translate remaining fasta scanner error codes

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

Index: pkg/front_end/lib/src/scanner/errors.dart
diff --git a/pkg/front_end/lib/src/scanner/errors.dart b/pkg/front_end/lib/src/scanner/errors.dart
index ca2a20972639926508bfc0aea952ad0044896006..93b7fb0d26f87e3896c2763cf5b583906d9a231a 100644
--- a/pkg/front_end/lib/src/scanner/errors.dart
+++ b/pkg/front_end/lib/src/scanner/errors.dart
@@ -5,13 +5,20 @@
 import 'package:front_end/src/base/errors.dart';
 import 'package:front_end/src/fasta/fasta_codes.dart';
 import 'package:front_end/src/fasta/scanner/error_token.dart';
-import 'package:front_end/src/scanner/token.dart' show Token;
+import 'package:front_end/src/scanner/token.dart' show Token, TokenType;
 import 'package:front_end/src/fasta/scanner/token_constants.dart';
 
 /**
  * The error codes used for errors detected by the scanner.
  */
 class ScannerErrorCode extends ErrorCode {
+  /**
+   * Parameters:
+   * 0: the token that was expected but not found
+   */
+  static const ScannerErrorCode EXPECTED_TOKEN =
+      const ScannerErrorCode('EXPECTED_TOKEN', "Expected to find '{0}'.");
+
   /**
    * Parameters:
    * 0: the illegal character
@@ -25,6 +32,9 @@ class ScannerErrorCode extends ErrorCode {
   static const ScannerErrorCode MISSING_HEX_DIGIT = const ScannerErrorCode(
       'MISSING_HEX_DIGIT', "Hexidecimal digit expected.");
 
+  static const ScannerErrorCode MISSING_IDENTIFIER =
+      const ScannerErrorCode('MISSING_IDENTIFIER', "Expected an identifier.");
+
   static const ScannerErrorCode MISSING_QUOTE =
       const ScannerErrorCode('MISSING_QUOTE', "Expected quote (' or \").");
 
@@ -119,9 +129,20 @@ void translateErrorToken(ErrorToken token, ReportError reportError) {
       return _makeError(ScannerErrorCode.ILLEGAL_CHARACTER, [token.character]);
 
     default:
-      if (errorCode == codeUnmatchedToken ||
-          errorCode == codeUnexpectedDollarInString) {
-        return null;
+      if (errorCode == codeUnmatchedToken) {
+        TokenType type = token.begin?.type;
+        if (type == TokenType.OPEN_CURLY_BRACKET ||
+            type == TokenType.STRING_INTERPOLATION_EXPRESSION) {
+          return _makeError(ScannerErrorCode.EXPECTED_TOKEN, ['}']);
+        }
+        if (type == TokenType.OPEN_SQUARE_BRACKET) {
+          return _makeError(ScannerErrorCode.EXPECTED_TOKEN, [']']);
+        }
+        if (type == TokenType.OPEN_PAREN) {
+          return _makeError(ScannerErrorCode.EXPECTED_TOKEN, [')']);
+        }
+      } else if (errorCode == codeUnexpectedDollarInString) {
+        return _makeError(ScannerErrorCode.MISSING_IDENTIFIER, null);
       }
       throw new UnimplementedError('$errorCode');
   }