options: deprecate --heartbeat-cmd

It's useless. --heartbeat-interval is also considered deprecated, but
this is not made explicit.

DOCS/interface-changes.rst

@@ -19,6 +19,8 @@ Interface changes
 
 ::
 
+ --- mpv 0.18.1 ---
+    - deprecate --heartbeat-cmd
  --- mpv 0.18.0 ---
     - now ab-loops are active even if one of the "ab-loop-a"/"-b" properties is
       unset ("no"), in which case the start of the file is used if the A loop

DOCS/man/options.rst

@@ -2019,6 +2019,14 @@ Window
     be the default behavior. Currently only affects X11 VOs.
 
 ``--heartbeat-cmd=<command>``
+
+    .. warning::
+
+        This option is redundant with Lua scripting. Further, it shouldn't be
+        needed for disabling screensaver anyway, since mpv will call
+        ``xdg-screensaver`` when using X11 backend. As a consequence this
+        option has been deprecated with no direct replacement.
+
     Command that is executed every 30 seconds during playback via *system()* -
     i.e. using the shell. The time between the commands can be customized with
     the ``--heartbeat-interval`` option. The command is not run while playback

options/options.c

@@ -469,7 +469,8 @@ const m_option_t mp_opts[] = {
     OPT_STRING("vo-mmcss-profile", vo.mmcss_profile, M_OPT_FIXED),
 #endif
 
-    OPT_STRING("heartbeat-cmd", heartbeat_cmd, 0),
+    OPT_STRING("heartbeat-cmd", heartbeat_cmd, 0,
+               .deprecation_message = "use Lua scripting instead"),
     OPT_FLOAT("heartbeat-interval", heartbeat_interval, CONF_MIN, 0),
 
     OPT_CHOICE_OR_INT("screen", vo.screen_id, 0, 0, 32,