When converting files to package URI's, favor longer directory matches.

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;
 
@@ skipping 59 matching lines @@
     }
     // Return a NonExistingSource instance.
     // This helps provide more meaningful error messages to users
     // (a missing file error, as opposed to an invalid URI error).
     return new NonExistingSource(uri.toString(), UriKind.PACKAGE_URI);
   }
 
   @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 (sourcePath.startsWith(pkgFolderPath + '/')) {
+        if (pkgFolderPath.length > bestMatchLength && sourcePath.startsWith(pkgFolderPath + '/')) {
           String relPath = sourcePath.substring(pkgFolderPath.length + 1);
           if (_isReversibleTranslation(pkgFolders, i, relPath)) {
-            return Uri.parse('$PACKAGE_SCHEME:$pkgName/$relPath');
+            bestMatch = Uri.parse('$PACKAGE_SCHEME:$pkgName/$relPath');
+            bestMatchLength = pkgFolderPath.length;
           }
         }
       }
     }
-    return null;
+    return bestMatch;
   }
 
   /**
    * A translation from file path to package URI has just been found for
    * using the [packageDirIndex]th element of [packageDirs], and appending the
    * relative path [relPath].  Determine whether the translation is reversible;
    * that is, whether translating the package URI pack to a file path will
    * produce the file path we started with.
    */
   bool _isReversibleTranslation(List<Folder> packageDirs, int packageDirIndex,
@@ skipping 12 matching lines @@
     return true;
   }
 
   /**
    * Returns `true` if [uri] is a `package` URI.
    */
   static bool isPackageUri(Uri uri) {
     return uri.scheme == PACKAGE_SCHEME;
   }
 }