From 8081e86c94119a99c8ed2462edee58f412e661b9 Mon Sep 17 00:00:00 2001
From: Oscar Bray <oscarbray@gmail.com>
Date: Mon, 16 Feb 2026 19:42:12 +0000
Subject: [PATCH] Port #![default_lib_allocator] to the new attribute parser

---
 .../rustc_attr_parsing/src/attributes/crate_level.rs     | 9 +++++++++
 compiler/rustc_attr_parsing/src/context.rs               | 1 +
 compiler/rustc_hir/src/attrs/data_structures.rs          | 3 +++
 compiler/rustc_hir/src/attrs/encode_cross_crate.rs       | 1 +
 compiler/rustc_metadata/src/rmeta/encoder.rs             | 5 +----
 compiler/rustc_passes/src/check_attr.rs                  | 2 +-
 6 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/compiler/rustc_attr_parsing/src/attributes/crate_level.rs b/compiler/rustc_attr_parsing/src/attributes/crate_level.rs
index bdfe7bfb8f1fb..3b3bbf4f0c8af 100644
--- a/compiler/rustc_attr_parsing/src/attributes/crate_level.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/crate_level.rs
@@ -292,3 +292,12 @@ impl<S: Stage> NoArgsAttributeParser<S> for RustcNoImplicitBoundsParser {
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Crate)]);
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNoImplicitBounds;
 }
+
+pub(crate) struct DefaultLibAllocatorParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for DefaultLibAllocatorParser {
+    const PATH: &[Symbol] = &[sym::default_lib_allocator];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Crate)]);
+    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::DefaultLibAllocator;
+}
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index 1bb6c8aa1866c..a0c672778ac12 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -235,6 +235,7 @@ attribute_parsers!(
         Single<WithoutArgs<ConstContinueParser>>,
         Single<WithoutArgs<ConstStabilityIndirectParser>>,
         Single<WithoutArgs<CoroutineParser>>,
+        Single<WithoutArgs<DefaultLibAllocatorParser>>,
         Single<WithoutArgs<DenyExplicitImplParser>>,
         Single<WithoutArgs<DynIncompatibleTraitParser>>,
         Single<WithoutArgs<EiiForeignItemParser>>,
diff --git a/compiler/rustc_hir/src/attrs/data_structures.rs b/compiler/rustc_hir/src/attrs/data_structures.rs
index 41970fb7d35a1..b8f3c898ed07f 100644
--- a/compiler/rustc_hir/src/attrs/data_structures.rs
+++ b/compiler/rustc_hir/src/attrs/data_structures.rs
@@ -897,6 +897,9 @@ pub enum AttributeKind {
     /// Represents `#[debugger_visualizer]`.
     DebuggerVisualizer(ThinVec<DebugVisualizer>),
 
+    /// Represents `#![default_lib_allocator]`
+    DefaultLibAllocator,
+
     /// Represents [`#[deprecated]`](https://doc.rust-lang.org/stable/reference/attributes/diagnostics.html#the-deprecated-attribute).
     Deprecation { deprecation: Deprecation, span: Span },
 
diff --git a/compiler/rustc_hir/src/attrs/encode_cross_crate.rs b/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
index c50a5c649ee4b..86eafb984121d 100644
--- a/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
+++ b/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
@@ -35,6 +35,7 @@ impl AttributeKind {
             CrateType(_) => No,
             CustomMir(_, _, _) => Yes,
             DebuggerVisualizer(..) => No,
+            DefaultLibAllocator => No,
             Deprecation { .. } => Yes,
             DoNotRecommend { .. } => Yes,
             Doc(_) => Yes,
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 3a85b0a050526..a3d8b07fb1d9a 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -734,10 +734,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
                 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
                 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
-                has_default_lib_allocator: ast::attr::contains_name(
-                    attrs,
-                    sym::default_lib_allocator,
-                ),
+                has_default_lib_allocator: find_attr!(attrs, AttributeKind::DefaultLibAllocator),
                 externally_implementable_items,
                 proc_macro_data,
                 debugger_visualizers,
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index ec0306371205b..11c9ee9d61aee 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -246,6 +246,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::CrateName { .. }
                     | AttributeKind::CrateType(..)
                     | AttributeKind::DebuggerVisualizer(..)
+                    | AttributeKind::DefaultLibAllocator
                     // `#[doc]` is actually a lot more than just doc comments, so is checked below
                     | AttributeKind::DocComment {..}
                     | AttributeKind::EiiDeclaration { .. }
@@ -399,7 +400,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             | sym::deny
                             | sym::forbid
                             // internal
-                            | sym::default_lib_allocator
                             | sym::rustc_inherit_overflow_checks
                             | sym::rustc_on_unimplemented
                             | sym::rustc_doc_primitive