[gcc r17-2241] gccrs: Fix field access on DST fat pointers

https://gcc.gnu.org/g:3db9835f404e1a908e5c4ff86d277f3654c5c11b

commit r17-2241-g3db9835f404e1a908e5c4ff86d277f3654c5c11b
Author: Yap Zhi Heng <[email protected]>
Date:   Thu Jun 18 23:02:19 2026 +0800

    gccrs: Fix field access on DST fat pointers
    
    gcc/rust/ChangeLog:
    
            * backend/rust-compile-expr.cc (CompileExpr::visit (FieldAccessExpr)):
            Handle DST fat pointers by reinterpreting the fat pointer as its field type.
    
    Signed-Off-By: Yap Zhi Heng <[email protected]>

Diff:
---
 gcc/rust/backend/rust-compile-expr.cc | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/gcc/rust/backend/rust-compile-expr.cc b/gcc/rust/backend/rust-compile-expr.cc
index 45765e72d688..7fabc25a5f8b 100644
--- a/gcc/rust/backend/rust-compile-expr.cc
+++ b/gcc/rust/backend/rust-compile-expr.cc
@@ -717,8 +717,23 @@ CompileExpr::visit (HIR::FieldAccessExpr &expr)
 				       nullptr, &field_index);
       rust_assert (ok);
 
-      tree indirect = indirect_expression (receiver_ref, expr.get_locus ());
-      receiver_ref = indirect;
+      // TODO this check is only used for CStr, test again when we support
+      // compilation of #[repr(transparent)] structs
+      if (RS_DST_FLAG_P (TREE_TYPE (receiver_ref)))
+	{
+	  const TyTy::StructFieldType *field
+	    = variant->get_field_at_index (field_index);
+	  tree field_type
+	    = TyTyResolveCompile::compile (ctx, field->get_field_type ());
+	  translated = fold_build1_loc (expr.get_locus (), VIEW_CONVERT_EXPR,
+					field_type, receiver_ref);
+	  return;
+	}
+      else
+	{
+	  tree indirect = indirect_expression (receiver_ref, expr.get_locus ());
+	  receiver_ref = indirect;
+	}
     }
 
   translated = Backend::struct_field_expression (receiver_ref, field_index,