Fix for NPE when convert error without source.

pkg/analyzer_experimental/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;
 
 import 'src/error.dart';
 import 'src/generated/ast.dart';
 import 'src/generated/error.dart';
 import 'src/generated/java_io.dart';
 import 'src/generated/parser.dart';
 import 'src/generated/scanner.dart';
 import 'src/generated/source_io.dart';
 
 export 'src/error.dart';
 export 'src/generated/ast.dart';
 export 'src/generated/error.dart';
 export 'src/generated/utilities_dart.dart';
 
 /// Parses a Dart file into an AST.
 CompilationUnit parseDartFile(String path) {
   var contents = new File(path).readAsStringSync();
   var errorCollector = new _ErrorCollector();
   var sourceFactory = new SourceFactory.con2([new FileUriResolver()]);
-  var source = sourceFactory.forUri(pathos.toUri(path).toString());
+
+  var absolutePath = pathos.absolute(path);
+  var source = sourceFactory.forUri(pathos.toUri(absolutePath).toString());
+  if (source == null) {

[Brian Wilkerson, 2013/07/30 14:03:01]

We might also want to check whether the source exists.

+    throw new ArgumentError("Can't get source for path $path");
+  }
+
   var scanner = new StringScanner(source, contents, 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) throw errorCollector.group;
 
   return unit;
 }
@@ skipping 17 matching lines @@
   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);
 }