Improve recovery in argument lists when missing a comma before a named argument (issue 29005)

pkg/analyzer/test/generated/parser_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 library analyzer.test.generated.parser_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
@@ skipping 9138 matching lines @@
       ParserErrorCode.MISSING_IDENTIFIER
     ]);
     EngineTestCase.assertInstanceOf((obj) => obj is BinaryExpression,
         BinaryExpression, expression.rightOperand);
   }
 
   void test_missing_commaInArgumentList() {
     parseExpression("f(x: 1 y: 2)", [ParserErrorCode.EXPECTED_TOKEN]);
   }
 
+  void test_missingComma_beforeNamedArgument() {
+    createParser('(a b: c)');
+    ArgumentList argumentList = parser.parseArgumentList();
+    expectNotNullIfNoErrors(argumentList);
+    listener.assertErrorsWithCodes([ParserErrorCode.EXPECTED_TOKEN]);
+    expect(argumentList.arguments, hasLength(2));
+  }
+
   void test_missingGet() {
     CompilationUnit unit = parseCompilationUnit(
         r'''
 class C {
   int length {}
   void foo() {}
 }''',
         [ParserErrorCode.MISSING_GET]);
     expect(unit, isNotNull);
     ClassDeclaration classDeclaration =
@@ skipping 5555 matching lines @@
     expect(functionType.returnType, isNotNull);
     expect(functionType.typeParameters, isNull);
   }
 
   void test_parseTypeAlias_genericFunction_withDocComment() {
     createParser('/// Doc\ntypedef F = bool Function();');
     var typeAlias = parseFullCompilationUnitMember() as GenericTypeAlias;
     expectCommentText(typeAlias.documentationComment, '/// Doc');
   }
 }