Refactor resolution code in the vm to properly handle ambiguity errors.

runtime/vm/resolver.cc

 // Copyright (c) 2011, 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/resolver.h"
 
 #include "vm/dart_entry.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 132 matching lines @@
   }
   return function.raw();
 }
 
 
 RawFunction* Resolver::ResolveStatic(const Library& library,
                                      const String& class_name,
                                      const String& function_name,
                                      intptr_t num_arguments,
                                      const Array& argument_names,
-                                     StaticResolveType resolve_type) {
+                                     StaticResolveType resolve_type,
+                                     String* ambiguity_error_msg) {
   ASSERT(!library.IsNull());
   Function& function = Function::Handle();
   if (class_name.IsNull() || (class_name.Length() == 0)) {
     // Check if we are referring to a top level function.
-    const Object& object = Object::Handle(library.LookupObject(function_name));
+    const Object& object = Object::Handle(
+        library.LookupObject(function_name, ambiguity_error_msg));
     if (!object.IsNull() && object.IsFunction()) {
       function ^= object.raw();
       if (!function.AreValidArguments(num_arguments, argument_names, NULL)) {
         if (FLAG_trace_resolving) {
           String& error_message = String::Handle();
           // Obtain more detailed error message.
           function.AreValidArguments(num_arguments,
                                      argument_names,
                                      &error_message);
           OS::Print("ResolveStatic error '%s': %s.\n",
                     function_name.ToCString(),
                     error_message.ToCString());
         }
         function = Function::null();
       }
     } else {
       if (FLAG_trace_resolving) {
         OS::Print("ResolveStatic error '%s': %s.\n",
-                  function_name.ToCString(), "top level function not found");
+                  function_name.ToCString(),
+                  ambiguity_error_msg->IsNull() ? "top level function not found"
+                      : ambiguity_error_msg->ToCString());
       }
     }
   } else {
     // Lookup class_name in the library's class dictionary to get at
     // the dart class object. If class_name is not found in the dictionary
     // ResolveStatic will return a NULL function object.
-    const Class& cls = Class::Handle(library.LookupClass(class_name));
-    function = ResolveStatic(cls,
-                             function_name,
-                             num_arguments,
-                             argument_names,
-                             resolve_type);
+    const Class& cls = Class::Handle(
+        library.LookupClass(class_name, ambiguity_error_msg));
+    if (!cls.IsNull()) {
+      function = ResolveStatic(cls,
+                               function_name,
+                               num_arguments,
+                               argument_names,
+                               resolve_type);
+    }
+    if (FLAG_trace_resolving && function.IsNull()) {
+      OS::Print("ResolveStatic error '%s.%s': %s.\n",
+                class_name.ToCString(),
+                function_name.ToCString(),
+                ambiguity_error_msg->IsNull() ? "static function not found"
+                    : ambiguity_error_msg->ToCString());
+    }
   }
   return function.raw();
 }
 
 
 RawFunction* Resolver::ResolveStaticByName(const Class&  cls,
                                            const String& function_name,
                                            StaticResolveType resolve_type) {
-  if (cls.IsNull()) {
-    // Can't resolve function if cls is null.
-    return Function::null();
-  }
+  ASSERT(!cls.IsNull());
 
   if (FLAG_trace_resolving) {
     OS::Print("ResolveStatic '%s'\n", function_name.ToCString());
   }
 
   // Now look for a static function whose name matches function_name
   // in the class.
   Function& function =
       Function::Handle(cls.LookupStaticFunction(function_name));
   if (resolve_type == kNotQualified) {
     // Walk the hierarchy.
     Class& super_class = Class::Handle(cls.SuperClass());
     while (function.IsNull()) {
       function = super_class.LookupStaticFunction(function_name);
       super_class = super_class.SuperClass();
       if (super_class.IsNull()) break;
     }
   }
   return function.raw();
 }
 
 
 
 RawFunction* Resolver::ResolveStatic(const Class&  cls,
                                      const String& function_name,
                                      intptr_t num_arguments,
                                      const Array& argument_names,
                                      StaticResolveType resolve_type) {
+  ASSERT(!cls.IsNull());
   const Function& function = Function::Handle(
       ResolveStaticByName(cls, function_name, resolve_type));
   if (function.IsNull() ||
       !function.AreValidArguments(num_arguments, argument_names, NULL)) {
     // Return a null function to signal to the upper levels to throw a
     // resolution error or maybe throw the error right here.
     if (FLAG_trace_resolving) {
       String& error_message = String::Handle(String::New("function not found"));
       if (!function.IsNull()) {
         // Obtain more detailed error message.
         function.AreValidArguments(num_arguments,
                                    argument_names,
                                    &error_message);
       }
       OS::Print("ResolveStatic error '%s': %s.\n",
                 function_name.ToCString(),
                 error_message.ToCString());
     }
     return Function::null();
   }
   return function.raw();
 }
 
 }  // namespace dart