fix duplicate script issue

pkg/polymer/lib/src/mirror_loader.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.
 
 /// Contains logic to initialize polymer apps during development. This
 /// implementation uses dart:mirrors to load each library as they are discovered
 /// through HTML imports. This is only meant to be during development in
 /// dartium, and the polymer transformers replace this implementation with
 /// codege generation in the polymer-build steps.
 library polymer.src.mirror_loader;
@@ skipping 47 matching lines @@
     }
   }
   return initializers;
 }
 
 /// Walks the HTML import structure to discover all script tags that are
 /// implicitly loaded. This code is only used in Dartium and should only be
 /// called after all HTML imports are resolved. Polymer ensures this by asking
 /// users to put their Dart script tags after all HTML imports (this is checked
 /// by the linter, and Dartium will otherwise show an error message).
-List<_ScriptInfo> _discoverScripts(Document doc, String baseUri, [_State state]) {
+List<_ScriptInfo> _discoverScripts(
+    Document doc, String baseUri, [_State state]) {
   if (state == null) state = new _State();
   if (doc == null) {
     print('warning: $baseUri not found.');
     return state.scripts;
   }
   if (!state.seen.add(doc)) return state.scripts;
 
   for (var node in doc.querySelectorAll('script,link[rel="import"]')) {
     if (node is LinkElement) {
       _discoverScripts(node.import, node.href, state);
     } else if (node is ScriptElement && node.type == 'application/dart') {
-      state.scripts.add(_scriptInfoFor(node, baseUri));
+      var info = _scriptInfoFor(node, baseUri);
+      // Bail and warn if this script has already been seen.
+      if (state.scripts.any((s) => s.resolvedUrl == info.resolvedUrl)) {

[Siggi Cherem (dart-lang), 2014/10/21 17:06:03]

similarly here, let's avoid the linear lookup. One option would be to add a Set
in _State for urls that we have already loaded, or make `scripts` a
LinkedHashMap, where the key is the resolvedUrl.

[jakemac, 2014/10/21 18:14:01]

Done.

+        print('warning: script `${info.resolvedUrl}` included more than once.');

[Siggi Cherem (dart-lang), 2014/10/21 17:06:03]

consider including the short link to the details here.

[jakemac, 2014/10/21 18:14:01]

Done.

+        continue;
+      };
+      state.scripts.add(info);
     }
   }
   return state.scripts;
 }
 
 /// Internal state used in [_discoverScripts].
 class _State {
   /// Documents that we have visited thus far.
   final Set<Document> seen = new Set();
 
@@ skipping 176 matching lines @@
         " ${method.simpleName} is not.");
     return;
   }
   if (!method.parameters.where((p) => !p.isOptional).isEmpty) {
     print("warning: methods marked with @initMethod should take no "
         "arguments, ${method.simpleName} expects some.");
     return;
   }
   initializers.add(() => obj.invoke(method.simpleName, const []));
 }