Added support for exports and re-exports.

lib/compiler/implementation/elements/elements.dart

Index: lib/compiler/implementation/elements/elements.dart
diff --git a/lib/compiler/implementation/elements/elements.dart b/lib/compiler/implementation/elements/elements.dart
index 71a7d0007dc859acdfd21e5800441658cf7d6755..60ac9bdf2753484cd40025f86cb1afcd6181a533 100644
--- a/lib/compiler/implementation/elements/elements.dart
+++ b/lib/compiler/implementation/elements/elements.dart
@@ -104,6 +104,9 @@ class ElementKind {
   static const ElementKind VOID =
     const ElementKind('void', ElementCategory.NONE);
 
+  static const ElementKind ERROR =
+      const ElementKind('error', ElementCategory.NONE);
+
   toString() => id;
 }
 
@@ -358,7 +361,8 @@ class ErroneousElement extends Element {
 
   ErroneousElement(this.messageKind, this.messageArguments,
                    this.targetName, Element enclosing)
-      : super(const SourceString('erroneous element'), null, enclosing);

[ahe, 2012/10/09 13:07:50]

Good catch!

+      : super(const SourceString('erroneous element'),
+              ElementKind.ERROR, enclosing);
 
   isErroneous() => true;
 
@@ -367,7 +371,6 @@ class ErroneousElement extends Element {
   }
 
   SourceString get name => unsupported();
-  ElementKind get kind => unsupported();
   Link<MetadataAnnotation> get metadata => unsupported();
 
   getLibrary() => enclosingElement.getLibrary();
@@ -617,8 +620,9 @@ class LibraryElement extends ScopeContainerElement {
    * detection of ambiguous uses of imported names.
    */
   void addImport(Element element, DiagnosticListener listener) {
-    Element existing = importScope.putIfAbsent(element.name, () => element);
-    if (existing !== element && existing !== null) {
+    Element existing = importScope[element.name];
+    importScope.putIfAbsent(element.name, () => element);

[ahe, 2012/10/09 13:07:50]

This should be:

Element existing = importScope.putIfAbsent(element.name, () => element);

[Johnni Winther, 2012/10/09 13:50:07]

Changed to not use [putIfAbsent].

+    if (existing !== null) {
       if (!existing.isErroneous()) {
         // TODO(johnniwinther): Provide access to both the new and existing
         // elements.
@@ -629,6 +633,33 @@ class LibraryElement extends ScopeContainerElement {
     }
   }
 
+  bool get exportsHandled => _exports !== null;

[ahe, 2012/10/09 13:07:50]

What is the purpose of this method?

[Johnni Winther, 2012/10/09 13:50:07]

To test whether the export scope has been computed for this library.

+
+  /**
+   * Link for elements exported either through export declarations or through
+   * declaration.
+   *
+   * [ImportExportHandler] sets this map when the library is loaded.
+   */
+  Link<Element> _exports;

[ahe, 2012/10/09 13:07:50]

Why is this private, and why is it not with all the other fields?

[Johnni Winther, 2012/10/09 13:50:07]

It is private so that setExports can ensure that it is only set once. It should
be with the other fields.

[ahe, 2012/10/09 14:41:33]

How does privacy ensure that it can only be set once?

[Johnni Winther, 2012/10/10 09:20:59]

It doesn't. Renamed to [slotForExports] and comment expanded to tell that this
field should be not be accessed by other methods that the getter and setExports.

+
+  Link<Element> get exports {
+    assert(invariant(this, exportsHandled,
+                     message: 'Exports not handled on $this'));
+    return _exports;
+  }
+
+  void setExports(Iterable<Element> iterable) {

[ahe, 2012/10/09 13:07:50]

Why is this not a setter?

[Johnni Winther, 2012/10/09 13:50:07]

Because it is not symmetric to the getter. It has a different type and must only
be called once.

[Bob Nystrom, 2012/10/09 16:20:37]

I agree with Johnni, I wouldn't make this a setter either. Setters should have
"field-like" semantics and one thing that implies (to me at least) is that you
can invoke them repeatedly.

My personal convention for methods like this is to call them "bind___". "bind"
as opposed to "set" to me implies more of a one-time occurrence. (Although it
might be confusing here since "bind" is already meaningful in the context of a
compiler.)

+    assert(invariant(this, !exportsHandled,
+                     message: 'Exports already set to $_exports on $this'));
+    assert(invariant(this, iterable !== null));
+    var builder = new LinkBuilder<Element>();
+    for (Element export in iterable) {
+      builder.addLast(export);
+    }
+    _exports = builder.toLink();
+  }
+
   LibraryElement getLibrary() => isPatch ? origin : this;
 
   /**
@@ -656,14 +687,7 @@ class LibraryElement extends ScopeContainerElement {
   }
 
   void forEachExport(f(Element element)) {
-    localScope.forEach((_, Element e) {
-      if (this === e.getLibrary()
-          && e.kind !== ElementKind.PREFIX
-          && e.kind !== ElementKind.FOREIGN
-          && !e.name.isPrivate()) {
-        f(e);
-      }
-    });
+    exports.forEach((Element e) => f(e));
   }
 
   void forEachLocalMember(f(Element element)) {