Support new import rules.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

 // Copyright (c) 2013, 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 elements.modelx;
 
 import 'dart:collection' show LinkedHashMap;
 
 import 'elements.dart';
 import '../../compiler.dart' as api;
@@ skipping 656 matching lines @@
    * Adds [element] to the import scope of this library.
    *
    * 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, Import import, DiagnosticListener listener) {
     importers[element] =
         importers.putIfAbsent(element, () => const Link<Import>())
         .prepend(import);
-    Element existing = importScope[element.name];
-    if (existing != null) {
-      // TODO(johnniwinther): Provide access to the import tags from which
-      // the elements came.
-      importScope[element.name] = new AmbiguousElementX(
-          MessageKind.DUPLICATE_IMPORT, {'name': element.name},
-          this, existing, element);
-    } else {
-      importScope[element.name] = element;
+    SourceString name = element.name;
+    Element existing = importScope.putIfAbsent(name, () => element);
+    if (existing != element) {
+      if (existing.getLibrary().isPlatformLibrary &&
+          !element.getLibrary().isPlatformLibrary) {
+        // [existing] is implicitly hidden.
+        importScope[name] = element;
+        listener.reportWarningCode(import, MessageKind.HIDDEN_IMPORT,
+            {'name': name,
+             'hiddenUri': existing.getLibrary().canonicalUri,
+             'hidingUri': element.getLibrary().canonicalUri});
+      } else if (!existing.getLibrary().isPlatformLibrary &&
+                 element.getLibrary().isPlatformLibrary) {
+        // [element] is implicitly hidden.
+        listener.reportWarningCode(import, MessageKind.HIDDEN_IMPORT,
+            {'name': name,
+             'hiddenUri': element.getLibrary().canonicalUri,
+             'hidingUri': existing.getLibrary().canonicalUri});
+      } else {
+        // TODO(johnniwinther): Provide access to the import tags from which
+        // the elements came.
+        importScope[name] = new AmbiguousElementX(
+            MessageKind.DUPLICATE_IMPORT, {'name': name},
+            this, existing, element);
+      }
     }
   }
 
   void addMember(Element element, DiagnosticListener listener) {
     localMembers = localMembers.prepend(element);
     addToScope(element, listener);
   }
 
   void addToScope(Element element, DiagnosticListener listener) {
     localScope.add(element, listener);
@@ skipping 1505 matching lines @@
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }