stats.lua: don't use io.write from builtin script

Scripts and especially internal scripts shouln't bypass msg.c logging
code for various resons, ranging from processing the input, filtering
the log levels, truncating the output and so on. io.write() is lazy way
of outputing to stdout without respecting mpv's logging module.

Uses osd message, because this has no prefixes. Added internal
flush-status-line command to flush current output without clearing
before exiting.

This commit will allow us to remove duplicated terminal handling code
from stats.lua, mpv core already handles all that and does it in better
way, without taking shortcuts.

player/command.c

@@ -6749,6 +6749,17 @@ static void cmd_context_menu(void *p)
         vo_control(vo, VOCTRL_SHOW_MENU, NULL);
 }
 
+static void cmd_flush_status_line(void *p)
+{
+    struct mp_cmd_ctx *cmd = p;
+    struct MPContext *mpctx = cmd->mpctx;
+
+    if (!mpctx->log)
+        return;
+
+    mp_msg_flush_status_line(mpctx->log, cmd->args[0].v.b);
+}
+
 /* This array defines all known commands.
  * The first field the command name used in libmpv and input.conf.
  * The second field is the handler function (see mp_cmd_def.handler and
@@ -7224,6 +7235,8 @@ const struct mp_cmd_def mp_cmds[] = {
 
     { "context-menu", cmd_context_menu },
 
+    { "flush-status-line", cmd_flush_status_line, { {"clear", OPT_BOOL(v.b)} } },
+
     {0}
 };
 

player/lua/stats.lua

@@ -1795,20 +1795,30 @@ mp.register_event("video-reconfig",
 
 --  --script-opts=stats-bindlist=[-]{yes|<TERM-WIDTH>}
 if o.bindlist ~= "no" then
-    mp.command("no-osd set really-quiet yes")
+    -- This is a special mode to print key bindings to the terminal,
+    -- Adjust the print format and level to make it print only the key bindings.
+    mp.set_property("msg-level", "all=no,statusline=status")
+    mp.set_property("term-osd", "force")
+    mp.set_property_bool("msg-module", false)
+    mp.set_property_bool("msg-time", false)
+    -- wait for all other scripts to finish init
+    mp.add_timeout(0, function()
         if o.bindlist:sub(1, 1) == "-" then
             o.bindlist = o.bindlist:sub(2)
             o.no_ass_b0 = ""
             o.no_ass_b1 = ""
         end
         local width = max(40, math.floor(tonumber(o.bindlist) or 79))
-    mp.add_timeout(0, function()  -- wait for all other scripts to finish init
         o.ass_formatting = false
         o.no_ass_indent = " "
         o.term_size = { w = width , h = 0}
-        io.write(keybinding_info(false, true) .. "\n")
+        mp.osd_message(keybinding_info(false, true))
+        -- wait for next tick to print status line and flush it without clearing
+        mp.add_timeout(0, function()
+            mp.command("flush-status-line no")
             mp.command("quit")
         end)
+    end)
 end
 
 mp.observe_property('osd-height', 'native', handle_osd_height_update)