clippy: fix manual_let_else lint

[xtqqczze]

https://rust-lang.github.io/rust-clippy/master/index.html#manual_let_else

[clarfonthey]

Why are you separating all of these into separate PRs? Also, what justification do you have for fixing these in this project when they're not clippy-default lints, since that means they're not recommended for general use, and mostly just preference?

[xtqqczze]

I prefer to keep PRs small and not mix unrelated changes, it’s usually easier to review too. It avoids conflating independent discussions, and if one change needs revision, it doesn’t block the others.

As for the pedantic lints, they can still catch patterns that affect readability or maintainability. In the case of manual_let_else, I think the changes are an improvement.

[clarfonthey]

That makes sense, although they are non-default for a reason.

In this case, it actually looks like it might make sense to use the unwrap_unchecked methods for a bunch of these since our MSRV supports it. Don't think there's currently a clippy lint checking for that.

[xtqqczze]

Good idea! I’ve opened #693 since the changes turned out to be a bit more involved. I’ll mark this PR as draft for now due to conflicts.

[clarfonthey]

Looking at the new version, I guess this is okay to merge. I'm kind of indifferent on this style and don't think that let-else is strictly an improvement, and there's a reason why clippy doesn't make this lint default. Will let someone else merge if they think it's an improvement.

[xtqqczze]

Why are you separating all of these into separate PRs?

Yeah, separate PRs aren't ideal when they create merge conflicts in Cargo.toml...