Remove underscore prefix from locals on compleition

[bbb651]

In this situation, after completing _foo

fn main() {
    let _foo = 0;
    _f|
}

The result is:

fn main() {
    let _foo = 0;
    _foo|
}

I expect the result to be:

fn main() {
    let foo = 0;
    foo|
}

Since by definition, after completion the variable is used, and saves the rename the user would have to do to avoid a warning.

I think this should be initially apply only to locals (including arguments), and possibly expanded to items which are comparatively rarer and have more unanswered questions (Should it only apply to items within the same scope? Which kind of items should it apply to? Should it only occur when visibility is pub(crate) or lower?).

Should the completion item itself appear as _foo or foo? I think the label should be foo but the filterText be _foo, that way it's clear the rename will take place, while making it still possible to find by typing _|. Would this make it appear too low when searching f|?

[ChayimFriedman2]

Perhaps the code you write is under some cfg, and without this cfg the variable will be unused. Perhaps you want to see if you need this variable here. Perhaps there is another reason the variable is prefixed with an underscore.

I don't think we should automatically remove the underscore, definitely not by default (without some setting). We can (if we don't already provide one) provide an assist to remove the underscore from used variables, although this is as simple as renaming it.

[Veykril]

An alternative would be to duplicate the completion, have one with and one without the prefix. Might get confusing though. We should definitely have a assist for that though I'd say either way

[vishruth-thimmaiah]

@rustbot claim