Add some missing class type checks

Some functions didn't check the class of objects they were passed but just
casted them to the type they expected. This lead to code like e.g. the following
to crash awesome:

  c.titlebar = c

This adds a new function luaA_object_ref_class() which works like
luaA_object_ref(), but which also checks the class of the object.

Additionally, this function is now used in all necessary places.

Signed-off-by: Uli Schlachter <psychon@znc.in>
Signed-off-by: Julien Danjou <julien@danjou.info>

common/luaobject.h

@@ -106,6 +106,20 @@ luaA_object_ref(lua_State *L, int oud)
     return p;
 }
 
+/** Reference an object and return a pointer to it checking its type.
+ * That only works with userdata.
+ * \param L The Lua VM state.
+ * \param oud The object index on the stack.
+ * \param class The class of object expected
+ * \return The object reference, or NULL if not referenceable.
+ */
+static inline void *
+luaA_object_ref_class(lua_State *L, int oud, lua_class_t *class)
+{
+    luaA_checkudata(L, oud, class);
+    return luaA_object_ref(L, oud);
+}
+
 /** Unreference an object and return a pointer to it.
  * That only works with userdata, table, thread or function.
  * \param L The Lua VM state.

root.c

@@ -126,7 +126,7 @@ luaA_root_keys(lua_State *L)
 
         lua_pushnil(L);
         while(lua_next(L, 1))
-            key_array_append(&globalconf.keys, luaA_object_ref(L, -1));
+            key_array_append(&globalconf.keys, luaA_object_ref_class(L, -1, &key_class));
 
         int nscreen = xcb_setup_roots_length(xcb_get_setup(globalconf.connection));
 

tag.c

@@ -127,7 +127,7 @@ tag_append_to_screen(lua_State *L, int udx, screen_t *s)
     int phys_screen = screen_virttophys(screen_index);
 
     tag->screen = s;
-    tag_array_append(&s->tags, luaA_object_ref(globalconf.L, udx));
+    tag_array_append(&s->tags, luaA_object_ref_class(globalconf.L, udx, &tag_class));
     ewmh_update_net_numbers_of_desktop(phys_screen);
     ewmh_update_net_desktop_names(phys_screen);
     ewmh_update_workarea(phys_screen);
@@ -210,7 +210,7 @@ tag_client_emit_signal(lua_State *L, tag_t *t, client_t *c, const char *signame)
 void
 tag_client(client_t *c)
 {
-    tag_t *t = luaA_object_ref(globalconf.L, -1);
+    tag_t *t = luaA_object_ref_class(globalconf.L, -1, &tag_class);
 
     /* don't tag twice */
     if(is_client_tagged(c, t))

titlebar.c

@@ -224,7 +224,7 @@ void
 titlebar_client_attach(client_t *c)
 {
     /* check if we can register the object */
-    wibox_t *t = luaA_object_ref(globalconf.L, -1);
+    wibox_t *t = luaA_object_ref_class(globalconf.L, -1, &wibox_class);
 
     titlebar_client_detach(c);
 

wibox.c

@@ -738,7 +738,7 @@ wibox_attach(lua_State *L, int udx, screen_t *s)
     /* duplicate wibox */
     lua_pushvalue(L, udx);
     /* ref it */
-    wibox_t *wibox = luaA_object_ref(globalconf.L, -1);
+    wibox_t *wibox = luaA_object_ref_class(globalconf.L, -1, &wibox_class);
 
     wibox_detach(L, udx);