lua: add new Log.open_topic() API

This allows lua scripts to work with log topics. A topic must be
opened at the top of the file, in global scope, and subsequently
all log commands should be executed on the returned object instead
of the Log global table

modules/module-lua-scripting/api/api.c

@@ -283,6 +283,27 @@ static const luaL_Reg core_funcs[] = {
 
 /* WpLog */
 
+typedef struct _WpLogTopic WpLuaLogTopic;
+
+static WpLuaLogTopic *
+wp_lua_log_topic_copy (WpLuaLogTopic *topic)
+{
+  WpLuaLogTopic *copy = g_new0 (WpLuaLogTopic, 1);
+  *copy = *topic;
+  g_ref_string_acquire ((char *) copy->topic_name);
+  return copy;
+}
+
+static void
+wp_lua_log_topic_free (WpLuaLogTopic *topic)
+{
+  g_ref_string_release ((char *) topic->topic_name);
+  g_free (topic);
+}
+
+G_DEFINE_BOXED_TYPE (WpLuaLogTopic, wp_lua_log_topic, wp_lua_log_topic_copy,
+    wp_lua_log_topic_free)
+
 static int
 log_log (lua_State *L, GLogLevelFlags lvl)
 {
@@ -292,21 +313,34 @@ log_log (lua_State *L, GLogLevelFlags lvl)
   gconstpointer instance = NULL;
   GType type = G_TYPE_INVALID;
   int index = 1;
+  WpLogTopic *topic = log_topic_lua_scripting;
 
-  if (!wp_log_topic_is_enabled (log_topic_lua_scripting, lvl))
+  /* if called with log topic object */
+  if (lua_istable (L, index)) {
+    if (lua_getmetatable (L, index)) {
+      lua_getfield (L, -1, "__topic");
+      if (wplua_isboxed (L, -1, wp_lua_log_topic_get_type ())) {
+        topic = wplua_toboxed (L, -1);
+      }
+      lua_pop (L, 2);
+    }
+    index++;
+  }
+
+  if (!wp_log_topic_is_enabled (topic, lvl))
     return 0;
 
   g_warn_if_fail (lua_getstack (L, 1, &ar) == 1);
   g_warn_if_fail (lua_getinfo (L, "nSl", &ar) == 1);
 
-  if (wplua_isobject (L, 1, G_TYPE_OBJECT)) {
+  if (wplua_isobject (L, index, G_TYPE_OBJECT)) {
-    instance = wplua_toobject (L, 1);
+    instance = wplua_toobject (L, index);
     type = G_TYPE_FROM_INSTANCE (instance);
     index++;
   }
-  else if (wplua_isboxed (L, 1, G_TYPE_BOXED)) {
+  else if (wplua_isboxed (L, index, G_TYPE_BOXED)) {
-    instance = wplua_toboxed (L, 1);
+    instance = wplua_toboxed (L, index);
-    type = wplua_gvalue_userdata_type (L, 1);
+    type = wplua_gvalue_userdata_type (L, index);
     index++;
   }
 
@@ -314,7 +348,7 @@ log_log (lua_State *L, GLogLevelFlags lvl)
   snprintf (line_str, 11, "%d", ar.currentline);
   ar.name = ar.name ? ar.name : "chunk";
 
-  wp_log_checked (log_topic_lua_scripting->topic_name, lvl,
+  wp_log_checked (topic->topic_name, lvl,
       ar.source, line_str, ar.name, type, instance, "%s", message);
   return 0;
 }
@@ -334,7 +368,36 @@ log_debug (lua_State *L) { return log_log (L, G_LOG_LEVEL_DEBUG); }
 static int
 log_trace (lua_State *L) { return log_log (L, WP_LOG_LEVEL_TRACE); }
 
+static const luaL_Reg log_obj_funcs[] = {
+  { "warning", log_warning },
+  { "message", log_message },
+  { "info", log_info },
+  { "debug", log_debug },
+  { "trace", log_trace },
+  { NULL, NULL }
+};
+
+static int
+log_open_topic (lua_State *L)
+{
+  const char *name = luaL_checkstring (L, 1);
+
+  WpLuaLogTopic *topic = g_new0 (WpLuaLogTopic, 1);
+  topic->topic_name = g_ref_string_new (name);
+  wp_log_topic_init (topic);
+
+  lua_newtable (L); // empty table
+  lua_newtable (L); // metatable
+  luaL_newlib (L, log_obj_funcs);
+  lua_setfield (L, -2, "__index");
+  wplua_pushboxed (L, wp_lua_log_topic_get_type (), topic);
+  lua_setfield (L, -2, "__topic");
+  lua_setmetatable (L, -2);
+  return 1;
+}
+
 static const luaL_Reg log_funcs[] = {
+  { "open_topic", log_open_topic },
   { "warning", log_warning },
   { "message", log_message },
   { "info", log_info },