Add configuration option to "forcefully" toggle undercurl when not detected.

[filipdutescu]

Description

Due to the way some distributions and package managers package the TermInfo file of various emulators, it is possible to have a false negative reading in Helix that the used emulator does not support undercurls. Even if it actually does (for example, Alacritty in ArchLinux shows as not supporting undercurls, when it acutally does).

Proposal

A configuration option could be added to "force" Helix to use undercurls even if its automated detection mechanism says they are not supported.

[pascalkuthe]

The necessary configuration should be part of the normal editor configuration and passed to CrossTermBackend::new and overwrite the autodetected value there

helix/helix-tui/src/backend/crossterm.rs

Line 61 in 39d5fb0

pub fn new(buffer: W) -> CrosstermBackend<W> {

[the-mikedavis]

We have a special case for WezTerm for the same term-info-installation reasons: 98c121c

We could add one for Alacritty too since it has been supported for some time now alacritty/alacritty#5837

[filipdutescu]

@pascalkuthe mentioned it might be better to handle it this way since it increases burden on us adding more and more exceptions.

[pascalkuthe]

We have a special case for WezTerm for the same term-info-installation reasons: 98c121c

We could add one for Alacritty too since it has been supported for some time now alacritty/alacritty#5837

just to note: Alacritty is detected just fine on every distro I tried but archlinux (and it's derivatives like manjaro), I probably missed some distros but this is not that the detection is not working for alacritty, just that the package is wrong. If you install the terminfo file from the alactritty repo there is no problem.

That's why sort of suggested adding an overwrite here because it doesn't seem sustainable to hardcode every emulator here by hand where any distro has ever messed up the terminfo file (even worse how do you deal with ssh...)

[the-mikedavis]

It's a little hacky but you could also set the VTE_VERSION environment variable to 5102 as a workaround without changing the Helix codebase.

A config option is probably fine for this though, we have a similar one for forcing true-color when the detection fails.