Perf issue: scrolling in the completion menu keeps triggering (re)parsing of the command line over and over

[blindFS]

Platform macOS
Terminal software ghostty

Found this issue during nushell/nushell#15270

Steps to reproduce

1. type in use std <tab>
2. hold ctrl-p/ctrl-n down for a while

rustc optimized nu release performs noticeably better.

Basically the menu next/prev event will trigger the parsing of the cli, which involves dozens of parse_module_file calls.

I guess it has something to do with the highlighting. But since the cli text doesn't change by those events (maybe I missed some config here to make it happen), I think it should be optimized.

Typing in cli after use std is also not very responsive due to the same reason, but that is probably harder to fix.

[fdncred]

Nice catch. Would be wonderful to figure out how to fix this.

[blindFS]

Ideally, highlighting better to be an async function and then we can set a debounce timeout for it.

I'm not sure if it worth the effort, since the only remaining situation that I can notice the lagging (but I only tested it on M4 pro chip) is use std <typing/left/right>. And that one seems to me a nu_parser issue.

[fdncred]

i would love to see some asyn in reedline to fix things like this and be a bit more powerful