player: deal with some corner cases with playlist navigation

The purpose is making accessing the current playlist entry saner when
commands are executed during initialization, termination, or after
playlist navigation commands.

For example, the "playlist_remove current" command will invalidate
playlist->current - but some things still access the playlist entry even
on uninit. Until now, checking stop_play implicitly took care of it, so
it worked, but it was still messy.

Introduce the mpctx->playing field, which points to the current playlist
entry, even if the entry was removed and/or the playlist's current entry
was moved (e.g. due to playlist navigation).

2 files changed, 23 insertions, 18 deletions

diff --git a/player/core.h b/player/core.h
index bd2a15d7d0..5c40e48674 100644
--- a/player/core.h
+++ b/player/core.h
@@ -187,7 +187,8 @@ typedef struct MPContext {
     struct osd_progbar_state osd_progbar;
 
     struct playlist *playlist;
-    char *filename; // currently playing file
+    struct playlist_entry *playing; // currently playing file
+    char *filename; // always the same as playing->filename (or NULL)
     struct mp_resolve_result *resolve_result;
     enum stop_play_reason stop_play;
     unsigned int initialized_flags;  // which subsystems have been initialized
diff --git a/player/loadfile.c b/player/loadfile.c
index d81bfa7bc8..2917569017 100644
--- a/player/loadfile.c
+++ b/player/loadfile.c
@@ -1024,11 +1024,12 @@ static void play_current_file(struct MPContext *mpctx)
 
     reset_playback_state(mpctx);
 
-    if (mpctx->playlist->current)
-        mpctx->filename = mpctx->playlist->current->filename;
-
-    if (!mpctx->filename)
+    mpctx->playing = mpctx->playlist->current;
+    if (!mpctx->playing || !mpctx->playing->filename)
         goto terminate_playback;
+    mpctx->playing->reserved += 1;
+
+    mpctx->filename = mpctx->playing->filename;
 
     mpctx->add_osd_seek_info &= OSD_SEEK_INFO_EDITION;
 
@@ -1050,8 +1051,8 @@ static void play_current_file(struct MPContext *mpctx)
     if (opts->position_resume)
         mp_load_playback_resume(mpctx, mpctx->filename);
 
-    load_per_file_options(mpctx->mconfig, mpctx->playlist->current->params,
-                          mpctx->playlist->current->num_params);
+    load_per_file_options(mpctx->mconfig, mpctx->playing->params,
+                          mpctx->playing->num_params);
 
 #if HAVE_LIBASS
     if (opts->ass_style_override)
@@ -1083,7 +1084,7 @@ static void play_current_file(struct MPContext *mpctx)
     }
     int stream_flags = STREAM_READ;
     if (!opts->load_unsafe_playlists)
-        stream_flags |= mpctx->playlist->current->stream_flags;
+        stream_flags |= mpctx->playing->stream_flags;
     mpctx->stream = stream_create(stream_filename, stream_flags, mpctx->global);
     if (!mpctx->stream) { // error...
         mp_process_input(mpctx);
@@ -1321,18 +1322,14 @@ terminate_playback:
     if (mpctx->stop_play != PT_RESTART)
         m_config_restore_backups(mpctx->mconfig);
 
-    mpctx->filename = NULL;
     mpctx->resolve_result = NULL;
-    talloc_free(tmp);
 
-    // Played/paused for longer than 3 seconds -> ok
-    bool playback_short = mpctx->stop_play == AT_END_OF_FILE &&
-                (playback_start < 0 || mp_time_sec() - playback_start < 3.0);
-    bool init_failed = mpctx->stop_play == AT_END_OF_FILE &&
-                (mpctx->shown_aframes == 0 && mpctx->shown_vframes == 0);
-    if (mpctx->playlist->current && !mpctx->playlist->current_was_replaced) {
-        mpctx->playlist->current->playback_short = playback_short;
-        mpctx->playlist->current->init_failed = init_failed;
+    if (mpctx->playing && mpctx->stop_play == AT_END_OF_FILE) {
+        // Played/paused for longer than 3 seconds -> ok
+        mpctx->playing->playback_short =
+            playback_start < 0 || mp_time_sec() - playback_start < 3.0;
+        mpctx->playing->init_failed =
+            mpctx->shown_aframes == 0 && mpctx->shown_vframes == 0;
     }
 
     mp_notify(mpctx, MPV_EVENT_TRACKS_CHANGED, NULL);
@@ -1348,6 +1345,13 @@ terminate_playback:
     default:                end_event.reason = -1; break;
     };
     mp_notify(mpctx, MPV_EVENT_END_FILE, &end_event);
+
+    if (mpctx->playing)
+        playlist_entry_unref(mpctx->playing);
+    mpctx->playing = NULL;
+    mpctx->filename = NULL;
+
+    talloc_free(tmp);
 }
 
 // Determine the next file to play. Note that if this function returns non-NULL,