[gcc r17-3101] gccrs: attr: Register needs_allocator

https://gcc.gnu.org/g:a2f3fb27c419d8a97b9b4a3dcf7c35e248182684

commit r17-3101-ga2f3fb27c419d8a97b9b4a3dcf7c35e248182684
Author: Enes Cevik <[email protected]>
Date:   Fri Jul 10 12:10:37 2026 +0300

    gccrs: attr: Register needs_allocator
    
    This patch registers the 'needs_allocator' attribute, which is required
    for compiling the 'alloc' crate.
    
    Currently, it is implemented as a stub that emits a compiler warning
    when encountered. The reoson for this temporary stub is that full
    handling of 'needs_allocator' strictly depends on the 'global_allocator'
    infrastructure and the 'core::alloc::GlobalAlloc' trait. Since gccrs
    does not yet have full support for the 'core' crate, a complete
    implementation is deferred.
    
    gcc/rust/ChangeLog:
    
            * checks/errors/rust-builtin-attribute-checker.cc
            (check_inner_attribute): Add warning for needs_allocator.
            * util/rust-attribute-values.h (class Attributes): Add
            NEEDS_ALLOCATOR constexpr.
            * util/rust-attributes.cc (__definitions): Add
            BuiltinAttrDefinition for new attribute.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/needs_allocator.rs: New test.
    
    Signed-off-by: Enes Cevik <[email protected]>

Diff:
---
 gcc/rust/checks/errors/rust-builtin-attribute-checker.cc | 7 +++++++
 gcc/rust/util/rust-attribute-values.h                    | 2 ++
 gcc/rust/util/rust-attributes.cc                         | 1 +
 gcc/testsuite/rust/compile/needs_allocator.rs            | 4 ++++
 4 files changed, 14 insertions(+)

diff --git a/gcc/rust/checks/errors/rust-builtin-attribute-checker.cc b/gcc/rust/checks/errors/rust-builtin-attribute-checker.cc
index fef94f5eaca2..c1ab0df5ecc9 100644
--- a/gcc/rust/checks/errors/rust-builtin-attribute-checker.cc
+++ b/gcc/rust/checks/errors/rust-builtin-attribute-checker.cc
@@ -38,6 +38,13 @@ check_inner_attribute (const AST::Attribute &attribute)
   if (Attributes::valid_outer_attribute (result.name))
     rust_error_at (attribute.get_locus (),
 		   "attribute cannot be used at crate level");
+
+  if (result.name == Values::Attributes::NEEDS_ALLOCATOR)
+    {
+      rust_warning_at (attribute.get_locus (), 0,
+		       "%<#[%s]%> is not implemented yet and has no effect",
+		       attribute.as_string ().c_str ());
+    }
 }
 
 /**
diff --git a/gcc/rust/util/rust-attribute-values.h b/gcc/rust/util/rust-attribute-values.h
index 2b8853c8039d..4f8860747ea8 100644
--- a/gcc/rust/util/rust-attribute-values.h
+++ b/gcc/rust/util/rust-attribute-values.h
@@ -111,6 +111,8 @@ public:
   static constexpr auto &RUSTC_ARGS_REQUIRED_CONST
     = "rustc_args_required_const";
 
+  static constexpr auto &NEEDS_ALLOCATOR = "needs_allocator";
+
   static constexpr auto &RUSTC_ALLOCATOR = "rustc_allocator";
   static constexpr auto &RUSTC_ALLOCATOR_NOUNWIND = "rustc_allocator_nounwind";
 };
diff --git a/gcc/rust/util/rust-attributes.cc b/gcc/rust/util/rust-attributes.cc
index 1b65f7729fb0..97f9edeea8b6 100644
--- a/gcc/rust/util/rust-attributes.cc
+++ b/gcc/rust/util/rust-attributes.cc
@@ -95,6 +95,7 @@ static const BuiltinAttrDefinition __definitions[]
      {Attrs::NON_EXHAUSTIVE, TYPE_CHECK},
      {Attrs::RUSTFMT, EXTERNAL},
      {Attrs::TEST, CODE_GENERATION},
+     {Attrs::NEEDS_ALLOCATOR, CODE_GENERATION},
      {Attrs::RUSTC_ALLOCATOR, CODE_GENERATION},
      {Attrs::RUSTC_ALLOCATOR_NOUNWIND, CODE_GENERATION},
      {Attrs::GLOBAL_ALLOCATOR, CODE_GENERATION}};
diff --git a/gcc/testsuite/rust/compile/needs_allocator.rs b/gcc/testsuite/rust/compile/needs_allocator.rs
new file mode 100644
index 000000000000..f39ff2187691
--- /dev/null
+++ b/gcc/testsuite/rust/compile/needs_allocator.rs
@@ -0,0 +1,4 @@
+#![feature(no_core)]
+#![no_core]
+
+#![needs_allocator] // { dg-warning "...needs_allocator.. is not implemented yet and has no effect" }