screen: Add a `name` property to the C API.

This will be useful to address the screens by roles/names in the client
and tag rules. Since the sceen rules will make setups where sceens are
attached and removed much easier to work with, using indexes or output
names in the rules becomes a limitation.

objects/screen.c

@@ -594,6 +594,15 @@ screen_add(lua_State *L, screen_array_t *screens)
     return new_screen;
 }
 
+static void
+screen_wipe(screen_t *c)
+{
+    if (c->name) {
+        free(c->name);
+        c->name = NULL;
+    }
+}
+
 /* Monitors were introduced in RandR 1.5 */
 #ifdef XCB_RANDR_GET_MONITORS
 
@@ -1516,7 +1525,9 @@ luaA_screen_module_index(lua_State *L)
         }
 
         foreach(screen, globalconf.screens)
-            if ((*screen)->viewport)
+            if ((*screen)->name && A_STREQ(name, (*screen)->name))
+                return luaA_object_push(L, *screen);
+            else if ((*screen)->viewport)
                 foreach(output, (*screen)->viewport->outputs)
                     if(A_STREQ(output->name, name))
                         return luaA_object_push(L, *screen);
@@ -1613,6 +1624,33 @@ luaA_screen_get_workarea(lua_State *L, screen_t *s)
     return 1;
 }
 
+static int
+luaA_screen_set_name(lua_State *L, screen_t *s)
+{
+    const char *buf = luaL_checkstring(L, -1);
+
+    if (s->name)
+        free(s->name);
+
+    s->name = a_strdup(buf);
+
+    return 0;
+}
+
+static int
+luaA_screen_get_name(lua_State *L, screen_t *s)
+{
+    lua_pushstring(L, s->name ? s->name : "screen");
+
+    /* Fallback to "screen1", "screen2", etc if no name is set */
+    if (!s->name) {
+        lua_pushinteger(L, screen_get_index(s));
+        lua_concat(L, 2);
+    }
+
+    return 1;
+}
+
 /** Get the number of screens.
  *
  * @return The screen count, at least 1.
@@ -1820,7 +1858,7 @@ screen_class_setup(lua_State *L)
 
     luaA_class_setup(L, &screen_class, "screen", NULL,
                      (lua_class_allocator_t) screen_new,
-                     (lua_class_collector_t) NULL,
+                     (lua_class_collector_t) screen_wipe,
                      (lua_class_checker_t) screen_checker,
                      luaA_class_index_miss_property, luaA_class_newindex_miss_property,
                      screen_methods, screen_meta);
@@ -1844,6 +1882,10 @@ screen_class_setup(lua_State *L)
                             NULL,
                             (lua_class_propfunc_t) luaA_screen_get_workarea,
                             NULL);
+    luaA_class_add_property(&screen_class, "name",
+                            (lua_class_propfunc_t) luaA_screen_set_name,
+                            (lua_class_propfunc_t) luaA_screen_get_name,
+                            (lua_class_propfunc_t) luaA_screen_set_name);
 }
 
 /* @DOC_cobject_COMMON@ */

objects/screen.h

@@ -47,6 +47,8 @@ struct a_screen
     area_t geometry;
     /** Screen workarea */
     area_t workarea;
+    /** The name of the screen */
+    char *name;
     /** Opaque pointer to the viewport */
     struct viewport_t *viewport;
     /** Some XID identifying this screen */