Add improved error when a field is redefined in a struct constructor

Fixes #2381

If a struct type is initialized with one of it's fields repeated it will currently issue an error at the use site. However we would like to give the rust error code and (like rustc) show both the specifications for the field to help the user diagnose the issue.

We move the check after the index for the field has been established so we can look up if the field has already been defined and get it's location.

We update the visit method to return if it has handled an error otherwise we then output a second fatal error as not all the field in the specification have been processed.

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-struct-field.h: Allow visit to return a bool
	* typecheck/rust-hir-type-check-struct.cc: Improve check of repeat fields

gcc/testsuite/ChangeLog:

	* rust/compile/repeated_constructor_fields.rs: Added case with constructor field repeated

Signed-off-by: Robert Goss <goss.robert@gmail.com>

3 files changed, 74 insertions, 32 deletions

diff --git a/gcc/rust/typecheck/rust-hir-type-check-struct-field.h b/gcc/rust/typecheck/rust-hir-type-check-struct-field.h
index df084f4..c1d7229 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-struct-field.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-struct-field.h
@@ -35,9 +35,9 @@ public:
 protected:
   void resolve (HIR::StructExprStructFields &struct_expr);
 
-  void visit (HIR::StructExprFieldIdentifierValue &field);
-  void visit (HIR::StructExprFieldIndexValue &field);
-  void visit (HIR::StructExprFieldIdentifier &field);
+  bool visit (HIR::StructExprFieldIdentifierValue &field);
+  bool visit (HIR::StructExprFieldIndexValue &field);
+  bool visit (HIR::StructExprFieldIdentifier &field);
 
 private:
   TypeCheckStructExpr (HIR::Expr *e);
diff --git a/gcc/rust/typecheck/rust-hir-type-check-struct.cc b/gcc/rust/typecheck/rust-hir-type-check-struct.cc
index 7a7c5cf..06b6551 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-struct.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-struct.cc
@@ -102,19 +102,26 @@ TypeCheckStructExpr::resolve (HIR::StructExprStructFields &struct_expr)
       switch (field->get_kind ())
 	{
 	case HIR::StructExprField::StructExprFieldKind::IDENTIFIER:
-	  visit (static_cast<HIR::StructExprFieldIdentifier &> (*field.get ()));
+	  ok = visit (
+	    static_cast<HIR::StructExprFieldIdentifier &> (*field.get ()));
 	  break;
 
 	case HIR::StructExprField::StructExprFieldKind::IDENTIFIER_VALUE:
-	  visit (
+	  ok = visit (
 	    static_cast<HIR::StructExprFieldIdentifierValue &> (*field.get ()));
 	  break;
 
 	case HIR::StructExprField::StructExprFieldKind::INDEX_VALUE:
-	  visit (static_cast<HIR::StructExprFieldIndexValue &> (*field.get ()));
+	  ok = visit (
+	    static_cast<HIR::StructExprFieldIndexValue &> (*field.get ()));
 	  break;
 	}
 
+      if (!ok)
+	{
+	  return;
+	}
+
       if (resolved_field_value_expr == nullptr)
 	{
 	  rust_fatal_error (field->get_locus (),
@@ -238,16 +245,9 @@ TypeCheckStructExpr::resolve (HIR::StructExprStructFields &struct_expr)
   resolved = struct_def;
 }
 
-void
+bool
 TypeCheckStructExpr::visit (HIR::StructExprFieldIdentifierValue &field)
 {
-  auto it = fields_assigned.find (field.field_name.as_string ());
-  if (it != fields_assigned.end ())
-    {
-      rust_fatal_error (field.get_locus (), "used more than once");
-      return;
-    }
-
   size_t field_index;
   TyTy::StructFieldType *field_type;
   bool ok = variant->lookup_field (field.field_name.as_string (), &field_type,
@@ -255,7 +255,20 @@ TypeCheckStructExpr::visit (HIR::StructExprFieldIdentifierValue &field)
   if (!ok)
     {
       rust_error_at (field.get_locus (), "unknown field");
-      return;
+      return true;
+    }
+
+  auto it = adtFieldIndexToField.find (field_index);
+  if (it != adtFieldIndexToField.end ())
+    {
+      rich_location repeat_location (line_table, field.get_locus ());
+      auto prev_field_locus = it->second->get_locus ();
+      repeat_location.add_range (prev_field_locus);
+
+      rust_error_at (repeat_location, ErrorCode::E0062,
+		     "field %<%s%> specified more than once",
+		     field.field_name.as_string ().c_str ());
+      return false;
     }
 
   TyTy::BaseType *value = TypeCheckExpr::Resolve (field.get_value ().get ());
@@ -273,18 +286,14 @@ TypeCheckStructExpr::visit (HIR::StructExprFieldIdentifierValue &field)
       fields_assigned.insert (field.field_name.as_string ());
       adtFieldIndexToField[field_index] = &field;
     }
+
+  return true;
 }
 
-void
+bool
 TypeCheckStructExpr::visit (HIR::StructExprFieldIndexValue &field)
 {
   std::string field_name (std::to_string (field.get_tuple_index ()));
-  auto it = fields_assigned.find (field_name);
-  if (it != fields_assigned.end ())
-    {
-      rust_fatal_error (field.get_locus (), "used more than once");
-      return;
-    }
 
   size_t field_index;
   TyTy::StructFieldType *field_type;
@@ -292,7 +301,20 @@ TypeCheckStructExpr::visit (HIR::StructExprFieldIndexValue &field)
   if (!ok)
     {
       rust_error_at (field.get_locus (), "unknown field");
-      return;
+      return true;
+    }
+
+  auto it = adtFieldIndexToField.find (field_index);
+  if (it != adtFieldIndexToField.end ())
+    {
+      rich_location repeat_location (line_table, field.get_locus ());
+      auto prev_field_locus = it->second->get_locus ();
+      repeat_location.add_range (prev_field_locus);
+
+      rust_error_at (repeat_location, ErrorCode::E0062,
+		     "field %<%s%> specified more than once",
+		     field_name.c_str ());
+      return false;
     }
 
   TyTy::BaseType *value = TypeCheckExpr::Resolve (field.get_value ().get ());
@@ -310,18 +332,13 @@ TypeCheckStructExpr::visit (HIR::StructExprFieldIndexValue &field)
       fields_assigned.insert (field_name);
       adtFieldIndexToField[field_index] = &field;
     }
+
+  return true;
 }
 
-void
+bool
 TypeCheckStructExpr::visit (HIR::StructExprFieldIdentifier &field)
 {
-  auto it = fields_assigned.find (field.get_field_name ().as_string ());
-  if (it != fields_assigned.end ())
-    {
-      rust_fatal_error (field.get_locus (), "used more than once");
-      return;
-    }
-
   size_t field_index;
   TyTy::StructFieldType *field_type;
   bool ok = variant->lookup_field (field.get_field_name ().as_string (),
@@ -329,7 +346,20 @@ TypeCheckStructExpr::visit (HIR::StructExprFieldIdentifier &field)
   if (!ok)
     {
       rust_error_at (field.get_locus (), "unknown field");
-      return;
+      return true;
+    }
+
+  auto it = adtFieldIndexToField.find (field_index);
+  if (it != adtFieldIndexToField.end ())
+    {
+      rich_location repeat_location (line_table, field.get_locus ());
+      auto prev_field_locus = it->second->get_locus ();
+      repeat_location.add_range (prev_field_locus);
+
+      rust_error_at (repeat_location, ErrorCode::E0062,
+		     "field %<%s%> specified more than once",
+		     field.get_field_name ().as_string ().c_str ());
+      return false;
     }
 
   // we can make the field look like a path expr to take advantage of existing
@@ -358,6 +388,8 @@ TypeCheckStructExpr::visit (HIR::StructExprFieldIdentifier &field)
       fields_assigned.insert (field.get_field_name ().as_string ());
       adtFieldIndexToField[field_index] = &field;
     }
+
+  return true;
 }
 
 } // namespace Resolver
diff --git a/gcc/testsuite/rust/compile/repeated_constructor_fields.rs b/gcc/testsuite/rust/compile/repeated_constructor_fields.rs
new file mode 100644
index 0000000..729001b
--- /dev/null
+++ b/gcc/testsuite/rust/compile/repeated_constructor_fields.rs
@@ -0,0 +1,10 @@
+struct Foo {
+    x: i32,
+}
+
+fn main() {
+    let x = Foo {
+        x: 0,
+        x: 0, // { dg-error "field 'x' specified more than once" }
+    };
+}