Split collecting and traversing.

lib/compiler/implementation/dart_backend/backend.dart

 // Copyright (c) 2012, 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.
 
 class DartBackend extends Backend {
   final List<CompilerTask> tasks;
 
   Map<Element, TreeElements> get resolvedElements() =>
       compiler.enqueuer.resolution.resolvedElements;
 
@@ skipping 20 matching lines @@
       LIBS_TO_IGNORE.indexOf(element.getLibrary()) == -1 &&
       !isDartCoreLib(compiler, element.getLibrary()) &&
       element is !AbstractFieldElement;
 
     final emptyTreeElements = new TreeElementMapping();
 
     Set<Element> topLevelElements = new Set<Element>();
     Map<ClassElement, Set<Element>> classMembers =
         new Map<ClassElement, Set<Element>>();
 
-    PlaceholderCollector collector = new PlaceholderCollector(compiler);
+    // Build all top level elements to emit and necessary class members.
     var newTypedefElementCallback, newClassElementCallback;
 
     processElement(element, treeElements) {
-      collector.collect(element, treeElements);
       new ReferencedElementCollector(
           compiler,
           element, treeElements,
           newTypedefElementCallback, newClassElementCallback).collect();
     }
 
     addTopLevel(element, treeElements) {
       if (topLevelElements.contains(element)) return;
       topLevelElements.add(element);
       processElement(element, treeElements);
@@ skipping 24 matching lines @@
         classMembers[enclosingClass].add(element);
         processElement(element, treeElements);
       } else {
         if (!element.isTopLevel()) {
           compiler.cancel(reason: 'Cannot process $element', element: element);
         }
         addTopLevel(element, treeElements);
       }
     });
 
+    // Create all necessary placeholders.
+    PlaceholderCollector collector = new PlaceholderCollector(compiler);
+    makePlaceholders(element) {
+      TreeElements treeElements = resolvedElements[element];
+      if (treeElements === null) treeElements = emptyTreeElements;
+      collector.collect(element, treeElements);
+      if (element is ClassElement) {
+        classMembers[element].forEach(makePlaceholders);
+      }
+    }
+    topLevelElements.forEach(makePlaceholders);
+
+    // Create renames.
     Map<Node, String> renames = new Map<Node, String>();
     Map<LibraryElement, String> imports = new Map<LibraryElement, String>();
     renamePlaceholders(compiler, collector, renames, imports);
 
     // Sort elements.
     compareElements(e0, e1) {
       compareBy(x, y, f) => f(x).compareTo(f(y));
       int result = compareBy(e0, e1, (e) => e.getLibrary().uri.toString());
       if (result != 0) return result;
       return compareBy(e0, e1, (e) => e.position().charOffset);
@@ skipping 72 matching lines @@
     if (typeElement.isClass()) newClassElementCallback(typeElement);
     typeAnnotation.visitChildren(this);
   }
 
   void collect() {
     compiler.withCurrentElement(rootElement, () {
       rootElement.parseNode(compiler).accept(this);
     });
   }
 }