lua: add mpv/lua directories to the lua path

Signed-off-by: wm4 <wm4@nowhere>

DOCS/man/lua.rst

@@ -2,9 +2,14 @@ LUA SCRIPTING
 =============
 
 mpv can load Lua scripts. Scripts in ``~/.mpv/lua/`` will be loaded on program
-start, or if passed to ``--lua``. mpv provides the built-in module ``mp``, which
-provides functions to send commands to the mpv core and to retrieve information
-about playback state, user settings, file information, and so on.
+start, or if passed to ``--lua``. mpv appends ``~/.mpv/lua`` to the end of
+lua's path so you can import them too. Since it's added to the end, don't name
+scripts you want to import the same as lua libraries because they will be
+overshadowed by them.
+
+mpv provides the built-in module ``mp``, which provides functions to send
+commands to the mpv core and to retrieve information about playback state, user
+settings, file information, and so on.
 
 These scripts can be used to control mpv in a similar way to slave mode.
 Technically, the Lua code uses the client API internally.

player/lua.c

@@ -215,6 +215,28 @@ static int load_scripts(lua_State *L)
     return 0;
 }
 
+static void set_path(lua_State *L)
+{
+    void *tmp = talloc_new(NULL);
+
+    lua_getglobal(L, "package"); // package
+    lua_getfield(L, -1, "path"); // package path
+    const char *path = lua_tostring(L, -1);
+
+    char *newpath = talloc_strdup(tmp, path ? path : "");
+    char **luadir = mp_find_all_config_files(tmp, get_mpctx(L)->global, "lua");
+    for (int i = 0; luadir && luadir[i]; i++) {
+        newpath = talloc_asprintf_append(newpath, ";%s",
+                mp_path_join(tmp, bstr0(luadir[i]), bstr0("?.lua")));
+    }
+
+    lua_pushstring(L, newpath);  // package path newpath
+    lua_setfield(L, -3, "path"); // package path
+    lua_pop(L, 2);  // -
+
+    talloc_free(tmp);
+}
+
 static int run_lua(lua_State *L)
 {
     struct script_ctx *ctx = lua_touserdata(L, -1);
@@ -268,6 +290,9 @@ static int run_lua(lua_State *L)
 
     assert(lua_gettop(L) == 0);
 
+    set_path(L);
+    assert(lua_gettop(L) == 0);
+
     // run this under an error handler that can do backtraces
     lua_pushcfunction(L, error_handler); // errf
     lua_pushcfunction(L, load_scripts); // errf fn