Nikolay Sivov (@nsivov) commented about dlls/win32u/message.c:
thread_info->msg_source = msg_source_unavailable; spy_enter_message( SPY_SENDMESSAGE, info->hwnd, info->msg, info->wparam, info->lparam );
- if (info->dest_tid != GetCurrentThreadId())
- if (info->dest_tid != GetCurrentThreadId() ||
/* undocumented behavior when callback pointer is NULL and data is 1. See test_nullCallback(). */
I would remove test reference from here, it's better to describe what happens instead - that it won't wait in such case. Otherwise seems fine.