[gcc r17-3115] gccrs: Small fixes for #[repr(transparent)]

https://gcc.gnu.org/g:1b839ec55be7b93beb0118da19c267a0c4d3fcb9

commit r17-3115-g1b839ec55be7b93beb0118da19c267a0c4d3fcb9
Author: Yap Zhi Heng <[email protected]>
Date:   Tue Jul 21 22:29:09 2026 +0800

    gccrs: Small fixes for #[repr(transparent)]
    
    gcc/rust/ChangeLog:
    
            * typecheck/rust-hir-type-check-item.cc (TypeCheckItem::visit(StructStruct)): Update
            E0690 error message to use the correct variable for number of fields.
            * typecheck/rust-tyty.cc (ArrayType::is_zero_sized): Catch edge case of array's element
            type being a ZST with capacity is more than 0.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/repr_transparent_fields.rs: Add more test cases.
    
    Signed-off-by: Yap Zhi Heng <[email protected]>

Diff:
---
 gcc/rust/typecheck/rust-hir-type-check-item.cc        |  2 +-
 gcc/rust/typecheck/rust-tyty.cc                       |  3 +++
 gcc/testsuite/rust/compile/repr_transparent_fields.rs | 12 ++++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/typecheck/rust-hir-type-check-item.cc b/gcc/rust/typecheck/rust-hir-type-check-item.cc
index 6c1d91132915..44d5434b1269 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-item.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-item.cc
@@ -378,7 +378,7 @@ TypeCheckItem::visit (HIR::StructStruct &struct_decl)
 	  rust_error_at (struct_decl.get_locus (), ErrorCode::E0690,
 			 "transparent struct needs at most one field with "
 			 "non-trivial size or alignment, but has %lu",
-			 (unsigned long) struct_decl.get_fields ().size ());
+			 (unsigned long) num_non_zst);
 	  return;
 	}
     }
diff --git a/gcc/rust/typecheck/rust-tyty.cc b/gcc/rust/typecheck/rust-tyty.cc
index 825febe6f6ee..bc26692058a2 100644
--- a/gcc/rust/typecheck/rust-tyty.cc
+++ b/gcc/rust/typecheck/rust-tyty.cc
@@ -2602,6 +2602,9 @@ ArrayType::is_equal (const BaseType &other) const
 bool
 ArrayType::is_zero_sized () const
 {
+  if (element_type.get_tyty ()->is_zero_sized ())
+    return true;
+
   auto *capacity_ty = get_capacity ();
   if (capacity_ty != nullptr
       && capacity_ty->get_kind () == TyTy::TypeKind::CONST)
diff --git a/gcc/testsuite/rust/compile/repr_transparent_fields.rs b/gcc/testsuite/rust/compile/repr_transparent_fields.rs
index 72219e486741..482460061310 100644
--- a/gcc/testsuite/rust/compile/repr_transparent_fields.rs
+++ b/gcc/testsuite/rust/compile/repr_transparent_fields.rs
@@ -26,3 +26,15 @@ struct Qux {
     foo: i32,
     phantom: PhantomData<i32>,
 }
+
+#[repr(transparent)]
+struct Quux {
+    phantom_array: [(); 6],
+    foo: i32,
+}
+
+#[repr(transparent)]
+struct Corge {
+    empty_array: [i32; 0],
+    foo: i32,
+}