Avoid creating invalid TypeMask.nonNullExact

pkg/compiler/lib/src/world.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.
 
 library dart2js.world;
 
 import 'closure.dart' show
     SynthesizedCallMethodElementX;
 import 'common.dart';
 import 'common/backend_api.dart' show
@@ skipping 111 matching lines @@
   bool hasAnySubclassThatMixes(ClassElement superclass, ClassElement mixin);
 
   /// Returns `true` if any subclass of [superclass] implements [type].
   bool hasAnySubclassThatImplements(ClassElement superclass, ClassElement type);
 
   /// Returns `true` if closed-world assumptions can be made, that is,
   /// incremental compilation isn't enabled.
   bool get hasClosedWorldAssumption;
 
   /// Returns a string representation of the closed world.
-  String dump();
+  ///
+  /// If [cls] is provided, the dump will contain only classes related to [cls].
+  String dump([ClassElement cls]);
 }
 
 class World implements ClassWorld {
   ClassElement get objectClass => compiler.objectClass;
   ClassElement get functionClass => compiler.functionClass;
   ClassElement get boolClass => compiler.boolClass;
   ClassElement get numClass => compiler.numClass;
   ClassElement get intClass => compiler.intClass;
   ClassElement get doubleClass => compiler.doubleClass;
   ClassElement get stringClass => compiler.stringClass;
@@ skipping 393 matching lines @@
     }
 
     // Use the [:seenClasses:] set to include non-instantiated
     // classes: if the superclass of these classes require RTI, then
     // they also need RTI, so that a constructor passes the type
     // variables to the super constructor.
     compiler.resolverWorld.directlyInstantiatedClasses.forEach(addSubtypes);
   }
 
   @override
-  String dump() {
+  String dump([ClassElement cls]) {
     StringBuffer sb = new StringBuffer();
-    sb.write("Instantiated classes in the closed world:\n");
+    if (cls != null) {
+      sb.write("Classes in the closed world related to $cls:\n");
+    } else {
+      sb.write("Instantiated classes in the closed world:\n");
+    }
     getClassHierarchyNode(compiler.objectClass)
-        .printOn(sb, ' ', instantiatedOnly: true);
+        .printOn(sb, ' ', instantiatedOnly: cls == null, withRespectTo: cls);
     return sb.toString();
   }
 
   void registerMixinUse(MixinApplicationElement mixinApplication,
                         ClassElement mixin) {
     // TODO(johnniwinther): Add map restricted to live classes.
     // We don't support patch classes as mixin.
     assert(mixin.isDeclaration);
     List<MixinApplicationElement> users =
         _mixinUses.putIfAbsent(mixin, () =>
@@ skipping 125 matching lines @@
     // function expressions's element.
     // TODO(herhut): Generate classes for function expressions earlier.
     if (element is SynthesizedCallMethodElementX) {
       return getMightBePassedToApply(element.expression);
     }
     return functionsThatMightBePassedToApply.contains(element);
   }
 
   bool get hasClosedWorldAssumption => !compiler.hasIncrementalSupport;
 }