player: don't decrement --loop-file=N and add remaining-file-loops

This stops decreasing numerical values of --loop-file on each iteration
so that loop-file=N loops every playlist entry without having to add
--loop-file to --reset-on-next-file.

The current behavior confuses users as seen in:

https://github.com/mpv-player/mpv/issues/2481
https://github.com/mpv-player/mpv/issues/5943
https://github.com/mpv-player/mpv/issues/11291
https://github.com/mpv-player/mpv/issues/13860
https://www.reddit.com/r/mpv/comments/rcwnrw/looping_each_file_n_times_in_a_playlist/

Also options are supposed to reflect the value configured by the user
and not change on their own.

A remaining-file-loops property is exposed as a replacement to check how
many loops are left.

DOCS/interface-changes/loop.txt

@@ -0,0 +1,2 @@
+numerical values of `--loop-file` no longer decrease on each iteration
+add `remaining-file-loops` property as a replacement to get the remaining loop count

DOCS/man/input.rst

@@ -2142,6 +2142,12 @@ Property list
     ``playback-time/full``
         ``playback-time`` with milliseconds.
 
+``remaining-file-loops``
+    How many more times the current file is going to be looped. This is
+    initialized from the value of ``--loop-file``. This counts the number of
+    times it causes the player to seek to the beginning of the file, so it is 0
+    the last the time is played. -1 corresponds to infinity.
+
 ``chapter`` (RW)
     Current chapter number. The number of the first chapter is 0.
 

player/command.c

@@ -869,6 +869,13 @@ static int mp_property_playtime_remaining(void *ctx, struct m_property *prop,
     return property_time(action, arg, remaining / speed);
 }
 
+static int mp_property_remaining_file_loops(void *ctx, struct m_property *prop,
+        int action, void *arg)
+{
+    MPContext *mpctx = ctx;
+    return m_property_int_ro(action, arg, mpctx->remaining_file_loops);
+}
+
 /// Current chapter (RW)
 static int mp_property_chapter(void *ctx, struct m_property *prop,
                                int action, void *arg)
@@ -3999,7 +4006,7 @@ static const struct m_property mp_properties_base[] = {
     {"audio-pts", mp_property_audio_pts},
     {"playtime-remaining", mp_property_playtime_remaining},
     M_PROPERTY_ALIAS("playback-time", "time-pos"),
-    {"chapter", mp_property_chapter},
+    {"remaining-file-loops", mp_property_remaining_file_loops},
     {"edition", mp_property_edition},
     {"current-edition", mp_property_current_edition},
     {"chapters", mp_property_chapters},
@@ -7484,6 +7491,11 @@ void mp_option_change_callback(void *ctx, struct m_config_option *co, int flags,
             mpctx->stop_play = PT_CURRENT_ENTRY;
     }
 
+    if (opt_ptr == &opts->loop_file) {
+        mpctx->remaining_file_loops = opts->loop_file;
+        mp_notify_property(mpctx, "remaining-file-loops");
+    }
+
     if (opt_ptr == &opts->ab_loop[0] || opt_ptr == &opts->ab_loop[1]) {
         update_ab_loop_clip(mpctx);
         // Update if visible

player/core.h

@@ -421,6 +421,8 @@ typedef struct MPContext {
     int max_frames;
     bool playing_msg_shown;
 
+    int remaining_file_loops;
+
     bool paused_for_cache;
     bool demux_underrun;
     double cache_stop_time;

player/loadfile.c

@@ -1633,6 +1633,9 @@ static void play_current_file(struct MPContext *mpctx)
     load_per_file_options(mpctx->mconfig, mpctx->playing->params,
                           mpctx->playing->num_params);
 
+    mpctx->remaining_file_loops = mpctx->opts->loop_file;
+    mp_notify_property(mpctx, "remaining-file-loops");
+
     mpctx->max_frames = opts->play_frames;
 
     handle_force_window(mpctx, false);

player/playloop.c

@@ -901,10 +901,10 @@ static void handle_loop_file(struct MPContext *mpctx)
         }
         target = ab[0];
         prec = MPSEEK_EXACT;
-    } else if (opts->loop_file) {
-        if (opts->loop_file > 0) {
-            opts->loop_file--;
-            m_config_notify_change_opt_ptr(mpctx->mconfig, &opts->loop_file);
+    } else if (mpctx->remaining_file_loops) {
+        if (mpctx->remaining_file_loops > 0) {
+            mpctx->remaining_file_loops--;
+            mp_notify_property(mpctx, "remaining-file-loops");
         }
         target = get_start_time(mpctx, mpctx->play_dir);
     }