Fix static type analysis of closure calls (issue 3959).

runtime/vm/intermediate_language.cc

 // 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.
 
 #include "vm/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 564 matching lines @@
 }
 
 
 RawAbstractType* StoreContextComp::StaticType() const {
   UNREACHABLE();
   return AbstractType::null();
 }
 
 
 RawAbstractType* ClosureCallComp::StaticType() const {
-  // The closure is the first argument to the call.
-  const AbstractType& function_type =
-      AbstractType::Handle(ArgumentAt(0)->StaticType());
-  if (function_type.IsDynamicType() || function_type.IsFunctionInterface()) {
-    // The function type is not statically known or simply Function.
-    return Type::DynamicType();
-  }
-  const Class& signature_class = Class::Handle(function_type.type_class());
-  const Function& signature_function =
-      Function::Handle(signature_class.signature_function());
-  if (signature_function.IsNull()) {
-    // Attempting to invoke a non-closure object.
-    return Type::DynamicType();
-  }
-  // TODO(regis): The result type may be generic. Consider upper bounds.
-  return signature_function.result_type();
+  // Because of function subtyping rules, the static return type of a closure
+  // call cannot be relied upon for static type analysis. For example, a
+  // function returning Dynamic can be assigned to a closure variable declared
+  // to return int and may actually return a double at run-time.
+  return Type::DynamicType();
 }
 
 
 RawAbstractType* InstanceCallComp::StaticType() const {
   return Type::DynamicType();
 }
 
 
 RawAbstractType* PolymorphicInstanceCallComp::StaticType() const {
   return Type::DynamicType();
@@ skipping 682 matching lines @@
   const ExternalLabel label(closure_function.ToCString(), stub.EntryPoint());
   compiler->GenerateCall(token_pos(), try_index(), &label,
                          PcDescriptors::kOther);
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 
 #undef __
 
 }  // namespace dart