As the title says!
I am posting this because I spent a good 25 minutes debugging it this morning, in the hopes that the next poor soul in this same situation will be able to find this information quickly.
At some point I had changed my shortmess setting, and the t option got dropped in the process. This was resulting in the dreaded “Press ENTER” prompt. Suggestions online tend to involve setting cmdheight=2, which works as long as the filename isn’t so long as to cover two lines, but I don’t want cmdheight=2. So I was racking my brains to figure out what might be causing this, going over my config and looking at verbose autocmd.
I spent a while poring over the shortmess docs in hope of finding something useful, but it was only about the 5th time re-reading that I found my answer, in the t option:
t truncate file message at the start if it is too long to fit
on the command-line, "<" will appear in the left most column.
Ignored in Ex mode.
It took me those 5 times to realize that the “file message” in question was in fact the message that was causing the “Press ENTER” prompt! Then I ran set shortmess+=t and the problem immediately went away.
If you are reading this, you probably don’t want these “Press ENTER” messages, and you probably do want shortmess+=t enabled.
So when you are setting options in your init file with shortmess=, make sure to include t! And if you mysteriously start getting “Press ENTER” prompts on file save, don’t waste time looking at autocommands. Check shortmess first, and make sure t is enabled!