Ambiguous type references require a compile time error in some special cases

runtime/vm/class_finalizer.h

 // 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.
 
 #ifndef VM_CLASS_FINALIZER_H_
 #define VM_CLASS_FINALIZER_H_
 
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
 
@@ skipping 15 matching lines @@
 // Traverses all pending, unfinalized classes, validates and marks them as
 // finalized.
 class ClassFinalizer : public AllStatic {
  public:
   // Modes for type resolution and finalization. The ordering is relevant.
   enum FinalizationKind {
     kIgnore,                   // Type is ignored and replaced by dynamic.
     kDoNotResolve,             // Type resolution is postponed.
     kTryResolve,               // Type resolution is attempted.
     kFinalize,                 // Type resolution and type finalization are
-                               // required; a malformed type is tolerated.
+                               // required; a malformed type is tolerated, since
+                               // the type may be used as a type annotation.
     kCanonicalize,             // Same as kFinalize, but with canonicalization.
-    kCanonicalizeForCreation,  // Same as kCanonicalize, but do not tolerate
-                               // wrong number of type arguments.
+    kCanonicalizeExpression,   // Same as kCanonicalize, but do not tolerate
+                               // wrong number of type arguments or ambiguous
+                               // type reference, since the type is not used as
+                               // a type annotation, but as a type expression.
     kCanonicalizeWellFormed    // Error-free resolution, finalization, and
                                // canonicalization are required; a malformed
                                // type is not tolerated.
   };
 
   // Finalize given type while parsing class cls.
   // Also canonicalize type if applicable.
   static RawAbstractType* FinalizeType(const Class& cls,
                                        const AbstractType& type,
                                        FinalizationKind finalization);
@@ skipping 73 matching lines @@
   static void ReportError(const Error& error);
   static void ReportError(const Script& script,
                           intptr_t token_index,
                           const char* format, ...) PRINTF_ATTRIBUTE(3, 4);
   static void ReportError(const char* format, ...) PRINTF_ATTRIBUTE(1, 2);
 };
 
 }  // namespace dart
 
 #endif  // VM_CLASS_FINALIZER_H_