Import scope rules updated.

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 72e3a9abfe799df7f460665595cecc8af2774902..25e51919a4594ae7780dc517a53c31a1832622d5 100644
--- a/lib/compiler/implementation/elements/elements.dart
+++ b/lib/compiler/implementation/elements/elements.dart
@@ -316,10 +316,12 @@ class Element implements Hashable {
  *   [: element == null :].
  */
 class ErroneousElement extends Element {
-  final Message errorMessage;
+  final MessageKind messageKind;
+  final List messageArguments;
   final SourceString targetName;
 
-  ErroneousElement(this.errorMessage, this.targetName, Element enclosing)
+  ErroneousElement(this.messageKind, this.messageArguments,
+                   this.targetName, Element enclosing)
       : super(const SourceString('erroneous element'), null, enclosing);
 
   isErroneous() => true;
@@ -337,9 +339,9 @@ class ErroneousElement extends Element {
 
 class ErroneousFunctionElement extends ErroneousElement
                                implements FunctionElement {
-  ErroneousFunctionElement(Message errorMessage, SourceString targetName,
-                           Element enclosing)
-      : super(errorMessage, targetName, enclosing);
+  ErroneousFunctionElement(MessageKind messageKind, List messageArguments,
+                           SourceString targetName, Element enclosing)
+      : super(messageKind, messageArguments, targetName, enclosing);
 
   get type => unsupported();
   get cachedNode => unsupported();
@@ -486,9 +488,11 @@ class LibraryElement extends ScopeContainerElement {
   ScriptTag libraryTag;
   bool canUseNative = false;
   LibraryElement patch = null;
+  final Map<SourceString, Element> importScope;

[Lasse Reichstein Nielsen, 2012/09/20 12:21:08]

Documentation. What is the meaning of this field? What is it used for?

Should this be a Scope instead of a Map? Or some other meaningful wrapping of
the map, to avoid people *fiddling* with the Map from the outside?

[Johnni Winther, 2012/09/21 14:00:05]

Comment added.

 
   LibraryElement(Script script, [Uri uri])
     : this.uri = ((uri === null) ? script.uri : uri),
+      importScope = new Map<SourceString, Element>(),
       super(new SourceString(script.name), ElementKind.LIBRARY, null) {
     entryCompilationUnit = new CompilationUnitElement(script, this);
   }
@@ -504,11 +508,39 @@ class LibraryElement extends ScopeContainerElement {
     tags = tags.prepend(tag);
   }
 
-  /** Look up a top-level element in this library. The element could
-    * potentially have been imported from another library. Returns
-    * null if no such element exist. */
+  /**
+   * Adds [element] to the imported scope of this library.

[Lasse Reichstein Nielsen, 2012/09/20 12:21:08]

"imported scope" -> "import scope". You don't import a scope. You import into
the scope.

[Johnni Winther, 2012/09/21 14:00:05]

Done.

+   *
+   * If an element by the same name is already in the imported scope, an
+   * [ErroneousElement] will be put in the imported scope, allowing for the
+   * 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) {

[Lasse Reichstein Nielsen, 2012/09/20 12:21:08]

Adding the same element twice is an error (according to current spec). It's
importing the same name twice that is not allowed, independently of the actual
name.

[Lasse Reichstein Nielsen, 2012/09/20 14:03:36]

... actual value, even.

[Johnni Winther, 2012/09/21 14:00:05]

I don't understand. Did you mean '... is not an error ...'? The created
[ErroneousElement] is used to report errors/warnings on usage.

+      if (!existing.isErroneous()) {
+        // TODO(johnniwinther): Provide access to both the new and existing
+        // elements.
+        importScope[element.name] = new ErroneousElement(
+            MessageKind.DUPLICATE_IMPORT,
+            [element.name], element.name, this);
+      }
+    }
+  }
+
+
+  /**
+   * Look up a top-level element in this library. The element could
+   * potentially have been imported from another library. Returns
+   * null if no such element exist and an [ErroneousElement] if multiple
+   * elements have been imported.
+   */
   Element find(SourceString elementName) {
-    return localScope[elementName];
+    Element result = localScope[elementName];
+    if (result === null) {
+      result = importScope[elementName];
+    }
+    return result;
   }
 
   /** Look up a top-level element in this library, but only look for