ES6: Make function name configurable

src/accessors.cc

Index: src/accessors.cc
diff --git a/src/accessors.cc b/src/accessors.cc
index 052108a9b065feba47aa9ae907d55a9f33d092ab..51fdee67f28e5b0cd0ca0070842e5124de7fb2a1 100644
--- a/src/accessors.cc
+++ b/src/accessors.cc
@@ -1131,12 +1131,44 @@ void Accessors::FunctionNameGetter(
 }
 
 
+MUST_USE_RESULT static MaybeHandle<Object> SetFunctionName(
+    Isolate* isolate, Handle<JSFunction> function, Handle<Object> value) {
+  Handle<Object> old_value;
+  bool is_observed = function->map()->is_observed();
+  if (is_observed) {
+    old_value = handle(function->shared()->name(), isolate);
+  }
+
+  Handle<Name> name = isolate->factory()->name_string();
+  LookupIterator it(function, name);
+  CHECK_EQ(LookupIterator::ACCESSOR, it.state());
+  DCHECK(it.HolderIsReceiverOrHiddenPrototype());
+  it.ReconfigureDataProperty(value, it.property_details().attributes());
+  value = it.WriteDataValue(value);
+
+  if (is_observed && !old_value->SameValue(*value)) {
+    return JSObject::EnqueueChangeRecord(function, "update", name, old_value);
+  }
+
+  return value;
+}
+
+
 void Accessors::FunctionNameSetter(
     v8::Local<v8::Name> name,
     v8::Local<v8::Value> val,
     const v8::PropertyCallbackInfo<void>& info) {
-  // Function name is non writable, non configurable.
-  UNREACHABLE();
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(info.GetIsolate());
+  HandleScope scope(isolate);
+  Handle<Object> value = Utils::OpenHandle(*val);
+
+  if (SetPropertyOnInstanceIfInherited(isolate, info, name, value)) return;
+
+  Handle<JSFunction> object =
+      Handle<JSFunction>::cast(Utils::OpenHandle(*info.Holder()));
+  if (SetFunctionName(isolate, object, value).is_null()) {
+    isolate->OptionalRescheduleException(false);
+  }
 }