Only parse the directives when rewriting imports.

pkg/analyzer/lib/analyzer.dart

 // Copyright (c) 2013, 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 analyzer;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as pathos;
 
@@ skipping 34 matching lines @@
 
   if (errorCollector.hasErrors) throw errorCollector.group;
 
   return unit;
 }
 
 /// Parses a string of Dart code into an AST.
 ///
 /// If [name] is passed, it's used in error messages as the name of the code
 /// being parsed.
+///
+/// Throws an [AnalyzerErrorGroup] if any errors occurred, unless
+/// [suppressErrors] is `true`, in which case any errors are discarded.
 CompilationUnit parseCompilationUnit(String contents,
     {String name, bool suppressErrors: false}) {
   if (name == null) name = '<unknown source>';
   var source = new StringSource(contents, name);
   var errorCollector = new _ErrorCollector();
   var reader = new CharSequenceReader(contents);
   var scanner = new Scanner(source, reader, errorCollector);
   var token = scanner.tokenize();
   var parser = new Parser(source, errorCollector);
   var unit = parser.parseCompilationUnit(token);
   unit.lineInfo = new LineInfo(scanner.lineStarts);
 
   if (errorCollector.hasErrors && !suppressErrors) throw errorCollector.group;
 
   return unit;
 }
 
+/// Parses the script tag and directives in a string of Dart code into an AST.
+///
+/// Stops parsing when the first non-directive is encountered. The rest of the
+/// string will not be parsed.
+///
+/// If [name] is passed, it's used in error messages as the name of the code
+/// being parsed.
+///
+/// Throws an [AnalyzerErrorGroup] if any errors occurred, unless
+/// [suppressErrors] is `true`, in which case any errors are discarded.
+CompilationUnit parseDirectives(String contents,
+    {String name, bool suppressErrors: false}) {
+  if (name == null) name = '<unknown source>';
+  var source = new StringSource(contents, name);
+  var errorCollector = new _ErrorCollector();
+  var reader = new CharSequenceReader(contents);
+  var scanner = new Scanner(source, reader, errorCollector);
+  var token = scanner.tokenize();
+  var parser = new Parser(source, errorCollector);
+  var unit = parser.parseDirectives(token);
+  unit.lineInfo = new LineInfo(scanner.lineStarts);
+
+  if (errorCollector.hasErrors && !suppressErrors) throw errorCollector.group;
+
+  return unit;
+}
+
 /// Converts an AST node representing a string literal into a [String].
 String stringLiteralToString(StringLiteral literal) {
   return literal.stringValue;
 }
 
 /// A simple error listener that collects errors into an [AnalysisErrorGroup].
 class _ErrorCollector extends AnalysisErrorListener {
   final _errors = <AnalysisError>[];
 
   /// Whether any errors where collected.
   bool get hasErrors => !_errors.isEmpty;
 
   /// The group of errors collected.
   AnalyzerErrorGroup get group =>
     new AnalyzerErrorGroup.fromAnalysisErrors(_errors);
 
   _ErrorCollector();
 
   void onError(AnalysisError error) => _errors.add(error);
 }