Handle fields with initializers in constant constructors.

pkg/compiler/lib/src/js_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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 1509 matching lines @@
     if (element.isConstructor &&
         element.enclosingClass == helpers.jsNullClass) {
       // Work around a problem compiling JSNull's constructor.
       return const CodegenImpact();
     }
     if (kind.category == ElementCategory.VARIABLE) {
       VariableElement variableElement = element;
       ConstantExpression constant = variableElement.constant;
       if (constant != null) {
         ConstantValue initialValue = constants.getConstantValue(constant);
-        assert(invariant(variableElement, initialValue != null,
-            message: "Constant expression without value: "
-                "${constant.toStructuredText()}."));
-        registerCompileTimeConstant(initialValue, work.registry);
-        addCompileTimeConstantForEmission(initialValue);
-        // We don't need to generate code for static or top-level
-        // variables. For instance variables, we may need to generate
-        // the checked setter.
-        if (Elements.isStaticOrTopLevel(element)) {
-          return impactTransformer
-              .transformCodegenImpact(work.registry.worldImpact);
+        if (initialValue != null) {
+          registerCompileTimeConstant(initialValue, work.registry);
+          addCompileTimeConstantForEmission(initialValue);
+          // We don't need to generate code for static or top-level
+          // variables. For instance variables, we may need to generate
+          // the checked setter.
+          if (Elements.isStaticOrTopLevel(element)) {
+            return impactTransformer
+                .transformCodegenImpact(work.registry.worldImpact);
+          }
+        } else {
+          assert(invariant(
+              variableElement,
+              variableElement.isInstanceMember ||
+                  constant.isImplicit ||
+                  constant.isPotential,
+              message: "Constant expression without value: "
+                  "${constant.toStructuredText()}."));
         }
       } else {
         // If the constant-handler was not able to produce a result we have to
         // go through the builder (below) to generate the lazy initializer for
         // the static variable.
         // We also need to register the use of the cyclic-error helper.
         compiler.enqueuer.codegen.registerStaticUse(new StaticUse.staticInvoke(
             helpers.cyclicThrowHelper, CallStructure.ONE_ARG));
       }
     }
@@ skipping 1576 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }