gracefully recover from extraneous top level modifiers

pkg/front_end/test/token_test.dart

 // Copyright (c) 2017, 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:front_end/src/fasta/scanner/string_scanner.dart';
 import 'package:front_end/src/fasta/scanner/token.dart' as fasta;
 import 'package:front_end/src/scanner/token.dart';
 import 'package:front_end/src/scanner/errors.dart' as analyzer;
 import 'package:front_end/src/scanner/reader.dart' as analyzer;
 import 'package:front_end/src/scanner/scanner.dart' as analyzer;
@@ skipping 154 matching lines @@
       Keyword.STATIC,
       Keyword.TYPEDEF,
     ]);
     for (Keyword keyword in Keyword.values) {
       var isBuiltIn = builtInKeywords.contains(keyword);
       expect(keyword.isBuiltIn, isBuiltIn, reason: keyword.name);
       expect(keyword.isBuiltIn, isBuiltIn, reason: keyword.name);
     }
   }
 
+  void test_isModifier() {
+    var modifierKeywords = new Set<Keyword>.from([
+      Keyword.ABSTRACT,
+      Keyword.CONST,
+      Keyword.FINAL,
+      Keyword.STATIC,
+    ]);
+    for (Keyword keyword in Keyword.values) {
+      var isModifier = modifierKeywords.contains(keyword);
+      var scanner = new StringScanner(keyword.lexeme, includeComments: true);
+      Token token = scanner.tokenize();
+      expect(token.isModifier, isModifier, reason: keyword.name);
+      if (isModifier) {
+        expect(token.isTopLevelKeyword, isFalse, reason: keyword.name);
+      }
+    }
+  }
+
+  void test_isTopLevelKeyword() {
+    var topLevelKeywords = new Set<Keyword>.from([
+      Keyword.CLASS,
+      Keyword.ENUM,
+      Keyword.EXPORT,
+      Keyword.IMPORT,
+      Keyword.LIBRARY,
+      Keyword.PART,
+      Keyword.TYPEDEF,
+    ]);
+    for (Keyword keyword in Keyword.values) {
+      var isTopLevelKeyword = topLevelKeywords.contains(keyword);
+      var scanner = new StringScanner(keyword.lexeme, includeComments: true);
+      Token token = scanner.tokenize();
+      expect(token.isTopLevelKeyword, isTopLevelKeyword, reason: keyword.name);
+      if (isTopLevelKeyword) {
+        expect(token.isModifier, isFalse, reason: keyword.name);
+      }
+    }
+  }
+
   void test_pseudo_keywords() {
     var pseudoKeywords = new Set<Keyword>.from([
       Keyword.ASYNC,
       Keyword.AWAIT,
       Keyword.FUNCTION,
       Keyword.HIDE,
       Keyword.NATIVE,
       Keyword.OF,
       Keyword.ON,
       Keyword.PATCH,
@@ skipping 28 matching lines @@
 class TestScanner extends analyzer.Scanner {
   TestScanner(analyzer.CharacterReader reader) : super.create(reader);
 
   @override
   void reportError(
       analyzer.ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     fail('Unexpected error $errorCode while scanning offset $offset\n'
         '   arguments: $arguments');
   }
 }