improve fasta interpolation recovery

pkg/front_end/test/scanner_fasta_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:analyzer/src/fasta/token_utils.dart';
+import 'package:front_end/src/fasta/fasta_codes.dart';
 import 'package:front_end/src/fasta/scanner/error_token.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/string_scanner.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/token.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/token_constants.dart' as fasta;
 import 'package:front_end/src/scanner/errors.dart';
 import 'package:front_end/src/scanner/token.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'scanner_test.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(ScannerTest_Fasta);
     defineReflectiveTests(ScannerTest_Fasta_Direct);
   });
 }
 
 @reflectiveTest
 class ScannerTest_Fasta extends ScannerTestBase {
+  ScannerTest_Fasta() {
+    usingFasta = true;
+  }
+
   @override
   Token scanWithListener(String source, ErrorListener listener,
       {bool genericMethodComments: false,
       bool lazyAssignmentOperators: false}) {
     var scanner = new fasta.StringScanner(source,
         includeComments: true,
         scanGenericMethodComments: genericMethodComments);
     var token = scanner.tokenize();
     return new ToAnalyzerTokenStreamConverter_WithListener(listener)
         .convertTokens(token);
@@ skipping 136 matching lines @@
       prepareTokens();
       c3.remove();
       expect(token.precedingComments, c1);
       expect(c1.next, c2);
       expect(c2.next, isNull);
     }
   }
 
   @override
   @failingTest
-  void test_incomplete_string_interpolation() {
-    // TODO(danrubel): fix ToAnalyzerTokenStreamConverter_WithListener
-    // to handle synthetic closers in token stream
-    super.test_incomplete_string_interpolation();
-  }
-
-  @override
-  @failingTest
   void test_mismatched_closer() {
     // TODO(paulberry,ahe): Fasta and analyzer recover this error differently.
     // Figure out which recovery technique we want the front end to use.
     super.test_mismatched_closer();
   }
 
   @override
   @failingTest
   void test_mismatched_opener() {
     // TODO(paulberry,ahe): Fasta and analyzer recover this error differently.
@@ skipping 296 matching lines @@
 }
 
 /// Scanner tests that exercise the Fasta scanner directly.
 @reflectiveTest
 class ScannerTest_Fasta_Direct extends ScannerTest_Fasta_Base {
   @override
   Token scan(String source) {
     var scanner = new fasta.StringScanner(source, includeComments: true);
     return scanner.tokenize();
   }
+
+  test_unterminated_string_with_unterminated_interpolation() {
+    Token token = scan(r'"foo ${bar');
+    BeginToken interpolationStart = token.next;
+
+    Token previous;
+    while (token.kind != fasta.BAD_INPUT_TOKEN) {
+      expect(token.isEof, isFalse);
+      previous = token;
+      token = token.next;
+    }
+
+    // Expect interpolation to be terminated before string is closed
+
+    token = previous;
+    expect(token.isSynthetic, isTrue);
+    expect(token.length, 0);
+    expect(token.stringValue, '}');
+
+    token = token.next;
+    expect((token as fasta.ErrorToken).errorCode, same(codeUnmatchedToken));
+    expect((token as fasta.UnmatchedToken).begin, same(interpolationStart));
+
+    token = token.next;
+    expect((token as fasta.ErrorToken).errorCode, same(codeUnterminatedString));
+  }
 }
 
 /// Override of [ToAnalyzerTokenStreamConverter] that verifies that there are no
 /// errors.
 class ToAnalyzerTokenStreamConverter_NoErrors
     extends ToAnalyzerTokenStreamConverter {
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     fail('Unexpected error: $errorCode, $offset, $arguments');
   }
 }
 
 /// Override of [ToAnalyzerTokenStreamConverter] that records errors in an
 /// [ErrorListener].
 class ToAnalyzerTokenStreamConverter_WithListener
     extends ToAnalyzerTokenStreamConverter {
   final ErrorListener _listener;
 
   ToAnalyzerTokenStreamConverter_WithListener(this._listener);
 
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     _listener.errors.add(new TestError(offset, errorCode, arguments));
   }
 }