command: add current-watch-later-dir property

It will be used in the next commit.

DOCS/interface-changes/current-watch-later-dir.txt

@@ -0,0 +1 @@
+add `current-watch-later-dir` property

DOCS/man/input.rst

@@ -3753,6 +3753,11 @@ Property list
     The working directory of the mpv process. Can be useful for JSON IPC users,
     because the command line player usually works with relative paths.
 
+``current-watch-later-dir``
+    The directory in which watch later config files are stored. This returns
+    ``--watch-later-dir``, or the default directory if ``--watch-later-dir`` has
+    not been modified, with tilde placeholders expanded.
+
 ``protocol-list``
     List of protocol prefixes potentially recognized by the player. They are
     returned without trailing ``://`` suffix (which is still always required).

player/command.c

@@ -3528,6 +3528,13 @@ static int mp_property_cwd(void *ctx, struct m_property *prop,
     return M_PROPERTY_NOT_IMPLEMENTED;
 }
 
+static int mp_property_current_watch_later_dir(void *ctx, struct m_property *prop,
+                                               int action, void *arg)
+{
+    MPContext *mpctx = ctx;
+    return m_property_strdup_ro(action, arg, mp_get_playback_resume_dir(mpctx));
+}
+
 static int mp_property_protocols(void *ctx, struct m_property *prop,
                                  int action, void *arg)
 {
@@ -4388,6 +4395,7 @@ static const struct m_property mp_properties_base[] = {
     {"ambient-light", mp_property_ambient_light},
 
     {"working-directory", mp_property_cwd},
+    {"current-watch-later-dir", mp_property_current_watch_later_dir},
 
     {"protocol-list", mp_property_protocols},
     {"decoder-list", mp_property_decoders},

player/configfiles.c

@@ -197,7 +197,7 @@ static bool copy_mtime(const char *f1, const char *f2)
     return true;
 }
 
-static char *mp_get_playback_resume_dir(struct MPContext *mpctx)
+char *mp_get_playback_resume_dir(struct MPContext *mpctx)
 {
     char *wl_dir = mpctx->opts->watch_later_dir;
     if (wl_dir && wl_dir[0]) {

player/core.h

@@ -510,6 +510,7 @@ void audio_start_ao(struct MPContext *mpctx);
 void mp_parse_cfgfiles(struct MPContext *mpctx);
 void mp_load_auto_profiles(struct MPContext *mpctx);
 bool mp_load_playback_resume(struct MPContext *mpctx, const char *file);
+char *mp_get_playback_resume_dir(struct MPContext *mpctx);
 void mp_write_watch_later_conf(struct MPContext *mpctx);
 void mp_delete_watch_later_conf(struct MPContext *mpctx, const char *file);
 struct playlist_entry *mp_check_playlist_resume(struct MPContext *mpctx,