1 files changed, 68 insertions, 0 deletions
diff --git a/js/xpconnect/src/xpcObjectHelper.h b/js/xpconnect/src/xpcObjectHelper.h
new file mode 100644
index 0000000000..1d83fdde15
--- /dev/null
+++ b/js/xpconnect/src/xpcObjectHelper.h
@@ -0,0 +1,68 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef xpcObjectHelper_h
+#define xpcObjectHelper_h
+
+// Including 'windows.h' will #define GetClassInfo to something else.
+#ifdef XP_WIN
+#  ifdef GetClassInfo
+#    undef GetClassInfo
+#  endif
+#endif
+
+#include "mozilla/Attributes.h"
+#include <stdint.h>
+#include "nsCOMPtr.h"
+#include "nsIClassInfo.h"
+#include "nsISupports.h"
+#include "nsIXPCScriptable.h"
+#include "nsWrapperCache.h"
+
+class xpcObjectHelper {
+ public:
+  explicit xpcObjectHelper(nsISupports* aObject,
+                           nsWrapperCache* aCache = nullptr)
+      : mObject(aObject), mCache(aCache) {
+    if (!mCache && aObject) {
+      CallQueryInterface(aObject, &mCache);
+    }
+  }
+
+  nsISupports* Object() { return mObject; }
+
+  nsIClassInfo* GetClassInfo() {
+    if (!mClassInfo) {
+      mClassInfo = do_QueryInterface(mObject);
+    }
+    return mClassInfo;
+  }
+
+  // We assert that we can reach an nsIXPCScriptable somehow.
+  uint32_t GetScriptableFlags() {
+    nsCOMPtr<nsIXPCScriptable> sinfo = do_QueryInterface(mObject);
+
+    // We should have something by now.
+    MOZ_ASSERT(sinfo);
+
+    // Grab the flags.
+    return sinfo->GetScriptableFlags();
+  }
+
+  nsWrapperCache* GetWrapperCache() { return mCache; }
+
+ private:
+  xpcObjectHelper(xpcObjectHelper& aOther) = delete;
+
+  nsISupports* MOZ_UNSAFE_REF(
+      "xpcObjectHelper has been specifically optimized "
+      "to avoid unnecessary AddRefs and Releases. "
+      "(see bug 565742)") mObject;
+  nsWrapperCache* mCache;
+  nsCOMPtr<nsIClassInfo> mClassInfo;
+};
+
+#endif