fix #543, export of properties should now work

lib/src/compiler/code_generator.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 73 matching lines @@
       new HashMap<LibraryElement, HashMap<String, JS.TemporaryId>>();
   final _initializingFormalTemps =
       new HashMap<ParameterElement, JS.TemporaryId>();
 
   final _dartxVar = new JS.Identifier('dartx');
   final _runtimeLibVar = new JS.Identifier('dart');
   final namedArgumentTemp = new JS.TemporaryId('opts');
 
   final _hasDeferredSupertype = new HashSet<ClassElement>();
 
+  final _eagerTopLevelFields = new HashSet<Element>.identity();
+
   /// The  type provider from the current Analysis [context].
   final TypeProvider types;
 
   final LibraryElement dartCoreLibrary;
   final LibraryElement dartJSLibrary;
 
   /// The dart:async `StreamIterator<>` type.
   final InterfaceType _asyncStreamIterator;
 
   /// The dart:_interceptors JSArray element.
@@ skipping 269 matching lines @@
 
   @override
   void visitExportDirective(ExportDirective node) {
     ExportElement element = node.element;
     var currentLibrary = element.library;
 
     var currentNames = currentLibrary.publicNamespace.definedNames;
     var exportedNames =
         new NamespaceBuilder().createExportNamespaceForDirective(element);
 
+    var libraryName = emitLibraryName(currentLibrary);
+
     // TODO(jmesserly): we could collect all of the names for bulk re-export,
     // but this is easier to implement for now.
     void emitExport(Element export, {String suffix: ''}) {
       var name = _emitTopLevelName(export, suffix: suffix);
-      _moduleItems.add(js.statement(
-          '#.# = #;', [emitLibraryName(currentLibrary), name.selector, name]));
+
+      if (export is TypeDefiningElement || export is FunctionElement ||
+          _eagerTopLevelFields.contains(export)) {
+        // classes, typedefs, functions, and eager init fields can be assigned
+        // directly.
+        // TODO(jmesserly): we don't know about eager init fields from other
+        // modules we import, so we will never go down this code path for them.
+        _moduleItems
+            .add(js.statement('#.# = #;', [libraryName, name.selector, name]));
+      } else {
+        // top-level fields, getters, setters need to copy the property
+        // descriptor.
+        _moduleItems.add(js.statement('dart.copyProperty(#, #, #);',

[vsm, 2016/05/03 21:59:14]

From a readability standpoint, perhaps "exportProperty"?

[Jennifer Messerly, 2016/05/03 23:37:28]

yeah, we used to call it "dart.export". restored that.

+            [libraryName, name.receiver, name.selector]));
+      }
     }
 
     for (var export in exportedNames.definedNames.values) {
+      if (export is PropertyAccessorElement) {
+        export = (export as PropertyAccessorElement).variable;
+      }
+
       // Don't allow redefining names from this library.
       if (currentNames.containsKey(export.name)) continue;
 
       _loader.emitDeclaration(export);
       if (export is ClassElement && export.typeParameters.isNotEmpty) {
         // Export the generic name as well.
         // TODO(jmesserly): revisit generic classes
         emitExport(export, suffix: r'$');
       }
       emitExport(export);
@@ skipping 2361 matching lines @@
       // later on when we emit lazy fields. That seems busted.
       jsInit = _visitInitializer(field);
       eagerInit = false;
     }
 
     // Treat `final x = JS('', '...')` as a const (non-lazy) to help compile
     // runtime helpers.
     // TODO(jmesserly): we don't track dependencies correctly for these.
     var isJSTopLevel = field.isFinal && _isFinalJSDecl(field);
     if (eagerInit || isJSTopLevel) {
+      // Remember that we emitted it this way, so re-export can take advantage
+      // of this fact.
+      _eagerTopLevelFields.add(element);
+
       return annotate(
           js.statement('# = #;', [_emitTopLevelName(element), jsInit]),
           field,
           element);
     }
 
     assert(element.library == currentLibrary);
     return _emitLazyFields(element.library, [field]);
   }
 
@@ skipping 1442 matching lines @@
 }
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;
 
 LibraryElement _getLibrary(AnalysisContext c, String uri) =>
     c.computeLibraryElement(c.sourceFactory.forUri(uri));
 
 bool _isDartRuntime(LibraryElement l) =>
     l.isInSdk && l.source.uri.toString() == 'dart:_runtime';