Update check-cfg blog post with recent Cargo change

Author: Urgau

posts/2024-05-06-check-cfg.md

@@ -52,6 +52,20 @@ fn win() {}
 
 ![cargo-check](../../../../images/2024-05-06-check-cfg/cargo-check.svg)
 
+## Expecting static cfgs
+
+*UPDATE: This section was added with the release of nightly-2024-05-19.*
+
+Some crates might use cfgs, like `loom`, `fuzzing` which are always statically known at compile time. For those cases, Cargo provides via the `[lints]` table a way to statically declare those cfgs as expected.
+
+It is done through the special `check-cfg` config under `[lints.rust.unexpected_cfgs]`:
+
+*`Cargo.toml`*
+```toml
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(loom)', 'cfg(fuzzing)'] }
+```
+
 ## Custom cfgs and build scripts
 
 > In Cargo point-of-view: a custom cfg is one that is neither defined by `rustc` nor by a Cargo feature. Think of `tokio_unstable`, `has_foo`, ... but not `feature = "lasers"`, `unix` or `debug_assertions`
@@ -115,9 +129,11 @@ This means that doing `RUSTFLAGS="--cfg tokio_unstable" cargo check` will not re
 
 ### How to expect custom cfgs without a `build.rs`?
 
-There is **currently no way** to expect a custom cfg other than with `cargo::rustc-check-cfg` in a `build.rs`.
+*UPDATE: Cargo with nightly-2024-05-19 now provides the `[lints.rust.unexpected_cfgs.check-cfg]` config to address the statically known custom cfgs.*
+
+~~There is **currently no way** to expect a custom cfg other than with `cargo::rustc-check-cfg` in a `build.rs`.~~
 
-Crate authors that don't want to use a `build.rs` are encouraged to use Cargo features instead.
+Crate authors that don't want to use a `build.rs` and cannot use `[lints.rust.unexpected_cfgs.check-cfg]`, are encouraged to use Cargo features instead.
 
 ### How does it interact with other build systems?