From e13277e56ec2c19b2cbc598ea5bbc31747367600 Mon Sep 17 00:00:00 2001
From: Yap Zhi Heng <yapzhhg@gmail.com>
Date: Sun, 28 Sep 2025 19:11:31 +0800
Subject: [PATCH] gccrs: Fix StructPattern type checking rejecting tuple struct
 scrutinee

Previously, type checking of StructPattern will throw an error if it is used
to match against a tuple struct, even though it is possible to do so in rustc.

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-pattern.cc (visit(StructPattern)): Add type check
	support for StructPatterns matching against a TUPLE type ADT.
	* backend/rust-compile-pattern.cc(CompilePatternBindings::visit(StructPattern)):
	Update assert to allow TUPLE type ADTs.
	* hir/tree/rust-hir.cc (StructPatternField::as_string()): Improve info dumped.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>
---
 gcc/rust/backend/rust-compile-pattern.cc      |  5 ++-
 gcc/rust/hir/tree/rust-hir.cc                 | 21 ++++++++++-
 .../typecheck/rust-hir-type-check-pattern.cc  | 37 ++++++++++++++++---
 3 files changed, 54 insertions(+), 9 deletions(-)

diff --git a/gcc/rust/backend/rust-compile-pattern.cc b/gcc/rust/backend/rust-compile-pattern.cc
index 149f6b07411..9ebb4d1dd63 100644
--- a/gcc/rust/backend/rust-compile-pattern.cc
+++ b/gcc/rust/backend/rust-compile-pattern.cc
@@ -885,8 +885,9 @@ CompilePatternBindings::visit (HIR::StructPattern &pattern)
       rust_assert (ok);
     }
 
-  rust_assert (variant->get_variant_type ()
-	       == TyTy::VariantDef::VariantType::STRUCT);
+  rust_assert (
+    variant->get_variant_type () == TyTy::VariantDef::VariantType::STRUCT
+    || variant->get_variant_type () == TyTy::VariantDef::VariantType::TUPLE);
 
   auto &struct_pattern_elems = pattern.get_struct_pattern_elems ();
   for (auto &field : struct_pattern_elems.get_struct_pattern_fields ())
diff --git a/gcc/rust/hir/tree/rust-hir.cc b/gcc/rust/hir/tree/rust-hir.cc
index 7aad4ef2730..ce10b02303c 100644
--- a/gcc/rust/hir/tree/rust-hir.cc
+++ b/gcc/rust/hir/tree/rust-hir.cc
@@ -2519,10 +2519,29 @@ StructPatternField::as_string () const
        * just the body */
       for (const auto &attr : outer_attrs)
 	{
-	  str += "\n  " + attr.as_string ();
+	  str += "\n    " + attr.as_string ();
 	}
     }
 
+  str += "\n   item type: ";
+  switch (get_item_type ())
+    {
+    case ItemType::TUPLE_PAT:
+      str += "TUPLE_PAT";
+      break;
+    case ItemType::IDENT_PAT:
+      str += "IDENT_PAT";
+      break;
+    case ItemType::IDENT:
+      str += "IDENT";
+      break;
+    default:
+      str += "UNKNOWN";
+      break;
+    }
+
+  str += "\n   mapping: " + mappings.as_string ();
+
   return str;
 }
 
diff --git a/gcc/rust/typecheck/rust-hir-type-check-pattern.cc b/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
index 7b405510bb3..e964318bf7c 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
@@ -299,7 +299,30 @@ TypeCheckPattern::visit (HIR::StructPattern &pattern)
 
   // error[E0532]: expected tuple struct or tuple variant, found struct
   // variant `Foo::D`
-  if (variant->get_variant_type () != TyTy::VariantDef::VariantType::STRUCT)
+  bool error_E0532 = false;
+  if (variant->get_variant_type () == TyTy::VariantDef::VariantType::TUPLE)
+    {
+      // Tuple structs can still be matched with struct patterns via index
+      // numbers e.g. Foo {0: a, .., 3: b}, so check whether the fields are of
+      // type TUPLE_PAT. Throw E0532 if not.
+      auto &struct_pattern_elems = pattern.get_struct_pattern_elems ();
+      for (auto &field : struct_pattern_elems.get_struct_pattern_fields ())
+	{
+	  if (field->get_item_type ()
+	      != HIR::StructPatternField::ItemType::TUPLE_PAT)
+	    {
+	      error_E0532 = true;
+	      break;
+	    }
+	}
+    }
+  else if (variant->get_variant_type ()
+	   != TyTy::VariantDef::VariantType::STRUCT)
+    {
+      error_E0532 = true;
+    }
+
+  if (error_E0532)
     {
       std::string variant_type
 	= TyTy::VariantDef::variant_type_string (variant->get_variant_type ());
@@ -508,7 +531,8 @@ TypeCheckPattern::visit (HIR::TuplePattern &pattern)
 	  {
 	    emit_pattern_size_error (pattern, par.get_fields ().size (),
 				     min_size_required);
-	    // TODO attempt to continue to do typechecking even after wrong size
+	    // TODO attempt to continue to do typechecking even after wrong
+	    // size
 	    break;
 	  }
 
@@ -680,10 +704,11 @@ TypeCheckPattern::visit (HIR::SlicePattern &pattern)
 
 	      if (cap_wi < pattern_min_cap)
 		{
-		  rust_error_at (
-		    pattern.get_locus (), ErrorCode::E0528,
-		    "pattern requires at least %lu elements but array has %lu",
-		    (unsigned long) pattern_min_cap, (unsigned long) cap_wi);
+		  rust_error_at (pattern.get_locus (), ErrorCode::E0528,
+				 "pattern requires at least %lu elements but "
+				 "array has %lu",
+				 (unsigned long) pattern_min_cap,
+				 (unsigned long) cap_wi);
 		  break;
 		}
 	    }
-- 
2.47.3