config: add a --config-dir option to force config directory

Useful for slave-mode like uses, and not as radical as --no-config.

DOCS/man/en/options.rst

@@ -557,6 +557,15 @@ OPTIONS
         It is advisable to use your graphics driver's color range option
         instead, if available.
 
+``--config-dir=<path>``
+    Force a different configuration directory. If this is set, the given
+    directory is used to load configuration files, and all other configuration
+    directories are ignored. This means the global mpv configuration directory
+    as well as per-user directories are ignored, and overrides through
+    environment variables (``MPV_HOME``) are also ignored.
+
+    Note that the ``--no-config`` option takes precedence over this option.
+
 ``--consolecontrols``, ``--no-consolecontrols``
     ``--no-consolecontrols`` prevents the player from reading key events from
     standard input. Useful when reading data from standard input. This is
@@ -1420,6 +1429,8 @@ OPTIONS
         Files explicitly requested by command line options, like
         ``--include`` or ``--use-filedir-conf``, will still be loaded.
 
+    Also see ``--config-dir``.
+
 ``--no-idx``
     Do not use index present in the file even if one is present.
 

options/options.c

@@ -236,6 +236,8 @@ const m_option_t mp_opts[] = {
     {"priority", &proc_priority, CONF_TYPE_STRING, 0, 0, 0, NULL},
 #endif
     OPT_FLAG("config", load_config, CONF_GLOBAL | CONF_NOCFG | CONF_PRE_PARSE),
+    OPT_STRING("config-dir", force_configdir,
+               CONF_GLOBAL | CONF_NOCFG | CONF_PRE_PARSE),
     OPT_STRINGLIST("reset-on-next-file", reset_options, CONF_GLOBAL),
 
 #if HAVE_LUA

options/options.h

@@ -106,6 +106,7 @@ typedef struct MPOpts {
     int merge_files;
     int quiet;
     int load_config;
+    char *force_configdir;
     int use_filedir_conf;
     int stream_cache_size;
     int stream_cache_def_size;

options/path.c

@@ -57,9 +57,14 @@ char *mp_find_config_file(void *talloc_ctx, struct mpv_global *global,
                           const char *filename)
 {
     struct MPOpts *opts = global->opts;
+
     if (!opts->load_config)
         return NULL;
 
+    // Always force the local config dir.
+    if (opts->force_configdir && opts->force_configdir[0])
+        return mp_find_user_config_file(talloc_ctx, global, filename);
+
     for (int i = 0; config_lookup_functions[i] != NULL; i++) {
         char *path = config_lookup_functions[i](talloc_ctx, global, filename);
         if (!path) continue;
@@ -76,9 +81,15 @@ char *mp_find_user_config_file(void *talloc_ctx, struct mpv_global *global,
                                const char *filename)
 {
     struct MPOpts *opts = global->opts;
+
     if (!opts->load_config)
         return NULL;
 
+    if (opts->force_configdir && opts->force_configdir[0]) {
+        return mp_path_join(talloc_ctx, bstr0(opts->force_configdir),
+                            bstr0(filename));
+    }
+
     char *homedir = getenv("MPV_HOME");
     char *configdir = NULL;
     char *result = NULL;
@@ -105,6 +116,10 @@ char *mp_find_user_config_file(void *talloc_ctx, struct mpv_global *global,
 char *mp_find_global_config_file(void *talloc_ctx, struct mpv_global *global,
                                  const char *filename)
 {
+    struct MPOpts *opts = global->opts;
+    if (!opts->load_config || (opts->force_configdir && opts->force_configdir[0]))
+        return NULL;
+
     if (filename) {
         return mp_path_join(talloc_ctx, bstr0(MPLAYER_CONFDIR), bstr0(filename));
     } else {