fix: cmdheight increase overwrites messages that need hit-enter

[nwounkn]

set laststatus=2 cmdheight=1
echo 'foo'
echo 'bar'
set cmdheight=2

Shows only hit-enter prompt.

[chrisbra]

what exact problem does this solve? I cannot seem to see a difference with or without that patch.

[nwounkn]

If you type :echo "one\ntwo\nthree\nfour" | set ch=2 in an already running vim with cmdheight=1, without the patch the lines 'three' and 'four' aren't shown, with the patch the message is shown completely. This is to fix neovim's issue neovim/neovim#22646 , but since vim is somewhat affected too, I decided to make the PR here.
Sorry for bothering, if it's too insignificant to fix.

[chrisbra]

hm, I not sure this is correct, I saw some rendering artifacts when using Vim with this patch and echoing something. Let me use this for a while and see if I can reproduce it or if this works correct.

[ychin]

I have found some other issues with this type of usages (with or without this patch). For example, try running (with a clean config or make sure cmdheight=1) this: :version | set ch=2.

What you see is a normal version output, and after hitting Enter it goes back to looking like cmdheight is 1, but it's actually set to 2. There are all kinds of weird things you can do after that, such as being able to set cmdheight to 0, which is disallowed in Vim, and in general there seems to be a permanent off-by-one-error that is stuck in the cmdheight calculation unless you manually drag the status bar using a mouse which would force the calculation to be done correctly.

Seems like in general the command_height function doesn't really work well when called when a message is shown with a pending hit-enter. I think this patch will fix some of the issues but it may leave others unfixed. I wonder if it's better to just delay calling the entire command_height until hit-enter to prevent any logic inconsistencies because otherwise I find it pretty hard to reason about each state change piecemeal. That said, maybe it's not a bad idea to find out why the remaining buggy behavior happens (in the example I gave above).

FWIW, what kind of situation does this come up in @nwounkn ? I'm curious why we would see an echo message and a cmdheight set on the same line. The current behavior is still a bug, of course, but I just don't see this pattern often.

[chrisbra]

yes, I assume this is some kind of a very specific problem. But it would be good if we could also fix the remaining problems if possible