make let-chains collapsable-if allow-by-default

[oriongonza]

Description

https://bsky.app/profile/lpalmieri.com/post/3lsgc44pxph2q

This will break many repos that have clippy on them. I think that it's a good idea to make collapsable-if allow-by-default on 1.87 and enable it back in 1.88 to give people time to adjust.

I don't know if this is possible now after the fact.
If it's not, maybe it's something that could be considered for the next time this happens?

[samueltardieu]

I am not sure this is a problem. Using "stable" in the CI exposes the user to new warnings when a new version of the compiler and Clippy is released. Some solutions to avoid this are:

• Use a toolchain with a chosen version (1.87)
• Or also use "beta" in your CI, possibly in a non-breaking mode, so that you can fix the issues beforehand

In this case, some possible ways of fixing the issue once it is detected would be:

• #![allow(clippy::collapsible_if)] until 1.88 is stable
• Use a package.rust-version = 1.87 in your Cargo.toml to get Clippy not to lint about things that would not work in 1.87