[wildcards] field name support for record positional fields

See: #56271

`DUPLICATE_FIELD_NAME` to be handled in a follow-up

Change-Id: I44b7302cc3d522636075e4ffccbf88c117306730
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/376203
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

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
@@ -17,12 +19,17 @@ import 'package:analyzer/src/error/codes.g.dart';
 class RecordTypeAnnotationResolver {
   final TypeProviderImpl typeProvider;
   final ErrorReporter errorReporter;
+  final LibraryElement libraryElement;
 
   RecordTypeAnnotationResolver({
     required this.typeProvider,
     required this.errorReporter,
+    required this.libraryElement,
   });
 
+  bool get isWildCardVariablesEnabled =>
+      libraryElement.featureSet.isEnabled(Feature.wildcard_variables);
+
   /// Report any named fields in the record type [node] that use a previously
   /// defined name.
   void reportDuplicateFieldDefinitions(RecordTypeAnnotationImpl node) {
@@ -51,10 +58,16 @@ class RecordTypeAnnotationResolver {
       if (nameToken != null) {
         var name = nameToken.lexeme;
         if (name.startsWith('_')) {
-          errorReporter.atToken(
-            nameToken,
-            CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE,
-          );
+          if (field is RecordTypeAnnotationPositionalField &&
+              name.length == 1 &&
+              isWildCardVariablesEnabled) {
+            // Positional record fields named `_` are legal w/ wildcards.
+          } else {
+            errorReporter.atToken(
+              nameToken,
+              CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE,
+            );
+          }
         } else {
           var index = RecordTypeExtension.positionalFieldIndex(name);
           if (index != null) {

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

@@ -138,6 +138,7 @@ class ResolutionVisitor extends RecursiveAstVisitor<void> {
     var recordTypeResolver = RecordTypeAnnotationResolver(
       typeProvider: typeProvider,
       errorReporter: errorReporter,
+      libraryElement: libraryElement,
     );
 
     return ResolutionVisitor._(

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

@@ -167,4 +167,40 @@ void f((int _a, int b) r) {}
       error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 12, 2),
     ]);
   }
+
+  void test_wildcard_named() async {
+    await assertErrorsInCode(r'''
+void f(({int _, int b}) r) {}
+''', [
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 13, 1),
+    ]);
+  }
+
+  void test_wildcard_named_preWildcards() async {
+    await assertErrorsInCode(r'''
+// @dart = 3.4
+// (pre wildcard-variables)
+
+void f(({int _, int b}) r) {}
+''', [
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 57, 1),
+    ]);
+  }
+
+  void test_wildcard_positional() async {
+    await assertNoErrorsInCode(r'''
+void f((int _, int b) r) {}
+''');
+  }
+
+  void test_wildcard_positional_preWildcards() async {
+    await assertErrorsInCode(r'''
+// @dart = 3.4
+// (pre wildcard-variables)
+
+void f((int _, int b) r) {}
+''', [
+      error(CompileTimeErrorCode.INVALID_FIELD_NAME_PRIVATE, 56, 1),
+    ]);
+  }
 }