options: add a 'once' idle mode

This allows to make mpv wait for file open events at start but close
after it is done playing the first playlist.

DOCS/man/options.rst

@@ -333,11 +333,14 @@ Program Behavior
 
     This option is useful for debugging only.
 
-``--idle``
+``--idle=<no|yes|once>``
     Makes mpv wait idly instead of quitting when there is no file to play.
     Mostly useful in slave mode, where mpv can be controlled through input
     commands (see also ``--slave-broken``).
 
+    ``once`` will only idle at start and let the player close once the
+    first playlist has finished playing back.
+
 ``--include=<configuration-file>``
     Specify configuration file to be parsed after the default ones.
 

options/options.c

@@ -541,7 +541,12 @@ const m_option_t mp_opts[] = {
     OPT_STRING("osd-msg2", osd_msg[1], 0),
     OPT_STRING("osd-msg3", osd_msg[2], 0),
 
-    OPT_FLAG("idle", player_idle_mode, M_OPT_GLOBAL),
+    OPT_CHOICE("idle", player_idle_mode, M_OPT_OPTIONAL_PARAM,
+               ({"no",   0},
+                {"once", 1},
+                {"yes",  2},
+                {"",     2})),
+
     OPT_FLAG("input-terminal", consolecontrols, CONF_GLOBAL),
 
     OPT_STRING("input-file", input_file, M_OPT_FILE | M_OPT_GLOBAL),

player/loadfile.c

@@ -1313,7 +1313,7 @@ void mp_play_files(struct MPContext *mpctx)
         mpctx->playlist->current_was_replaced = false;
         mpctx->stop_play = 0;
 
-        if (!mpctx->playlist->current && !mpctx->opts->player_idle_mode)
+        if (!mpctx->playlist->current && mpctx->opts->player_idle_mode < 2)
             break;
     }
 }