Custom handling for const-stability of assign operators in `assign_op_pattern` lint should be removed

[clarfonthey]

Issue #14871 was filed because, historically, these assign-operators were not usable in const context, even though the regular operators were. However, rust-lang/rust#143949 aims to fix this, and it currently uses a #[clippy::msrv = "1.88"] hack to avoid the tests triggering an error.

Longer-term, this special handling should be removed, since all of this is dependent on what will eventually be an older version of the nightly compiler, and my understanding is that while clippy handles MSRV, distinguishing between nightly versions is not supported.

Relevant discussion: https://github.com/rust-lang/rust/pull/143949/files#r2208466376

[samueltardieu]

I think I have a fix for this, but I can't test it completely in the Clippy repository, as AddAssign is not const. I can test it in rust repository though, on top of your patch. You can look at it at samueltardieu/rust@1a44ac9 (it is built on top of a merge commit from your branch and master).

However, this is probably too complex a patch to go directly into the compiler repository without an in-depth review from another Clippy maintainer. I'll provide you with a simpler temporary patch that disables the lint in a const context (which was almost what it was doing up-to-now anyway), and we'll deal with the more powerful solution on the Clippy side after the next sync.

What do you think?

[clarfonthey]

Hmm, honestly, I'm kind of leaning toward just removing the test entirely (commenting it out) for now, since you're right that the MSRV attribute is a bit misleading.

It's technically doing the right thing; it's just that the condition it's checking for will no longer apply, ever.