1 files changed, 59 insertions, 0 deletions
diff --git a/widget/gtk/nsGtkUtils.h b/widget/gtk/nsGtkUtils.h
new file mode 100644
index 0000000000..ae26049e7f
--- /dev/null
+++ b/widget/gtk/nsGtkUtils.h
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:expandtab:shiftwidth=4:tabstop=4:
+ */
+/* 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 nsGtkUtils_h__
+#define nsGtkUtils_h__
+
+#include <glib.h>
+
+// Some gobject functions expect functions for gpointer arguments.
+// gpointer is void* but C++ doesn't like casting functions to void*.
+template <class T>
+static inline gpointer FuncToGpointer(T aFunction) {
+  return reinterpret_cast<gpointer>(
+      reinterpret_cast<uintptr_t>
+      // This cast just provides a warning if T is not a function.
+      (reinterpret_cast<void (*)()>(aFunction)));
+}
+
+// Type-safe alternative to glib's g_clear_pointer.
+//
+// Using `g_clear_pointer` itself causes UBSan to report undefined
+// behavior. The function-based definition of `g_clear_pointer` (as
+// opposed to the older preprocessor macro) treats the `destroy`
+// function as a `void (*)(void *)`, but the actual destroy functions
+// that are used (say `wl_buffer_destroy`) usually have more specific
+// pointer types.
+//
+// C++ draft n4901 [expr.call] para 6:
+//
+//     Calling a function through an expression whose function type E
+//     is different from the function type F of the called function’s
+//     definition results in undefined behavior unless the type
+//     “pointer to F” can be converted to the type “pointer to E” via
+//     a function pointer conversion (7.3.14).
+//
+// §7.3.14 only talks about converting between noexcept and ordinary
+// function pointers.
+template <class T>
+static inline void MozClearPointer(T*& pointer, void (*destroy)(T*)) {
+  T* hold = pointer;
+  pointer = nullptr;
+  if (hold) {
+    destroy(hold);
+  }
+}
+
+template <class T>
+static inline void MozClearHandleID(T& handle, gboolean (*destroy)(T)) {
+  if (handle) {
+    destroy(handle);
+    handle = 0;
+  }
+}
+
+#endif  // nsGtkUtils_h__