feature request: #[feature] awareness in MSRV-gated lints

[tamird]

Some lints, such as borrow_as_ptr have conditional behavior based on MSRV:

rust-clippy/clippy_lints/src/casts/borrow_as_ptr.rs

Line 31 in fe4dd5b

let (suggestion, span) = if msrv.meets(cx, msrvs::RAW_REF_OP) {

In Rust-for-Linux, this is not sufficient because we enable a number of unstable features when we are reasonably confident their behavior won't change before stabilization, or because we know they have been stabilized without API change in a version that exceeds our configured MSRV.

It would be extremely helpful if these MSRV checks could be taught to also respect #[feature] attributes that enable unstable features ahead of the MSRV having been met. This is especially tricky when API has actually changed between the configured MSRV and the feature's actual stabilization.

[ojeda]

Cc Rust-for-Linux/linux#1152.

I assume this could work with a list of unstable features (or perhaps a list of lints that would ignore the msrv behavior).

In any case, if it is tricky to do this, then I guess we could for the time being avoid using the msrv field -- some notes at Rust-for-Linux/linux#1152 (comment). Eventually we will not use unstable features like today, so it is not a critical feature, but it would be nice to be able to use unstable features without having to lose the msrv feature.

because we enable a number of unstable features

To clarify, we also use a few others in https://github.com/Rust-for-Linux/linux/blob/e6ea10d5dbe082c54add289b44f08c9fcfe658af/rust/kernel/lib.rs#L15-L28 (and for derive_coerce_pointee we have to do it conditionally).

[samueltardieu]

We can check for enabled features for features that are probably stable indeed. We already do that, for example in the manual_div_ceil lint: we lint on unsigned integers manual div_ceil() provided the MSRV is ok, and on signed integers as well if the int_roundings feature is enabled, because div_ceil() on signed integers is still unstable.

Is that what you need? If this is, don't hesitate to request such additions on a lint+feature basis, as a feature request (ah ah).