Respect the configured MSRV in implicit_saturating_sub's if x != 0 { x -= 1 } rewrite

[shulaoda]

Fixes #17403

implicit_saturating_sub rewrites if x != 0 { x -= 1 } into x = x.saturating_sub(1). saturating_sub is only usable in a const fn since Rust 1.47, so in a const fn with a lower configured MSRV the rewrite does not compile.

#16309 already added this MSRV check to the if a >= b { 0 } else { b - a } path, but the condition path (if x != 0 { x -= 1 }) was left unguarded. This threads the MSRV into that path and applies the same check, so the lint stays quiet when the suggested saturating_sub would be too new for the const context.

The lint reads the MSRV but was missing from the list of MSRV affected lints in the configuration docs, so this registers it there as well.

changelog: [implicit_saturating_sub]: respect the configured MSRV in const contexts for the if x != 0 { x -= 1 } rewrite

[rustbot]

Thanks for the pull request. A reviewer will take a look after it receives 2 community reviews.

In the meantime, we would highly appreciate if you could try to review any of PRs waiting on community reviews.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

• @rustbot author: the review is finished, PR author should check the comments and take action accordingly
• @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

[rustbot]

r? @Jarcho

rustbot has assigned @Jarcho for the project review.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: 8 candidates
• 8 candidates expanded to 8 candidates
• Random selection from Jarcho, llogiq

[Jarcho]

Thank you.

@rustbot merge

View changes since this review

[shulaoda]

Thank you, everyone! 🙏