Allow trailing comma in assert

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.
 
 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';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 12248 matching lines @@
     assertNoErrors();
     expect(statement.assertKeyword, isNotNull);
     expect(statement.leftParenthesis, isNotNull);
     expect(statement.condition, isNotNull);
     expect(statement.comma, isNotNull);
     expect(statement.message, isNotNull);
     expect(statement.rightParenthesis, isNotNull);
     expect(statement.semicolon, isNotNull);
   }
 
+  void test_parseAssertStatement_trailingComma_message() {
+    var statement = parseStatement('assert (x, "m",);') as AssertStatement;
+    assertNoErrors();
+    expect(statement.assertKeyword, isNotNull);
+    expect(statement.leftParenthesis, isNotNull);
+    expect(statement.condition, isNotNull);
+    expect(statement.comma, isNotNull);
+    expect(statement.message, isNotNull);
+    expect(statement.rightParenthesis, isNotNull);
+    expect(statement.semicolon, isNotNull);
+  }
+
+  void test_parseAssertStatement_trailingComma_noMessage() {
+    var statement = parseStatement('assert (x,);') as AssertStatement;
+    assertNoErrors();
+    expect(statement.assertKeyword, isNotNull);
+    expect(statement.leftParenthesis, isNotNull);
+    expect(statement.condition, isNotNull);
+    expect(statement.comma, isNull);
+    expect(statement.message, isNull);
+    expect(statement.rightParenthesis, isNotNull);
+    expect(statement.semicolon, isNotNull);
+  }
+
   void test_parseBlock_empty() {
     var block = parseStatement('{}') as Block;
     assertNoErrors();
     expect(block.leftBracket, isNotNull);
     expect(block.statements, hasLength(0));
     expect(block.rightBracket, isNotNull);
   }
 
   void test_parseBlock_nonEmpty() {
     var block = parseStatement('{;}') as Block;
@@ skipping 2886 matching lines @@
     expectCommentText(typeVariable.documentationComment, '/// Doc');
   }
 
   /**
    * Assert that the given [name] is in declaration context.
    */
   void _assertIsDeclarationName(SimpleIdentifier name) {
     expect(name.inDeclarationContext(), isTrue);
   }
 }