lua: add a Core.require_api() utility function

This function loads and enables "api" plugins and makes them
available in the specified callback. This is intended to be used
by interactive scripts in order to get access to "api" plugins
such as the new "default-nodes-api" and "mixer-api"

modules/module-lua-scripting/api.c

@@ -19,17 +19,23 @@ void wp_lua_scripting_pod_init (lua_State *L);
 static WpCore *
 get_wp_core (lua_State *L)
 {
+  WpCore *core = NULL;
   lua_pushliteral (L, "wireplumber_core");
   lua_gettable (L, LUA_REGISTRYINDEX);
-  return lua_touserdata (L, -1);
+  core = lua_touserdata (L, -1);
+  lua_pop (L, 1);
+  return core;
 }
 
 static WpCore *
 get_wp_export_core (lua_State *L)
 {
+  WpCore *core = NULL;
   lua_pushliteral (L, "wireplumber_export_core");
   lua_gettable (L, LUA_REGISTRYINDEX);
-  return lua_touserdata (L, -1);
+  core = lua_touserdata (L, -1);
+  lua_pop (L, 1);
+  return core;
 }
 
 /* GSource */
@@ -148,12 +154,29 @@ core_quit (lua_State *L)
   return 0;
 }
 
+#include "require.c"
+
+static int
+core_require_api (lua_State *L)
+{
+  WpCore * core = get_wp_core (L);
+  g_autoptr (WpProperties) p = wp_core_get_properties (core);
+  const gchar *interactive = wp_properties_get (p, "wireplumber.interactive");
+  if (!interactive || g_strcmp0 (interactive, "true") != 0) {
+    wp_warning ("script attempted to load an API module, but wireplumber "
+        "is not running in script interactive mode; ignoring");
+    return 0;
+  }
+  return wp_require_api_transition_new_from_lua (L, core);
+}
+
 static const luaL_Reg core_funcs[] = {
   { "get_info", core_get_info },
   { "idle_add", core_idle_add },
   { "timeout_add", core_timeout_add },
   { "sync", core_sync },
   { "quit", core_quit },
+  { "require_api", core_require_api },
   { NULL, NULL }
 };