fasta scanner recovery and error code translation improvements

pkg/front_end/lib/src/fasta/scanner.dart

 // Copyright (c) 2016, 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.md file.
 
 library fasta.scanner;
 
 import 'dart:convert' show UNICODE_REPLACEMENT_CHARACTER_RUNE;
 
 import 'scanner/token.dart' show Token;
 
+import 'scanner/string_scanner.dart' show StringScanner;
+
 import 'scanner/utf8_bytes_scanner.dart' show Utf8BytesScanner;
 
 import 'scanner/recover.dart' show defaultRecoveryStrategy;
 
 export 'scanner/token.dart'
     show
         BeginGroupToken,
         KeywordToken,
         StringToken,
         SymbolToken,
@@ skipping 24 matching lines @@
   bool get hasErrors;
 
   List<int> get lineStarts;
 
   Token tokenize();
 }
 
 class ScannerResult {
   final Token tokens;
   final List<int> lineStarts;
+  final bool hasErrors;
 
-  ScannerResult(this.tokens, this.lineStarts);
+  ScannerResult(this.tokens, this.lineStarts, this.hasErrors);
 }
 
+/// Scan/tokenize the given UTF8 [bytes].
+/// If [recover] is null, then the [defaultRecoveryStrategy] is used.
 ScannerResult scan(List<int> bytes,
     {bool includeComments: false, Recover recover}) {
   if (bytes.last != 0) {
     throw new ArgumentError("[bytes]: the last byte must be null.");
   }
   Scanner scanner =
       new Utf8BytesScanner(bytes, includeComments: includeComments);
+  return _tokenizeAndRecover(scanner, recover, bytes);
+}
+
+/// Scan/tokenize the given [source].
+/// If [recover] is null, then the [defaultRecoveryStrategy] is used.
+ScannerResult scanString(String source,
+    {bool includeComments: false, Recover recover}) {
+  assert(source != null, 'source must not be null');
+  StringScanner scanner =
+      new StringScanner(source, includeComments: includeComments);
+  // TODO(danrubel): what should be passed for the "bytes" argument?
+  // does the Recover API need to be adjusted for a String source?
+  return _tokenizeAndRecover(scanner, recover, null);
+}
+
+ScannerResult _tokenizeAndRecover(
+    Scanner scanner, Recover recover, List<int> bytes) {
   Token tokens = scanner.tokenize();
   if (scanner.hasErrors) {
     recover ??= defaultRecoveryStrategy;
     tokens = recover(bytes, tokens, scanner.lineStarts);
   }
-  return new ScannerResult(tokens, scanner.lineStarts);
+  return new ScannerResult(tokens, scanner.lineStarts, scanner.hasErrors);
 }