RFC: Resolution based tree-shaking.

dart/lib/compiler/implementation/enqueue.dart

Index: dart/lib/compiler/implementation/enqueue.dart
diff --git a/dart/lib/compiler/implementation/enqueue.dart b/dart/lib/compiler/implementation/enqueue.dart
index 855c539fa1d4a28b9b0a875062deca3965ceb5cf..e134016e95aea740b4fd788bd36e18564f0ba72a 100644
--- a/dart/lib/compiler/implementation/enqueue.dart
+++ b/dart/lib/compiler/implementation/enqueue.dart
@@ -22,7 +22,8 @@ class Enqueuer {
   final Map<String, Link<Element>> instanceMembersByName;
   final Set<ClassElement> seenClasses;
   final Universe universe;
-  final Queue<WorkItem> queue;
+  final Queue<WorkItem> _queue;
+  final Map<Element, TreeElements> resolvedElements;
   bool queueIsClosed = false;
   EnqueueTask task;
 
@@ -30,16 +31,39 @@ class Enqueuer {
     : instanceMembersByName = new Map<String, Link<Element>>(),
       seenClasses = new Set<ClassElement>(),
       universe = new Universe(),
-      queue = new Queue<WorkItem>();
+      _queue = new Queue<WorkItem>(),
+      resolvedElements = new Map<Element, TreeElements>();
+
+  bool get isFirstQueue() => compiler.enqueuer.resolution === this;
+
+  TreeElements getCachedElements(Element element) {
+    Element owner = element.getOutermostEnclosingMemberOrTopLevel();
+    return compiler.enqueuer.resolution.resolvedElements[owner];
+  }
 
   void addToWorkList(Element element, [TreeElements elements]) {
-    if (queueIsClosed) {
+    // int allowed = ElementCategory.VARIABLE | ElementCategory.FUNCTION
+    //   | ElementCategory.FACTORY;
+    // if (element is AbstractFieldElement) return;
+    // if (!element.isAccessor() && (element.kind.category & allowed) == 0) return;
+    // if (!element.isParameter() && !element.isTopLevel() && !element.enclosingElement.isClass()) return;
+    if (element.isForeign()) return;
+    if (queueIsClosed && !isFirstQueue) {
       compiler.internalErrorOnElement(element, "Work list is closed.");
     }
     if (element.kind === ElementKind.GENERATIVE_CONSTRUCTOR) {
       registerInstantiatedClass(element.enclosingElement);
     }
-    queue.add(new WorkItem(element, elements));
+    if (elements === null) {
+      elements = getCachedElements(element);
+      if (!isFirstQueue && elements === null) {
+        if (element.getLibrary() !== compiler.interceptorsLibrary &&
+            element.getLibrary() !== compiler.jsHelperLibrary) {
+          // compiler.internalErrorOnElement(element, 'Unresolved element');
+        }
+      }
+    }
+    _queue.add(new WorkItem(element, elements));
   }
 
   void registerInstantiatedClass(ClassElement cls) {
@@ -86,6 +110,7 @@ class Enqueuer {
 
   void processInstantiatedClassMember(Element member) {
     if (universe.generatedCode.containsKey(member)) return;
+    if (resolvedElements[member] !== null) return;
 
     if (!member.isInstanceMember()) return;
     if (member.isField()) return;
@@ -227,4 +252,10 @@ class Enqueuer {
   void registerIsCheck(Element element) {
     universe.isChecks.add(element);
   }
+
+  void forEach(f(WorkItem work)) {
+    while (!_queue.isEmpty()) {
+      f(_queue.removeLast());
+    }
+  }
 }