improve fasta export directive recovery

pkg/analyzer/test/generated/parser_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/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart' as analyzer;
 import 'package:analyzer/dart/ast/token.dart' show TokenType;
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart' show ErrorReporter;
 import 'package:analyzer/src/dart/scanner/scanner.dart';
@@ skipping 617 matching lines @@
   }
 
   @override
   @failingTest
   void test_expectedToken_parseStatement_afterVoid() {
     super.test_expectedToken_parseStatement_afterVoid();
   }
 
   @override
   @failingTest
-  void test_expectedToken_semicolonMissingAfterExport() {
-    super.test_expectedToken_semicolonMissingAfterExport();
-  }
-
-  @override
-  @failingTest
   void test_expectedToken_semicolonMissingAfterExpression() {
     super.test_expectedToken_semicolonMissingAfterExpression();
   }
 
   @override
   @failingTest
   void test_expectedToken_semicolonMissingAfterImport() {
     super.test_expectedToken_semicolonMissingAfterImport();
   }
 
@@ skipping 1714 matching lines @@
   }
 
   @override
   Expression parseConstExpression(String code) {
     return _parseExpression(code);
   }
 
   @override
   ConstructorInitializer parseConstructorInitializer(String code) {
     String source = 'class __Test { __Test() : $code; }';
-    var unit =
-        _runParser(source, (parser) => parser.parseUnit) as CompilationUnit;
+    var unit = _runParser(source, null) as CompilationUnit;
     var clazz = unit.declarations[0] as ClassDeclaration;
     var constructor = clazz.members[0] as ConstructorDeclaration;
     return constructor.initializers.single;
   }
 
   @override
   CompilationUnit parseDirectives(String source,
       [List<ErrorCode> errorCodes = const <ErrorCode>[]]) {
-    return _runParser(source, (parser) => parser.parseUnit, errorCodes);
+    return _runParser(source, null, errorCodes);
   }
 
   @override
   BinaryExpression parseEqualityExpression(String code) {
     return _parseExpression(code);
   }
 
   @override
   Expression parseExpression(String source,
       [List<ErrorCode> errorCodes = const <ErrorCode>[]]) {
@@ skipping 408 matching lines @@
     _astBuilder.className = className;
     _eventListener.begin('CompilationUnit');
     var result = _run((parser) => parser.parseMember) as ClassMember;
     _eventListener.end('CompilationUnit');
     _astBuilder.className = null;
     return result;
   }
 
   @override
   CompilationUnit parseCompilationUnit2() {
-    var result = _run((parser) => parser.parseUnit) as CompilationUnit;
+    var result = _run(null) as CompilationUnit;
     _eventListener.expectEmpty();
     return result;
   }
 
   AnnotatedNode parseTopLevelDeclaration(bool isDirective) {
     _eventListener.begin('CompilationUnit');
     _currentFastaToken =
         _fastaParser.parseTopLevelDeclaration(_currentFastaToken);
     expect(_currentFastaToken.isEof, isTrue);
     expect(_astBuilder.stack, hasLength(0));
     expect(_astBuilder.scriptTag, isNull);
     expect(_astBuilder.directives, hasLength(isDirective ? 1 : 0));
     expect(_astBuilder.declarations, hasLength(isDirective ? 0 : 1));
     _eventListener.end('CompilationUnit');
     return (isDirective ? _astBuilder.directives : _astBuilder.declarations)
         .first;
   }
 
   /**
    * Runs a single parser function, and returns the result as an analyzer AST.
    */
   Object _run(ParseFunction getParseFunction(fasta.Parser parser)) {
-    var parseFunction = getParseFunction(_fastaParser);
+    ParseFunction parseFunction;
+    if (getParseFunction != null) {
+      parseFunction = getParseFunction(_fastaParser);
+      _fastaParser.firstToken = _currentFastaToken;
+    } else {
+      parseFunction = _fastaParser.parseUnit;
+      // firstToken should be set by beginCompilationUnit event.
+    }
     _currentFastaToken = parseFunction(_currentFastaToken);
     expect(_currentFastaToken.isEof, isTrue);
     expect(_astBuilder.stack, hasLength(1));
     return _astBuilder.pop();
   }
 }
 
 /**
  * Proxy implementation of [Scope] used by Fasta parser tests.
  *
@@ skipping 175 matching lines @@
     assertNoErrors();
   }
 
   @failingTest
   void test_parseCompilationUnitMember_abstractAsPrefix2() {
     // TODO(danrubel): should not be generating an error
     super.test_parseCompilationUnitMember_abstractAsPrefix();
     assertNoErrors();
   }
 }