How to make a cfg known to clippy in workspace level

[gnaaman-dn]

Greetings,

We have a Rust workspace where we run clippy with export RUSTFLAGS+=--cfg=my_cfg.
After upgrading from 1.78 version to 1.85, unexpected_cfg started kicking in:

warning: unexpected `cfg` condition name: `my_cfg`
 --> my_lib/src/lib.rs:1:11
  |
1 | #[cfg(not(my_cfg))]
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^

We can of-course disable this lint, but it is useful, so it's preferable to keep it but allow my_cfg.

Currently we're adding this little snippet in every package in our workspace:

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

We could put it in the workspace's Cargo.toml and use lints.workspace = true in each package,
but this would mean that specific packages would not be able to configure additional lints,
which currently do.

---

Is there an alternative solution I'm missing?

Thank you!

[flip1995]

Not a Clippy lint, but happy to answer:

taiki-e/cargo-llvm-cov#370 (comment)
https://doc.rust-lang.org/cargo/reference/workspaces.html#the-lints-table

So it seems like the only way to do that is with lints.workspace = true, which is unfortunate.

Pinging @Urgau , as they might know of a better way to do this.

[gnaaman-dn]

Oh, apologies, I assumed it's clippy because that's where I encountered it.
Does this lint come directly from rustc? If so, it's weird that it would lint for a cfg that it is aware of from --cfg.

[Alexendoo]

You could add the --check-cfg=cfg(my_cfg) to RUSTFLAGS, but this would mean you still get a warning when not using those RUSTFLAGS. Could show up in editors for example

lints.workspace = true and move per package configuration into top level #![allow/warn/etc] is an option, in the future it's likely cargo will gain the ability to do inheritance and per package config in Cargo.toml - rust-lang/cargo#13157

[gnaaman-dn]

Thank you!