loadfile: handle --watch-history-path like --watch-later-directory

In other words, leave the option value unset by default and use
mp_find_user_file to get the desired state directory path. Default
values are stored as is, so the old way of setting ~~/state directly
didn't map well to the abstraction of trying to automatically parse
M_OPT_FILE options since leaving the value as the default doesn't result
in any parsing (or any operation on that specific option value).

Author: Dudemanguy

DOCS/man/options.rst

@@ -1165,8 +1165,11 @@ Watch History
         disabled by default.
 
 ``--watch-history-path=<path>``
-    The path in which to store the watch history. Default:
-    ``~~state/watch_history.jsonl`` (see `FILES`_).
+    The path in which to store the watch history.
+
+    If this option is unset, the file will be stored as ``watch_history.jsonl``
+    in the local state directory. This is usually ``~/.local/state/mpv/`` (see
+    `FILES`_).
 
     This file contains one JSON object per line. Its ``time`` field is the UNIX
     timestamp when the file was opened, its ``path`` field is the normalized

options/options.c

@@ -1013,7 +1013,6 @@ static const struct MPOpts mp_default_opts = {
     .sync_max_factor = 5,
     .load_config = true,
     .position_resume = true,
-    .watch_history_path = "~~state/watch_history.jsonl",
     .autoload_files = true,
     .demuxer_thread = true,
     .demux_termination_timeout = 0.1,

player/loadfile.c

@@ -1546,6 +1546,8 @@ static void append_to_watch_history(struct MPContext *mpctx)
 
     void *ctx = talloc_new(NULL);
     char *history_path = mpctx->opts->watch_history_path;
+    if (!history_path || !history_path[0])
+        history_path = mp_find_user_file(ctx, mpctx->log, "state", "watch_history.jsonl");
     char *history_path_dir = bstrto0(ctx, mp_dirname(history_path));
     mp_mkdirp(history_path_dir);