Auto merge of #151291 - jhpratt:rollup-CVsL9ZN, r=jhpratt

Rollup of 8 pull requests

Successful merges:

 - #148769 (Stabilize `alloc_layout_extra`)
 - #150200 (Add title field to `ice.md` issue template)
 - #150955 (Underscore-prefixed bindings are explicitly allowed to be unused)
 - #151200 (time: Add saturating arithmetic for `SystemTime`)
 - #151235 (Change field `bit_width: usize` to `bits: u32` in type info)
 - #151242 (Port #[needs_allocator] to attribute parser)
 - #151274 (Include a link to `count_ones` in the docs for `uN::count_zeros` [docs only])
 - #151279 (remove trailing periods in built-in attribute gate messages)

r? @ghost

Author: bors

.github/ISSUE_TEMPLATE/ice.md

@@ -2,6 +2,7 @@
 name: Internal Compiler Error
 about: Create a report for an internal compiler error in rustc.
 labels: C-bug, I-ICE, T-compiler
+title: "[ICE]: "
 ---
 <!--
 Thank you for finding an Internal Compiler Error! 🧊  If possible, try to provide

compiler/rustc_attr_parsing/src/attributes/link_attrs.rs

@@ -658,3 +658,12 @@ impl<S: Stage> SingleAttributeParser<S> for LinkageParser {
         Some(AttributeKind::Linkage(linkage, cx.attr_span))
     }
 }
+
+pub(crate) struct NeedsAllocatorParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for NeedsAllocatorParser {
+    const PATH: &[Symbol] = &[sym::needs_allocator];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Crate)]);
+    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::NeedsAllocator;
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -41,7 +41,7 @@ use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
 use crate::attributes::instruction_set::InstructionSetParser;
 use crate::attributes::link_attrs::{
     ExportStableParser, FfiConstParser, FfiPureParser, LinkNameParser, LinkOrdinalParser,
-    LinkParser, LinkSectionParser, LinkageParser, StdInternalSymbolParser,
+    LinkParser, LinkSectionParser, LinkageParser, NeedsAllocatorParser, StdInternalSymbolParser,
 };
 use crate::attributes::lint_helpers::{
     AsPtrParser, AutomaticallyDerivedParser, PassByValueParser, PubTransparentParser,
@@ -259,6 +259,7 @@ attribute_parsers!(
         Single<WithoutArgs<MacroEscapeParser>>,
         Single<WithoutArgs<MarkerParser>>,
         Single<WithoutArgs<MayDangleParser>>,
+        Single<WithoutArgs<NeedsAllocatorParser>>,
         Single<WithoutArgs<NoCoreParser>>,
         Single<WithoutArgs<NoImplicitPreludeParser>>,
         Single<WithoutArgs<NoLinkParser>>,

compiler/rustc_codegen_cranelift/patches/0027-sysroot_tests-128bit-atomic-operations.patch

@@ -14,11 +14,10 @@ diff --git a/coretests/tests/lib.rs b/coretests/tests/lib.rs
 index 1e336bf..35e6f54 100644
 --- a/coretests/tests/lib.rs
 +++ b/coretests/tests/lib.rs
-@@ -2,5 +2,4 @@
+@@ -2,4 +2,3 @@
  // tidy-alphabetical-start
 -#![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
  #![cfg_attr(test, feature(cfg_select))]
- #![feature(alloc_layout_extra)]
  #![feature(array_ptr_get)]
 diff --git a/coretests/tests/atomic.rs b/coretests/tests/atomic.rs
 index b735957..ea728b6 100644

compiler/rustc_const_eval/src/const_eval/type_info.rs

@@ -257,8 +257,8 @@ impl<'tcx> InterpCx<'tcx, CompileTimeMachine<'tcx>> {
         {
             let field_place = self.project_field(&place, field_idx)?;
             match field.name {
-                sym::bit_width => self.write_scalar(
-                    ScalarInt::try_from_target_usize(bit_width, self.tcx.tcx).unwrap(),
+                sym::bits => self.write_scalar(
+                    Scalar::from_u32(bit_width.try_into().expect("bit_width overflowed")),
                     &field_place,
                 )?,
                 sym::signed => self.write_scalar(Scalar::from_bool(signed), &field_place)?,
@@ -278,8 +278,8 @@ impl<'tcx> InterpCx<'tcx, CompileTimeMachine<'tcx>> {
         {
             let field_place = self.project_field(&place, field_idx)?;
             match field.name {
-                sym::bit_width => self.write_scalar(
-                    ScalarInt::try_from_target_usize(bit_width, self.tcx.tcx).unwrap(),
+                sym::bits => self.write_scalar(
+                    Scalar::from_u32(bit_width.try_into().expect("bit_width overflowed")),
                     &field_place,
                 )?,
                 other => span_bug!(self.tcx.def_span(field.did), "unimplemented field {other}"),

compiler/rustc_feature/src/builtin_attrs.rs

@@ -678,7 +678,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     rustc_attr!(
         rustc_pass_indirectly_in_non_rustic_abis, Normal, template!(Word), ErrorFollowing,
         EncodeCrossCrate::No,
-        "types marked with `#[rustc_pass_indirectly_in_non_rustic_abis]` are always passed indirectly by non-Rustic abis."
+        "types marked with `#[rustc_pass_indirectly_in_non_rustic_abis]` are always passed indirectly by non-Rustic ABIs"
     ),
 
     // Limits:
@@ -1275,38 +1275,38 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     rustc_attr!(
         rustc_as_ptr, Normal, template!(Word), ErrorFollowing,
         EncodeCrossCrate::Yes,
-        "`#[rustc_as_ptr]` is used to mark functions returning pointers to their inner allocations."
+        "`#[rustc_as_ptr]` is used to mark functions returning pointers to their inner allocations"
     ),
     rustc_attr!(
         rustc_should_not_be_called_on_const_items, Normal, template!(Word), ErrorFollowing,
         EncodeCrossCrate::Yes,
-        "`#[rustc_should_not_be_called_on_const_items]` is used to mark methods that don't make sense to be called on interior mutable consts."
+        "`#[rustc_should_not_be_called_on_const_items]` is used to mark methods that don't make sense to be called on interior mutable consts"
     ),
     rustc_attr!(
         rustc_pass_by_value, Normal, template!(Word), ErrorFollowing,
         EncodeCrossCrate::Yes,
-        "`#[rustc_pass_by_value]` is used to mark types that must be passed by value instead of reference."
+        "`#[rustc_pass_by_value]` is used to mark types that must be passed by value instead of reference"
     ),
     rustc_attr!(
         rustc_never_returns_null_ptr, Normal, template!(Word), ErrorFollowing,
         EncodeCrossCrate::Yes,
-        "`#[rustc_never_returns_null_ptr]` is used to mark functions returning non-null pointers."
+        "`#[rustc_never_returns_null_ptr]` is used to mark functions returning non-null pointers"
     ),
     rustc_attr!(
         rustc_no_implicit_autorefs, AttributeType::Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::Yes,
-        "`#[rustc_no_implicit_autorefs]` is used to mark functions for which an autoref to the dereference of a raw pointer should not be used as an argument."
+        "`#[rustc_no_implicit_autorefs]` is used to mark functions for which an autoref to the dereference of a raw pointer should not be used as an argument"
     ),
     rustc_attr!(
         rustc_coherence_is_core, AttributeType::CrateLevel, template!(Word), ErrorFollowing, EncodeCrossCrate::No,
-        "`#![rustc_coherence_is_core]` allows inherent methods on builtin types, only intended to be used in `core`."
+        "`#![rustc_coherence_is_core]` allows inherent methods on builtin types, only intended to be used in `core`"
     ),
     rustc_attr!(
         rustc_coinductive, AttributeType::Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No,
-        "`#[rustc_coinductive]` changes a trait to be coinductive, allowing cycles in the trait solver."
+        "`#[rustc_coinductive]` changes a trait to be coinductive, allowing cycles in the trait solver"
     ),
     rustc_attr!(
         rustc_allow_incoherent_impl, AttributeType::Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::No,
-        "`#[rustc_allow_incoherent_impl]` has to be added to all impl items of an incoherent inherent impl."
+        "`#[rustc_allow_incoherent_impl]` has to be added to all impl items of an incoherent inherent impl"
     ),
     rustc_attr!(
         rustc_preserve_ub_checks, AttributeType::CrateLevel, template!(Word), ErrorFollowing, EncodeCrossCrate::No,
@@ -1333,7 +1333,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_has_incoherent_inherent_impls, AttributeType::Normal, template!(Word),
         ErrorFollowing, EncodeCrossCrate::Yes,
         "`#[rustc_has_incoherent_inherent_impls]` allows the addition of incoherent inherent impls for \
-         the given type by annotating all impl items with `#[rustc_allow_incoherent_impl]`."
+         the given type by annotating all impl items with `#[rustc_allow_incoherent_impl]`"
     ),
 
     BuiltinAttribute {
@@ -1396,7 +1396,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::No,
         "the `#[rustc_skip_during_method_dispatch]` attribute is used to exclude a trait \
         from method dispatch when the receiver is of the following type, for compatibility in \
-        editions < 2021 (array) or editions < 2024 (boxed_slice)."
+        editions < 2021 (array) or editions < 2024 (boxed_slice)"
     ),
     rustc_attr!(
         rustc_must_implement_one_of, Normal, template!(List: &["function1, function2, ..."]),

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -840,6 +840,9 @@ pub enum AttributeKind {
     /// Represents `#[naked]`
     Naked(Span),
 
+    /// Represents `#[needs_allocator]`
+    NeedsAllocator,
+
     /// Represents `#[no_core]`
     NoCore(Span),
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -75,6 +75,7 @@ impl AttributeKind {
             MustNotSupend { .. } => Yes,
             MustUse { .. } => Yes,
             Naked(..) => No,
+            NeedsAllocator => No,
             NoCore(..) => No,
             NoImplicitPrelude(..) => No,
             NoLink => No,

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -742,7 +742,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 proc_macro_data,
                 debugger_visualizers,
                 compiler_builtins: ast::attr::contains_name(attrs, sym::compiler_builtins),
-                needs_allocator: ast::attr::contains_name(attrs, sym::needs_allocator),
+                needs_allocator: find_attr!(attrs, AttributeKind::NeedsAllocator),
                 needs_panic_runtime: ast::attr::contains_name(attrs, sym::needs_panic_runtime),
                 no_builtins: ast::attr::contains_name(attrs, sym::no_builtins),
                 panic_runtime: ast::attr::contains_name(attrs, sym::panic_runtime),

compiler/rustc_mir_transform/src/liveness.rs

@@ -1086,6 +1086,11 @@ impl<'a, 'tcx> AssignmentResult<'a, 'tcx> {
 
             let Some((name, decl_span)) = self.checked_places.names[index] else { continue };
 
+            // By convention, underscore-prefixed bindings are explicitly allowed to be unused.
+            if name.as_str().starts_with('_') {
+                continue;
+            }
+
             let is_maybe_drop_guard = maybe_drop_guard(
                 tcx,
                 self.typing_env,