improve missing hex digit recovery

Dan Rubel · commit-bot@chromium.org · commit 24d1e511df19 · 2019-07-24T18:38:43.000Z
Change-Id: I12d9e3fe314e850a6ee9599187d67dfa5455b18a Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/110143 Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/pkg/front_end/lib/src/fasta/scanner/abstract_scanner.dart b/pkg/front_end/lib/src/fasta/scanner/abstract_scanner.dart
@@ -35,8 +35,7 @@ import 'error_token.dart'
 
 import 'keyword_state.dart' show KeywordState;
 
-import 'token.dart'
-    show CommentToken, DartDocToken, LanguageVersionToken, SyntheticStringToken;
+import 'token.dart' show CommentToken, DartDocToken, LanguageVersionToken;
 
 import 'token_constants.dart';
 
@@ -1117,8 +1116,8 @@ abstract class AbstractScanner implements Scanner {
           prependErrorToken(new UnterminatedToken(
               messageExpectedHexDigit, start, stringOffset));
           // Recovery
-          // TODO(danrubel): append actual characters not "0"
-          appendToken(SyntheticStringToken(TokenType.INT, "0", tokenStart));
+          appendSyntheticSubstringToken(
+              TokenType.HEXADECIMAL, start, true, "0");
           return next;
         }
         appendSubstringToken(TokenType.HEXADECIMAL, start, true);
diff --git a/pkg/front_end/test/scanner_test.dart b/pkg/front_end/test/scanner_test.dart
@@ -303,7 +303,12 @@ abstract class ScannerTestBase {
   }
 
   void test_hexadecimal_missingDigit() {
-    _assertError(ScannerErrorCode.MISSING_HEX_DIGIT, 5, "a = 0x");
+    var token = _assertError(ScannerErrorCode.MISSING_HEX_DIGIT, 5, "a = 0x");
+    expect(token.lexeme, 'a');
+    token = token.next;
+    expect(token.lexeme, '=');
+    token = token.next;
+    expect(token.lexeme, '0x0');
   }
 
   void test_identifier() {
@@ -1299,13 +1304,14 @@ abstract class ScannerTestBase {
    * [expectedOffset] the string offset that should be associated with the error
    * [source] the source to be scanned to produce the error
    */
-  void _assertError(
+  Token _assertError(
       ScannerErrorCode expectedError, int expectedOffset, String source,
       [List<Object> arguments]) {
     ErrorListener listener = new ErrorListener();
-    scanWithListener(source, listener);
+    var tokens = scanWithListener(source, listener);
     listener.assertErrors(
         [new TestError(expectedOffset, expectedError, arguments)]);
+    return tokens;
   }
 
   /**
