diff --git a/Cargo.lock b/Cargo.lock
index f03b033db6fe0..10889139e8d66 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 509b24dd703a6..4706744f35307 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 8b666c9100f1f..20be21446098b 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_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 308d669cf352d..2113345eda3ac 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 d7370c1ff53f7..74d02ac22276c 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_middle/src/query/arena_cached.rs b/compiler/rustc_middle/src/query/arena_cached.rs
new file mode 100644
index 0000000000000..ec6e466ff688c
--- /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 65e93c3a1cc75..05ded71dbeb51 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 2cb6f6d8c6e87..1c157f33a813b 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 f9168112216ab..451c215566be2 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 4faa243c02a64..513fc9355c8b5 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 9a3e79c16b4df..5418f054bebd2 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
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 60f1154dc6d02..10f1ce376ef55 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 dc63ea1999e5b..ad38ea228bf53 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_trait_selection/src/error_reporting/infer/suggest.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
index 36270e0da78b6..21124cf20e5dd 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 0000000000000..61e61019b508c
--- /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/lib.rs b/library/alloc/src/lib.rs
index b4f08debc932a..28e4217e30394 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 0000000000000..74e07f3d242cd
--- /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 ec1aed53eaf72..00300328b64c1 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/lib.rs b/library/core/src/lib.rs
index f58eab3b1b1a2..01ed3cc69a2cc 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 0000000000000..5fecd0a4084c7
--- /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/std/src/bstr.rs b/library/std/src/bstr.rs
new file mode 100644
index 0000000000000..dd49177162833
--- /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 39f234e4ba661..acb3a0578e505 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/doc/rustc-dev-guide/examples/rustc-driver-example.rs b/src/doc/rustc-dev-guide/examples/rustc-driver-example.rs
index 576bbcea965d9..8983915d78a9c 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 90a85d5db2108..c894b60444ac4 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 a6234dc129ffe..40500e6bc7a5f 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/core.rs b/src/librustdoc/core.rs
index 0dda3466a7173..ad67c2ba24536 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 009e9662933ae..8c3e28ecec38c 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/lib.rs b/src/librustdoc/lib.rs
index f07f8273e6ce4..bb954a31891ad 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -74,8 +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;
@@ -159,7 +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",
         |_| (),
@@ -180,7 +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);
@@ -769,11 +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,
@@ -826,8 +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
@@ -860,7 +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/tools/clippy/src/driver.rs b/src/tools/clippy/src/driver.rs
index 75ef60a5dc8ac..68edefd3095cf 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 570b2c374c0e6..19340b5d07a11 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 22c15c8405fdf..a2e9c63f79e13 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, ValidationMode,
@@ -370,13 +370,10 @@ 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)
@@ -467,8 +464,7 @@ 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" {
@@ -492,16 +488,11 @@ 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);
@@ -735,9 +726,5 @@ 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 5fb47c87e501f..d6148dfec43ce 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 8ea2ac6197199..f8064c245a872 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 bcc235e58ed33..f414c961627dd 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 c5260adbed43a..88db361171919 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 01482a9cb1fb6..84a1a3166ad64 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 45a226c31f840..2ca52b2d5f53b 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 b48be16a24c8e..3cc4377514a21 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/impl-trait/issue-102605.stderr b/tests/ui/impl-trait/issue-102605.stderr
index dcb22797173cb..ed6663fa61f93 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 02c92c1c11d02..a26f9a1ff5618 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 6391672f8617d..2d09f667ae2cf 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/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 0000000000000..dc96652f82ff0
--- /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() {}