improve fasta export directive recovery

pkg/analyzer/lib/src/fasta/ast_builder.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 file.
 
 library fasta.analyzer.ast_builder;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast_factory.dart' show AstFactory;
 import 'package:analyzer/dart/ast/standard_ast_factory.dart' as standard;
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 1120 matching lines @@
   void handleInvalidTopLevelDeclaration(Token endToken) {
     debugEvent("InvalidTopLevelDeclaration");
     pop(); // metadata star
     // TODO(danrubel): consider creating a AST node
     // representing the invalid declaration to better support code completion,
     // quick fixes, etc, rather than discarding the metadata and token
   }
 
   @override
   void beginCompilationUnit(Token token) {
+    super.beginCompilationUnit(token);
     push(token);
   }
 
   @override
   void endCompilationUnit(int count, Token endToken) {
     debugEvent("CompilationUnit");
     Token beginToken = pop();
     checkEmpty(endToken.charOffset);
 
     push(ast.compilationUnit(
@@ skipping 738 matching lines @@
     switch (code.analyzerCode) {
       case "EXPECTED_TYPE_NAME":
         errorReporter?.reportErrorForOffset(
             ParserErrorCode.EXPECTED_TYPE_NAME, charOffset, 1);
         return;
       case "EXPECTED_STRING_LITERAL":
         errorReporter?.reportErrorForOffset(
             ParserErrorCode.EXPECTED_STRING_LITERAL, charOffset, 1);
         return;
       case "UNEXPECTED_TOKEN":
-        var text = arguments['string'];
+        String text = arguments['string'];
         if (text == null) {
           Token token = arguments['token'];
           if (token != null) {
             text = token.lexeme;
           }
         }
-        errorReporter?.reportErrorForOffset(
-            ParserErrorCode.UNEXPECTED_TOKEN, charOffset, 1, [text]);
+        if (text == ';') {
+          errorReporter?.reportErrorForOffset(
+              ParserErrorCode.EXPECTED_TOKEN, charOffset, text.length, [text]);
+        } else {
+          errorReporter?.reportErrorForOffset(
+              ParserErrorCode.UNEXPECTED_TOKEN, charOffset, 1, [text]);
+        }
         return;
       default:
       // fall through
     }
     library.addCompileTimeError(message, charOffset, uri);
   }
 }
 
 /// Data structure placed on the stack to represent a class body.
 ///
@@ skipping 93 matching lines @@
       } else if (identical('var', s)) {
         finalConstOrVarKeyword = token;
       } else if (identical('covariant', s)) {
         covariantKeyword = token;
       } else {
         unhandled("$s", "modifier", token.charOffset, null);
       }
     }
   }
 }