handle unexpected_cfgs

[dswij]

See e.g. https://github.com/tokio-rs/mio/actions/runs/8986077701/job/24682502223 due to rust-lang/cargo#13571

[Thomasdezeeuw]

I don't think is the way to solve it.

We probably we want to add #![allow(unexpected_cfgs)], but we'll have to take a look at whether not that requires a MSRV increase.

[Thomasdezeeuw]

I meant remove all the CI setup stuff, just #![allow(unexpected_cfgs)].

[Darksonn]

You probably need #![allow(unknown_lints, unexpected_cfgs)]. See also tokio-rs/tokio#6538.

[Urgau]

Heads up, with the release of rust-lang/cargo#13913 (in nightly-2024-05-19), there is no longer any need for the kind of workarounds employed in this PR. Cargo has now gain the ability to declare --check-cfg args directly inside the [lints] table with [lints.rust.unexpected_cfgs.check-cfg]¹:

Cargo.toml:

[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(foo)'] }

Note that the diagnostic output of the lint has been updated to suggest the [lints] approach first. You can use it to guide you through the --check-cfg arguments that may need to be added.

Footnotes

1. take effect on Rust 1.80 (current nightly), is ignored on Rust 1.79 (current beta), and produce an unused warning below (only in local-dev, not when used as a dep) ↩

[Thomasdezeeuw]

Closing in favour of #1787, which adds the two expected cfgs instead of ignore the lint (since I think it's quite useful for Mio).