Improve resolution/codegen separation invariant.

BUG=
R=asgerf@google.com

Review URL: https://codereview.chromium.org//1126163002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@45593 260f80e4-7a28-3924-810f-c04153c831b5

pkg/compiler/lib/src/compiler.dart

@@ -25,6 +25,7 @@ abstract class WorkItem {
    * Invariant: [element] must be a declaration element.
    */
   final AstElement element;
+
   TreeElements get resolutionTree;
 
   WorkItem(this.element, this.compilationContext) {
@@ -186,16 +187,30 @@ class CodegenRegistry extends Registry {
 /// [WorkItem] used exclusively by the [CodegenEnqueuer].
 class CodegenWorkItem extends WorkItem {
   Registry registry;
-  final TreeElements resolutionTree;
 
-  CodegenWorkItem(AstElement element,
-                  ItemCompilationContext compilationContext)
-      : this.resolutionTree = element.resolvedAst.elements,
-        super(element, compilationContext) {
-    assert(invariant(element, resolutionTree != null,
+  factory CodegenWorkItem(
+      Compiler compiler,
+      AstElement element,
+      ItemCompilationContext compilationContext) {
+    // If this assertion fails, the resolution callbacks of the backend may be
+    // missing call of form registry.registerXXX. Alternatively, the code
+    // generation could spuriously be adding dependencies on things we know we
+    // don't need.
+    assert(invariant(element,
+        compiler.enqueuer.resolution.hasBeenResolved(element),
+        message: "$element has not been resolved."));
+    assert(invariant(element, element.resolvedAst.elements != null,
         message: 'Resolution tree is null for $element in codegen work item'));
+    return new CodegenWorkItem.internal(element, compilationContext);
   }
 
+  CodegenWorkItem.internal(
+      AstElement element,
+      ItemCompilationContext compilationContext)
+      : super(element, compilationContext);
+
+  TreeElements get resolutionTree => element.resolvedAst.elements;
+
   void run(Compiler compiler, CodegenEnqueuer world) {
     if (world.isProcessed(element)) return;
 

pkg/compiler/lib/src/enqueue.dart

@@ -853,7 +853,7 @@ class CodegenEnqueuer extends Enqueuer {
           "Codegen work list is closed. Trying to add $element");
     }
     CodegenWorkItem workItem = new CodegenWorkItem(
-        element, itemCompilationContextCreator());
+        compiler, element, itemCompilationContextCreator());
     queue.add(workItem);
     return true;
   }

tests/compiler/dart2js/compiler_helper.dart

@@ -75,7 +75,7 @@ Future<String> compile(String code,
         new leg.ResolutionWorkItem(element, context);
     resolutionWork.run(compiler, compiler.enqueuer.resolution);
     leg.CodegenWorkItem work =
-        new leg.CodegenWorkItem(element, context);
+        new leg.CodegenWorkItem(compiler, element, context);
     compiler.phase = Compiler.PHASE_COMPILING;
     work.run(compiler, compiler.enqueuer.codegen);
     js.JavaScriptBackend backend = compiler.backend;