Unicode characters make the prompt disappear

[shreve]

$ fish --version
fish, version 3.1.0

$ echo $TERM
xterm-256color

Since upgrading to 3.1.0 my prompt has been behaving oddly. The right prompt would shift around and if I resized my window the left prompt would completely disappear.

I tried the blank environment and the issue went away.
I disabled Oh My Fish, reverting back to the default prompt and the issue also went away.
I tried to rebuild my prompt from scratch and the issue was gone until I added back in special characters.

The difference between these two sessions is the presence of ↓ in the left prompt.

One of the characters I had previously tried was an emoji, so I tried different values of $fish_emoji_width, but to no avail.

I'm currently using Konsole, but this also happens in Alacritty.

Even just the presence of a special character in the input seems to break rendering.

[faho]

"↓" is not an emoji, it is a character of ambiguous width.

I.e. set fish_ambiguous_width to 1.

[shreve]

That didn't result in any difference.

[faho]

Set it to 2?

Otherwise the remaining possibility is that you have more than 1 ambiguous character in your prompt, and that they're rendered of different width.

Can you try reducing it to a simple prompt and share the code?

Also what OS is this on?

[faho]

Oh, wait, this is a duplicate of #6736

You are using a C locale. Stop that and it'll work.

The 3.1.1 release will handle this better, but setting a C locale and using non-ASCII characters is still misconfiguration.

[shreve]

I had to reconfigure the locale and reboot (that's arch for you), but setting LANG=en_US.UTF-8 resolved this.
@faho Thank you for this, and thank you for all the work you do on fish.