Skip spurious constants in deferred computation.

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index 6141447892f5802c8efe4f4af2bbd0affa5ab5a7..695f33e6b022e8f58baf91fe4689c1a7e00f7540 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -336,16 +336,25 @@ class DeferredLoadTask extends CompilerTask {
         TreeElements treeElements = analyzableElement.resolvedAst.elements;
         assert(treeElements != null);
 
+        // TODO(johnniwinther): Add only expressions that are actually needed.
+        // Currently some potential expressions are visited that should never
+        // be added, and some implicit constant expression that should be

[Siggi Cherem (dart-lang), 2016/05/09 20:03:04]

rephrase? (I'm not sure I understood the last phrase)

[Johnni Winther, 2016/05/10 09:26:16]

Done.

+        // allowed. See dartbug.com/26406 for context.
         treeElements
             .forEachConstantNode((Node node, ConstantExpression expression) {
           // Explicitly depend on the backend constants.
-          ConstantValue value;
-          value = backend.constants.getConstantValue(expression);
-          // TODO(johnniwinther): ensure `value` is not null or use directly the
-          // expression to calculate dependencies. See dartbug.com/26406 for
-          // context.
-          if (value != null) {
+          if (backend.constants.hasConstantValue(expression)) {
+            ConstantValue value =
+                backend.constants.getConstantValue(expression);
+            assert(invariant(node, value != null,
+                message: "Constant expression without value: "
+                         "${expression.toStructuredText()}."));
             constants.add(value);
+          } else {
+            assert(invariant(node,
+                expression.isImplicit || expression.isPotential,
+                message: "Unexpected unevaluated constant expression: "
+                    "${expression.toStructuredText()}."));
           }
         });
       }