Suggested test setup causes cargo warnings

[simonwuelker]

The suggested setup for tests using loom¹ involves using a custom configuration. (#[cfg(loom)])

Unfortunately, this triggers the new rustc lint for unexpected cfg parameters ² (only available on the latest nightly version).

What is the suggested way to deal with this? Ideally one would not need to add a build.rs file just to register a custom cfg name.

(This issue stems from faern/oneshot#34)

Footnotes

1. https://docs.rs/loom/latest/loom/#writing-tests ↩

2. https://blog.rust-lang.org/2024/05/06/check-cfg.html ↩

[Darksonn]

This is a new warning. For now the suggestion is to use a build script or add #![allow(unknown_lints, unexpected_cfgs)] at the top of your lib.rs file. Compare with tokio-rs/tokio#6538 for a more sophisticated setup.

[Urgau]

Heads up, with the release of rust-lang/cargo#13913 (in nightly-2024-05-19), 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(loom)'] }

Footnotes

1. take effect on Rust 1.80 (current nightly), is ignored on Rust 1.79 (current beta), and produce an unused warning below ↩