[wildcards] duplicate field name support for record positional fields

See: #56271

Change-Id: If471de5174f0ea1fae9daf6fbe3956a3abce40a4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/376460
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/analyzer/lib/src/dart/resolver/record_type_annotation_resolver.dart

@@ -30,13 +30,21 @@ class RecordTypeAnnotationResolver {
   bool get isWildCardVariablesEnabled =>
       libraryElement.featureSet.isEnabled(Feature.wildcard_variables);
 
+  bool isPositionalWildCard(AstNode field, String name) =>
+      field is RecordTypeAnnotationPositionalField &&
+      name == '_' &&
+      isWildCardVariablesEnabled;
+
   /// Report any named fields in the record type [node] that use a previously
   /// defined name.
   void reportDuplicateFieldDefinitions(RecordTypeAnnotationImpl node) {
     var usedNames = <String, RecordTypeAnnotationField>{};
     for (var field in node.fields) {
       var name = field.name?.lexeme;
       if (name != null) {
+        // Multiple positional `_`s are legal with wildcards.
+        if (isPositionalWildCard(field, name)) continue;
+
         var previousField = usedNames[name];
         if (previousField != null) {
           errorReporter.reportError(DiagnosticFactory()
@@ -58,11 +66,8 @@ class RecordTypeAnnotationResolver {
       if (nameToken != null) {
         var name = nameToken.lexeme;
         if (name.startsWith('_')) {
-          if (field is RecordTypeAnnotationPositionalField &&
-              name.length == 1 &&
-              isWildCardVariablesEnabled) {
-            // Positional record fields named `_` are legal w/ wildcards.
-          } else {
+          // Positional record fields named `_` are legal w/ wildcards.
+          if (!isPositionalWildCard(field, name)) {
             errorReporter.atToken(
               nameToken,
               CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE,

pkg/analyzer/test/src/diagnostics/duplicate_field_name_test.dart

@@ -62,6 +62,38 @@ void f((int a, {int a}) r) {}
     ]);
   }
 
+  void test_duplicated_wildcard_named() async {
+    await assertErrorsInCode(r'''
+void f(({int _, int _}) r) {}
+''', [
+      // Only positional wildcard fields can be duplicated.
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 13, 1),
+      error(CompileTimeErrorCode.DUPLICATE_FIELD_NAME, 20, 1,
+          contextMessages: [message(testFile, 13, 1)]),
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 20, 1),
+    ]);
+  }
+
+  void test_duplicated_wildcard_positional() async {
+    await assertNoErrorsInCode(r'''
+void f((int _, int _) r) {}
+''');
+  }
+
+  void test_duplicated_wildcard_positional_preWildcards() async {
+    await assertErrorsInCode(r'''
+// @dart = 3.4
+// (pre wildcard-variables)
+
+void f((int _, int _) r) {}
+''', [
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 56, 1),
+      error(CompileTimeErrorCode.DUPLICATE_FIELD_NAME, 63, 1,
+          contextMessages: [message(testFile, 56, 1)]),
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 63, 1),
+    ]);
+  }
+
   void test_notDuplicated_named() async {
     await assertNoErrorsInCode(r'''
 void f(({int a, int b}) r) {}