[gcc r17-3129] gccrs: lang: Register lang items for alloc crate

https://gcc.gnu.org/g:2be06e73fcefc311a78bceb15f725b5ae7c6bee6

commit r17-3129-g2be06e73fcefc311a78bceb15f725b5ae7c6bee6
Author: Enes Cevik <[email protected]>
Date:   Mon Jul 13 13:08:32 2026 +0300

    gccrs: lang: Register lang items for alloc crate
    
    This patch registers several lang items as stubs to progress towards
    compiling the 'alloc' crate.
    
    - 'oom', 'alloc_layout': Require no specific handling; symbol generation
      is sufficient.
    - 'box_free': Full implementation requires a mature drop infrastructure.
      Registered as a stub for now.
    - 'drop_in_place': Full implementation requires a mature drop
      infrastructure. Registered as a stub for now.
    - 'maybe_uninit': Requires layout engine maturity and niche-filling
      mechanisms. Registered as a stub.
    - 'future_trait', 'poll', 'Ready', 'Pending': Registered as stubs due
      to lack of async support.
    - 'generator', 'generator_state': Registered as stubs due to lack of
      generator support.
    
    The 'Ready' and 'Pending' lang items are excluded from the new test
    cases because lang item attributes on enum variants are not currently
    handled (see Rust-GCC/gccrs#4703).
    
    gcc/rust/ChangeLog:
    
            * hir/rust-ast-lower-base.cc (warn_if_stub_lang_item): New
            function.
            (ASTLoweringBase::handle_lang_item_attribute): Emit a warning
            if lang item is stub.
            * util/rust-lang-item.cc (Rust::LangItem::lang_items): Add new
            lang items to the BiMap.
            * util/rust-lang-item.h (class LangItem): Add new lang items
            to Kind enum.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/lang-items-stub.rs: New test.
            * rust/compile/lang-items-symbol.rs: New test.
    
    Signed-off-by: Enes Cevik <[email protected]>

Diff:
---
 gcc/rust/hir/rust-ast-lower-base.cc             | 29 ++++++++++++++++++--
 gcc/rust/util/rust-lang-item.cc                 | 12 +++++++++
 gcc/rust/util/rust-lang-item.h                  | 12 +++++++++
 gcc/testsuite/rust/compile/lang-items-stub.rs   | 36 +++++++++++++++++++++++++
 gcc/testsuite/rust/compile/lang-items-symbol.rs |  8 ++++++
 5 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/gcc/rust/hir/rust-ast-lower-base.cc b/gcc/rust/hir/rust-ast-lower-base.cc
index ffa7a0f39db5..7cbe52af6298 100644
--- a/gcc/rust/hir/rust-ast-lower-base.cc
+++ b/gcc/rust/hir/rust-ast-lower-base.cc
@@ -853,6 +853,28 @@ ASTLoweringBase::handle_doc_item_attribute (const ItemWrapper &,
   rust_assert (meta_item);
 }
 
+static void
+warn_if_stub_lang_item (location_t locus, LangItem::Kind kind)
+{
+  switch (kind)
+    {
+    case LangItem::Kind::FUTURE_TRAIT:
+    case LangItem::Kind::POLL:
+    case LangItem::Kind::READY:
+    case LangItem::Kind::PENDING:
+    case LangItem::Kind::GENERATOR:
+    case LangItem::Kind::GENERATOR_STATE:
+    case LangItem::Kind::MAYBE_UNINIT:
+    case LangItem::Kind::BOX_FREE:
+    case LangItem::Kind::DROP_IN_PLACE:
+      rust_warning_at (locus, 0, "%qs is not implemented and has no effect",
+		       LangItem::PrettyString (kind).c_str ());
+      break;
+    default:
+      break;
+    }
+}
+
 void
 ASTLoweringBase::handle_lang_item_attribute (const ItemWrapper &item,
 					     const AST::Attribute &attr)
@@ -863,8 +885,11 @@ ASTLoweringBase::handle_lang_item_attribute (const ItemWrapper &item,
   auto lang_item_type = LangItem::Parse (*lang_item_type_str);
 
   if (lang_item_type)
-    mappings.insert_lang_item (*lang_item_type,
-			       item.get_mappings ().get_defid ());
+    {
+      mappings.insert_lang_item (*lang_item_type,
+				 item.get_mappings ().get_defid ());
+      warn_if_stub_lang_item (attr.get_locus (), *lang_item_type);
+    }
   else
     rust_error_at (attr.get_locus (), "unknown lang item");
 }
diff --git a/gcc/rust/util/rust-lang-item.cc b/gcc/rust/util/rust-lang-item.cc
index 731fd23f3148..c58ab401fd1c 100644
--- a/gcc/rust/util/rust-lang-item.cc
+++ b/gcc/rust/util/rust-lang-item.cc
@@ -124,9 +124,21 @@ const BiMap<std::string, LangItem::Kind> Rust::LangItem::lang_items = {{
   {"discriminant_kind", Kind::DISCRIMINANT_KIND},
   {"discriminant_type", Kind::DISCRIMINANT_TYPE},
   {"manually_drop", Kind::MANUALLY_DROP},
+  {"drop_in_place", Kind::DROP_IN_PLACE},
 
   {"exchange_malloc", Kind::EXCHANGE_MALLOC},
   {"owned_box", Kind::OWNED_BOX},
+  {"oom", Kind::OOM},
+  {"alloc_layout", Kind::ALLOC_LAYOUT},
+  {"box_free", Kind::BOX_FREE},
+  {"maybe_uninit", Kind::MAYBE_UNINIT},
+
+  {"future_trait", Kind::FUTURE_TRAIT},
+  {"poll", Kind::POLL},
+  {"Ready", Kind::READY},
+  {"Pending", Kind::PENDING},
+  {"generator", Kind::GENERATOR},
+  {"generator_state", Kind::GENERATOR_STATE},
 }};
 
 tl::optional<LangItem::Kind>
diff --git a/gcc/rust/util/rust-lang-item.h b/gcc/rust/util/rust-lang-item.h
index 9684148f7554..d6bea1a8e432 100644
--- a/gcc/rust/util/rust-lang-item.h
+++ b/gcc/rust/util/rust-lang-item.h
@@ -160,9 +160,21 @@ public:
     DISCRIMINANT_KIND,
 
     MANUALLY_DROP,
+    DROP_IN_PLACE,
 
     EXCHANGE_MALLOC,
     OWNED_BOX,
+    OOM,
+    ALLOC_LAYOUT,
+    BOX_FREE,
+    MAYBE_UNINIT,
+
+    FUTURE_TRAIT,
+    POLL,
+    READY,
+    PENDING,
+    GENERATOR,
+    GENERATOR_STATE,
   };
 
   static const BiMap<std::string, Kind> lang_items;
diff --git a/gcc/testsuite/rust/compile/lang-items-stub.rs b/gcc/testsuite/rust/compile/lang-items-stub.rs
new file mode 100644
index 000000000000..09dd06e0ebe5
--- /dev/null
+++ b/gcc/testsuite/rust/compile/lang-items-stub.rs
@@ -0,0 +1,36 @@
+#![feature(no_core, lang_items)]
+#![no_core]
+
+
+#[lang = "sized"]
+pub trait Sized {}
+
+#[lang = "future_trait"] // { dg-warning "...lang = .future_trait... is not implemented and has no effect" }
+pub trait Future {
+    #[lang = "poll"] // { dg-warning "...lang = .poll... is not implemented and has no effect" }
+    fn poll() {}
+}
+
+#[lang = "generator"] // { dg-warning "...lang = .generator... is not implemented and has no effect" }
+pub trait Generator {}
+
+#[lang = "generator_state"] // { dg-warning "...lang = .generator_state... is not implemented and has no effect" }
+pub enum GeneratorState {}
+
+#[lang = "box_free"] // { dg-warning "...lang = .box_free... is not implemented and has no effect" }
+pub fn _box_free() {}
+
+#[repr(transparent)]
+pub struct ManuallyDrop<T: ?Sized> {
+    _value: T,
+}
+
+#[lang = "maybe_uninit"] // { dg-warning "...lang = .maybe_uninit... is not implemented and has no effect" }
+#[repr(transparent)]
+pub union MaybeUninit<T> {
+    uninit: (),
+    value: ManuallyDrop<T>,
+}
+
+#[lang = "drop_in_place"] // { dg-warning "...lang = .drop_in_place... is not implemented and has no effect" }
+pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {}
diff --git a/gcc/testsuite/rust/compile/lang-items-symbol.rs b/gcc/testsuite/rust/compile/lang-items-symbol.rs
new file mode 100644
index 000000000000..bc113d52b57f
--- /dev/null
+++ b/gcc/testsuite/rust/compile/lang-items-symbol.rs
@@ -0,0 +1,8 @@
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "alloc_layout"]
+pub struct Layout;
+
+#[lang = "oom"]
+pub fn _oom() {}