,7 +3231,7 @@ impl Step for RustInstaller {
             bootstrap_host,
             bootstrap_host,
         );
-        run_cargo_test(cargo, &[], &[], "installer", None, compiler, bootstrap_host, builder);
+        run_cargo_test(cargo, &[], &[], "installer", None, bootstrap_host, builder);
 
         // We currently don't support running the test.sh script outside linux(?) environments.
         // Eventually this should likely migrate to #[test]s in rust-installer proper rather than a
@@ -3639,16 +3616,7 @@ impl Step for TestFloatParse {
             &[],
         );
 
-        run_cargo_test(
-            cargo_test,
-            &[],
-            &[],
-            crate_name,
-            crate_name,
-            compiler,
-            bootstrap_host,
-            builder,
-        );
+        run_cargo_test(cargo_test, &[], &[], crate_name, crate_name, bootstrap_host, builder);
 
         // Run the actual parse tests.
         let mut cargo_run = tool::prepare_tool_cargo(
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index f9fb19ddb09..6b792108784 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -121,6 +121,10 @@ impl Cargo {
         cargo
     }
 
+    pub fn compiler(&self) -> Compiler {
+        self.compiler
+    }
+
     pub fn into_cmd(self) -> BootstrapCommand {
         self.into()
     }
diff --git a/src/bootstrap/src/core/config/tests.rs b/src/bootstrap/src/core/config/tests.rs
index c5e578ff351..f0a185ee3a7 100644
--- a/src/bootstrap/src/core/config/tests.rs
+++ b/src/bootstrap/src/core/config/tests.rs
@@ -92,7 +92,7 @@ fn detect_src_and_out() {
             //     `{build-dir}/bootstrap/debug/deps/bootstrap-c7ee91d5661e2804`
             // `{build-dir}` can be anywhere, not just in the rust project directory.
             let dep = Path::new(args.first().unwrap());
-            let expected_out = dep.ancestors().nth(4).unwrap();
+            let expected_out = dep.ancestors().nth(5).unwrap();
 
             assert_eq!(&cfg.out, expected_out);
         }
diff --git a/src/ci/github-actions/jobs.yml b/src/ci/github-actions/jobs.yml
index c5b33a45db7..5e95e3721df 100644
--- a/src/ci/github-actions/jobs.yml
+++ b/src/ci/github-actions/jobs.yml
@@ -48,6 +48,8 @@ runners:
     <<: *base-job
 
   - &job-aarch64-linux
+    # Free some disk space to avoid running out of space during the build.
+    free_disk: true
     os: ubuntu-22.04-arm
 
 envs:
diff --git a/src/doc/rustc-dev-guide/examples/rustc-driver-example.rs b/src/doc/rustc-dev-guide/examples/rustc-driver-example.rs
index 576bbcea965..8983915d78a 100644
--- a/src/doc/rustc-dev-guide/examples/rustc-driver-example.rs
+++ b/src/doc/rustc-dev-guide/examples/rustc-driver-example.rs
@@ -18,8 +18,8 @@ use std::path::Path;
 
 use rustc_ast_pretty::pprust::item_to_string;
 use rustc_data_structures::sync::Lrc;
-use rustc_driver::{Compilation, RunCompiler};
-use rustc_interface::interface::Compiler;
+use rustc_driver::{Compilation, run_compiler};
+use rustc_interface::interface::{Compiler, Config};
 use rustc_middle::ty::TyCtxt;
 
 struct MyFileLoader;
@@ -51,6 +51,10 @@ fn main() {
 struct MyCallbacks;
 
 impl rustc_driver::Callbacks for MyCallbacks {
+    fn config(&mut self, config: &mut Config) {
+        config.file_loader = Some(Box::new(MyFileLoader));
+    }
+
     fn after_crate_root_parsing(
         &mut self,
         _compiler: &Compiler,
@@ -83,10 +87,5 @@ impl rustc_driver::Callbacks for MyCallbacks {
 }
 
 fn main() {
-    match RunCompiler::new(&["main.rs".to_string()], &mut MyCallbacks) {
-        mut compiler => {
-            compiler.set_file_loader(Some(Box::new(MyFileLoader)));
-            compiler.run();
-        }
-    }
+    run_compiler(&["main.rs".to_string()], &mut MyCallbacks);
 }
diff --git a/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs b/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs
index 90a85d5db21..c894b60444a 100644
--- a/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs
+++ b/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs
@@ -18,8 +18,8 @@ use std::path::Path;
 
 use rustc_ast_pretty::pprust::item_to_string;
 use rustc_data_structures::sync::Lrc;
-use rustc_driver::{Compilation, RunCompiler};
-use rustc_interface::interface::Compiler;
+use rustc_driver::{Compilation, run_compiler};
+use rustc_interface::interface::{Compiler, Config};
 use rustc_middle::ty::TyCtxt;
 
 struct MyFileLoader;
@@ -51,6 +51,10 @@ fn main() {
 struct MyCallbacks;
 
 impl rustc_driver::Callbacks for MyCallbacks {
+    fn config(&mut self, config: &mut Config) {
+        config.file_loader = Some(Box::new(MyFileLoader));
+    }
+
     fn after_crate_root_parsing(
         &mut self,
         _compiler: &Compiler,
@@ -90,10 +94,5 @@ impl rustc_driver::Callbacks for MyCallbacks {
 }
 
 fn main() {
-    match RunCompiler::new(&["main.rs".to_string()], &mut MyCallbacks) {
-        mut compiler => {
-            compiler.set_file_loader(Some(Box::new(MyFileLoader)));
-            compiler.run();
-        }
-    }
+    run_compiler(&["main.rs".to_string()], &mut MyCallbacks);
 }
diff --git a/src/doc/rustc-dev-guide/src/rustc-driver/intro.md b/src/doc/rustc-dev-guide/src/rustc-driver/intro.md
index a6234dc129f..40500e6bc7a 100644
--- a/src/doc/rustc-dev-guide/src/rustc-driver/intro.md
+++ b/src/doc/rustc-dev-guide/src/rustc-driver/intro.md
@@ -6,7 +6,7 @@ The [`rustc_driver`] is essentially `rustc`'s `main` function.
 It acts as the glue for running the various phases of the compiler in the correct order,
 using the interface defined in the [`rustc_interface`] crate. Where possible, using [`rustc_driver`] rather than [`rustc_interface`] is recommended.
 
-The main entry point of [`rustc_driver`] is [`rustc_driver::RunCompiler`][rd_rc].
+The main entry point of [`rustc_driver`] is [`rustc_driver::run_compiler`][rd_rc].
 This builder accepts the same command-line args as rustc as well as an implementation of [`Callbacks`][cb] and a couple of other optional options.
 [`Callbacks`][cb] is a `trait` that allows for custom compiler configuration,
 as well as allowing custom code to run after different phases of the compilation.
@@ -40,7 +40,7 @@ specifically [`rustc_driver_impl::run_compiler`][rdi_rc]
 [cb]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/trait.Callbacks.html
 [example]: https://github.com/rust-lang/rustc-dev-guide/blob/master/examples/rustc-interface-example.rs
 [i_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/interface/fn.run_compiler.html
-[rd_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/struct.RunCompiler.html
+[rd_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/fn.run_compiler.html
 [rdi_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver_impl/fn.run_compiler.html
 [stupid-stats]: https://github.com/nrc/stupid-stats
 [`nightly-rustc`]: https://doc.rust-lang.org/nightly/nightly-rustc/
diff --git a/src/librustdoc/clean/cfg.rs b/src/librustdoc/clean/cfg.rs
index bfa789b1f39..bdd44b4a993 100644
--- a/src/librustdoc/clean/cfg.rs
+++ b/src/librustdoc/clean/cfg.rs
@@ -389,6 +389,49 @@ fn write_with_opt_paren<T: fmt::Display>(
     Ok(())
 }
 
+impl Display<'_> {
+    fn display_sub_cfgs(
+        &self,
+        fmt: &mut fmt::Formatter<'_>,
+        sub_cfgs: &[Cfg],
+        separator: &str,
+    ) -> fmt::Result {
+        let short_longhand = self.1.is_long() && {
+            let all_crate_features =
+                sub_cfgs.iter().all(|sub_cfg| matches!(sub_cfg, Cfg::Cfg(sym::feature, Some(_))));
+            let all_target_features = sub_cfgs
+                .iter()
+                .all(|sub_cfg| matches!(sub_cfg, Cfg::Cfg(sym::target_feature, Some(_))));
+
+            if all_crate_features {
+                fmt.write_str("crate features ")?;
+                true
+            } else if all_target_features {
+                fmt.write_str("target features ")?;
+                true
+            } else {
+                false
+            }
+        };
+
+        for (i, sub_cfg) in sub_cfgs.iter().enumerate() {
+            if i != 0 {
+                fmt.write_str(separator)?;
+            }
+            if let (true, Cfg::Cfg(_, Some(feat))) = (short_longhand, sub_cfg) {
+                if self.1.is_html() {
+                    write!(fmt, "<code>{feat}</code>")?;
+                } else {
+                    write!(fmt, "`{feat}`")?;
+                }
+            } else {
+                write_with_opt_paren(fmt, !sub_cfg.is_all(), Display(sub_cfg, self.1))?;
+            }
+        }
+        Ok(())
+    }
+}
+
 impl fmt::Display for Display<'_> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self.0 {
@@ -408,79 +451,9 @@ impl fmt::Display for Display<'_> {
 
             Cfg::Any(ref sub_cfgs) => {
                 let separator = if sub_cfgs.iter().all(Cfg::is_simple) { " or " } else { ", or " };
-
-                let short_longhand = self.1.is_long() && {
-                    let all_crate_features = sub_cfgs
-                        .iter()
-                        .all(|sub_cfg| matches!(sub_cfg, Cfg::Cfg(sym::feature, Some(_))));
-                    let all_target_features = sub_cfgs
-                        .iter()
-                        .all(|sub_cfg| matches!(sub_cfg, Cfg::Cfg(sym::target_feature, Some(_))));
-
-                    if all_crate_features {
-                        fmt.write_str("crate features ")?;
-                        true
-                    } else if all_target_features {
-                        fmt.write_str("target features ")?;
-                        true
-                    } else {
-                        false
-                    }
-                };
-
-                for (i, sub_cfg) in sub_cfgs.iter().enumerate() {
-                    if i != 0 {
-                        fmt.write_str(separator)?;
-                    }
-                    if let (true, Cfg::Cfg(_, Some(feat))) = (short_longhand, sub_cfg) {
-                        if self.1.is_html() {
-                            write!(fmt, "<code>{feat}</code>")?;
-                        } else {
-                            write!(fmt, "`{feat}`")?;
-                        }
-                    } else {
-                        write_with_opt_paren(fmt, !sub_cfg.is_all(), Display(sub_cfg, self.1))?;
-                    }
-                }
-                Ok(())
-            }
-
-            Cfg::All(ref sub_cfgs) => {
-                let short_longhand = self.1.is_long() && {
-                    let all_crate_features = sub_cfgs
-                        .iter()
-                        .all(|sub_cfg| matches!(sub_cfg, Cfg::Cfg(sym::feature, Some(_))));
-                    let all_target_features = sub_cfgs
-                        .iter()
-                        .all(|sub_cfg| matches!(sub_cfg, Cfg::Cfg(sym::target_feature, Some(_))));
-
-                    if all_crate_features {
-                        fmt.write_str("crate features ")?;
-                        true
-                    } else if all_target_features {
-                        fmt.write_str("target features ")?;
-                        true
-                    } else {
-                        false
-                    }
-                };
-
-                for (i, sub_cfg) in sub_cfgs.iter().enumerate() {
-                    if i != 0 {
-                        fmt.write_str(" and ")?;
-                    }
-                    if let (true, Cfg::Cfg(_, Some(feat))) = (short_longhand, sub_cfg) {
-                        if self.1.is_html() {
-                            write!(fmt, "<code>{feat}</code>")?;
-                        } else {
-                            write!(fmt, "`{feat}`")?;
-                        }
-                    } else {
-                        write_with_opt_paren(fmt, !sub_cfg.is_simple(), Display(sub_cfg, self.1))?;
-                    }
-                }
-                Ok(())
+                self.display_sub_cfgs(fmt, sub_cfgs, separator)
             }
+            Cfg::All(ref sub_cfgs) => self.display_sub_cfgs(fmt, sub_cfgs, " and "),
 
             Cfg::True => fmt.write_str("everywhere"),
             Cfg::False => fmt.write_str("nowhere"),
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 0dda3466a71..ad67c2ba245 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -1,10 +1,10 @@
-use std::sync::atomic::AtomicBool;
-use std::sync::{Arc, LazyLock};
+use std::sync::LazyLock;
 use std::{io, mem};
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::unord::UnordSet;
+use rustc_driver::USING_INTERNAL_FEATURES;
 use rustc_errors::TerminalUrl;
 use rustc_errors::codes::*;
 use rustc_errors::emitter::{
@@ -221,7 +221,6 @@ pub(crate) fn create_config(
         ..
     }: RustdocOptions,
     RenderOptions { document_private, .. }: &RenderOptions,
-    using_internal_features: Arc<AtomicBool>,
 ) -> rustc_interface::Config {
     // Add the doc cfg into the doc build.
     cfgs.push("doc".to_string());
@@ -316,7 +315,7 @@ pub(crate) fn create_config(
         make_codegen_backend: None,
         registry: rustc_driver::diagnostics_registry(),
         ice_file: None,
-        using_internal_features,
+        using_internal_features: &USING_INTERNAL_FEATURES,
         expanded_args,
     }
 }
diff --git a/src/librustdoc/doctest.rs b/src/librustdoc/doctest.rs
index 009e9662933..8c3e28ecec3 100644
--- a/src/librustdoc/doctest.rs
+++ b/src/librustdoc/doctest.rs
@@ -193,7 +193,7 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
         make_codegen_backend: None,
         registry: rustc_driver::diagnostics_registry(),
         ice_file: None,
-        using_internal_features: Arc::default(),
+        using_internal_features: &rustc_driver::USING_INTERNAL_FEATURES,
         expanded_args: options.expanded_args.clone(),
     };
 
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 92935c72b47..20a8dc72491 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -150,8 +150,9 @@ pub(crate) fn comma_sep<T: Display>(
     items: impl Iterator<Item = T>,
     space_after_comma: bool,
 ) -> impl Display {
-    display_fn(move |f| {
-        for (i, item) in items.enumerate() {
+    let items = Cell::new(Some(items));
+    fmt::from_fn(move |f| {
+        for (i, item) in items.take().unwrap().enumerate() {
             if i != 0 {
                 write!(f, ",{}", if space_after_comma { " " } else { "" })?;
             }
@@ -165,7 +166,7 @@ pub(crate) fn print_generic_bounds<'a, 'tcx: 'a>(
     bounds: &'a [clean::GenericBound],
     cx: &'a Context<'tcx>,
 ) -> impl Display + 'a + Captures<'tcx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         let mut bounds_dup = FxHashSet::default();
 
         for (i, bound) in bounds.iter().filter(|b| bounds_dup.insert(*b)).enumerate() {
@@ -183,7 +184,7 @@ impl clean::GenericParamDef {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match &self.kind {
+        fmt::from_fn(move |f| match &self.kind {
             clean::GenericParamDefKind::Lifetime { outlives } => {
                 write!(f, "{}", self.name)?;
 
@@ -238,7 +239,7 @@ impl clean::Generics {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             let mut real_params = self.params.iter().filter(|p| !p.is_synthetic_param()).peekable();
             if real_params.peek().is_none() {
                 return Ok(());
@@ -268,12 +269,12 @@ pub(crate) fn print_where_clause<'a, 'tcx: 'a>(
     indent: usize,
     ending: Ending,
 ) -> impl Display + 'a + Captures<'tcx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         let mut where_predicates = gens
             .where_predicates
             .iter()
             .map(|pred| {
-                display_fn(move |f| {
+                fmt::from_fn(move |f| {
                     if f.alternate() {
                         f.write_str(" ")?;
                     } else {
@@ -376,17 +377,15 @@ impl clean::Lifetime {
 impl clean::ConstantKind {
     pub(crate) fn print(&self, tcx: TyCtxt<'_>) -> impl Display + '_ {
         let expr = self.expr(tcx);
-        display_fn(
-            move |f| {
-                if f.alternate() { f.write_str(&expr) } else { write!(f, "{}", Escape(&expr)) }
-            },
-        )
+        fmt::from_fn(move |f| {
+            if f.alternate() { f.write_str(&expr) } else { write!(f, "{}", Escape(&expr)) }
+        })
     }
 }
 
 impl clean::PolyTrait {
     fn print<'a, 'tcx: 'a>(&'a self, cx: &'a Context<'tcx>) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             print_higher_ranked_params_with_space(&self.generic_params, cx, "for").fmt(f)?;
             self.trait_.print(cx).fmt(f)
         })
@@ -398,7 +397,7 @@ impl clean::GenericBound {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match self {
+        fmt::from_fn(move |f| match self {
             clean::GenericBound::Outlives(lt) => write!(f, "{}", lt.print()),
             clean::GenericBound::TraitBound(ty, modifiers) => {
                 // `const` and `~const` trait bounds are experimental; don't render them.
@@ -430,7 +429,7 @@ impl clean::GenericBound {
 
 impl clean::GenericArgs {
     fn print<'a, 'tcx: 'a>(&'a self, cx: &'a Context<'tcx>) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             match self {
                 clean::GenericArgs::AngleBracketed { args, constraints } => {
                     if !args.is_empty() || !constraints.is_empty() {
@@ -950,7 +949,7 @@ fn tybounds<'a, 'tcx: 'a>(
     lt: &'a Option<clean::Lifetime>,
     cx: &'a Context<'tcx>,
 ) -> impl Display + 'a + Captures<'tcx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         for (i, bound) in bounds.iter().enumerate() {
             if i > 0 {
                 write!(f, " + ")?;
@@ -971,7 +970,7 @@ fn print_higher_ranked_params_with_space<'a, 'tcx: 'a>(
     cx: &'a Context<'tcx>,
     keyword: &'static str,
 ) -> impl Display + 'a + Captures<'tcx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         if !params.is_empty() {
             f.write_str(keyword)?;
             f.write_str(if f.alternate() { "<" } else { "&lt;" })?;
@@ -982,13 +981,13 @@ fn print_higher_ranked_params_with_space<'a, 'tcx: 'a>(
     })
 }
 
-pub(crate) fn anchor<'a, 'cx: 'a>(
+pub(crate) fn anchor<'a: 'cx, 'cx>(
     did: DefId,
     text: Symbol,
-    cx: &'cx Context<'_>,
-) -> impl Display + 'a {
-    let parts = href(did, cx);
-    display_fn(move |f| {
+    cx: &'cx Context<'a>,
+) -> impl Display + Captures<'a> + 'cx {
+    fmt::from_fn(move |f| {
+        let parts = href(did, cx);
         if let Ok((url, short_ty, fqp)) = parts {
             write!(
                 f,
@@ -1150,7 +1149,7 @@ fn fmt_type(
             }
         }
         clean::BorrowedRef { lifetime: ref l, mutability, type_: ref ty } => {
-            let lt = display_fn(|f| match l {
+            let lt = fmt::from_fn(|f| match l {
                 Some(l) => write!(f, "{} ", l.print()),
                 _ => Ok(()),
             });
@@ -1270,7 +1269,7 @@ impl clean::Type {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'b + Captures<'tcx> {
-        display_fn(move |f| fmt_type(self, f, false, cx))
+        fmt::from_fn(move |f| fmt_type(self, f, false, cx))
     }
 }
 
@@ -1279,7 +1278,7 @@ impl clean::Path {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'b + Captures<'tcx> {
-        display_fn(move |f| resolved_path(f, self.def_id(), self, false, false, cx))
+        fmt::from_fn(move |f| resolved_path(f, self.def_id(), self, false, false, cx))
     }
 }
 
@@ -1289,7 +1288,7 @@ impl clean::Impl {
         use_absolute: bool,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             f.write_str("impl")?;
             self.generics.print(cx).fmt(f)?;
             f.write_str(" ")?;
@@ -1407,7 +1406,7 @@ impl clean::Arguments {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             for (i, input) in self.values.iter().enumerate() {
                 write!(f, "{}: ", input.name)?;
                 input.type_.print(cx).fmt(f)?;
@@ -1447,7 +1446,7 @@ impl clean::FnDecl {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'b + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             let ellipsis = if self.c_variadic { ", ..." } else { "" };
             if f.alternate() {
                 write!(
@@ -1481,10 +1480,10 @@ impl clean::FnDecl {
         indent: usize,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             // First, generate the text form of the declaration, with no line wrapping, and count the bytes.
             let mut counter = WriteCounter(0);
-            write!(&mut counter, "{:#}", display_fn(|f| { self.inner_full_print(None, f, cx) }))
+            write!(&mut counter, "{:#}", fmt::from_fn(|f| { self.inner_full_print(None, f, cx) }))
                 .unwrap();
             // If the text form was over 80 characters wide, we will line-wrap our output.
             let line_wrapping_indent =
@@ -1566,7 +1565,7 @@ impl clean::FnDecl {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match &self.output {
+        fmt::from_fn(move |f| match &self.output {
             clean::Tuple(tys) if tys.is_empty() => Ok(()),
             ty if f.alternate() => {
                 write!(f, " -> {:#}", ty.print(cx))
@@ -1618,7 +1617,7 @@ pub(crate) fn visibility_print_with_space<'a, 'tcx: 'a>(
     };
 
     let is_doc_hidden = item.is_doc_hidden();
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         if is_doc_hidden {
             f.write_str("#[doc(hidden)] ")?;
         }
@@ -1692,7 +1691,7 @@ impl clean::Import {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match self.kind {
+        fmt::from_fn(move |f| match self.kind {
             clean::ImportKind::Simple(name) => {
                 if name == self.source.path.last() {
                     write!(f, "use {};", self.source.print(cx))
@@ -1716,7 +1715,7 @@ impl clean::ImportSource {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match self.did {
+        fmt::from_fn(move |f| match self.did {
             Some(did) => resolved_path(f, did, &self.path, true, false, cx),
             _ => {
                 for seg in &self.path.segments[..self.path.segments.len() - 1] {
@@ -1744,7 +1743,7 @@ impl clean::AssocItemConstraint {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| {
+        fmt::from_fn(move |f| {
             f.write_str(self.assoc.name.as_str())?;
             self.assoc.args.print(cx).fmt(f)?;
             match self.kind {
@@ -1765,7 +1764,7 @@ impl clean::AssocItemConstraint {
 }
 
 pub(crate) fn print_abi_with_space(abi: ExternAbi) -> impl Display {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         let quot = if f.alternate() { "\"" } else { "&quot;" };
         match abi {
             ExternAbi::Rust => Ok(()),
@@ -1783,7 +1782,7 @@ impl clean::GenericArg {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match self {
+        fmt::from_fn(move |f| match self {
             clean::GenericArg::Lifetime(lt) => lt.print().fmt(f),
             clean::GenericArg::Type(ty) => ty.print(cx).fmt(f),
             clean::GenericArg::Const(ct) => ct.print(cx.tcx()).fmt(f),
@@ -1797,24 +1796,9 @@ impl clean::Term {
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match self {
+        fmt::from_fn(move |f| match self {
             clean::Term::Type(ty) => ty.print(cx).fmt(f),
             clean::Term::Constant(ct) => ct.print(cx.tcx()).fmt(f),
         })
     }
 }
-
-pub(crate) fn display_fn(f: impl FnOnce(&mut fmt::Formatter<'_>) -> fmt::Result) -> impl Display {
-    struct WithFormatter<F>(Cell<Option<F>>);
-
-    impl<F> Display for WithFormatter<F>
-    where
-        F: FnOnce(&mut fmt::Formatter<'_>) -> fmt::Result,
-    {
-        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            (self.0.take()).unwrap()(f)
-        }
-    }
-
-    WithFormatter(Cell::new(Some(f)))
-}
diff --git a/src/librustdoc/html/highlight.rs b/src/librustdoc/html/highlight.rs
index 62cf2b63f7f..7b2aee4b4a5 100644
--- a/src/librustdoc/html/highlight.rs
+++ b/src/librustdoc/html/highlight.rs
@@ -233,7 +233,7 @@ pub(super) fn write_code(
     out: &mut impl Write,
     src: &str,
     href_context: Option<HrefContext<'_, '_>>,
-    decoration_info: Option<DecorationInfo>,
+    decoration_info: Option<&DecorationInfo>,
 ) {
     // This replace allows to fix how the code source with DOS backline characters is displayed.
     let src = src.replace("\r\n", "\n");
@@ -510,12 +510,12 @@ struct Decorations {
 }
 
 impl Decorations {
-    fn new(info: DecorationInfo) -> Self {
+    fn new(info: &DecorationInfo) -> Self {
         // Extract tuples (start, end, kind) into separate sequences of (start, kind) and (end).
         let (mut starts, mut ends): (Vec<_>, Vec<_>) = info
             .0
-            .into_iter()
-            .flat_map(|(kind, ranges)| ranges.into_iter().map(move |(lo, hi)| ((lo, kind), hi)))
+            .iter()
+            .flat_map(|(&kind, ranges)| ranges.into_iter().map(move |&(lo, hi)| ((lo, kind), hi)))
             .unzip();
 
         // Sort the sequences in document order.
@@ -542,7 +542,7 @@ struct Classifier<'src> {
 impl<'src> Classifier<'src> {
     /// Takes as argument the source code to HTML-ify, the rust edition to use and the source code
     /// file span which will be used later on by the `span_correspondence_map`.
-    fn new(src: &str, file_span: Span, decoration_info: Option<DecorationInfo>) -> Classifier<'_> {
+    fn new(src: &'src str, file_span: Span, decoration_info: Option<&DecorationInfo>) -> Self {
         let tokens = PeekIter::new(TokenIter { src, cursor: Cursor::new(src) });
         let decorations = decoration_info.map(Decorations::new);
         Classifier {
diff --git a/src/librustdoc/html/highlight/tests.rs b/src/librustdoc/html/highlight/tests.rs
index fd5275189d6..fccbb98f80f 100644
--- a/src/librustdoc/html/highlight/tests.rs
+++ b/src/librustdoc/html/highlight/tests.rs
@@ -78,7 +78,7 @@ let a = 4;";
         decorations.insert("example2", vec![(22, 32)]);
 
         let mut html = Buffer::new();
-        write_code(&mut html, src, None, Some(DecorationInfo(decorations)));
+        write_code(&mut html, src, None, Some(&DecorationInfo(decorations)));
         expect_file!["fixtures/decorations.html"].assert_eq(&html.into_inner());
     });
 }
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 9a9ce31caaa..a27a9d202eb 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -69,9 +69,9 @@ use crate::formats::cache::Cache;
 use crate::formats::item_type::ItemType;
 use crate::html::escape::Escape;
 use crate::html::format::{
-    Buffer, Ending, HrefError, PrintWithSpace, display_fn, href, join_with_double_colon,
-    print_abi_with_space, print_constness_with_space, print_default_space, print_generic_bounds,
-    print_where_clause, visibility_print_with_space,
+    Buffer, Ending, HrefError, PrintWithSpace, href, join_with_double_colon, print_abi_with_space,
+    print_constness_with_space, print_default_space, print_generic_bounds, print_where_clause,
+    visibility_print_with_space,
 };
 use crate::html::markdown::{
     HeadingOffset, IdMap, Markdown, MarkdownItemInfo, MarkdownSummaryLine,
@@ -82,13 +82,14 @@ use crate::scrape_examples::{CallData, CallLocation};
 use crate::{DOC_RUST_LANG_ORG_CHANNEL, try_none};
 
 pub(crate) fn ensure_trailing_slash(v: &str) -> impl fmt::Display + '_ {
-    crate::html::format::display_fn(move |f| {
+    fmt::from_fn(move |f| {
         if !v.ends_with('/') && !v.is_empty() { write!(f, "{v}/") } else { f.write_str(v) }
     })
 }
 
 /// Specifies whether rendering directly implemented trait items or ones from a certain Deref
 /// impl.
+#[derive(Copy, Clone)]
 pub(crate) enum AssocItemRender<'a> {
     All,
     DerefFor { trait_: &'a clean::Path, type_: &'a clean::Type, deref_mut_: bool },
@@ -309,9 +310,7 @@ impl ItemEntry {
 
 impl ItemEntry {
     pub(crate) fn print(&self) -> impl fmt::Display + '_ {
-        crate::html::format::display_fn(move |f| {
-            write!(f, "<a href=\"{}\">{}</a>", self.url, Escape(&self.name))
-        })
+        fmt::from_fn(move |f| write!(f, "<a href=\"{}\">{}</a>", self.url, Escape(&self.name)))
     }
 }
 
@@ -513,7 +512,7 @@ fn document<'a, 'cx: 'a>(
         info!("Documenting {name}");
     }
 
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         document_item_info(cx, item, parent).render_into(f).unwrap();
         if parent.is_none() {
             write!(f, "{}", document_full_collapsible(item, cx, heading_offset))
@@ -530,7 +529,7 @@ fn render_markdown<'a, 'cx: 'a>(
     links: Vec<RenderedLink>,
     heading_offset: HeadingOffset,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         write!(
             f,
             "<div class=\"docblock\">{}</div>",
@@ -557,7 +556,7 @@ fn document_short<'a, 'cx: 'a>(
     parent: &'a clean::Item,
     show_def_docs: bool,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         document_item_info(cx, item, Some(parent)).render_into(f).unwrap();
         if !show_def_docs {
             return Ok(());
@@ -605,7 +604,7 @@ fn document_full_inner<'a, 'cx: 'a>(
     is_collapsible: bool,
     heading_offset: HeadingOffset,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         if let Some(s) = item.opt_doc_value() {
             debug!("Doc block: =====\n{s}\n=====");
             if is_collapsible {
@@ -1159,7 +1158,7 @@ fn render_attributes_in_pre<'a, 'tcx: 'a>(
     prefix: &'a str,
     cx: &'a Context<'tcx>,
 ) -> impl fmt::Display + Captures<'a> + Captures<'tcx> {
-    crate::html::format::display_fn(move |f| {
+    fmt::from_fn(move |f| {
         for a in it.attributes(cx.tcx(), cx.cache(), false) {
             writeln!(f, "{prefix}{a}")?;
         }
@@ -1256,9 +1255,9 @@ fn render_assoc_items<'a, 'cx: 'a>(
     it: DefId,
     what: AssocItemRender<'a>,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    let mut derefs = DefIdSet::default();
-    derefs.insert(it);
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
+        let mut derefs = DefIdSet::default();
+        derefs.insert(it);
         render_assoc_items_inner(f, cx, containing_item, it, what, &mut derefs);
         Ok(())
     })
@@ -2577,7 +2576,7 @@ fn render_call_locations<W: fmt::Write>(mut w: W, cx: &Context<'_>, item: &clean
             file_span,
             cx,
             &cx.root_path(),
-            highlight::DecorationInfo(decoration_info),
+            &highlight::DecorationInfo(decoration_info),
             sources::SourceContext::Embedded(sources::ScrapedInfo {
                 needs_expansion,
                 offset: line_min,
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index 01e40f823d9..37fea09ace3 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -30,7 +30,7 @@ use crate::formats::Impl;
 use crate::formats::item_type::ItemType;
 use crate::html::escape::{Escape, EscapeBodyTextWithWbr};
 use crate::html::format::{
-    Buffer, Ending, PrintWithSpace, display_fn, join_with_double_colon, print_abi_with_space,
+    Buffer, Ending, PrintWithSpace, join_with_double_colon, print_abi_with_space,
     print_constness_with_space, print_where_clause, visibility_print_with_space,
 };
 use crate::html::markdown::{HeadingOffset, MarkdownSummaryLine};
@@ -92,7 +92,7 @@ macro_rules! item_template_methods {
     () => {};
     (document $($rest:tt)*) => {
         fn document<'b>(&'b self) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let (item, cx) = self.item_and_cx();
                 let v = document(cx, item, None, HeadingOffset::H2);
                 write!(f, "{v}")
@@ -102,7 +102,7 @@ macro_rules! item_template_methods {
     };
     (document_type_layout $($rest:tt)*) => {
         fn document_type_layout<'b>(&'b self) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let (item, cx) = self.item_and_cx();
                 let def_id = item.item_id.expect_def_id();
                 let v = document_type_layout(cx, def_id);
@@ -113,7 +113,7 @@ macro_rules! item_template_methods {
     };
     (render_attributes_in_pre $($rest:tt)*) => {
         fn render_attributes_in_pre<'b>(&'b self) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let (item, cx) = self.item_and_cx();
                 let v = render_attributes_in_pre(item, "", cx);
                 write!(f, "{v}")
@@ -123,7 +123,7 @@ macro_rules! item_template_methods {
     };
     (render_assoc_items $($rest:tt)*) => {
         fn render_assoc_items<'b>(&'b self) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let (item, cx) = self.item_and_cx();
                 let def_id = item.item_id.expect_def_id();
                 let v = render_assoc_items(cx, item, def_id, AssocItemRender::All);
@@ -520,13 +520,13 @@ fn extra_info_tags<'a, 'tcx: 'a>(
     parent: &'a clean::Item,
     import_def_id: Option<DefId>,
 ) -> impl fmt::Display + 'a + Captures<'tcx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         fn tag_html<'a>(
             class: &'a str,
             title: &'a str,
             contents: &'a str,
         ) -> impl fmt::Display + 'a {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 write!(
                     f,
                     r#"<wbr><span class="stab {class}" title="{title}">{contents}</span>"#,
@@ -1375,7 +1375,7 @@ fn item_union(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Uni
 
     impl<'a, 'cx: 'a> ItemUnion<'a, 'cx> {
         fn render_union<'b>(&'b self) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let v = render_union(self.it, Some(&self.s.generics), &self.s.fields, self.cx);
                 write!(f, "{v}")
             })
@@ -1385,7 +1385,7 @@ fn item_union(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Uni
             &'b self,
             field: &'a clean::Item,
         ) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let v = document(self.cx, field, Some(self.it), HeadingOffset::H3);
                 write!(f, "{v}")
             })
@@ -1399,7 +1399,7 @@ fn item_union(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Uni
             &'b self,
             ty: &'a clean::Type,
         ) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
-            display_fn(move |f| {
+            fmt::from_fn(move |f| {
                 let v = ty.print(self.cx);
                 write!(f, "{v}")
             })
@@ -1426,7 +1426,7 @@ fn print_tuple_struct_fields<'a, 'cx: 'a>(
     cx: &'a Context<'cx>,
     s: &'a [clean::Item],
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    display_fn(|f| {
+    fmt::from_fn(|f| {
         if !s.is_empty()
             && s.iter().all(|field| {
                 matches!(field.kind, clean::StrippedItem(box clean::StructFieldItem(..)))
@@ -2151,7 +2151,7 @@ fn render_union<'a, 'cx: 'a>(
     fields: &'a [clean::Item],
     cx: &'a Context<'cx>,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    display_fn(move |mut f| {
+    fmt::from_fn(move |mut f| {
         write!(f, "{}union {}", visibility_print_with_space(it, cx), it.name.unwrap(),)?;
 
         let where_displayed = g
@@ -2331,7 +2331,7 @@ fn document_non_exhaustive_header(item: &clean::Item) -> &str {
 }
 
 fn document_non_exhaustive(item: &clean::Item) -> impl fmt::Display + '_ {
-    display_fn(|f| {
+    fmt::from_fn(|f| {
         if item.is_non_exhaustive() {
             write!(
                 f,
diff --git a/src/librustdoc/html/render/sidebar.rs b/src/librustdoc/html/render/sidebar.rs
index 881df8b0050..23ac568fdf8 100644
--- a/src/librustdoc/html/render/sidebar.rs
+++ b/src/librustdoc/html/render/sidebar.rs
@@ -100,18 +100,17 @@ impl<'a> Link<'a> {
 }
 
 pub(crate) mod filters {
-    use std::fmt::Display;
+    use std::fmt::{self, Display};
 
     use rinja::filters::Safe;
 
     use crate::html::escape::EscapeBodyTextWithWbr;
-    use crate::html::render::display_fn;
     pub(crate) fn wrapped<T>(v: T) -> rinja::Result<Safe<impl Display>>
     where
         T: Display,
     {
         let string = v.to_string();
-        Ok(Safe(display_fn(move |f| EscapeBodyTextWithWbr(&string).fmt(f))))
+        Ok(Safe(fmt::from_fn(move |f| EscapeBodyTextWithWbr(&string).fmt(f))))
     }
 }
 
diff --git a/src/librustdoc/html/render/type_layout.rs b/src/librustdoc/html/render/type_layout.rs
index 9317844956d..0f01db5f6bc 100644
--- a/src/librustdoc/html/render/type_layout.rs
+++ b/src/librustdoc/html/render/type_layout.rs
@@ -9,7 +9,6 @@ use rustc_middle::ty::layout::LayoutError;
 use rustc_middle::ty::{self};
 use rustc_span::symbol::Symbol;
 
-use crate::html::format::display_fn;
 use crate::html::render::Context;
 
 #[derive(Template)]
@@ -31,7 +30,7 @@ pub(crate) fn document_type_layout<'a, 'cx: 'a>(
     cx: &'a Context<'cx>,
     ty_def_id: DefId,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
-    display_fn(move |f| {
+    fmt::from_fn(move |f| {
         if !cx.shared.show_type_layout {
             return Ok(());
         }
diff --git a/src/librustdoc/html/sources.rs b/src/librustdoc/html/sources.rs
index 9827f97d28d..1ac0c10c612 100644
--- a/src/librustdoc/html/sources.rs
+++ b/src/librustdoc/html/sources.rs
@@ -17,7 +17,7 @@ use crate::clean::utils::has_doc_flag;
 use crate::docfs::PathError;
 use crate::error::Error;
 use crate::html::render::Context;
-use crate::html::{format, highlight, layout};
+use crate::html::{highlight, layout};
 use crate::visit::DocVisitor;
 
 pub(crate) fn render(cx: &mut Context<'_>, krate: &clean::Crate) -> Result<(), Error> {
@@ -249,7 +249,7 @@ impl SourceCollector<'_, '_> {
                     file_span,
                     self.cx,
                     &root_path,
-                    highlight::DecorationInfo::default(),
+                    &highlight::DecorationInfo::default(),
                     SourceContext::Standalone { file_path },
                 )
             },
@@ -328,13 +328,13 @@ pub(crate) fn print_src(
     file_span: rustc_span::Span,
     context: &Context<'_>,
     root_path: &str,
-    decoration_info: highlight::DecorationInfo,
+    decoration_info: &highlight::DecorationInfo,
     source_context: SourceContext<'_>,
 ) {
-    let current_href = context
-        .href_from_span(clean::Span::new(file_span), false)
-        .expect("only local crates should have sources emitted");
-    let code = format::display_fn(move |fmt| {
+    let code = fmt::from_fn(move |fmt| {
+        let current_href = context
+            .href_from_span(clean::Span::new(file_span), false)
+            .expect("only local crates should have sources emitted");
         highlight::write_code(
             fmt,
             s,
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index ba620b6cb6b..bb954a31891 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -5,6 +5,7 @@
 #![feature(rustc_private)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
+#![feature(debug_closure_helpers)]
 #![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(impl_trait_in_assoc_type)]
@@ -73,8 +74,6 @@ extern crate tikv_jemalloc_sys as jemalloc_sys;
 use std::env::{self, VarError};
 use std::io::{self, IsTerminal};
 use std::process;
-use std::sync::Arc;
-use std::sync::atomic::AtomicBool;
 
 use rustc_errors::DiagCtxtHandle;
 use rustc_interface::interface;
@@ -158,7 +157,7 @@ pub fn main() {
 
     let mut early_dcx = EarlyDiagCtxt::new(ErrorOutputType::default());
 
-    let using_internal_features = rustc_driver::install_ice_hook(
+    rustc_driver::install_ice_hook(
         "https://github.com/rust-lang/rust/issues/new\
     ?labels=C-bug%2C+I-ICE%2C+T-rustdoc&template=ice.md",
         |_| (),
@@ -179,7 +178,7 @@ pub fn main() {
 
     let exit_code = rustc_driver::catch_with_exit_code(|| {
         let at_args = rustc_driver::args::raw_args(&early_dcx)?;
-        main_args(&mut early_dcx, &at_args, using_internal_features);
+        main_args(&mut early_dcx, &at_args);
         Ok(())
     });
     process::exit(exit_code);
@@ -768,11 +767,7 @@ fn run_merge_finalize(opt: config::RenderOptions) -> Result<(), error::Error> {
     Ok(())
 }
 
-fn main_args(
-    early_dcx: &mut EarlyDiagCtxt,
-    at_args: &[String],
-    using_internal_features: Arc<AtomicBool>,
-) {
+fn main_args(early_dcx: &mut EarlyDiagCtxt, at_args: &[String]) {
     // Throw away the first argument, the name of the binary.
     // In case of at_args being empty, as might be the case by
     // passing empty argument array to execve under some platforms,
@@ -825,8 +820,7 @@ fn main_args(
         (false, Some(md_input)) => {
             let md_input = md_input.to_owned();
             let edition = options.edition;
-            let config =
-                core::create_config(input, options, &render_options, using_internal_features);
+            let config = core::create_config(input, options, &render_options);
 
             // `markdown::render` can invoke `doctest::make_test`, which
             // requires session globals and a thread pool, so we use
@@ -859,7 +853,7 @@ fn main_args(
     let scrape_examples_options = options.scrape_examples_options.clone();
     let bin_crate = options.bin_crate;
 
-    let config = core::create_config(input, options, &render_options, using_internal_features);
+    let config = core::create_config(input, options, &render_options);
 
     let registered_lints = config.register_lints.is_some();
 
diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
index 5a99977ded5..916f0ab3cc8 100644
--- a/src/rustdoc-json-types/lib.rs
+++ b/src/rustdoc-json-types/lib.rs
@@ -1099,8 +1099,7 @@ pub struct Trait {
     pub is_auto: bool,
     /// Whether the trait is marked as `unsafe`.
     pub is_unsafe: bool,
-    // FIXME(dyn_compat_renaming): Update the URL once the Reference is updated and hits stable.
-    /// Whether the trait is [dyn compatible](https://doc.rust-lang.org/reference/items/traits.html#object-safety)[^1].
+    /// Whether the trait is [dyn compatible](https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility)[^1].
     ///
     /// [^1]: Formerly known as "object safe".
     pub is_dyn_compatible: bool,
diff --git a/src/tools/clippy/src/driver.rs b/src/tools/clippy/src/driver.rs
index 75ef60a5dc8..68edefd3095 100644
--- a/src/tools/clippy/src/driver.rs
+++ b/src/tools/clippy/src/driver.rs
@@ -186,7 +186,7 @@ pub fn main() {
 
     rustc_driver::init_rustc_env_logger(&early_dcx);
 
-    let using_internal_features = rustc_driver::install_ice_hook(BUG_REPORT_URL, |dcx| {
+    rustc_driver::install_ice_hook(BUG_REPORT_URL, |dcx| {
         // FIXME: this macro calls unwrap internally but is called in a panicking context!  It's not
         // as simple as moving the call from the hook to main, because `install_ice_hook` doesn't
         // accept a generic closure.
@@ -236,7 +236,7 @@ pub fn main() {
             let mut args: Vec<String> = orig_args.clone();
             pass_sysroot_env_if_given(&mut args, sys_root_env);
 
-            rustc_driver::RunCompiler::new(&args, &mut DefaultCallbacks).run();
+            rustc_driver::run_compiler(&args, &mut DefaultCallbacks);
             return Ok(());
         }
 
@@ -295,13 +295,9 @@ pub fn main() {
         let clippy_enabled = !cap_lints_allow && relevant_package && !info_query;
         if clippy_enabled {
             args.extend(clippy_args);
-            rustc_driver::RunCompiler::new(&args, &mut ClippyCallbacks { clippy_args_var })
-                .set_using_internal_features(using_internal_features)
-                .run();
+            rustc_driver::run_compiler(&args, &mut ClippyCallbacks { clippy_args_var });
         } else {
-            rustc_driver::RunCompiler::new(&args, &mut RustcCallbacks { clippy_args_var })
-                .set_using_internal_features(using_internal_features)
-                .run();
+            rustc_driver::run_compiler(&args, &mut RustcCallbacks { clippy_args_var });
         }
         Ok(())
     }))
diff --git a/src/tools/linkchecker/main.rs b/src/tools/linkchecker/main.rs
index 570b2c374c0..19340b5d07a 100644
--- a/src/tools/linkchecker/main.rs
+++ b/src/tools/linkchecker/main.rs
@@ -50,6 +50,29 @@ const LINKCHECK_EXCEPTIONS: &[(&str, &[&str])] = &[
     ("alloc/slice/trait.Concat.html", &["#method.concat"]),
     ("alloc/slice/index.html", &["#method.concat", "#method.join"]),
     ("alloc/vec/struct.Vec.html", &["#method.sort_by_key", "#method.sort_by_cached_key"]),
+    ("alloc/bstr/struct.ByteStr.html", &[
+        "#method.to_ascii_uppercase",
+        "#method.to_ascii_lowercase",
+        "core/slice::sort_by_key",
+        "core\\slice::sort_by_key",
+        "#method.sort_by_cached_key",
+        "#method.sort_by_key"
+    ]),
+    ("alloc/bstr/struct.ByteString.html", &[
+        "#method.to_ascii_uppercase",
+        "#method.to_ascii_lowercase",
+        "core/slice::sort_by_key",
+        "core\\slice::sort_by_key",
+        "#method.sort_by_cached_key",
+        "#method.sort_by_key"
+    ]),
+    ("core/bstr/struct.ByteStr.html", &[
+        "#method.to_ascii_uppercase",
+        "#method.to_ascii_lowercase",
+        "core/bstr/slice::sort_by_key",
+        "core\\bstr\\slice::sort_by_key",
+        "#method.sort_by_cached_key"
+    ]),
     ("core/primitive.str.html", &["#method.to_ascii_uppercase", "#method.to_ascii_lowercase"]),
     ("core/primitive.slice.html", &["#method.to_ascii_uppercase", "#method.to_ascii_lowercase",
                                     "core/slice::sort_by_key", "core\\slice::sort_by_key",
diff --git a/src/tools/miri/src/bin/miri.rs b/src/tools/miri/src/bin/miri.rs
index 9cd84332204..af7c9956eb9 100644
--- a/src/tools/miri/src/bin/miri.rs
+++ b/src/tools/miri/src/bin/miri.rs
@@ -30,7 +30,7 @@ use std::ops::Range;
 use std::path::PathBuf;
 use std::str::FromStr;
 use std::sync::atomic::{AtomicI32, Ordering};
-use std::sync::{Arc, Once};
+use std::sync::Once;
 
 use miri::{
     BacktraceStyle, BorrowTrackerMethod, MiriConfig, MiriEntryFnType, ProvenanceMode, RetagFields,
@@ -371,13 +371,10 @@ fn init_late_loggers(early_dcx: &EarlyDiagCtxt, tcx: TyCtxt<'_>) {
 fn run_compiler_and_exit(
     args: &[String],
     callbacks: &mut (dyn rustc_driver::Callbacks + Send),
-    using_internal_features: Arc<std::sync::atomic::AtomicBool>,
 ) -> ! {
     // Invoke compiler, and handle return code.
     let exit_code = rustc_driver::catch_with_exit_code(move || {
-        rustc_driver::RunCompiler::new(args, callbacks)
-            .set_using_internal_features(using_internal_features)
-            .run();
+        rustc_driver::run_compiler(args, callbacks);
         Ok(())
     });
     std::process::exit(exit_code)
@@ -468,8 +465,7 @@ fn main() {
     // If the environment asks us to actually be rustc, then do that.
     if let Some(crate_kind) = env::var_os("MIRI_BE_RUSTC") {
         // Earliest rustc setup.
-        let using_internal_features =
-            rustc_driver::install_ice_hook(rustc_driver::DEFAULT_BUG_REPORT_URL, |_| ());
+        rustc_driver::install_ice_hook(rustc_driver::DEFAULT_BUG_REPORT_URL, |_| ());
         rustc_driver::init_rustc_env_logger(&early_dcx);
 
         let target_crate = if crate_kind == "target" {
@@ -493,16 +489,11 @@ fn main() {
         }
 
         // We cannot use `rustc_driver::main` as we want it to use `args` as the CLI arguments.
-        run_compiler_and_exit(
-            &args,
-            &mut MiriBeRustCompilerCalls { target_crate },
-            using_internal_features,
-        )
+        run_compiler_and_exit(&args, &mut MiriBeRustCompilerCalls { target_crate })
     }
 
     // Add an ICE bug report hook.
-    let using_internal_features =
-        rustc_driver::install_ice_hook("https://github.com/rust-lang/miri/issues/new", |_| ());
+    rustc_driver::install_ice_hook("https://github.com/rust-lang/miri/issues/new", |_| ());
 
     // Init loggers the Miri way.
     init_early_loggers(&early_dcx);
@@ -736,9 +727,5 @@ fn main() {
 
     debug!("rustc arguments: {:?}", rustc_args);
     debug!("crate arguments: {:?}", miri_config.args);
-    run_compiler_and_exit(
-        &rustc_args,
-        &mut MiriCompilerCalls::new(miri_config, many_seeds),
-        using_internal_features,
-    )
+    run_compiler_and_exit(&rustc_args, &mut MiriCompilerCalls::new(miri_config, many_seeds))
 }
diff --git a/tests/ui-fulldeps/compiler-calls.rs b/tests/ui-fulldeps/compiler-calls.rs
index 5fb47c87e50..d6148dfec43 100644
--- a/tests/ui-fulldeps/compiler-calls.rs
+++ b/tests/ui-fulldeps/compiler-calls.rs
@@ -25,7 +25,7 @@ fn main() {
     let mut count = 1;
     let args = vec!["compiler-calls".to_string(), "foo.rs".to_string()];
     rustc_driver::catch_fatal_errors(|| -> interface::Result<()> {
-        rustc_driver::RunCompiler::new(&args, &mut TestCalls { count: &mut count }).run();
+        rustc_driver::run_compiler(&args, &mut TestCalls { count: &mut count });
         Ok(())
     })
     .ok();
diff --git a/tests/ui-fulldeps/obtain-borrowck.rs b/tests/ui-fulldeps/obtain-borrowck.rs
index 8ea2ac61971..f8064c245a8 100644
--- a/tests/ui-fulldeps/obtain-borrowck.rs
+++ b/tests/ui-fulldeps/obtain-borrowck.rs
@@ -47,7 +47,7 @@ fn main() {
         rustc_args.push("-Zpolonius".to_owned());
         let mut callbacks = CompilerCalls::default();
         // Call the Rust compiler with our callbacks.
-        rustc_driver::RunCompiler::new(&rustc_args, &mut callbacks).run();
+        rustc_driver::run_compiler(&rustc_args, &mut callbacks);
         Ok(())
     });
     std::process::exit(exit_code);
diff --git a/tests/ui-fulldeps/run-compiler-twice.rs b/tests/ui-fulldeps/run-compiler-twice.rs
index bcc235e58ed..f414c961627 100644
--- a/tests/ui-fulldeps/run-compiler-twice.rs
+++ b/tests/ui-fulldeps/run-compiler-twice.rs
@@ -72,7 +72,7 @@ fn compile(code: String, output: PathBuf, sysroot: PathBuf, linker: Option<&Path
         override_queries: None,
         make_codegen_backend: None,
         registry: rustc_driver::diagnostics_registry(),
-        using_internal_features: std::sync::Arc::default(),
+        using_internal_features: &rustc_driver::USING_INTERNAL_FEATURES,
         expanded_args: Default::default(),
     };
 
diff --git a/tests/ui/associated-types/associated-types-in-ambiguous-context.stderr b/tests/ui/associated-types/associated-types-in-ambiguous-context.stderr
index c5260adbed4..88db3611719 100644
--- a/tests/ui/associated-types/associated-types-in-ambiguous-context.stderr
+++ b/tests/ui/associated-types/associated-types-in-ambiguous-context.stderr
@@ -40,14 +40,14 @@ LL | type X = std::ops::Deref::Target;
    |
 help: use fully-qualified syntax
    |
+LL | type X = <ByteStr as Deref>::Target;
+   |          ~~~~~~~~~~~~~~~~~~~~~~~~~~
+LL | type X = <ByteString as Deref>::Target;
+   |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 LL | type X = <CString as Deref>::Target;
    |          ~~~~~~~~~~~~~~~~~~~~~~~~~~
 LL | type X = <IoSlice<'_> as Deref>::Target;
    |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-LL | type X = <IoSliceMut<'_> as Deref>::Target;
-   |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-LL | type X = <OsString as Deref>::Target;
-   |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~
      and N other candidates
 
 error: aborting due to 5 previous errors
diff --git a/tests/ui/async-await/coroutine-desc.stderr b/tests/ui/async-await/coroutine-desc.stderr
index 01482a9cb1f..84a1a3166ad 100644
--- a/tests/ui/async-await/coroutine-desc.stderr
+++ b/tests/ui/async-await/coroutine-desc.stderr
@@ -30,7 +30,6 @@ LL |     fun(one(), two());
    |     |   expected all arguments to be this future type because they need to match the type of this parameter
    |     arguments to this function are incorrect
    |
-   = help: consider `await`ing on both `Future`s
    = note: distinct uses of `impl Trait` result in different opaque types
 note: function defined here
   --> $DIR/coroutine-desc.rs:7:4
diff --git a/tests/ui/async-await/dont-suggest-missing-await.stderr b/tests/ui/async-await/dont-suggest-missing-await.stderr
index 45a226c31f8..2ca52b2d5f5 100644
--- a/tests/ui/async-await/dont-suggest-missing-await.stderr
+++ b/tests/ui/async-await/dont-suggest-missing-await.stderr
@@ -6,20 +6,11 @@ LL |         take_u32(x)
    |         |
    |         arguments to this function are incorrect
    |
-note: calling an async function returns a future
-  --> $DIR/dont-suggest-missing-await.rs:14:18
-   |
-LL |         take_u32(x)
-   |                  ^
 note: function defined here
   --> $DIR/dont-suggest-missing-await.rs:5:4
    |
 LL | fn take_u32(x: u32) {}
    |    ^^^^^^^^ ------
-help: consider `await`ing on the `Future`
-   |
-LL |         take_u32(x.await)
-   |                   ++++++
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/consts/too_generic_eval_ice.stderr b/tests/ui/consts/too_generic_eval_ice.stderr
index b48be16a24c..3cc4377514a 100644
--- a/tests/ui/consts/too_generic_eval_ice.stderr
+++ b/tests/ui/consts/too_generic_eval_ice.stderr
@@ -32,13 +32,13 @@ LL |         [5; Self::HOST_SIZE] == [6; 0]
    = help: the following other types implement trait `PartialEq<Rhs>`:
              `&[T]` implements `PartialEq<Vec<U, A>>`
              `&[T]` implements `PartialEq<[U; N]>`
+             `&[u8; N]` implements `PartialEq<ByteStr>`
+             `&[u8; N]` implements `PartialEq<ByteString>`
+             `&[u8]` implements `PartialEq<ByteStr>`
+             `&[u8]` implements `PartialEq<ByteString>`
              `&mut [T]` implements `PartialEq<Vec<U, A>>`
              `&mut [T]` implements `PartialEq<[U; N]>`
-             `[T; N]` implements `PartialEq<&[U]>`
-             `[T; N]` implements `PartialEq<&mut [U]>`
-             `[T; N]` implements `PartialEq<[U; N]>`
-             `[T; N]` implements `PartialEq<[U]>`
-           and 3 others
+           and 11 others
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_off.rs b/tests/ui/debuginfo/windows_gnu_split_debuginfo_off.rs
new file mode 100644
index 00000000000..3a8d9c998cf
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_off.rs
@@ -0,0 +1,29 @@
+//@ revisions: aarch64_gl i686_g i686_gl i686_uwp_g x86_64_g x86_64_gl x86_64_uwp_g
+//@ compile-flags: --crate-type cdylib -Csplit-debuginfo=off
+//@ check-pass
+
+//@[aarch64_gl] compile-flags: --target aarch64-pc-windows-gnullvm
+//@[aarch64_gl] needs-llvm-components: aarch64
+
+//@[i686_g] compile-flags: --target i686-pc-windows-gnu
+//@[i686_g] needs-llvm-components: x86
+
+//@[i686_gl] compile-flags: --target i686-pc-windows-gnullvm
+//@[i686_gl] needs-llvm-components: x86
+
+//@[i686_uwp_g] compile-flags: --target i686-uwp-windows-gnu
+//@[i686_uwp_g] needs-llvm-components: x86
+
+//@[x86_64_g] compile-flags: --target x86_64-pc-windows-gnu
+//@[x86_64_g] needs-llvm-components: x86
+
+//@[x86_64_gl] compile-flags: --target x86_64-pc-windows-gnullvm
+//@[x86_64_gl] needs-llvm-components: x86
+
+//@[x86_64_uwp_g] compile-flags: --target x86_64-uwp-windows-gnu
+//@[x86_64_uwp_g] needs-llvm-components: x86
+
+#![feature(no_core)]
+
+#![no_core]
+#![no_std]
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.aarch64_gl.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.aarch64_gl.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.aarch64_gl.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_g.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_gl.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_gl.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_gl.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_uwp_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_uwp_g.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.i686_uwp_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.rs b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.rs
new file mode 100644
index 00000000000..896bbac7d8e
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.rs
@@ -0,0 +1,29 @@
+//@ revisions: aarch64_gl i686_g i686_gl i686_uwp_g x86_64_g x86_64_gl x86_64_uwp_g
+//@ compile-flags: --crate-type cdylib -Csplit-debuginfo=packed
+//@ error-pattern: error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+//@[aarch64_gl] compile-flags: --target aarch64-pc-windows-gnullvm
+//@[aarch64_gl] needs-llvm-components: aarch64
+
+//@[i686_g] compile-flags: --target i686-pc-windows-gnu
+//@[i686_g] needs-llvm-components: x86
+
+//@[i686_gl] compile-flags: --target i686-pc-windows-gnullvm
+//@[i686_gl] needs-llvm-components: x86
+
+//@[i686_uwp_g] compile-flags: --target i686-uwp-windows-gnu
+//@[i686_uwp_g] needs-llvm-components: x86
+
+//@[x86_64_g] compile-flags: --target x86_64-pc-windows-gnu
+//@[x86_64_g] needs-llvm-components: x86
+
+//@[x86_64_gl] compile-flags: --target x86_64-pc-windows-gnullvm
+//@[x86_64_gl] needs-llvm-components: x86
+
+//@[x86_64_uwp_g] compile-flags: --target x86_64-uwp-windows-gnu
+//@[x86_64_uwp_g] needs-llvm-components: x86
+
+#![feature(no_core)]
+
+#![no_core]
+#![no_std]
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_g.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_gl.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_gl.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_gl.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_uwp_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_uwp_g.stderr
new file mode 100644
index 00000000000..f3465e64976
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_packed.x86_64_uwp_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=packed` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.aarch64_gl.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.aarch64_gl.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.aarch64_gl.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_g.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_gl.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_gl.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_gl.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_uwp_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_uwp_g.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.i686_uwp_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.rs b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.rs
new file mode 100644
index 00000000000..54a88c91217
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.rs
@@ -0,0 +1,29 @@
+//@ revisions: aarch64_gl i686_g i686_gl i686_uwp_g x86_64_g x86_64_gl x86_64_uwp_g
+//@ compile-flags: --crate-type cdylib -Csplit-debuginfo=unpacked
+//@ error-pattern: error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+//@[aarch64_gl] compile-flags: --target aarch64-pc-windows-gnullvm
+//@[aarch64_gl] needs-llvm-components: aarch64
+
+//@[i686_g] compile-flags: --target i686-pc-windows-gnu
+//@[i686_g] needs-llvm-components: x86
+
+//@[i686_gl] compile-flags: --target i686-pc-windows-gnullvm
+//@[i686_gl] needs-llvm-components: x86
+
+//@[i686_uwp_g] compile-flags: --target i686-uwp-windows-gnu
+//@[i686_uwp_g] needs-llvm-components: x86
+
+//@[x86_64_g] compile-flags: --target x86_64-pc-windows-gnu
+//@[x86_64_g] needs-llvm-components: x86
+
+//@[x86_64_gl] compile-flags: --target x86_64-pc-windows-gnullvm
+//@[x86_64_gl] needs-llvm-components: x86
+
+//@[x86_64_uwp_g] compile-flags: --target x86_64-uwp-windows-gnu
+//@[x86_64_uwp_g] needs-llvm-components: x86
+
+#![feature(no_core)]
+
+#![no_core]
+#![no_std]
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_g.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_gl.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_gl.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_gl.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_uwp_g.stderr b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_uwp_g.stderr
new file mode 100644
index 00000000000..0964e21b13b
--- /dev/null
+++ b/tests/ui/debuginfo/windows_gnu_split_debuginfo_unpacked.x86_64_uwp_g.stderr
@@ -0,0 +1,4 @@
+error: `-Csplit-debuginfo=unpacked` is unstable on this platform
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/impl-trait/issue-102605.stderr b/tests/ui/impl-trait/issue-102605.stderr
index dcb22797173..ed6663fa61f 100644
--- a/tests/ui/impl-trait/issue-102605.stderr
+++ b/tests/ui/impl-trait/issue-102605.stderr
@@ -14,20 +14,11 @@ LL |     convert_result(foo())
    |     |
    |     arguments to this function are incorrect
    |
-note: calling an async function returns a future
-  --> $DIR/issue-102605.rs:13:20
-   |
-LL |     convert_result(foo())
-   |                    ^^^^^
 note: function defined here
   --> $DIR/issue-102605.rs:7:4
    |
 LL | fn convert_result<T, E>(r: Result<T, E>) -> Option<T> {
    |    ^^^^^^^^^^^^^^       ---------------
-help: consider `await`ing on the `Future`
-   |
-LL |     convert_result(foo().await)
-   |                         ++++++
 help: try wrapping the expression in `Err`
    |
 LL |     convert_result(Err(foo()))
diff --git a/tests/ui/inference/issue-72616.stderr b/tests/ui/inference/issue-72616.stderr
index 02c92c1c11d..a26f9a1ff56 100644
--- a/tests/ui/inference/issue-72616.stderr
+++ b/tests/ui/inference/issue-72616.stderr
@@ -6,11 +6,14 @@ LL |         if String::from("a") == "a".try_into().unwrap() {}
    |                              |
    |                              type must be known at this point
    |
-   = note: multiple `impl`s satisfying `String: PartialEq<_>` found in the `alloc` crate:
-           - impl PartialEq for String;
-           - impl<'a, 'b> PartialEq<&'a str> for String;
-           - impl<'a, 'b> PartialEq<Cow<'a, str>> for String;
-           - impl<'a, 'b> PartialEq<str> for String;
+   = note: cannot satisfy `String: PartialEq<_>`
+   = help: the following types implement trait `PartialEq<Rhs>`:
+             `String` implements `PartialEq<&str>`
+             `String` implements `PartialEq<ByteStr>`
+             `String` implements `PartialEq<ByteString>`
+             `String` implements `PartialEq<Cow<'_, str>>`
+             `String` implements `PartialEq<str>`
+             `String` implements `PartialEq`
 help: try using a fully qualified path to specify the expected types
    |
 LL |         if String::from("a") == <&str as TryInto<T>>::try_into("a").unwrap() {}
diff --git a/tests/ui/inference/issue-72690.stderr b/tests/ui/inference/issue-72690.stderr
index 6391672f861..2d09f667ae2 100644
--- a/tests/ui/inference/issue-72690.stderr
+++ b/tests/ui/inference/issue-72690.stderr
@@ -15,6 +15,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -41,6 +42,7 @@ LL |     |x| String::from("x".as_ref());
    |                          ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -57,6 +59,7 @@ LL |     let _ = "x".as_ref();
    |         ^       ------ type must be known at this point
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -83,6 +86,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -109,6 +113,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -135,6 +140,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -161,6 +167,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -187,6 +194,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
@@ -213,6 +221,7 @@ LL |     String::from("x".as_ref());
    |                      ^^^^^^
    |
    = note: multiple `impl`s satisfying `str: AsRef<_>` found in the following crates: `core`, `std`:
+           - impl AsRef<ByteStr> for str;
            - impl AsRef<OsStr> for str;
            - impl AsRef<Path> for str;
            - impl AsRef<[u8]> for str;
diff --git a/tests/ui/layout/reprc-power-alignment.rs b/tests/ui/layout/reprc-power-alignment.rs
new file mode 100644
index 00000000000..f6c1df55988
--- /dev/null
+++ b/tests/ui/layout/reprc-power-alignment.rs
@@ -0,0 +1,152 @@
+//@ check-pass
+//@ compile-flags: --target powerpc64-ibm-aix
+//@ needs-llvm-components: powerpc
+//@ add-core-stubs
+#![feature(no_core)]
+#![no_core]
+#![no_std]
+
+extern crate minicore;
+use minicore::*;
+
+#[warn(uses_power_alignment)]
+
+#[repr(C)]
+pub struct Floats {
+    a: f64,
+    b: u8,
+    c: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    d: f32,
+}
+
+pub struct Floats2 {
+    a: f64,
+    b: u32,
+    c: f64,
+}
+
+#[repr(C)]
+pub struct Floats3 {
+    a: f32,
+    b: f32,
+    c: i64,
+}
+
+#[repr(C)]
+pub struct Floats4 {
+    a: u64,
+    b: u32,
+    c: f32,
+}
+
+#[repr(C)]
+pub struct Floats5 {
+    a: f32,
+    b: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    c: f32,
+}
+
+#[repr(C)]
+pub struct FloatAgg1 {
+    x: Floats,
+    y: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+
+#[repr(C)]
+pub struct FloatAgg2 {
+    x: i64,
+    y: Floats, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+
+#[repr(C)]
+pub struct FloatAgg3 {
+    x: FloatAgg1,
+    // NOTE: the "power" alignment rule is infectious to nested struct fields.
+    y: FloatAgg2, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    z: FloatAgg2, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+
+#[repr(C)]
+pub struct FloatAgg4 {
+    x: FloatAgg1,
+    y: FloatAgg2, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+
+#[repr(C)]
+pub struct FloatAgg5 {
+    x: FloatAgg1,
+    y: FloatAgg2, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    z: FloatAgg3, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+
+#[repr(C)]
+pub struct FloatAgg6 {
+    x: i64,
+    y: Floats, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    z: u8,
+}
+
+#[repr(C)]
+pub struct FloatAgg7 {
+    x: i64,
+    y: Floats, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    z: u8,
+    zz: f32,
+}
+
+#[repr(C)]
+pub struct A {
+  d: f64,
+}
+#[repr(C)]
+pub struct B {
+  a: A,
+  f: f32,
+  d: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+#[repr(C)]
+pub struct C {
+  c: u8,
+  b: B, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+#[repr(C)]
+pub struct D {
+  x: f64,
+}
+#[repr(C)]
+pub struct E {
+  x: i32,
+  d: D, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+#[repr(C)]
+pub struct F {
+  a: u8,
+  b: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+#[repr(C)]
+pub struct G {
+    a: u8,
+    b: u8,
+    c: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+    d: f32,
+    e: f64, //~ WARNING repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+}
+// Should not warn on #[repr(packed)].
+#[repr(packed)]
+pub struct H {
+    a: u8,
+    b: u8,
+    c: f64,
+    d: f32,
+    e: f64,
+}
+#[repr(C, packed)]
+pub struct I {
+    a: u8,
+    b: u8,
+    c: f64,
+    d: f32,
+    e: f64,
+}
+
+fn main() { }
diff --git a/tests/ui/layout/reprc-power-alignment.stderr b/tests/ui/layout/reprc-power-alignment.stderr
new file mode 100644
index 00000000000..18664e4d655
--- /dev/null
+++ b/tests/ui/layout/reprc-power-alignment.stderr
@@ -0,0 +1,112 @@
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:18:5
+   |
+LL |     c: f64,
+   |     ^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/reprc-power-alignment.rs:12:8
+   |
+LL | #[warn(uses_power_alignment)]
+   |        ^^^^^^^^^^^^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:45:5
+   |
+LL |     b: f64,
+   |     ^^^^^^
+   |
+   = note: `#[warn(uses_power_alignment)]` on by default
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:52:5
+   |
+LL |     y: f64,
+   |     ^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:58:5
+   |
+LL |     y: Floats,
+   |     ^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:65:5
+   |
+LL |     y: FloatAgg2,
+   |     ^^^^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:66:5
+   |
+LL |     z: FloatAgg2,
+   |     ^^^^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:72:5
+   |
+LL |     y: FloatAgg2,
+   |     ^^^^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:78:5
+   |
+LL |     y: FloatAgg2,
+   |     ^^^^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:79:5
+   |
+LL |     z: FloatAgg3,
+   |     ^^^^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:85:5
+   |
+LL |     y: Floats,
+   |     ^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:92:5
+   |
+LL |     y: Floats,
+   |     ^^^^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:105:3
+   |
+LL |   d: f64,
+   |   ^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:110:3
+   |
+LL |   b: B,
+   |   ^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:119:3
+   |
+LL |   d: D,
+   |   ^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:124:3
+   |
+LL |   b: f64,
+   |   ^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:130:5
+   |
+LL |     c: f64,
+   |     ^^^^^^
+
+warning: repr(C) does not follow the power alignment rule. This may affect platform C ABI compatibility for this type
+  --> $DIR/reprc-power-alignment.rs:132:5
+   |
+LL |     e: f64,
+   |     ^^^^^^
+
+warning: 17 warnings emitted
+
diff --git a/tests/ui/lint/clashing-extern-fn.rs b/tests/ui/lint/clashing-extern-fn.rs
index a12fe81eecd..9bbb20246df 100644
--- a/tests/ui/lint/clashing-extern-fn.rs
+++ b/tests/ui/lint/clashing-extern-fn.rs
@@ -248,6 +248,7 @@ mod sameish_members {
 
 mod same_sized_members_clash {
     mod a {
+        #[allow(uses_power_alignment)]
         #[repr(C)]
         struct Point3 {
             x: f32,
diff --git a/tests/ui/lint/clashing-extern-fn.stderr b/tests/ui/lint/clashing-extern-fn.stderr
index b30dd476a1d..48dd1adbc1f 100644
--- a/tests/ui/lint/clashing-extern-fn.stderr
+++ b/tests/ui/lint/clashing-extern-fn.stderr
@@ -1,5 +1,5 @@
 warning: `extern` block uses type `Option<TransparentNoNiche>`, which is not FFI-safe
-  --> $DIR/clashing-extern-fn.rs:482:55
+  --> $DIR/clashing-extern-fn.rs:483:55
    |
 LL |             fn hidden_niche_transparent_no_niche() -> Option<TransparentNoNiche>;
    |                                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -9,7 +9,7 @@ LL |             fn hidden_niche_transparent_no_niche() -> Option<TransparentNoN
    = note: `#[warn(improper_ctypes)]` on by default
 
 warning: `extern` block uses type `Option<UnsafeCell<NonZero<usize>>>`, which is not FFI-safe
-  --> $DIR/clashing-extern-fn.rs:486:46
+  --> $DIR/clashing-extern-fn.rs:487:46
    |
 LL |             fn hidden_niche_unsafe_cell() -> Option<UnsafeCell<NonZero<usize>>>;
    |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -151,7 +151,7 @@ LL |             fn draw_point(p: Point);
               found `unsafe extern "C" fn(sameish_members::b::Point)`
 
 warning: `origin` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:269:13
+  --> $DIR/clashing-extern-fn.rs:270:13
    |
 LL |             fn origin() -> Point3;
    |             ---------------------- `origin` previously declared here
@@ -163,7 +163,7 @@ LL |             fn origin() -> Point3;
               found `unsafe extern "C" fn() -> same_sized_members_clash::b::Point3`
 
 warning: `transparent_incorrect` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:292:13
+  --> $DIR/clashing-extern-fn.rs:293:13
    |
 LL |             fn transparent_incorrect() -> T;
    |             -------------------------------- `transparent_incorrect` previously declared here
@@ -175,7 +175,7 @@ LL |             fn transparent_incorrect() -> isize;
               found `unsafe extern "C" fn() -> isize`
 
 warning: `missing_return_type` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:310:13
+  --> $DIR/clashing-extern-fn.rs:311:13
    |
 LL |             fn missing_return_type() -> usize;
    |             ---------------------------------- `missing_return_type` previously declared here
@@ -187,7 +187,7 @@ LL |             fn missing_return_type();
               found `unsafe extern "C" fn()`
 
 warning: `non_zero_usize` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:328:13
+  --> $DIR/clashing-extern-fn.rs:329:13
    |
 LL |             fn non_zero_usize() -> core::num::NonZero<usize>;
    |             ------------------------------------------------- `non_zero_usize` previously declared here
@@ -199,7 +199,7 @@ LL |             fn non_zero_usize() -> usize;
               found `unsafe extern "C" fn() -> usize`
 
 warning: `non_null_ptr` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:330:13
+  --> $DIR/clashing-extern-fn.rs:331:13
    |
 LL |             fn non_null_ptr() -> core::ptr::NonNull<usize>;
    |             ----------------------------------------------- `non_null_ptr` previously declared here
@@ -211,7 +211,7 @@ LL |             fn non_null_ptr() -> *const usize;
               found `unsafe extern "C" fn() -> *const usize`
 
 warning: `option_non_zero_usize_incorrect` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:424:13
+  --> $DIR/clashing-extern-fn.rs:425:13
    |
 LL |             fn option_non_zero_usize_incorrect() -> usize;
    |             ---------------------------------------------- `option_non_zero_usize_incorrect` previously declared here
@@ -223,7 +223,7 @@ LL |             fn option_non_zero_usize_incorrect() -> isize;
               found `unsafe extern "C" fn() -> isize`
 
 warning: `option_non_null_ptr_incorrect` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:426:13
+  --> $DIR/clashing-extern-fn.rs:427:13
    |
 LL |             fn option_non_null_ptr_incorrect() -> *const usize;
    |             --------------------------------------------------- `option_non_null_ptr_incorrect` previously declared here
@@ -235,7 +235,7 @@ LL |             fn option_non_null_ptr_incorrect() -> *const isize;
               found `unsafe extern "C" fn() -> *const isize`
 
 warning: `hidden_niche_transparent_no_niche` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:482:13
+  --> $DIR/clashing-extern-fn.rs:483:13
    |
 LL |             fn hidden_niche_transparent_no_niche() -> usize;
    |             ------------------------------------------------ `hidden_niche_transparent_no_niche` previously declared here
@@ -247,7 +247,7 @@ LL |             fn hidden_niche_transparent_no_niche() -> Option<TransparentNoN
               found `unsafe extern "C" fn() -> Option<TransparentNoNiche>`
 
 warning: `hidden_niche_unsafe_cell` redeclared with a different signature
-  --> $DIR/clashing-extern-fn.rs:486:13
+  --> $DIR/clashing-extern-fn.rs:487:13
    |
 LL |             fn hidden_niche_unsafe_cell() -> usize;
    |             --------------------------------------- `hidden_niche_unsafe_cell` previously declared here
diff --git a/tests/ui/traits/next-solver/non-wf-in-coerce-pointers.rs b/tests/ui/traits/next-solver/non-wf-in-coerce-pointers.rs
new file mode 100644
index 00000000000..d05def2cb75
--- /dev/null
+++ b/tests/ui/traits/next-solver/non-wf-in-coerce-pointers.rs
@@ -0,0 +1,17 @@
+//@ compile-flags: -Znext-solver
+
+trait Wf {
+    type Assoc;
+}
+
+struct S {
+    f: &'static <() as Wf>::Assoc,
+    //~^ ERROR the trait bound `(): Wf` is not satisfied
+}
+
+fn main() {
+    let x: S = todo!();
+    let y: &() = x.f;
+    //~^ ERROR mismatched types
+    //~| ERROR the trait bound `(): Wf` is not satisfied
+}
diff --git a/tests/ui/traits/next-solver/non-wf-in-coerce-pointers.stderr b/tests/ui/traits/next-solver/non-wf-in-coerce-pointers.stderr
new file mode 100644
index 00000000000..32a7766a638
--- /dev/null
+++ b/tests/ui/traits/next-solver/non-wf-in-coerce-pointers.stderr
@@ -0,0 +1,39 @@
+error[E0277]: the trait bound `(): Wf` is not satisfied
+  --> $DIR/non-wf-in-coerce-pointers.rs:8:17
+   |
+LL |     f: &'static <() as Wf>::Assoc,
+   |                 ^^^^^^^^^^^^^^^^^ the trait `Wf` is not implemented for `()`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/non-wf-in-coerce-pointers.rs:3:1
+   |
+LL | trait Wf {
+   | ^^^^^^^^
+
+error[E0308]: mismatched types
+  --> $DIR/non-wf-in-coerce-pointers.rs:14:18
+   |
+LL |     let y: &() = x.f;
+   |            ---   ^^^ types differ
+   |            |
+   |            expected due to this
+   |
+   = note: expected reference `&()`
+              found reference `&'static <() as Wf>::Assoc`
+
+error[E0277]: the trait bound `(): Wf` is not satisfied
+  --> $DIR/non-wf-in-coerce-pointers.rs:14:18
+   |
+LL |     let y: &() = x.f;
+   |                  ^^^ the trait `Wf` is not implemented for `()`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/non-wf-in-coerce-pointers.rs:3:1
+   |
+LL | trait Wf {
+   | ^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.
diff --git a/tests/ui/traits/next-solver/normalization-shadowing/global-trait-with-project.rs b/tests/ui/traits/next-solver/normalization-shadowing/global-trait-with-project.rs
new file mode 100644
index 00000000000..dc96652f82f
--- /dev/null
+++ b/tests/ui/traits/next-solver/normalization-shadowing/global-trait-with-project.rs
@@ -0,0 +1,21 @@
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// `(): Trait` is a global where-bound with a projection bound.
+// This previously resulted in ambiguity as we considered both
+// the impl and the where-bound while normalizing.
+
+trait Trait {
+    type Assoc;
+}
+impl Trait for () {
+    type Assoc = &'static ();
+}
+
+fn foo<'a>(x: <() as Trait>::Assoc)
+where
+    (): Trait<Assoc = &'a ()>,
+{
+}
+
+fn main() {}