Deal better with missing sources in code_transformers and polymer

pkg/code_transformers/lib/src/resolver_impl.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 code_transformer.src.resolver_impl;
 
 import 'dart:async';
 import 'package:analyzer/analyzer.dart' show parseCompilationUnit;
 import 'package:analyzer/src/generated/ast.dart' hide ConstantEvaluator;
 import 'package:analyzer/src/generated/constant.dart' show ConstantEvaluator,
@@ skipping 118 matching lines @@
         source.updateDependencies(contents);
         toUpdate.add(new _PendingUpdate(source, contents));
         source.dependentAssets.where((id) => !visited.contains(id))
             .forEach(processAsset);
       }, onError: (e) {
         var source = sources[assetId];
         if (source != null && source.exists()) {
           _context.applyChanges(
               new ChangeSet()..removedSource(source));
           sources[assetId].updateContents(null);
+        } else if (source == null) {
+          transform.logger.warning('Asset not found: $assetId');

[Siggi Cherem (dart-lang), 2014/04/10 20:05:47]

we already compute the span inside dependentsAssets below, so one option would
be to pass that through. If you think it's worth it, I'm happy to add that.

         }
       }));
     }
     entryPoints.forEach(processAsset);
 
     // Once we have all asset sources updated with the new contents then
     // resolve everything.
     return visiting.future.then((_) {
       var changeSet = new ChangeSet();
       toUpdate.forEach((pending) => pending.apply(changeSet));
       var unreachableAssets = sources.keys.toSet()
           .difference(visited)
           .map((id) => sources[id]);
       for (var unreachable in unreachableAssets) {
         changeSet.removedSource(unreachable);
         unreachable.updateContents(null);
         sources.remove(unreachable.assetId);
       }
 
       // Update the analyzer context with the latest sources
       _context.applyChanges(changeSet);
       // Force resolve each entry point (the getter will ensure the library is
       // computed first).
-      _entryLibraries = entryPoints
-          .map((id) => _context.computeLibraryElement(sources[id])).toList();
+      _entryLibraries = entryPoints.map((id) {
+        var source = sources[id];
+        if (source == null) return null;
+        return _context.computeLibraryElement(source);
+      }).toList();
     });
   }
 
   Iterable<LibraryElement> get libraries {
     if (_libraries == null) {
       // Note: we don't use `lib.visibleLibraries` because that excludes the
       // exports seen in the entry libraries.
       _libraries = new Set<LibraryElement>();
       _entryLibraries.forEach(_collectLibraries);
     }
@@ skipping 449 matching lines @@
 
   void apply(ChangeSet changeSet) {
     if (!source.updateContents(content)) return;
     if (source._revision == 1 && source._contents != null) {
       changeSet.addedSource(source);
     } else {
       changeSet.changedSource(source);
     }
   }
 }