Improve unnecessary_map_or lint with negated expressions

[chrisduerr]

Description

The unnecessary_map_or lint just (almost) caused a bug in one of my projects, due to the way its suggestions work:

alacritty/crossfont#72 (comment)

If you take a close look at the suggestion, it's clear that the leading ! is not part of the suggestion:

However my argument is that this mistake is far too easy to make, effectively making this suggestion have an unreasonably high chance to break something. It's possible this might apply to other clippy lints too, I'm not aware of all of them.

Humans are pretty bad at this whole reading thing, so my suggestion would be to explicitly include leading ! into the expression if possible. I think this would reduce the chance of bugs like this happening. Replacing an entire line is always going to be easier for people than replacing just a part of it.

I'm curious if this is something you'd be interested in. This would obviously only work in a best-effort heuristic manner, but I do think it could actually help people and prevent bugs. I have no doubt that sooner or later this would cause bugs otherwise (and maybe it already has).

Version

Additional Labels

@rustbot label +C-enhancement
@rustbot label +C-question

[y21]

Another option could be to emit a verbose multipart suggestion that only changes the map_or to is_some_and and removes the false, argument rather than printing the whole expression to begin with. IMO that also helps readability a fair amount in highlighting exactly what needs to change: