Make it possible for Lua to emulate arbitrary properties

This makes it possible to add something similar to a __index / __newindex
metamethod to all our C objects. Based on this, Lua can then easily implement
arbitrary properties on our capi objects.

common/luaclass.c

@@ -251,6 +251,8 @@ luaA_class_setup(lua_State *L, lua_class_t *class,
     class->parent = parent;
     class->tostring = NULL;
     class->instances = 0;
+    class->index_miss_handler = LUA_REFNIL;
+    class->newindex_miss_handler = LUA_REFNIL;
 
     signal_add(&class->signals, "new");
 
@@ -361,6 +363,40 @@ luaA_class_property_get(lua_State *L, lua_class_t *lua_class, int fieldidx)
     return NULL;
 }
 
+/** Call a registered function.
+ * \param L The Lua VM state.
+ * \param handler The function to call.
+ * \return The number of elements pushed on stack.
+ */
+static
+int luaA_class_call_handler(lua_State *L, int handler)
+{
+    /* This is based on luaA_dofunction, but allows multiple return values */
+    assert(handler != LUA_REFNIL);
+
+    int nargs = lua_gettop(L);
+
+    /* Push error handling function and move it before args */
+    lua_pushcfunction(L, luaA_dofunction_error);
+    lua_insert(L, - nargs - 1);
+    int error_func_pos = 1;
+
+    /* push function and move it before args */
+    lua_rawgeti(L, LUA_REGISTRYINDEX, handler);
+    lua_insert(L, - nargs - 1);
+
+    if(lua_pcall(L, nargs, LUA_MULTRET, error_func_pos))
+    {
+        warn("%s", lua_tostring(L, -1));
+        /* Remove error function and error string */
+        lua_pop(L, 2);
+        return 0;
+    }
+    /* Remove error function */
+    lua_remove(L, error_func_pos);
+    return lua_gettop(L);
+}
+
 /** Generic index meta function for objects.
  * \param L The Lua VM state.
  * \return The number of elements pushed on stack.
@@ -397,6 +433,8 @@ luaA_class_index(lua_State *L)
     }
     else
     {
+        if(class->index_miss_handler != LUA_REFNIL)
+            return luaA_class_call_handler(L, class->index_miss_handler);
         if(class->index_miss_property)
             return class->index_miss_property(L, luaA_checkudata(L, 1, class));
     }
@@ -427,6 +465,8 @@ luaA_class_newindex(lua_State *L)
     }
     else
     {
+        if(class->newindex_miss_handler != LUA_REFNIL)
+            return luaA_class_call_handler(L, class->newindex_miss_handler);
         if(class->newindex_miss_property)
             return class->newindex_miss_property(L, luaA_checkudata(L, 1, class));
     }

common/luaclass.h

@@ -74,6 +74,10 @@ struct lua_class_t
     unsigned int instances;
     /** Class tostring method */
     lua_class_propfunc_t tostring;
+    /** Function to call on index misses */
+    int index_miss_handler;
+    /** Function to call on newindex misses */
+    int newindex_miss_handler;
 };
 
 const char * luaA_typename(lua_State *, int);
@@ -152,6 +156,18 @@ luaA_checkudataornil(lua_State *L, int udx, lua_class_t *class)
     {                                                                          \
         lua_pushnumber(L, (lua_class).instances);                              \
         return 1;                                                              \
+    }                                                                          \
+                                                                               \
+    static inline int                                                          \
+    luaA_##prefix##_set_index_miss_handler(lua_State *L)                       \
+    {                                                                          \
+        return luaA_registerfct(L, 1, &(lua_class).index_miss_handler);        \
+    }                                                                          \
+                                                                               \
+    static inline int                                                          \
+    luaA_##prefix##_set_newindex_miss_handler(lua_State *L)                    \
+    {                                                                          \
+        return luaA_registerfct(L, 1, &(lua_class).newindex_miss_handler);     \
     }
 
 #define LUA_CLASS_METHODS(class) \
@@ -160,6 +176,8 @@ luaA_checkudataornil(lua_State *L, int udx, lua_class_t *class)
     { "disconnect_signal", luaA_##class##_class_disconnect_signal }, \
     { "emit_signal", luaA_##class##_class_emit_signal }, \
     { "instances", luaA_##class##_class_instances }, \
+    { "set_index_miss_handler", luaA_##class##_set_index_miss_handler }, \
+    { "set_newindex_miss_handler", luaA_##class##_set_newindex_miss_handler }, \
 
 #define LUA_CLASS_META \
     { "__index", luaA_class_index }, \

objects/button.c

@@ -49,6 +49,16 @@
  * @function instances
  */
 
+/** Set a __index metamethod for all button instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all button instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 /** Create a new mouse button bindings.
  * \param L The Lua VM state.
  * \return The number of elements pushed on stack.

objects/client.c

@@ -126,6 +126,16 @@
  * @function instances
  */
 
+/** Set a __index metamethod for all client instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all client instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 static area_t titlebar_get_area(client_t *c, client_titlebar_t bar);
 static drawable_t *titlebar_get_drawable(lua_State *L, client_t *c, int cl_idx, client_titlebar_t bar);
 

objects/drawable.c

@@ -49,6 +49,16 @@
  * @function instances
  */
 
+/** Set a __index metamethod for all drawable instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all drawable instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 static lua_class_t drawable_class;
 
 LUA_OBJECT_FUNCS(drawable_class, drawable_t, drawable)

objects/drawin.c

@@ -83,6 +83,16 @@
  * @function instances
  */
 
+/** Set a __index metamethod for all drawin instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all drawin instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 LUA_OBJECT_FUNCS(drawin_class, drawin_t, drawin)
 
 /** Kick out systray windows.

objects/key.c

@@ -61,6 +61,16 @@
  * @function instances
  */
 
+/** Set a __index metamethod for all key instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all key instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 static void
 luaA_keystore(lua_State *L, int ud, const char *str, ssize_t len)
 {

objects/screen.c

@@ -54,6 +54,22 @@
  * @table screen
  */
 
+/** Get the number of instances.
+ *
+ * @return The number of screen objects alive.
+ * @function instances
+ */
+
+/** Set a __index metamethod for all screen instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all screen instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 struct screen_output_t
 {
     /** The XRandR names of the output */

objects/tag.c

@@ -54,6 +54,16 @@
  * @function instances
  */
 
+/** Set a __index metamethod for all tag instances.
+ * @tparam function cb The meta-method
+ * @function set_index_miss_handler
+ */
+
+/** Set a __newindex metamethod for all tag instances.
+ * @tparam function cb The meta-method
+ * @function set_newindex_miss_handler
+ */
+
 /** Tag type */
 struct tag
 {

tests/test-miss-handlers.lua

@@ -0,0 +1,26 @@
+-- Test set_{,new}index_miss_handler
+
+local class = tag
+local obj = class({})
+
+awesome.connect_signal("debug::index::miss", error)
+awesome.connect_signal("debug::newindex::miss", error)
+
+class.set_index_miss_handler(function(o, k)
+    assert(o == obj)
+    assert(k == "key")
+    return 42
+end)
+assert(obj.key == 42)
+
+local called = false
+class.set_newindex_miss_handler(function(o, k, v)
+    assert(o == obj)
+    assert(k == "key")
+    assert(v == 42)
+    called = true
+end)
+obj.key = 42
+assert(called)
+
+require("_runner").run_steps({ function() return true end })