Issue 23133. Fix for restoring 'package:' uris on Windows.

pkg/analyzer/lib/source/package_map_resolver.dart

 // Copyright (c) 2014, 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 source.package_map_resolver;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/util/asserts.dart' as asserts;
+import 'package:path/path.dart' as pathos;
 
 /**
  * A [UriResolver] implementation for the `package:` scheme that uses a map of
  * package names to their directories.
  */
 class PackageMapUriResolver extends UriResolver {
   /**
    * The name of the `package` scheme.
    */
   static const String PACKAGE_SCHEME = "package";
@@ skipping 56 matching lines @@
   @override
   Uri restoreAbsolute(Source source) {
     String sourcePath = source.fullName;
     Uri bestMatch;
     int bestMatchLength = -1;
     for (String pkgName in packageMap.keys) {
       List<Folder> pkgFolders = packageMap[pkgName];
       for (int i = 0; i < pkgFolders.length; i++) {
         Folder pkgFolder = pkgFolders[i];
         String pkgFolderPath = pkgFolder.path;
-        // TODO(paulberry): figure out the right thing to do for Windows.
         if (pkgFolderPath.length > bestMatchLength &&
-            sourcePath.startsWith(pkgFolderPath + '/')) {
+            sourcePath.startsWith(pkgFolderPath + pathos.context.separator)) {
           String relPath = sourcePath.substring(pkgFolderPath.length + 1);
           if (_isReversibleTranslation(pkgFolders, i, relPath)) {
-            bestMatch = Uri.parse('$PACKAGE_SCHEME:$pkgName/$relPath');
+            List<String> relPathComponents = pathos.context.split(relPath);
+            String relUriPath = pathos.posix.joinAll(relPathComponents);
+            bestMatch = Uri.parse('$PACKAGE_SCHEME:$pkgName/$relUriPath');
             bestMatchLength = pkgFolderPath.length;
           }
         }
       }
     }
     return bestMatch;
   }
 
   /**
    * A translation from file path to package URI has just been found for
@@ skipping 18 matching lines @@
     return true;
   }
 
   /**
    * Returns `true` if [uri] is a `package` URI.
    */
   static bool isPackageUri(Uri uri) {
     return uri.scheme == PACKAGE_SCHEME;
   }
 }