lua: restore recent end-file event, and deprecate it

Lua changed behavior for this specific event. I considered the change
minor enough that it would not need to go through deprecation, but
someone hit it immediately and ask on the -dev channel.

It's probably better to restore the behavior. But mark it as deprecated,
since it's problematic (mismatch with the C API). Unfortunately, no
automatic warning is possible. (Or maybe it is, by playing sophisticated
Lua tricks such as setting a metatable and overriding indexing, but
let's not.)

DOCS/interface-changes.rst

@@ -54,8 +54,10 @@ Interface changes
       Using the "playlist-play-index" command is recommended instead.
     - add "playlist-play-index" command
     - add playlist-current-pos, playlist-playing-pos properties
-    - Lua end-file events do not set the "error" field anymore, use "file_error"
-      instead.
+    - Lua end-file events set the "error" field; this is deprecated; use the
+      "file_error" instead for this specific event. Scripts relying on the
+      "error" field for end-file will silently break at some point in the
+      future.
     - deprecate encoding mode (lack of maintainer)
  --- mpv 0.32.0 ---
     - change behavior when using legacy option syntax with options that start

DOCS/man/input.rst

@@ -1350,8 +1350,9 @@ This list uses the event name field value, and the C API symbol in brackets:
     ``file_error``
         Set to mpv error string describing the approximate reason why playback
         failed. Unset if no error known. (In Lua scripting, this value was set
-        on the ``error`` field directly before mpv 0.33.0. Now the ``error``
-        field always indicates success, i.e. is not set.)
+        on the ``error`` field directly. This is deprecated since mpv 0.33.0.
+        In the future, this ``error`` field will be unset for this specific
+        event.)
 
 ``file-loaded``  (``MPV_EVENT_FILE_LOADED``)
     Happens after a file was loaded and begins playback.

player/lua.c

@@ -498,7 +498,7 @@ static int script_resume_all(lua_State *L)
 
 static void pushnode(lua_State *L, mpv_node *node);
 
-static int script_wait_event(lua_State *L)
+static int script_raw_wait_event(lua_State *L)
 {
     struct script_ctx *ctx = get_ctx(L);
 
@@ -1159,7 +1159,7 @@ static const struct fn_entry main_fns[] = {
     FN_ENTRY(suspend),
     FN_ENTRY(resume),
     FN_ENTRY(resume_all),
-    FN_ENTRY(wait_event),
+    FN_ENTRY(raw_wait_event),
     FN_ENTRY(request_event),
     FN_ENTRY(find_config_file),
     FN_ENTRY(get_script_directory),

player/lua/defaults.lua

@@ -475,6 +475,15 @@ _G.print = mp.msg.info
 package.loaded["mp"] = mp
 package.loaded["mp.msg"] = mp.msg
 
+function mp.wait_event(t)
+    local r = mp.raw_wait_event(t)
+    if r and r.file_error and not r.error then
+        -- compat; deprecated
+        r.error = r.file_error
+    end
+    return r
+end
+
 _G.mp_event_loop = function()
     mp.dispatch_events(true)
 end