Delay 'supertype' for ClassElementImpl and EnumElementImpl.

pkg/analyzer/lib/src/context/context.dart

Index: pkg/analyzer/lib/src/context/context.dart
diff --git a/pkg/analyzer/lib/src/context/context.dart b/pkg/analyzer/lib/src/context/context.dart
index 23cae4a19f758d42274dfcd27ce07939dd07b9c8..97f5f2dfbf2033006c7f3baaac7a211694dff7c8 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -466,10 +466,6 @@ class AnalysisContextImpl implements InternalAnalysisContext {
 
   @override
   TypeProvider get typeProvider {
-    // Make sure a task didn't accidentally try to call back into the context
-    // to retrieve the type provider.
-    assert(!driver.isTaskRunning);

[Brian Wilkerson, 2016/06/01 22:23:28]

Instead of removing this completely, would it work to move it after the null
check on line 472, and then ensure that any tasks that might be asking for the
supertype require the type provider?

[Paul Berry, 2016/06/01 22:25:55]

+1 to this.  The reason we added this check in the first place was to avoid
reentrancy into the task manager, and I would like to make sure we are still
successfully avoiding that :)

[scheglov, 2016/06/02 00:20:40]

That's a great idea.
Thank you!
Done.

-
     if (_typeProvider != null) {
       return _typeProvider;
     }