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authorbors <bors@rust-lang.org>2025-01-15 18:26:54 +0000
committerbors <bors@rust-lang.org>2025-01-15 18:26:54 +0000
commit419b3e2d3e350822550eee0e82eeded4d324d584 (patch)
tree03a4cb06d80de0496f0d1492436d2d71155d6f02
parent27f336106db859435f6edcf507e38f90b1e2af43 (diff)
parent01ae58bff1ca6199ad2b64c5d73501d5abb15a0c (diff)
Auto merge of #135540 - GuillaumeGomez:rollup-40lfb7l, r=GuillaumeGomez
Rollup of 6 pull requests

Successful merges:

 - #132654 (std: lazily allocate the main thread handle)
 - #135003 (deprecate `std::intrinsics::transmute` etc, use `std::mem::*` instead)
 - #135428 (rustdoc: Remove `AttributesExt` trait magic that added needless complexity)
 - #135498 (Prefer lower `TraitUpcasting` candidates in selection)
 - #135507 (TRPL: incorporate all backward-compatible Edition changes)
 - #135529 (remove outdated FIXME)

r? `@ghost`
`@rustbot` modify labels: rollup
-rw-r--r--compiler/rustc_ast/src/attr/mod.rs2
-rw-r--r--compiler/rustc_attr_data_structures/src/stability.rs15
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/stability.rs21
-rw-r--r--compiler/rustc_feature/src/builtin_attrs.rs2
-rw-r--r--compiler/rustc_middle/src/middle/stability.rs21
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/trait_goals.rs8
-rw-r--r--compiler/rustc_passes/src/stability.rs136
-rw-r--r--compiler/rustc_trait_selection/src/solve/select.rs4
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/confirmation.rs2
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/mod.rs12
-rw-r--r--compiler/rustc_type_ir/src/solve/mod.rs5
-rw-r--r--library/core/src/intrinsics/mod.rs24
-rw-r--r--library/std/src/panicking.rs39
-rw-r--r--library/std/src/rt.rs23
-rw-r--r--library/std/src/sys/pal/unix/stack_overflow.rs9
-rw-r--r--library/std/src/sys/pal/windows/stack_overflow.rs8
-rw-r--r--library/std/src/thread/current.rs39
-rw-r--r--library/std/src/thread/mod.rs276
-rw-r--r--src/bootstrap/src/core/build_steps/doc.rs2
m---------src/doc/book0
-rw-r--r--src/librustdoc/clean/inline.rs17
-rw-r--r--src/librustdoc/clean/mod.rs20
-rw-r--r--src/librustdoc/clean/types.rs233
-rw-r--r--src/librustdoc/doctest/rust.rs7
-rw-r--r--src/librustdoc/formats/cache.rs2
-rw-r--r--src/librustdoc/passes/propagate_stability.rs6
-rw-r--r--src/librustdoc/visit_ast.rs6
-rw-r--r--src/tools/clippy/clippy_lints/src/std_instead_of_core.rs2
-rw-r--r--src/tools/clippy/tests/ui/std_instead_of_core.fixed2
-rw-r--r--src/tools/clippy/tests/ui/std_instead_of_core.rs2
-rw-r--r--src/tools/clippy/tests/ui/transmute.rs22
-rw-r--r--src/tools/clippy/tests/ui/transmute.stderr36
-rw-r--r--tests/debuginfo/thread.rs8
-rw-r--r--tests/ui/stability-attribute/accidental-stable-in-unstable.rs1
-rw-r--r--tests/ui/stability-attribute/accidental-stable-in-unstable.stderr10
-rw-r--r--tests/ui/stability-attribute/allowed-through-unstable.rs1
-rw-r--r--tests/ui/stability-attribute/allowed-through-unstable.stderr12
-rw-r--r--tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs4
-rw-r--r--tests/ui/traits/trait-upcasting/prefer-lower-candidates.rs29
39 files changed, 604 insertions, 464 deletions
diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index 97385b2eaab..51f18580013 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -723,6 +723,8 @@ impl MetaItemLit {
 pub trait AttributeExt: Debug {
     fn id(&self) -> AttrId;
 
+    /// For a single-segment attribute (i.e., `#[attr]` and not `#[path::atrr]`),
+    /// return the name of the attribute, else return the empty identifier.
     fn name_or_empty(&self) -> Symbol {
         self.ident().unwrap_or_else(Ident::empty).name
     }
diff --git a/compiler/rustc_attr_data_structures/src/stability.rs b/compiler/rustc_attr_data_structures/src/stability.rs
index 3c77d4c766c..dfda04387ec 100644
--- a/compiler/rustc_attr_data_structures/src/stability.rs
+++ b/compiler/rustc_attr_data_structures/src/stability.rs
@@ -101,6 +101,16 @@ impl PartialConstStability {
     }
 }
 
+#[derive(Encodable, Decodable, PartialEq, Copy, Clone, Debug, Eq, Hash)]
+#[derive(HashStable_Generic)]
+pub enum AllowedThroughUnstableModules {
+    /// This does not get a deprecation warning. We still generally would prefer people to use the
+    /// fully stable path, and a warning will likely be emitted in the future.
+    WithoutDeprecation,
+    /// Emit the given deprecation warning.
+    WithDeprecation(Symbol),
+}
+
 /// The available stability levels.
 #[derive(Encodable, Decodable, PartialEq, Copy, Clone, Debug, Eq, Hash)]
 #[derive(HashStable_Generic)]
@@ -137,9 +147,8 @@ pub enum StabilityLevel {
     Stable {
         /// Rust release which stabilized this feature.
         since: StableSince,
-        /// Is this item allowed to be referred to on stable, despite being contained in unstable
-        /// modules?
-        allowed_through_unstable_modules: bool,
+        /// This is `Some` if this item allowed to be referred to on stable via unstable modules.
+        allowed_through_unstable_modules: Option<AllowedThroughUnstableModules>,
     },
 }
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/stability.rs b/compiler/rustc_attr_parsing/src/attributes/stability.rs
index 89937e1c593..bfbe51b27d8 100644
--- a/compiler/rustc_attr_parsing/src/attributes/stability.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/stability.rs
@@ -6,8 +6,8 @@ use rustc_ast::MetaItem;
 use rustc_ast::attr::AttributeExt;
 use rustc_ast_pretty::pprust;
 use rustc_attr_data_structures::{
-    ConstStability, DefaultBodyStability, Stability, StabilityLevel, StableSince, UnstableReason,
-    VERSION_PLACEHOLDER,
+    AllowedThroughUnstableModules, ConstStability, DefaultBodyStability, Stability, StabilityLevel,
+    StableSince, UnstableReason, VERSION_PLACEHOLDER,
 };
 use rustc_errors::ErrorGuaranteed;
 use rustc_session::Session;
@@ -24,11 +24,16 @@ pub fn find_stability(
     item_sp: Span,
 ) -> Option<(Stability, Span)> {
     let mut stab: Option<(Stability, Span)> = None;
-    let mut allowed_through_unstable_modules = false;
+    let mut allowed_through_unstable_modules = None;
 
     for attr in attrs {
         match attr.name_or_empty() {
-            sym::rustc_allowed_through_unstable_modules => allowed_through_unstable_modules = true,
+            sym::rustc_allowed_through_unstable_modules => {
+                allowed_through_unstable_modules = Some(match attr.value_str() {
+                    Some(msg) => AllowedThroughUnstableModules::WithDeprecation(msg),
+                    None => AllowedThroughUnstableModules::WithoutDeprecation,
+                })
+            }
             sym::unstable => {
                 if stab.is_some() {
                     sess.dcx().emit_err(session_diagnostics::MultipleStabilityLevels {
@@ -56,15 +61,15 @@ pub fn find_stability(
         }
     }
 
-    if allowed_through_unstable_modules {
+    if let Some(allowed_through_unstable_modules) = allowed_through_unstable_modules {
         match &mut stab {
             Some((
                 Stability {
-                    level: StabilityLevel::Stable { allowed_through_unstable_modules, .. },
+                    level: StabilityLevel::Stable { allowed_through_unstable_modules: in_stab, .. },
                     ..
                 },
                 _,
-            )) => *allowed_through_unstable_modules = true,
+            )) => *in_stab = Some(allowed_through_unstable_modules),
             _ => {
                 sess.dcx()
                     .emit_err(session_diagnostics::RustcAllowedUnstablePairing { span: item_sp });
@@ -283,7 +288,7 @@ fn parse_stability(sess: &Session, attr: &impl AttributeExt) -> Option<(Symbol,
 
     match feature {
         Ok(feature) => {
-            let level = StabilityLevel::Stable { since, allowed_through_unstable_modules: false };
+            let level = StabilityLevel::Stable { since, allowed_through_unstable_modules: None };
             Some((feature, level))
         }
         Err(ErrorGuaranteed { .. }) => None,
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index c28a4360f6f..5510e7e09e5 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -623,7 +623,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::No, "allow_internal_unsafe side-steps the unsafe_code lint",
     ),
     rustc_attr!(
-        rustc_allowed_through_unstable_modules, Normal, template!(Word),
+        rustc_allowed_through_unstable_modules, Normal, template!(Word, NameValueStr: "deprecation message"),
         WarnFollowing, EncodeCrossCrate::No,
         "rustc_allowed_through_unstable_modules special cases accidental stabilizations of stable items \
         through unstable paths"
diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index 75ca289056e..77a7da2c74b 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -249,9 +249,18 @@ fn late_report_deprecation(
         return;
     }
 
+    let is_in_effect = depr.is_in_effect();
+    let lint = deprecation_lint(is_in_effect);
+
+    // Calculating message for lint involves calling `self.def_path_str`,
+    // which will by default invoke the expensive `visible_parent_map` query.
+    // Skip all that work if the lint is allowed anyway.
+    if tcx.lint_level_at_node(lint, hir_id).0 == Level::Allow {
+        return;
+    }
+
     let def_path = with_no_trimmed_paths!(tcx.def_path_str(def_id));
     let def_kind = tcx.def_descr(def_id);
-    let is_in_effect = depr.is_in_effect();
 
     let method_span = method_span.unwrap_or(span);
     let suggestion =
@@ -267,7 +276,7 @@ fn late_report_deprecation(
         note: depr.note,
         since_kind: deprecated_since_kind(is_in_effect, depr.since),
     };
-    tcx.emit_node_span_lint(deprecation_lint(is_in_effect), hir_id, method_span, diag);
+    tcx.emit_node_span_lint(lint, hir_id, method_span, diag);
 }
 
 /// Result of `TyCtxt::eval_stability`.
@@ -377,13 +386,7 @@ impl<'tcx> TyCtxt<'tcx> {
                 // hierarchy.
                 let depr_attr = &depr_entry.attr;
                 if !skip || depr_attr.is_since_rustc_version() {
-                    // Calculating message for lint involves calling `self.def_path_str`.
-                    // Which by default to calculate visible path will invoke expensive `visible_parent_map` query.
-                    // So we skip message calculation altogether, if lint is allowed.
-                    let lint = deprecation_lint(depr_attr.is_in_effect());
-                    if self.lint_level_at_node(lint, id).0 != Level::Allow {
-                        late_report_deprecation(self, depr_attr, span, method_span, id, def_id);
-                    }
+                    late_report_deprecation(self, depr_attr, span, method_span, id, def_id);
                 }
             };
         }
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 d68fca60829..f4d7c3ce76c 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -741,12 +741,14 @@ where
                 a_data.principal(),
             ));
         } else if let Some(a_principal) = a_data.principal() {
-            for new_a_principal in
-                elaborate::supertraits(self.cx(), a_principal.with_self_ty(cx, a_ty)).skip(1)
+            for (idx, new_a_principal) in
+                elaborate::supertraits(self.cx(), a_principal.with_self_ty(cx, a_ty))
+                    .enumerate()
+                    .skip(1)
             {
                 responses.extend(self.consider_builtin_upcast_to_principal(
                     goal,
-                    CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting),
+                    CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting(idx)),
                     a_data,
                     a_region,
                     b_data,
diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index aabc33b015e..60734122e63 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -5,8 +5,8 @@ use std::mem::replace;
 use std::num::NonZero;
 
 use rustc_attr_parsing::{
-    self as attr, ConstStability, DeprecatedSince, Stability, StabilityLevel, StableSince,
-    UnstableReason, VERSION_PLACEHOLDER,
+    self as attr, AllowedThroughUnstableModules, ConstStability, DeprecatedSince, Stability,
+    StabilityLevel, StableSince, UnstableReason, VERSION_PLACEHOLDER,
 };
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::unord::{ExtendUnord, UnordMap, UnordSet};
@@ -20,11 +20,16 @@ use rustc_hir::{FieldDef, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::middle::lib_features::{FeatureStability, LibFeatures};
 use rustc_middle::middle::privacy::EffectiveVisibilities;
-use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
+use rustc_middle::middle::stability::{
+    AllowUnstable, Deprecated, DeprecationEntry, EvalResult, Index,
+};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_session::lint;
-use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
+use rustc_session::lint::builtin::{
+    DEPRECATED, INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED,
+};
 use rustc_span::{Span, Symbol, sym};
 use tracing::{debug, info};
 
@@ -874,42 +879,95 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                 },
             );
 
-            let is_allowed_through_unstable_modules = |def_id| {
-                self.tcx.lookup_stability(def_id).is_some_and(|stab| match stab.level {
-                    StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
-                        allowed_through_unstable_modules
+            if item_is_allowed {
+                // The item itself is allowed; check whether the path there is also allowed.
+                let is_allowed_through_unstable_modules: Option<AllowedThroughUnstableModules> =
+                    self.tcx.lookup_stability(def_id).and_then(|stab| match stab.level {
+                        StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
+                            allowed_through_unstable_modules
+                        }
+                        _ => None,
+                    });
+
+                if is_allowed_through_unstable_modules.is_none() {
+                    // Check parent modules stability as well if the item the path refers to is itself
+                    // stable. We only emit warnings for unstable path segments if the item is stable
+                    // or allowed because stability is often inherited, so the most common case is that
+                    // both the segments and the item are unstable behind the same feature flag.
+                    //
+                    // We check here rather than in `visit_path_segment` to prevent visiting the last
+                    // path segment twice
+                    //
+                    // We include special cases via #[rustc_allowed_through_unstable_modules] for items
+                    // that were accidentally stabilized through unstable paths before this check was
+                    // added, such as `core::intrinsics::transmute`
+                    let parents = path.segments.iter().rev().skip(1);
+                    for path_segment in parents {
+                        if let Some(def_id) = path_segment.res.opt_def_id() {
+                            // use `None` for id to prevent deprecation check
+                            self.tcx.check_stability_allow_unstable(
+                                def_id,
+                                None,
+                                path.span,
+                                None,
+                                if is_unstable_reexport(self.tcx, id) {
+                                    AllowUnstable::Yes
+                                } else {
+                                    AllowUnstable::No
+                                },
+                            );
+                        }
                     }
-                    _ => false,
-                })
-            };
-
-            if item_is_allowed && !is_allowed_through_unstable_modules(def_id) {
-                // Check parent modules stability as well if the item the path refers to is itself
-                // stable. We only emit warnings for unstable path segments if the item is stable
-                // or allowed because stability is often inherited, so the most common case is that
-                // both the segments and the item are unstable behind the same feature flag.
-                //
-                // We check here rather than in `visit_path_segment` to prevent visiting the last
-                // path segment twice
-                //
-                // We include special cases via #[rustc_allowed_through_unstable_modules] for items
-                // that were accidentally stabilized through unstable paths before this check was
-                // added, such as `core::intrinsics::transmute`
-                let parents = path.segments.iter().rev().skip(1);
-                for path_segment in parents {
-                    if let Some(def_id) = path_segment.res.opt_def_id() {
-                        // use `None` for id to prevent deprecation check
-                        self.tcx.check_stability_allow_unstable(
-                            def_id,
-                            None,
-                            path.span,
-                            None,
-                            if is_unstable_reexport(self.tcx, id) {
-                                AllowUnstable::Yes
-                            } else {
-                                AllowUnstable::No
-                            },
-                        );
+                } else if let Some(AllowedThroughUnstableModules::WithDeprecation(deprecation)) =
+                    is_allowed_through_unstable_modules
+                {
+                    // Similar to above, but we cannot use `check_stability_allow_unstable` as that would
+                    // immediately show the stability error. We just want to know the result and disaplay
+                    // our own kind of error.
+                    let parents = path.segments.iter().rev().skip(1);
+                    for path_segment in parents {
+                        if let Some(def_id) = path_segment.res.opt_def_id() {
+                            // use `None` for id to prevent deprecation check
+                            let eval_result = self.tcx.eval_stability_allow_unstable(
+                                def_id,
+                                None,
+                                path.span,
+                                None,
+                                if is_unstable_reexport(self.tcx, id) {
+                                    AllowUnstable::Yes
+                                } else {
+                                    AllowUnstable::No
+                                },
+                            );
+                            let is_allowed = matches!(eval_result, EvalResult::Allow);
+                            if !is_allowed {
+                                // Calculating message for lint involves calling `self.def_path_str`,
+                                // which will by default invoke the expensive `visible_parent_map` query.
+                                // Skip all that work if the lint is allowed anyway.
+                                if self.tcx.lint_level_at_node(DEPRECATED, id).0
+                                    == lint::Level::Allow
+                                {
+                                    return;
+                                }
+                                // Show a deprecation message.
+                                let def_path =
+                                    with_no_trimmed_paths!(self.tcx.def_path_str(def_id));
+                                let def_kind = self.tcx.def_descr(def_id);
+                                let diag = Deprecated {
+                                    sub: None,
+                                    kind: def_kind.to_owned(),
+                                    path: def_path,
+                                    note: Some(deprecation),
+                                    since_kind: lint::DeprecatedSinceKind::InEffect,
+                                };
+                                self.tcx.emit_node_span_lint(
+                                    DEPRECATED,
+                                    id,
+                                    method_span.unwrap_or(path.span),
+                                    diag,
+                                );
+                            }
+                        }
                     }
                 }
             }
diff --git a/compiler/rustc_trait_selection/src/solve/select.rs b/compiler/rustc_trait_selection/src/solve/select.rs
index 1661852903c..b0b6274907d 100644
--- a/compiler/rustc_trait_selection/src/solve/select.rs
+++ b/compiler/rustc_trait_selection/src/solve/select.rs
@@ -117,6 +117,10 @@ fn candidate_should_be_dropped_in_favor_of<'tcx>(
             CandidateSource::BuiltinImpl(BuiltinImplSource::Object(a)),
             CandidateSource::BuiltinImpl(BuiltinImplSource::Object(b)),
         ) => a >= b,
+        (
+            CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting(a)),
+            CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting(b)),
+        ) => a >= b,
         // Prefer dyn candidates over non-dyn candidates. This is necessary to
         // handle the unsoundness between `impl<T: ?Sized> Any for T` and `dyn Any: Any`.
         (
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 3619d16cde2..0ccb0fc0615 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -1090,7 +1090,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             )?
             .expect("did not expect ambiguity during confirmation");
 
-        Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting, nested))
+        Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting(idx), nested))
     }
 
     fn confirm_builtin_unsize_candidate(
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 9e7da5eb368..5581ea46882 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1895,6 +1895,18 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             Some(None) => {}
             None => return None,
         }
+        // Same for upcasting.
+        let upcast_bound = candidates
+            .iter()
+            .filter_map(|c| {
+                if let TraitUpcastingUnsizeCandidate(i) = c.candidate { Some(i) } else { None }
+            })
+            .try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
+        match upcast_bound {
+            Some(Some(index)) => return Some(TraitUpcastingUnsizeCandidate(index)),
+            Some(None) => {}
+            None => return None,
+        }
 
         // Finally, handle overlapping user-written impls.
         let impls = candidates.iter().filter_map(|c| {
diff --git a/compiler/rustc_type_ir/src/solve/mod.rs b/compiler/rustc_type_ir/src/solve/mod.rs
index 1ae904d50e0..fbb5c7430eb 100644
--- a/compiler/rustc_type_ir/src/solve/mod.rs
+++ b/compiler/rustc_type_ir/src/solve/mod.rs
@@ -177,8 +177,9 @@ pub enum BuiltinImplSource {
     /// A built-in implementation of `Upcast` for trait objects to other trait objects.
     ///
     /// This can be removed when `feature(dyn_upcasting)` is stabilized, since we only
-    /// use it to detect when upcasting traits in hir typeck.
-    TraitUpcasting,
+    /// use it to detect when upcasting traits in hir typeck. The index is only used
+    /// for winnowing.
+    TraitUpcasting(usize),
     /// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
     ///
     /// This can be removed when `feature(tuple_unsizing)` is stabilized, since we only
diff --git a/library/core/src/intrinsics/mod.rs b/library/core/src/intrinsics/mod.rs
index 7b31bbec754..41b2ffad668 100644
--- a/library/core/src/intrinsics/mod.rs
+++ b/library/core/src/intrinsics/mod.rs
@@ -1897,7 +1897,11 @@ pub const fn forget<T: ?Sized>(_: T) {
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_allowed_through_unstable_modules]
+#[cfg_attr(bootstrap, rustc_allowed_through_unstable_modules)]
+#[cfg_attr(
+    not(bootstrap),
+    rustc_allowed_through_unstable_modules = "import this function via `std::mem` instead"
+)]
 #[rustc_const_stable(feature = "const_transmute", since = "1.56.0")]
 #[rustc_diagnostic_item = "transmute"]
 #[rustc_nounwind]
@@ -4325,7 +4329,11 @@ pub const fn ptr_metadata<P: ptr::Pointee<Metadata = M> + ?Sized, M>(_ptr: *cons
 /// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
 #[doc(alias = "memcpy")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_allowed_through_unstable_modules]
+#[cfg_attr(bootstrap, rustc_allowed_through_unstable_modules)]
+#[cfg_attr(
+    not(bootstrap),
+    rustc_allowed_through_unstable_modules = "import this function via `std::mem` instead"
+)]
 #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
 #[inline(always)]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@@ -4429,7 +4437,11 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
 /// ```
 #[doc(alias = "memmove")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_allowed_through_unstable_modules]
+#[cfg_attr(bootstrap, rustc_allowed_through_unstable_modules)]
+#[cfg_attr(
+    not(bootstrap),
+    rustc_allowed_through_unstable_modules = "import this function via `std::mem` instead"
+)]
 #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
 #[inline(always)]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@@ -4512,7 +4524,11 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 /// ```
 #[doc(alias = "memset")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_allowed_through_unstable_modules]
+#[cfg_attr(bootstrap, rustc_allowed_through_unstable_modules)]
+#[cfg_attr(
+    not(bootstrap),
+    rustc_allowed_through_unstable_modules = "import this function via `std::mem` instead"
+)]
 #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
 #[inline(always)]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
diff --git a/library/std/src/panicking.rs b/library/std/src/panicking.rs
index 3b02254548b..8e50bf11dd0 100644
--- a/library/std/src/panicking.rs
+++ b/library/std/src/panicking.rs
@@ -258,31 +258,34 @@ fn default_hook(info: &PanicHookInfo<'_>) {
     let location = info.location().unwrap();
 
     let msg = payload_as_str(info.payload());
-    let thread = thread::try_current();
-    let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
     let write = #[optimize(size)]
     |err: &mut dyn crate::io::Write| {
         // Use a lock to prevent mixed output in multithreading context.
         // Some platforms also require it when printing a backtrace, like `SymFromAddr` on Windows.
         let mut lock = backtrace::lock();
-        // Try to write the panic message to a buffer first to prevent other concurrent outputs
-        // interleaving with it.
-        let mut buffer = [0u8; 512];
-        let mut cursor = crate::io::Cursor::new(&mut buffer[..]);
-
-        let write_msg = |dst: &mut dyn crate::io::Write| {
-            // We add a newline to ensure the panic message appears at the start of a line.
-            writeln!(dst, "\nthread '{name}' panicked at {location}:\n{msg}")
-        };
 
-        if write_msg(&mut cursor).is_ok() {
-            let pos = cursor.position() as usize;
-            let _ = err.write_all(&buffer[0..pos]);
-        } else {
-            // The message did not fit into the buffer, write it directly instead.
-            let _ = write_msg(err);
-        };
+        thread::with_current_name(|name| {
+            let name = name.unwrap_or("<unnamed>");
+
+            // Try to write the panic message to a buffer first to prevent other concurrent outputs
+            // interleaving with it.
+            let mut buffer = [0u8; 512];
+            let mut cursor = crate::io::Cursor::new(&mut buffer[..]);
+
+            let write_msg = |dst: &mut dyn crate::io::Write| {
+                // We add a newline to ensure the panic message appears at the start of a line.
+                writeln!(dst, "\nthread '{name}' panicked at {location}:\n{msg}")
+            };
+
+            if write_msg(&mut cursor).is_ok() {
+                let pos = cursor.position() as usize;
+                let _ = err.write_all(&buffer[0..pos]);
+            } else {
+                // The message did not fit into the buffer, write it directly instead.
+                let _ = write_msg(err);
+            };
+        });
 
         static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 
diff --git a/library/std/src/rt.rs b/library/std/src/rt.rs
index 24a362072ab..384369b0012 100644
--- a/library/std/src/rt.rs
+++ b/library/std/src/rt.rs
@@ -23,7 +23,7 @@ pub use core::panicking::{panic_display, panic_fmt};
 #[rustfmt::skip]
 use crate::any::Any;
 use crate::sync::Once;
-use crate::thread::{self, Thread};
+use crate::thread::{self, main_thread};
 use crate::{mem, panic, sys};
 
 // Prints to the "panic output", depending on the platform this may be:
@@ -102,24 +102,9 @@ unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
         sys::init(argc, argv, sigpipe)
     };
 
-    // Set up the current thread handle to give it the right name.
-    //
-    // When code running before main uses `ReentrantLock` (for example by
-    // using `println!`), the thread ID can become initialized before we
-    // create this handle. Since `set_current` fails when the ID of the
-    // handle does not match the current ID, we should attempt to use the
-    // current thread ID here instead of unconditionally creating a new
-    // one. Also see #130210.
-    let thread = unsafe { Thread::new_main(thread::current_id()) };
-    if let Err(_thread) = thread::set_current(thread) {
-        // `thread::current` will create a new handle if none has been set yet.
-        // Thus, if someone uses it before main, this call will fail. That's a
-        // bad idea though, as we then cannot set the main thread name here.
-        //
-        // FIXME: detect the main thread in `thread::current` and use the
-        //        correct name there.
-        rtabort!("code running before main must not use thread::current");
-    }
+    // Remember the main thread ID to give it the correct name.
+    // SAFETY: this is the only time and place where we call this function.
+    unsafe { main_thread::set(thread::current_id()) };
 }
 
 /// Clean up the thread-local runtime state. This *should* be run after all other
diff --git a/library/std/src/sys/pal/unix/stack_overflow.rs b/library/std/src/sys/pal/unix/stack_overflow.rs
index 69b31da427f..db5c6bd3a1c 100644
--- a/library/std/src/sys/pal/unix/stack_overflow.rs
+++ b/library/std/src/sys/pal/unix/stack_overflow.rs
@@ -100,10 +100,11 @@ mod imp {
         // If the faulting address is within the guard page, then we print a
         // message saying so and abort.
         if start <= addr && addr < end {
-            rtprintpanic!(
-                "\nthread '{}' has overflowed its stack\n",
-                thread::current().name().unwrap_or("<unknown>")
-            );
+            thread::with_current_name(|name| {
+                let name = name.unwrap_or("<unknown>");
+                rtprintpanic!("\nthread '{name}' has overflowed its stack\n");
+            });
+
             rtabort!("stack overflow");
         } else {
             // Unregister ourselves by reverting back to the default behavior.
diff --git a/library/std/src/sys/pal/windows/stack_overflow.rs b/library/std/src/sys/pal/windows/stack_overflow.rs
index 467e21ab56a..734cd30bed0 100644
--- a/library/std/src/sys/pal/windows/stack_overflow.rs
+++ b/library/std/src/sys/pal/windows/stack_overflow.rs
@@ -18,10 +18,10 @@ unsafe extern "system" fn vectored_handler(ExceptionInfo: *mut c::EXCEPTION_POIN
         let code = rec.ExceptionCode;
 
         if code == c::EXCEPTION_STACK_OVERFLOW {
-            rtprintpanic!(
-                "\nthread '{}' has overflowed its stack\n",
-                thread::current().name().unwrap_or("<unknown>")
-            );
+            thread::with_current_name(|name| {
+                let name = name.unwrap_or("<unknown>");
+                rtprintpanic!("\nthread '{name}' has overflowed its stack\n");
+            });
         }
         c::EXCEPTION_CONTINUE_SEARCH
     }
diff --git a/library/std/src/thread/current.rs b/library/std/src/thread/current.rs
index 3d2c288b360..414711298f0 100644
--- a/library/std/src/thread/current.rs
+++ b/library/std/src/thread/current.rs
@@ -15,7 +15,7 @@ local_pointer! {
 ///
 /// We store the thread ID so that it never gets destroyed during the lifetime
 /// of a thread, either using `#[thread_local]` or multiple `local_pointer!`s.
-mod id {
+pub(super) mod id {
     use super::*;
 
     cfg_if::cfg_if! {
@@ -27,7 +27,7 @@ mod id {
 
             pub(super) const CHEAP: bool = true;
 
-            pub(super) fn get() -> Option<ThreadId> {
+            pub(crate) fn get() -> Option<ThreadId> {
                 ID.get()
             }
 
@@ -44,7 +44,7 @@ mod id {
 
             pub(super) const CHEAP: bool = false;
 
-            pub(super) fn get() -> Option<ThreadId> {
+            pub(crate) fn get() -> Option<ThreadId> {
                 let id0 = ID0.get().addr() as u64;
                 let id16 = ID16.get().addr() as u64;
                 let id32 = ID32.get().addr() as u64;
@@ -67,7 +67,7 @@ mod id {
 
             pub(super) const CHEAP: bool = false;
 
-            pub(super) fn get() -> Option<ThreadId> {
+            pub(crate) fn get() -> Option<ThreadId> {
                 let id0 = ID0.get().addr() as u64;
                 let id32 = ID32.get().addr() as u64;
                 ThreadId::from_u64((id32 << 32) + id0)
@@ -85,7 +85,7 @@ mod id {
 
             pub(super) const CHEAP: bool = true;
 
-            pub(super) fn get() -> Option<ThreadId> {
+            pub(crate) fn get() -> Option<ThreadId> {
                 let id = ID.get().addr() as u64;
                 ThreadId::from_u64(id)
             }
@@ -112,7 +112,7 @@ mod id {
 
 /// Tries to set the thread handle for the current thread. Fails if a handle was
 /// already set or if the thread ID of `thread` would change an already-set ID.
-pub(crate) fn set_current(thread: Thread) -> Result<(), Thread> {
+pub(super) fn set_current(thread: Thread) -> Result<(), Thread> {
     if CURRENT.get() != NONE {
         return Err(thread);
     }
@@ -140,28 +140,31 @@ pub(crate) fn current_id() -> ThreadId {
     // to retrieve it from the current thread handle, which will only take one
     // TLS access.
     if !id::CHEAP {
-        let current = CURRENT.get();
-        if current > DESTROYED {
-            unsafe {
-                let current = ManuallyDrop::new(Thread::from_raw(current));
-                return current.id();
-            }
+        if let Some(id) = try_with_current(|t| t.map(|t| t.id())) {
+            return id;
         }
     }
 
     id::get_or_init()
 }
 
-/// Gets a handle to the thread that invokes it, if the handle has been initialized.
-pub(crate) fn try_current() -> Option<Thread> {
+/// Gets a reference to the handle of the thread that invokes it, if the handle
+/// has been initialized.
+pub(super) fn try_with_current<F, R>(f: F) -> R
+where
+    F: FnOnce(Option<&Thread>) -> R,
+{
     let current = CURRENT.get();
     if current > DESTROYED {
+        // SAFETY: `Arc` does not contain interior mutability, so it does not
+        // matter that the address of the handle might be different depending
+        // on where this is called.
         unsafe {
             let current = ManuallyDrop::new(Thread::from_raw(current));
-            Some((*current).clone())
+            f(Some(&current))
         }
     } else {
-        None
+        f(None)
     }
 }
 
@@ -176,7 +179,7 @@ pub(crate) fn current_or_unnamed() -> Thread {
             (*current).clone()
         }
     } else if current == DESTROYED {
-        Thread::new_unnamed(id::get_or_init())
+        Thread::new(id::get_or_init(), None)
     } else {
         init_current(current)
     }
@@ -221,7 +224,7 @@ fn init_current(current: *mut ()) -> Thread {
         CURRENT.set(BUSY);
         // If the thread ID was initialized already, use it.
         let id = id::get_or_init();
-        let thread = Thread::new_unnamed(id);
+        let thread = Thread::new(id, None);
 
         // Make sure that `crate::rt::thread_cleanup` will be run, which will
         // call `drop_current`.
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index b6ee00a253a..59b395336f2 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -158,12 +158,9 @@
 #[cfg(all(test, not(any(target_os = "emscripten", target_os = "wasi"))))]
 mod tests;
 
-use core::cell::SyncUnsafeCell;
-use core::ffi::CStr;
-use core::mem::MaybeUninit;
-
 use crate::any::Any;
 use crate::cell::UnsafeCell;
+use crate::ffi::CStr;
 use crate::marker::PhantomData;
 use crate::mem::{self, ManuallyDrop, forget};
 use crate::num::NonZero;
@@ -186,7 +183,8 @@ mod current;
 
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use current::current;
-pub(crate) use current::{current_id, current_or_unnamed, drop_current, set_current, try_current};
+pub(crate) use current::{current_id, current_or_unnamed, drop_current};
+use current::{set_current, try_with_current};
 
 mod spawnhook;
 
@@ -501,10 +499,7 @@ impl Builder {
         });
 
         let id = ThreadId::new();
-        let my_thread = match name {
-            Some(name) => Thread::new(id, name),
-            None => Thread::new_unnamed(id),
-        };
+        let my_thread = Thread::new(id, name);
 
         let hooks = if no_hooks {
             spawnhook::ChildSpawnHooks::default()
@@ -1235,7 +1230,7 @@ impl ThreadId {
         }
     }
 
-    #[cfg(not(target_thread_local))]
+    #[cfg(any(not(target_thread_local), target_has_atomic = "64"))]
     fn from_u64(v: u64) -> Option<ThreadId> {
         NonZero::new(v).map(ThreadId)
     }
@@ -1261,29 +1256,14 @@ impl ThreadId {
 
 // This module ensures private fields are kept private, which is necessary to enforce the safety requirements.
 mod thread_name_string {
-    use core::str;
-
     use crate::ffi::{CStr, CString};
+    use crate::str;
 
     /// Like a `String` it's guaranteed UTF-8 and like a `CString` it's null terminated.
     pub(crate) struct ThreadNameString {
         inner: CString,
     }
 
-    impl ThreadNameString {
-        pub fn as_str(&self) -> &str {
-            // SAFETY: `self.inner` is only initialised via `String`, which upholds the validity invariant of `str`.
-            unsafe { str::from_utf8_unchecked(self.inner.to_bytes()) }
-        }
-    }
-
-    impl core::ops::Deref for ThreadNameString {
-        type Target = CStr;
-        fn deref(&self) -> &CStr {
-            &self.inner
-        }
-    }
-
     impl From<String> for ThreadNameString {
         fn from(s: String) -> Self {
             Self {
@@ -1291,82 +1271,124 @@ mod thread_name_string {
             }
         }
     }
-}
-pub(crate) use thread_name_string::ThreadNameString;
-
-static MAIN_THREAD_INFO: SyncUnsafeCell<(MaybeUninit<ThreadId>, MaybeUninit<Parker>)> =
-    SyncUnsafeCell::new((MaybeUninit::uninit(), MaybeUninit::uninit()));
-
-/// The internal representation of a `Thread` that is not the main thread.
-struct OtherInner {
-    name: Option<ThreadNameString>,
-    id: ThreadId,
-    parker: Parker,
-}
-
-/// The internal representation of a `Thread` handle.
-#[derive(Clone)]
-enum Inner {
-    /// Represents the main thread. May only be constructed by Thread::new_main.
-    Main(&'static (ThreadId, Parker)),
-    /// Represents any other thread.
-    Other(Pin<Arc<OtherInner>>),
-}
-
-impl Inner {
-    fn id(&self) -> ThreadId {
-        match self {
-            Self::Main((thread_id, _)) => *thread_id,
-            Self::Other(other) => other.id,
-        }
-    }
 
-    fn cname(&self) -> Option<&CStr> {
-        match self {
-            Self::Main(_) => Some(c"main"),
-            Self::Other(other) => other.name.as_deref(),
+    impl ThreadNameString {
+        pub fn as_cstr(&self) -> &CStr {
+            &self.inner
         }
-    }
 
-    fn name(&self) -> Option<&str> {
-        match self {
-            Self::Main(_) => Some("main"),
-            Self::Other(other) => other.name.as_ref().map(ThreadNameString::as_str),
+        pub fn as_str(&self) -> &str {
+            // SAFETY: `ThreadNameString` is guaranteed to be UTF-8.
+            unsafe { str::from_utf8_unchecked(self.inner.to_bytes()) }
         }
     }
+}
 
-    fn into_raw(self) -> *const () {
-        match self {
-            // Just return the pointer to `MAIN_THREAD_INFO`.
-            Self::Main(ptr) => crate::ptr::from_ref(ptr).cast(),
-            Self::Other(arc) => {
-                // Safety: We only expose an opaque pointer, which maintains the `Pin` invariant.
-                let inner = unsafe { Pin::into_inner_unchecked(arc) };
-                Arc::into_raw(inner) as *const ()
+use thread_name_string::ThreadNameString;
+
+/// Store the ID of the main thread.
+///
+/// The thread handle for the main thread is created lazily, and this might even
+/// happen pre-main. Since not every platform has a way to identify the main
+/// thread when that happens – macOS's `pthread_main_np` function being a notable
+/// exception – we cannot assign it the right name right then. Instead, in our
+/// runtime startup code, we remember the thread ID of the main thread (through
+/// this modules `set` function) and use it to identify the main thread from then
+/// on. This works reliably and has the additional advantage that we can report
+/// the right thread name on main even after the thread handle has been destroyed.
+/// Note however that this also means that the name reported in pre-main functions
+/// will be incorrect, but that's just something we have to live with.
+pub(crate) mod main_thread {
+    cfg_if::cfg_if! {
+        if #[cfg(target_has_atomic = "64")] {
+            use super::ThreadId;
+            use crate::sync::atomic::AtomicU64;
+            use crate::sync::atomic::Ordering::Relaxed;
+
+            static MAIN: AtomicU64 = AtomicU64::new(0);
+
+            pub(super) fn get() -> Option<ThreadId> {
+                ThreadId::from_u64(MAIN.load(Relaxed))
             }
-        }
-    }
 
-    /// # Safety
-    ///
-    /// See [`Thread::from_raw`].
-    unsafe fn from_raw(ptr: *const ()) -> Self {
-        // If the pointer is to `MAIN_THREAD_INFO`, we know it is the `Main` variant.
-        if crate::ptr::eq(ptr.cast(), &MAIN_THREAD_INFO) {
-            Self::Main(unsafe { &*ptr.cast() })
+            /// # Safety
+            /// May only be called once.
+            pub(crate) unsafe fn set(id: ThreadId) {
+                MAIN.store(id.as_u64().get(), Relaxed)
+            }
         } else {
-            // Safety: Upheld by caller
-            Self::Other(unsafe { Pin::new_unchecked(Arc::from_raw(ptr as *const OtherInner)) })
+            use super::ThreadId;
+            use crate::mem::MaybeUninit;
+            use crate::sync::atomic::AtomicBool;
+            use crate::sync::atomic::Ordering::{Acquire, Release};
+
+            static INIT: AtomicBool = AtomicBool::new(false);
+            static mut MAIN: MaybeUninit<ThreadId> = MaybeUninit::uninit();
+
+            pub(super) fn get() -> Option<ThreadId> {
+                if INIT.load(Acquire) {
+                    Some(unsafe { MAIN.assume_init() })
+                } else {
+                    None
+                }
+            }
+
+            /// # Safety
+            /// May only be called once.
+            pub(crate) unsafe fn set(id: ThreadId) {
+                unsafe { MAIN = MaybeUninit::new(id) };
+                INIT.store(true, Release);
+            }
         }
     }
+}
 
-    fn parker(&self) -> Pin<&Parker> {
-        match self {
-            Self::Main((_, parker_ref)) => Pin::static_ref(parker_ref),
-            Self::Other(inner) => unsafe {
-                Pin::map_unchecked(inner.as_ref(), |inner| &inner.parker)
-            },
+/// Run a function with the current thread's name.
+///
+/// Modulo thread local accesses, this function is safe to call from signal
+/// handlers and in similar circumstances where allocations are not possible.
+pub(crate) fn with_current_name<F, R>(f: F) -> R
+where
+    F: FnOnce(Option<&str>) -> R,
+{
+    try_with_current(|thread| {
+        if let Some(thread) = thread {
+            // If there is a current thread handle, try to use the name stored
+            // there.
+            if let Some(name) = &thread.inner.name {
+                return f(Some(name.as_str()));
+            } else if Some(thread.inner.id) == main_thread::get() {
+                // The main thread doesn't store its name in the handle, we must
+                // identify it through its ID. Since we already have the `Thread`,
+                // we can retrieve the ID from it instead of going through another
+                // thread local.
+                return f(Some("main"));
+            }
+        } else if let Some(main) = main_thread::get()
+            && let Some(id) = current::id::get()
+            && id == main
+        {
+            // The main thread doesn't always have a thread handle, we must
+            // identify it through its ID instead. The checks are ordered so
+            // that the current ID is only loaded if it is actually needed,
+            // since loading it from TLS might need multiple expensive accesses.
+            return f(Some("main"));
         }
+
+        f(None)
+    })
+}
+
+/// The internal representation of a `Thread` handle
+struct Inner {
+    name: Option<ThreadNameString>,
+    id: ThreadId,
+    parker: Parker,
+}
+
+impl Inner {
+    fn parker(self: Pin<&Self>) -> Pin<&Parker> {
+        unsafe { Pin::map_unchecked(self, |inner| &inner.parker) }
     }
 }
 
@@ -1390,47 +1412,21 @@ impl Inner {
 /// docs of [`Builder`] and [`spawn`] for more details.
 ///
 /// [`thread::current`]: current::current
-pub struct Thread(Inner);
+pub struct Thread {
+    inner: Pin<Arc<Inner>>,
+}
 
 impl Thread {
-    /// Used only internally to construct a thread object without spawning.
-    pub(crate) fn new(id: ThreadId, name: String) -> Thread {
-        Self::new_inner(id, Some(ThreadNameString::from(name)))
-    }
+    pub(crate) fn new(id: ThreadId, name: Option<String>) -> Thread {
+        let name = name.map(ThreadNameString::from);
 
-    pub(crate) fn new_unnamed(id: ThreadId) -> Thread {
-        Self::new_inner(id, None)
-    }
-
-    /// Used in runtime to construct main thread
-    ///
-    /// # Safety
-    ///
-    /// This must only ever be called once, and must be called on the main thread.
-    pub(crate) unsafe fn new_main(thread_id: ThreadId) -> Thread {
-        // Safety: As this is only called once and on the main thread, nothing else is accessing MAIN_THREAD_INFO
-        // as the only other read occurs in `main_thread_info` *after* the main thread has been constructed,
-        // and this function is the only one that constructs the main thread.
-        //
-        // Pre-main thread spawning cannot hit this either, as the caller promises that this is only called on the main thread.
-        let main_thread_info = unsafe { &mut *MAIN_THREAD_INFO.get() };
-
-        unsafe { Parker::new_in_place((&raw mut main_thread_info.1).cast()) };
-        main_thread_info.0.write(thread_id);
-
-        // Store a `'static` ref to the initialised ThreadId and Parker,
-        // to avoid having to repeatedly prove initialisation.
-        Self(Inner::Main(unsafe { &*MAIN_THREAD_INFO.get().cast() }))
-    }
-
-    fn new_inner(id: ThreadId, name: Option<ThreadNameString>) -> Thread {
         // We have to use `unsafe` here to construct the `Parker` in-place,
         // which is required for the UNIX implementation.
         //
         // SAFETY: We pin the Arc immediately after creation, so its address never
         // changes.
         let inner = unsafe {
-            let mut arc = Arc::<OtherInner>::new_uninit();
+            let mut arc = Arc::<Inner>::new_uninit();
             let ptr = Arc::get_mut_unchecked(&mut arc).as_mut_ptr();
             (&raw mut (*ptr).name).write(name);
             (&raw mut (*ptr).id).write(id);
@@ -1438,7 +1434,7 @@ impl Thread {
             Pin::new_unchecked(arc.assume_init())
         };
 
-        Self(Inner::Other(inner))
+        Thread { inner }
     }
 
     /// Like the public [`park`], but callable on any handle. This is used to
@@ -1447,7 +1443,7 @@ impl Thread {
     /// # Safety
     /// May only be called from the thread to which this handle belongs.
     pub(crate) unsafe fn park(&self) {
-        unsafe { self.0.parker().park() }
+        unsafe { self.inner.as_ref().parker().park() }
     }
 
     /// Like the public [`park_timeout`], but callable on any handle. This is
@@ -1456,7 +1452,7 @@ impl Thread {
     /// # Safety
     /// May only be called from the thread to which this handle belongs.
     pub(crate) unsafe fn park_timeout(&self, dur: Duration) {
-        unsafe { self.0.parker().park_timeout(dur) }
+        unsafe { self.inner.as_ref().parker().park_timeout(dur) }
     }
 
     /// Atomically makes the handle's token available if it is not already.
@@ -1492,7 +1488,7 @@ impl Thread {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn unpark(&self) {
-        self.0.parker().unpark();
+        self.inner.as_ref().parker().unpark();
     }
 
     /// Gets the thread's unique identifier.
@@ -1512,7 +1508,7 @@ impl Thread {
     #[stable(feature = "thread_id", since = "1.19.0")]
     #[must_use]
     pub fn id(&self) -> ThreadId {
-        self.0.id()
+        self.inner.id
     }
 
     /// Gets the thread's name.
@@ -1555,11 +1551,13 @@ impl Thread {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
     pub fn name(&self) -> Option<&str> {
-        self.0.name()
-    }
-
-    fn cname(&self) -> Option<&CStr> {
-        self.0.cname()
+        if let Some(name) = &self.inner.name {
+            Some(name.as_str())
+        } else if main_thread::get() == Some(self.inner.id) {
+            Some("main")
+        } else {
+            None
+        }
     }
 
     /// Consumes the `Thread`, returning a raw pointer.
@@ -1583,7 +1581,9 @@ impl Thread {
     /// ```
     #[unstable(feature = "thread_raw", issue = "97523")]
     pub fn into_raw(self) -> *const () {
-        self.0.into_raw()
+        // Safety: We only expose an opaque pointer, which maintains the `Pin` invariant.
+        let inner = unsafe { Pin::into_inner_unchecked(self.inner) };
+        Arc::into_raw(inner) as *const ()
     }
 
     /// Constructs a `Thread` from a raw pointer.
@@ -1605,7 +1605,17 @@ impl Thread {
     #[unstable(feature = "thread_raw", issue = "97523")]
     pub unsafe fn from_raw(ptr: *const ()) -> Thread {
         // Safety: Upheld by caller.
-        unsafe { Thread(Inner::from_raw(ptr)) }
+        unsafe { Thread { inner: Pin::new_unchecked(Arc::from_raw(ptr as *const Inner)) } }
+    }
+
+    fn cname(&self) -> Option<&CStr> {
+        if let Some(name) = &self.inner.name {
+            Some(name.as_cstr())
+        } else if main_thread::get() == Some(self.inner.id) {
+            Some(c"main")
+        } else {
+            None
+        }
     }
 }
 
diff --git a/src/bootstrap/src/core/build_steps/doc.rs b/src/bootstrap/src/core/build_steps/doc.rs
index dc09d2d1093..0eb4080c053 100644
--- a/src/bootstrap/src/core/build_steps/doc.rs
+++ b/src/bootstrap/src/core/build_steps/doc.rs
@@ -65,8 +65,6 @@ macro_rules! book {
 // NOTE: When adding a book here, make sure to ALSO build the book by
 // adding a build step in `src/bootstrap/code/builder/mod.rs`!
 // NOTE: Make sure to add the corresponding submodule when adding a new book.
-// FIXME: Make checking for a submodule automatic somehow (maybe by having a list of all submodules
-// and checking against it?).
 book!(
     CargoBook, "src/tools/cargo/src/doc", "cargo", &[];
     ClippyBook, "src/tools/clippy/book", "clippy", &[];
diff --git a/src/doc/book b/src/doc/book
-Subproject 5a65e2af063ff701ae858f1f7536ee347b3cfe6
+Subproject 8a0eee28f769387e543882352b12d956aa1b7c3
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 019a888bd2f..3d51ab1967d 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -17,12 +17,12 @@ use rustc_span::symbol::{Symbol, sym};
 use thin_vec::{ThinVec, thin_vec};
 use tracing::{debug, trace};
 
-use super::Item;
+use super::{Item, extract_cfg_from_attrs};
 use crate::clean::{
-    self, Attributes, AttributesExt, ImplKind, ItemId, Type, clean_bound_vars, clean_generics,
-    clean_impl_item, clean_middle_assoc_item, clean_middle_field, clean_middle_ty,
-    clean_poly_fn_sig, clean_trait_ref_with_constraints, clean_ty, clean_ty_alias_inner_type,
-    clean_ty_generics, clean_variant_def, utils,
+    self, Attributes, ImplKind, ItemId, Type, clean_bound_vars, clean_generics, clean_impl_item,
+    clean_middle_assoc_item, clean_middle_field, clean_middle_ty, clean_poly_fn_sig,
+    clean_trait_ref_with_constraints, clean_ty, clean_ty_alias_inner_type, clean_ty_generics,
+    clean_variant_def, utils,
 };
 use crate::core::DocContext;
 use crate::formats::item_type::ItemType;
@@ -408,10 +408,13 @@ pub(crate) fn merge_attrs(
             } else {
                 Attributes::from_hir(&both)
             },
-            both.cfg(cx.tcx, &cx.cache.hidden_cfg),
+            extract_cfg_from_attrs(both.iter(), cx.tcx, &cx.cache.hidden_cfg),
         )
     } else {
-        (Attributes::from_hir(old_attrs), old_attrs.cfg(cx.tcx, &cx.cache.hidden_cfg))
+        (
+            Attributes::from_hir(old_attrs),
+            extract_cfg_from_attrs(old_attrs.iter(), cx.tcx, &cx.cache.hidden_cfg),
+        )
     }
 }
 
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index f619b2c66ac..fbd934bf718 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -186,8 +186,7 @@ fn generate_item_with_correct_attrs(
         // For glob re-exports the item may or may not exist to be re-exported (potentially the cfgs
         // on the path up until the glob can be removed, and only cfgs on the globbed item itself
         // matter), for non-inlined re-exports see #85043.
-        let is_inline = inline::load_attrs(cx, import_id.to_def_id())
-            .lists(sym::doc)
+        let is_inline = hir_attr_lists(inline::load_attrs(cx, import_id.to_def_id()), sym::doc)
             .get_word_attr(sym::inline)
             .is_some()
             || (is_glob_import(cx.tcx, import_id)
@@ -199,8 +198,14 @@ fn generate_item_with_correct_attrs(
         // We only keep the item's attributes.
         target_attrs.iter().map(|attr| (Cow::Borrowed(attr), None)).collect()
     };
-
-    let cfg = attrs.cfg(cx.tcx, &cx.cache.hidden_cfg);
+    let cfg = extract_cfg_from_attrs(
+        attrs.iter().map(move |(attr, _)| match attr {
+            Cow::Borrowed(attr) => *attr,
+            Cow::Owned(attr) => attr,
+        }),
+        cx.tcx,
+        &cx.cache.hidden_cfg,
+    );
     let attrs = Attributes::from_hir_iter(attrs.iter().map(|(attr, did)| (&**attr, *did)), false);
 
     let name = renamed.or(Some(name));
@@ -979,13 +984,14 @@ fn clean_proc_macro<'tcx>(
 ) -> ItemKind {
     let attrs = cx.tcx.hir().attrs(item.hir_id());
     if kind == MacroKind::Derive
-        && let Some(derive_name) = attrs.lists(sym::proc_macro_derive).find_map(|mi| mi.ident())
+        && let Some(derive_name) =
+            hir_attr_lists(attrs, sym::proc_macro_derive).find_map(|mi| mi.ident())
     {
         *name = derive_name.name;
     }
 
     let mut helpers = Vec::new();
-    for mi in attrs.lists(sym::proc_macro_derive) {
+    for mi in hir_attr_lists(attrs, sym::proc_macro_derive) {
         if !mi.has_name(sym::attributes) {
             continue;
         }
@@ -2985,7 +2991,7 @@ fn clean_use_statement_inner<'tcx>(
 
     let visibility = cx.tcx.visibility(import.owner_id);
     let attrs = cx.tcx.hir().attrs(import.hir_id());
-    let inline_attr = attrs.lists(sym::doc).get_word_attr(sym::inline);
+    let inline_attr = hir_attr_lists(attrs, sym::doc).get_word_attr(sym::inline);
     let pub_underscore = visibility.is_public() && name == kw::Underscore;
     let current_mod = cx.tcx.parent_module_from_def_id(import.owner_id.def_id);
     let import_def_id = import.owner_id.def_id;
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index ff1c0294fb8..6e817af0d6e 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -1,4 +1,3 @@
-use std::borrow::Cow;
 use std::hash::Hash;
 use std::path::PathBuf;
 use std::sync::{Arc, OnceLock as OnceCell};
@@ -6,7 +5,9 @@ use std::{fmt, iter};
 
 use arrayvec::ArrayVec;
 use rustc_abi::{ExternAbi, VariantIdx};
-use rustc_attr_parsing::{ConstStability, Deprecation, Stability, StableSince};
+use rustc_attr_parsing::{
+    AllowedThroughUnstableModules, ConstStability, Deprecation, Stability, StableSince,
+};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE, LocalDefId};
@@ -406,15 +407,19 @@ impl Item {
             // were never supposed to work at all.
             let stab = self.stability(tcx)?;
             if let rustc_attr_parsing::StabilityLevel::Stable {
-                allowed_through_unstable_modules: true,
+                allowed_through_unstable_modules: Some(note),
                 ..
             } = stab.level
             {
+                let note = match note {
+                    AllowedThroughUnstableModules::WithDeprecation(note) => Some(note),
+                    // FIXME: Would be better to say *something* here about the *path* being
+                    // deprecated rather than the item.
+                    AllowedThroughUnstableModules::WithoutDeprecation => None,
+                };
                 Some(Deprecation {
-                    // FIXME(#131676, #135003): when a note is added to this stability tag,
-                    // translate it here
                     since: rustc_attr_parsing::DeprecatedSince::Unspecified,
-                    note: None,
+                    note,
                     suggestion: None,
                 })
             } else {
@@ -479,7 +484,7 @@ impl Item {
             name,
             kind,
             Attributes::from_hir(hir_attrs),
-            hir_attrs.cfg(cx.tcx, &cx.cache.hidden_cfg),
+            extract_cfg_from_attrs(hir_attrs.iter(), cx.tcx, &cx.cache.hidden_cfg),
         )
     }
 
@@ -990,147 +995,107 @@ pub(crate) struct Module {
     pub(crate) span: Span,
 }
 
-pub(crate) trait AttributesExt {
-    type AttributeIterator<'a>: Iterator<Item = ast::MetaItemInner>
-    where
-        Self: 'a;
-    type Attributes<'a>: Iterator<Item = &'a hir::Attribute>
-    where
-        Self: 'a;
-
-    fn lists(&self, name: Symbol) -> Self::AttributeIterator<'_>;
-
-    fn iter(&self) -> Self::Attributes<'_>;
-
-    fn cfg(&self, tcx: TyCtxt<'_>, hidden_cfg: &FxHashSet<Cfg>) -> Option<Arc<Cfg>> {
-        let sess = tcx.sess;
-        let doc_cfg_active = tcx.features().doc_cfg();
-        let doc_auto_cfg_active = tcx.features().doc_auto_cfg();
-
-        fn single<T: IntoIterator>(it: T) -> Option<T::Item> {
-            let mut iter = it.into_iter();
-            let item = iter.next()?;
-            if iter.next().is_some() {
-                return None;
-            }
-            Some(item)
+pub(crate) fn hir_attr_lists<'a, I: IntoIterator<Item = &'a hir::Attribute>>(
+    attrs: I,
+    name: Symbol,
+) -> impl Iterator<Item = ast::MetaItemInner> + use<'a, I> {
+    attrs
+        .into_iter()
+        .filter(move |attr| attr.has_name(name))
+        .filter_map(ast::attr::AttributeExt::meta_item_list)
+        .flatten()
+}
+
+pub(crate) fn extract_cfg_from_attrs<'a, I: Iterator<Item = &'a hir::Attribute> + Clone>(
+    attrs: I,
+    tcx: TyCtxt<'_>,
+    hidden_cfg: &FxHashSet<Cfg>,
+) -> Option<Arc<Cfg>> {
+    let sess = tcx.sess;
+    let doc_cfg_active = tcx.features().doc_cfg();
+    let doc_auto_cfg_active = tcx.features().doc_auto_cfg();
+
+    fn single<T: IntoIterator>(it: T) -> Option<T::Item> {
+        let mut iter = it.into_iter();
+        let item = iter.next()?;
+        if iter.next().is_some() {
+            return None;
         }
+        Some(item)
+    }
 
-        let mut cfg = if doc_cfg_active || doc_auto_cfg_active {
-            let mut doc_cfg = self
-                .iter()
-                .filter(|attr| attr.has_name(sym::doc))
-                .flat_map(|attr| attr.meta_item_list().unwrap_or_default())
+    let mut cfg = if doc_cfg_active || doc_auto_cfg_active {
+        let mut doc_cfg = attrs
+            .clone()
+            .filter(|attr| attr.has_name(sym::doc))
+            .flat_map(|attr| attr.meta_item_list().unwrap_or_default())
+            .filter(|attr| attr.has_name(sym::cfg))
+            .peekable();
+        if doc_cfg.peek().is_some() && doc_cfg_active {
+            doc_cfg
+                .filter_map(|attr| Cfg::parse(&attr).ok())
+                .fold(Cfg::True, |cfg, new_cfg| cfg & new_cfg)
+        } else if doc_auto_cfg_active {
+            // If there is no `doc(cfg())`, then we retrieve the `cfg()` attributes (because
+            // `doc(cfg())` overrides `cfg()`).
+            attrs
+                .clone()
                 .filter(|attr| attr.has_name(sym::cfg))
-                .peekable();
-            if doc_cfg.peek().is_some() && doc_cfg_active {
-                doc_cfg
-                    .filter_map(|attr| Cfg::parse(&attr).ok())
-                    .fold(Cfg::True, |cfg, new_cfg| cfg & new_cfg)
-            } else if doc_auto_cfg_active {
-                // If there is no `doc(cfg())`, then we retrieve the `cfg()` attributes (because
-                // `doc(cfg())` overrides `cfg()`).
-                self.iter()
-                    .filter(|attr| attr.has_name(sym::cfg))
-                    .filter_map(|attr| single(attr.meta_item_list()?))
-                    .filter_map(|attr| {
-                        Cfg::parse_without(attr.meta_item()?, hidden_cfg).ok().flatten()
-                    })
-                    .fold(Cfg::True, |cfg, new_cfg| cfg & new_cfg)
-            } else {
-                Cfg::True
-            }
+                .filter_map(|attr| single(attr.meta_item_list()?))
+                .filter_map(|attr| Cfg::parse_without(attr.meta_item()?, hidden_cfg).ok().flatten())
+                .fold(Cfg::True, |cfg, new_cfg| cfg & new_cfg)
         } else {
             Cfg::True
-        };
-
-        for attr in self.iter() {
-            // #[doc]
-            if attr.doc_str().is_none() && attr.has_name(sym::doc) {
-                // #[doc(...)]
-                if let Some(list) = attr.meta_item_list() {
-                    for item in list {
-                        // #[doc(hidden)]
-                        if !item.has_name(sym::cfg) {
-                            continue;
-                        }
-                        // #[doc(cfg(...))]
-                        if let Some(cfg_mi) = item
-                            .meta_item()
-                            .and_then(|item| rustc_expand::config::parse_cfg(item, sess))
-                        {
-                            match Cfg::parse(cfg_mi) {
-                                Ok(new_cfg) => cfg &= new_cfg,
-                                Err(e) => {
-                                    sess.dcx().span_err(e.span, e.msg);
-                                }
+        }
+    } else {
+        Cfg::True
+    };
+
+    for attr in attrs.clone() {
+        // #[doc]
+        if attr.doc_str().is_none() && attr.has_name(sym::doc) {
+            // #[doc(...)]
+            if let Some(list) = attr.meta_item_list() {
+                for item in list {
+                    // #[doc(hidden)]
+                    if !item.has_name(sym::cfg) {
+                        continue;
+                    }
+                    // #[doc(cfg(...))]
+                    if let Some(cfg_mi) = item
+                        .meta_item()
+                        .and_then(|item| rustc_expand::config::parse_cfg(item, sess))
+                    {
+                        match Cfg::parse(cfg_mi) {
+                            Ok(new_cfg) => cfg &= new_cfg,
+                            Err(e) => {
+                                sess.dcx().span_err(e.span, e.msg);
                             }
                         }
                     }
                 }
             }
         }
+    }
 
-        // treat #[target_feature(enable = "feat")] attributes as if they were
-        // #[doc(cfg(target_feature = "feat"))] attributes as well
-        for attr in self.lists(sym::target_feature) {
-            if attr.has_name(sym::enable) {
-                if attr.value_str().is_some() {
-                    // Clone `enable = "feat"`, change to `target_feature = "feat"`.
-                    // Unwrap is safe because `value_str` succeeded above.
-                    let mut meta = attr.meta_item().unwrap().clone();
-                    meta.path = ast::Path::from_ident(Ident::with_dummy_span(sym::target_feature));
-
-                    if let Ok(feat_cfg) = Cfg::parse(&ast::MetaItemInner::MetaItem(meta)) {
-                        cfg &= feat_cfg;
-                    }
+    // treat #[target_feature(enable = "feat")] attributes as if they were
+    // #[doc(cfg(target_feature = "feat"))] attributes as well
+    for attr in hir_attr_lists(attrs, sym::target_feature) {
+        if attr.has_name(sym::enable) {
+            if attr.value_str().is_some() {
+                // Clone `enable = "feat"`, change to `target_feature = "feat"`.
+                // Unwrap is safe because `value_str` succeeded above.
+                let mut meta = attr.meta_item().unwrap().clone();
+                meta.path = ast::Path::from_ident(Ident::with_dummy_span(sym::target_feature));
+
+                if let Ok(feat_cfg) = Cfg::parse(&ast::MetaItemInner::MetaItem(meta)) {
+                    cfg &= feat_cfg;
                 }
             }
         }
-
-        if cfg == Cfg::True { None } else { Some(Arc::new(cfg)) }
-    }
-}
-
-impl AttributesExt for [hir::Attribute] {
-    type AttributeIterator<'a> = impl Iterator<Item = ast::MetaItemInner> + 'a;
-    type Attributes<'a> = impl Iterator<Item = &'a hir::Attribute> + 'a;
-
-    fn lists(&self, name: Symbol) -> Self::AttributeIterator<'_> {
-        self.iter()
-            .filter(move |attr| attr.has_name(name))
-            .filter_map(ast::attr::AttributeExt::meta_item_list)
-            .flatten()
-    }
-
-    fn iter(&self) -> Self::Attributes<'_> {
-        self.iter()
     }
-}
-
-impl AttributesExt for [(Cow<'_, hir::Attribute>, Option<DefId>)] {
-    type AttributeIterator<'a>
-        = impl Iterator<Item = ast::MetaItemInner> + 'a
-    where
-        Self: 'a;
-    type Attributes<'a>
-        = impl Iterator<Item = &'a hir::Attribute> + 'a
-    where
-        Self: 'a;
 
-    fn lists(&self, name: Symbol) -> Self::AttributeIterator<'_> {
-        AttributesExt::iter(self)
-            .filter(move |attr| attr.has_name(name))
-            .filter_map(hir::Attribute::meta_item_list)
-            .flatten()
-    }
-
-    fn iter(&self) -> Self::Attributes<'_> {
-        self.iter().map(move |(attr, _)| match attr {
-            Cow::Borrowed(attr) => *attr,
-            Cow::Owned(attr) => attr,
-        })
-    }
+    if cfg == Cfg::True { None } else { Some(Arc::new(cfg)) }
 }
 
 pub(crate) trait NestedAttributesExt {
@@ -1196,7 +1161,7 @@ pub(crate) struct Attributes {
 
 impl Attributes {
     pub(crate) fn lists(&self, name: Symbol) -> impl Iterator<Item = ast::MetaItemInner> + '_ {
-        self.other_attrs.lists(name)
+        hir_attr_lists(&self.other_attrs[..], name)
     }
 
     pub(crate) fn has_doc_flag(&self, flag: Symbol) -> bool {
@@ -1263,7 +1228,9 @@ impl Attributes {
     pub(crate) fn get_doc_aliases(&self) -> Box<[Symbol]> {
         let mut aliases = FxIndexSet::default();
 
-        for attr in self.other_attrs.lists(sym::doc).filter(|a| a.has_name(sym::alias)) {
+        for attr in
+            hir_attr_lists(&self.other_attrs[..], sym::doc).filter(|a| a.has_name(sym::alias))
+        {
             if let Some(values) = attr.meta_item_list() {
                 for l in values {
                     if let Some(lit) = l.lit()
diff --git a/src/librustdoc/doctest/rust.rs b/src/librustdoc/doctest/rust.rs
index 0903baddabe..bd292efeb7e 100644
--- a/src/librustdoc/doctest/rust.rs
+++ b/src/librustdoc/doctest/rust.rs
@@ -13,8 +13,7 @@ use rustc_span::source_map::SourceMap;
 use rustc_span::{BytePos, DUMMY_SP, FileName, Pos, Span};
 
 use super::{DocTestVisitor, ScrapedDocTest};
-use crate::clean::Attributes;
-use crate::clean::types::AttributesExt;
+use crate::clean::{Attributes, extract_cfg_from_attrs};
 use crate::html::markdown::{self, ErrorCodes, LangString, MdRelLine};
 
 struct RustCollector {
@@ -97,7 +96,9 @@ impl HirCollector<'_> {
         nested: F,
     ) {
         let ast_attrs = self.tcx.hir().attrs(self.tcx.local_def_id_to_hir_id(def_id));
-        if let Some(ref cfg) = ast_attrs.cfg(self.tcx, &FxHashSet::default()) {
+        if let Some(ref cfg) =
+            extract_cfg_from_attrs(ast_attrs.iter(), self.tcx, &FxHashSet::default())
+        {
             if !cfg.matches(&self.tcx.sess.psess, Some(self.tcx.features())) {
                 return;
             }
diff --git a/src/librustdoc/formats/cache.rs b/src/librustdoc/formats/cache.rs
index cbb3ce6abe6..4760e579199 100644
--- a/src/librustdoc/formats/cache.rs
+++ b/src/librustdoc/formats/cache.rs
@@ -316,7 +316,7 @@ impl DocFolder for CacheBuilder<'_, '_> {
 
                 let skip_because_unstable = matches!(
                     item.stability.map(|stab| stab.level),
-                    Some(StabilityLevel::Stable { allowed_through_unstable_modules: true, .. })
+                    Some(StabilityLevel::Stable { allowed_through_unstable_modules: Some(_), .. })
                 );
 
                 if (!self.cache.stripped_mod && !skip_because_unstable) || self.is_json_output {
diff --git a/src/librustdoc/passes/propagate_stability.rs b/src/librustdoc/passes/propagate_stability.rs
index febb52a3b00..9c958710c42 100644
--- a/src/librustdoc/passes/propagate_stability.rs
+++ b/src/librustdoc/passes/propagate_stability.rs
@@ -119,7 +119,7 @@ fn merge_stability(
     parent_stability: Option<Stability>,
 ) -> Option<Stability> {
     if let Some(own_stab) = own_stability
-        && let StabilityLevel::Stable { since: own_since, allowed_through_unstable_modules: false } =
+        && let StabilityLevel::Stable { since: own_since, allowed_through_unstable_modules: None } =
             own_stab.level
         && let Some(parent_stab) = parent_stability
         && (parent_stab.is_unstable()
@@ -127,12 +127,12 @@ fn merge_stability(
     {
         parent_stability
     } else if let Some(mut own_stab) = own_stability
-        && let StabilityLevel::Stable { since, allowed_through_unstable_modules: true } =
+        && let StabilityLevel::Stable { since, allowed_through_unstable_modules: Some(_) } =
             own_stab.level
         && parent_stability.is_some_and(|stab| stab.is_stable())
     {
         // this property does not apply transitively through re-exports
-        own_stab.level = StabilityLevel::Stable { since, allowed_through_unstable_modules: false };
+        own_stab.level = StabilityLevel::Stable { since, allowed_through_unstable_modules: None };
         Some(own_stab)
     } else {
         own_stability
diff --git a/src/librustdoc/visit_ast.rs b/src/librustdoc/visit_ast.rs
index 794ea54b3ef..d46b0dee36c 100644
--- a/src/librustdoc/visit_ast.rs
+++ b/src/librustdoc/visit_ast.rs
@@ -19,7 +19,7 @@ use tracing::debug;
 
 use crate::clean::cfg::Cfg;
 use crate::clean::utils::{inherits_doc_hidden, should_ignore_res};
-use crate::clean::{AttributesExt, NestedAttributesExt, reexport_chain};
+use crate::clean::{NestedAttributesExt, hir_attr_lists, reexport_chain};
 use crate::core;
 
 /// This module is used to store stuff from Rust's AST in a more convenient
@@ -247,8 +247,8 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
         let document_hidden = self.cx.render_options.document_hidden;
         let use_attrs = tcx.hir().attrs(tcx.local_def_id_to_hir_id(def_id));
         // Don't inline `doc(hidden)` imports so they can be stripped at a later stage.
-        let is_no_inline = use_attrs.lists(sym::doc).has_word(sym::no_inline)
-            || (document_hidden && use_attrs.lists(sym::doc).has_word(sym::hidden));
+        let is_no_inline = hir_attr_lists(use_attrs, sym::doc).has_word(sym::no_inline)
+            || (document_hidden && hir_attr_lists(use_attrs, sym::doc).has_word(sym::hidden));
 
         if is_no_inline {
             return false;
diff --git a/src/tools/clippy/clippy_lints/src/std_instead_of_core.rs b/src/tools/clippy/clippy_lints/src/std_instead_of_core.rs
index 82ff13a5aff..8ec7bfe9edd 100644
--- a/src/tools/clippy/clippy_lints/src/std_instead_of_core.rs
+++ b/src/tools/clippy/clippy_lints/src/std_instead_of_core.rs
@@ -180,7 +180,7 @@ fn is_stable(cx: &LateContext<'_>, mut def_id: DefId, msrv: &Msrv) -> bool {
         if let Some(stability) = cx.tcx.lookup_stability(def_id)
             && let StabilityLevel::Stable {
                 since,
-                allowed_through_unstable_modules: false,
+                allowed_through_unstable_modules: None,
             } = stability.level
         {
             let stable = match since {
diff --git a/src/tools/clippy/tests/ui/std_instead_of_core.fixed b/src/tools/clippy/tests/ui/std_instead_of_core.fixed
index 227b98c683e..ec158ee02de 100644
--- a/src/tools/clippy/tests/ui/std_instead_of_core.fixed
+++ b/src/tools/clippy/tests/ui/std_instead_of_core.fixed
@@ -1,7 +1,7 @@
 //@aux-build:proc_macro_derive.rs
 
 #![warn(clippy::std_instead_of_core)]
-#![allow(unused_imports)]
+#![allow(unused_imports, deprecated)]
 
 extern crate alloc;
 
diff --git a/src/tools/clippy/tests/ui/std_instead_of_core.rs b/src/tools/clippy/tests/ui/std_instead_of_core.rs
index 01bb78dd3bf..9c3c1658d8f 100644
--- a/src/tools/clippy/tests/ui/std_instead_of_core.rs
+++ b/src/tools/clippy/tests/ui/std_instead_of_core.rs
@@ -1,7 +1,7 @@
 //@aux-build:proc_macro_derive.rs
 
 #![warn(clippy::std_instead_of_core)]
-#![allow(unused_imports)]
+#![allow(unused_imports, deprecated)]
 
 extern crate alloc;
 
diff --git a/src/tools/clippy/tests/ui/transmute.rs b/src/tools/clippy/tests/ui/transmute.rs
index eeea3f080b1..7f5bdea4acf 100644
--- a/src/tools/clippy/tests/ui/transmute.rs
+++ b/src/tools/clippy/tests/ui/transmute.rs
@@ -24,31 +24,31 @@ fn my_vec() -> MyVec<i32> {
 #[warn(clippy::useless_transmute)]
 unsafe fn _generic<'a, T, U: 'a>(t: &'a T) {
     // FIXME: should lint
-    // let _: &'a T = core::intrinsics::transmute(t);
+    // let _: &'a T = core::mem::transmute(t);
 
-    let _: &'a U = core::intrinsics::transmute(t);
+    let _: &'a U = core::mem::transmute(t);
 
-    let _: *const T = core::intrinsics::transmute(t);
+    let _: *const T = core::mem::transmute(t);
     //~^ ERROR: transmute from a reference to a pointer
     //~| NOTE: `-D clippy::useless-transmute` implied by `-D warnings`
 
-    let _: *mut T = core::intrinsics::transmute(t);
+    let _: *mut T = core::mem::transmute(t);
     //~^ ERROR: transmute from a reference to a pointer
 
-    let _: *const U = core::intrinsics::transmute(t);
+    let _: *const U = core::mem::transmute(t);
     //~^ ERROR: transmute from a reference to a pointer
 }
 
 #[warn(clippy::useless_transmute)]
 fn useless() {
     unsafe {
-        let _: Vec<i32> = core::intrinsics::transmute(my_vec());
+        let _: Vec<i32> = core::mem::transmute(my_vec());
         //~^ ERROR: transmute from a type (`std::vec::Vec<i32>`) to itself
 
         let _: Vec<i32> = core::mem::transmute(my_vec());
         //~^ ERROR: transmute from a type (`std::vec::Vec<i32>`) to itself
 
-        let _: Vec<i32> = std::intrinsics::transmute(my_vec());
+        let _: Vec<i32> = std::mem::transmute(my_vec());
         //~^ ERROR: transmute from a type (`std::vec::Vec<i32>`) to itself
 
         let _: Vec<i32> = std::mem::transmute(my_vec());
@@ -94,17 +94,17 @@ fn crosspointer() {
     let int_mut_ptr: *mut Usize = &mut int as *mut Usize;
 
     unsafe {
-        let _: Usize = core::intrinsics::transmute(int_const_ptr);
+        let _: Usize = core::mem::transmute(int_const_ptr);
         //~^ ERROR: transmute from a type (`*const Usize`) to the type that it points to (
         //~| NOTE: `-D clippy::crosspointer-transmute` implied by `-D warnings`
 
-        let _: Usize = core::intrinsics::transmute(int_mut_ptr);
+        let _: Usize = core::mem::transmute(int_mut_ptr);
         //~^ ERROR: transmute from a type (`*mut Usize`) to the type that it points to (`U
 
-        let _: *const Usize = core::intrinsics::transmute(my_int());
+        let _: *const Usize = core::mem::transmute(my_int());
         //~^ ERROR: transmute from a type (`Usize`) to a pointer to that type (`*const Usi
 
-        let _: *mut Usize = core::intrinsics::transmute(my_int());
+        let _: *mut Usize = core::mem::transmute(my_int());
         //~^ ERROR: transmute from a type (`Usize`) to a pointer to that type (`*mut Usize
     }
 }
diff --git a/src/tools/clippy/tests/ui/transmute.stderr b/src/tools/clippy/tests/ui/transmute.stderr
index 41a10f381dc..b5032772856 100644
--- a/src/tools/clippy/tests/ui/transmute.stderr
+++ b/src/tools/clippy/tests/ui/transmute.stderr
@@ -1,8 +1,8 @@
 error: transmute from a reference to a pointer
   --> tests/ui/transmute.rs:31:23
    |
-LL |     let _: *const T = core::intrinsics::transmute(t);
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T`
+LL |     let _: *const T = core::mem::transmute(t);
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T`
    |
    = note: `-D clippy::useless-transmute` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::useless_transmute)]`
@@ -10,20 +10,20 @@ LL |     let _: *const T = core::intrinsics::transmute(t);
 error: transmute from a reference to a pointer
   --> tests/ui/transmute.rs:35:21
    |
-LL |     let _: *mut T = core::intrinsics::transmute(t);
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T as *mut T`
+LL |     let _: *mut T = core::mem::transmute(t);
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T as *mut T`
 
 error: transmute from a reference to a pointer
   --> tests/ui/transmute.rs:38:23
    |
-LL |     let _: *const U = core::intrinsics::transmute(t);
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T as *const U`
+LL |     let _: *const U = core::mem::transmute(t);
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `t as *const T as *const U`
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
   --> tests/ui/transmute.rs:45:27
    |
-LL |         let _: Vec<i32> = core::intrinsics::transmute(my_vec());
-   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let _: Vec<i32> = core::mem::transmute(my_vec());
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
   --> tests/ui/transmute.rs:48:27
@@ -34,8 +34,8 @@ LL |         let _: Vec<i32> = core::mem::transmute(my_vec());
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
   --> tests/ui/transmute.rs:51:27
    |
-LL |         let _: Vec<i32> = std::intrinsics::transmute(my_vec());
-   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let _: Vec<i32> = std::mem::transmute(my_vec());
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`std::vec::Vec<i32>`) to itself
   --> tests/ui/transmute.rs:54:27
@@ -64,8 +64,8 @@ LL |         let _: *const usize = std::mem::transmute(1 + 1usize);
 error: transmute from a type (`*const Usize`) to the type that it points to (`Usize`)
   --> tests/ui/transmute.rs:97:24
    |
-LL |         let _: Usize = core::intrinsics::transmute(int_const_ptr);
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let _: Usize = core::mem::transmute(int_const_ptr);
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::crosspointer-transmute` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::crosspointer_transmute)]`
@@ -73,20 +73,20 @@ LL |         let _: Usize = core::intrinsics::transmute(int_const_ptr);
 error: transmute from a type (`*mut Usize`) to the type that it points to (`Usize`)
   --> tests/ui/transmute.rs:101:24
    |
-LL |         let _: Usize = core::intrinsics::transmute(int_mut_ptr);
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let _: Usize = core::mem::transmute(int_mut_ptr);
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`Usize`) to a pointer to that type (`*const Usize`)
   --> tests/ui/transmute.rs:104:31
    |
-LL |         let _: *const Usize = core::intrinsics::transmute(my_int());
-   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let _: *const Usize = core::mem::transmute(my_int());
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a type (`Usize`) to a pointer to that type (`*mut Usize`)
   --> tests/ui/transmute.rs:107:29
    |
-LL |         let _: *mut Usize = core::intrinsics::transmute(my_int());
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         let _: *mut Usize = core::mem::transmute(my_int());
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: transmute from a `u8` to a `bool`
   --> tests/ui/transmute.rs:114:28
diff --git a/tests/debuginfo/thread.rs b/tests/debuginfo/thread.rs
index dc8cb083219..0415f586f5d 100644
--- a/tests/debuginfo/thread.rs
+++ b/tests/debuginfo/thread.rs
@@ -12,15 +12,15 @@
 // cdb-check:join_handle,d    [Type: std::thread::JoinHandle<tuple$<> >]
 // cdb-check:    [...] __0              [Type: std::thread::JoinInner<tuple$<> >]
 //
-// cdb-command:dx -r3 t,d
+// cdb-command:dx t,d
 // cdb-check:t,d              : [...] [Type: std::thread::Thread *]
-// cdb-check:    [...] __0              : Other [Type: enum2$<std::thread::Inner>]
-// cdb-check:         [...] __0              [Type: core::pin::Pin<alloc::sync::Arc<std::thread::OtherInner,[...]> >]
+// cdb-check:[...] inner [...][Type: core::pin::Pin<alloc::sync::Arc<std::thread::Inner,alloc::alloc::Global> >]
 
 use std::thread;
 
 #[allow(unused_variables)]
-fn main() {
+fn main()
+{
     let join_handle = thread::spawn(|| {
         println!("Initialize a thread");
     });
diff --git a/tests/ui/stability-attribute/accidental-stable-in-unstable.rs b/tests/ui/stability-attribute/accidental-stable-in-unstable.rs
index 86a9d2066eb..a36a78ee442 100644
--- a/tests/ui/stability-attribute/accidental-stable-in-unstable.rs
+++ b/tests/ui/stability-attribute/accidental-stable-in-unstable.rs
@@ -8,3 +8,4 @@ use core::unicode::UNICODE_VERSION; //~ ERROR use of unstable library feature `u
 // Known accidental stabilizations with known users
 // fully stable @ core::mem::transmute
 use core::intrinsics::transmute; // depended upon by rand_core
+//~^WARN deprecated
diff --git a/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr b/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr
index 9943e6d7ac6..16e3676aa65 100644
--- a/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr
+++ b/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr
@@ -7,6 +7,14 @@ LL | use core::unicode::UNICODE_VERSION;
    = help: add `#![feature(unicode_internals)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 1 previous error
+warning: use of deprecated module `std::intrinsics`: import this function via `std::mem` instead
+  --> $DIR/accidental-stable-in-unstable.rs:10:23
+   |
+LL | use core::intrinsics::transmute; // depended upon by rand_core
+   |                       ^^^^^^^^^
+   |
+   = note: `#[warn(deprecated)]` on by default
+
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/stability-attribute/allowed-through-unstable.rs b/tests/ui/stability-attribute/allowed-through-unstable.rs
index 29911a70be9..e03417a4dae 100644
--- a/tests/ui/stability-attribute/allowed-through-unstable.rs
+++ b/tests/ui/stability-attribute/allowed-through-unstable.rs
@@ -6,4 +6,5 @@
 extern crate allowed_through_unstable_core;
 
 use allowed_through_unstable_core::unstable_module::OldStableTraitAllowedThoughUnstable;
+use allowed_through_unstable_core::unstable_module::OldStableTraitAllowedThoughUnstableWithDeprecation; //~WARN use of deprecated module `allowed_through_unstable_core::unstable_module`: use the new path instead
 use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowedThroughUnstable; //~ ERROR use of unstable library feature `unstable_test_feature`
diff --git a/tests/ui/stability-attribute/allowed-through-unstable.stderr b/tests/ui/stability-attribute/allowed-through-unstable.stderr
index 00eea9f730d..8d07b0cf9e8 100644
--- a/tests/ui/stability-attribute/allowed-through-unstable.stderr
+++ b/tests/ui/stability-attribute/allowed-through-unstable.stderr
@@ -1,5 +1,13 @@
+warning: use of deprecated module `allowed_through_unstable_core::unstable_module`: use the new path instead
+  --> $DIR/allowed-through-unstable.rs:9:53
+   |
+LL | use allowed_through_unstable_core::unstable_module::OldStableTraitAllowedThoughUnstableWithDeprecation;
+   |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(deprecated)]` on by default
+
 error[E0658]: use of unstable library feature `unstable_test_feature`
-  --> $DIR/allowed-through-unstable.rs:9:5
+  --> $DIR/allowed-through-unstable.rs:10:5
    |
 LL | use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowedThroughUnstable;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -8,6 +16,6 @@ LL | use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowe
    = help: add `#![feature(unstable_test_feature)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 1 previous error
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs b/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs
index b597009a309..9dfbb451d04 100644
--- a/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs
+++ b/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs
@@ -10,5 +10,9 @@ pub mod unstable_module {
     pub trait OldStableTraitAllowedThoughUnstable {}
 
     #[stable(feature = "stable_test_feature", since = "1.2.0")]
+    #[rustc_allowed_through_unstable_modules = "use the new path instead"]
+    pub trait OldStableTraitAllowedThoughUnstableWithDeprecation {}
+
+    #[stable(feature = "stable_test_feature", since = "1.2.0")]
     pub trait NewStableTraitNotAllowedThroughUnstable {}
 }
diff --git a/tests/ui/traits/trait-upcasting/prefer-lower-candidates.rs b/tests/ui/traits/trait-upcasting/prefer-lower-candidates.rs
new file mode 100644
index 00000000000..4bc59b09fb5
--- /dev/null
+++ b/tests/ui/traits/trait-upcasting/prefer-lower-candidates.rs
@@ -0,0 +1,29 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@ check-pass
+
+// Ensure we don't have ambiguity when upcasting to two supertraits
+// that are identical modulo normalization.
+
+#![feature(trait_upcasting)]
+
+trait Supertrait<T> {
+    fn method(&self) {}
+}
+impl<T> Supertrait<T> for () {}
+
+trait Identity {
+    type Selff;
+}
+impl<Selff> Identity for Selff {
+    type Selff = Selff;
+}
+trait Trait<P>: Supertrait<()> + Supertrait<<P as Identity>::Selff> {}
+
+impl<P> Trait<P> for () {}
+
+fn main() {
+    let x: &dyn Trait<()> = &();
+    let x: &dyn Supertrait<()> = x;
+}