RFC: Resolution based tree-shaking.

dart/lib/compiler/implementation/enqueue.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 EnqueueTask extends CompilerTask {
   final Enqueuer codegen;
   final Enqueuer resolution;
 
   String get name() => 'Enqueue';
 
   EnqueueTask(Compiler compiler)
     : codegen = new Enqueuer(compiler),
       resolution = new Enqueuer(compiler),
       super(compiler) {
     codegen.task = this;
     resolution.task = this;
   }
 }
 
 class Enqueuer {
   final Compiler compiler; // TODO(ahe): Remove this dependency.
   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;
 
   Enqueuer(this.compiler)
     : 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) {
     universe.instantiatedClasses.add(cls);
     onRegisterInstantiatedClass(cls);
   }
 
   bool checkNoEnqueuedInvokedInstanceMethods() {
     task.measure(() {
       // Run through the classes and see if we need to compile methods.
@@ skipping 26 matching lines @@
           for (Selector selector in invokedSelectors) {
             registerDynamicInvocation(Namer.CLOSURE_INVOCATION_NAME, selector);
           }
         }
       }
     });
   }
 
   void processInstantiatedClassMember(Element member) {
     if (universe.generatedCode.containsKey(member)) return;
+    if (resolvedElements[member] !== null) return;
 
     if (!member.isInstanceMember()) return;
     if (member.isField()) return;
 
     String memberName = member.name.slowToString();
     Link<Element> members = instanceMembersByName.putIfAbsent(
         memberName, () => const EmptyLink<Element>());
     instanceMembersByName[memberName] = members.prepend(member);
 
     if (member.kind === ElementKind.GETTER ||
@@ skipping 121 matching lines @@
   }
 
   void registerDynamicSetter(SourceString methodName, Selector selector) {
     registerSetter(methodName, selector);
   }
 
   // TODO(ngeoffray): This should get a type.
   void registerIsCheck(Element element) {
     universe.isChecks.add(element);
   }
+
+  void forEach(f(WorkItem work)) {
+    while (!_queue.isEmpty()) {
+      f(_queue.removeLast());
+    }
+  }
 }