Jonathan Brouwer b9f8e25f6e Rollup merge of #146961 - Jules-Bertholet:expr-cfg, r=JonathanBrouwer ...

Allow passing `expr` metavariable as `cfg` predicate

This PR allows expanding `expr` metavariables inside the configuration predicates of `cfg` and `cfg_attr` invocations.
For example, the following code will now compile:

```rust
macro_rules! mac {
    ($e:expr) => {
        #[cfg_attr($e, inline)]
        #[cfg($e)]
        fn func() {}

        #[cfg(not($e))]
        fn func() {
            panic!()
        }
    }
}

mac!(any(unix, feature = "foo"));
```

There is currently no `macro_rules` fragment specifier that can represent all valid `cfg` predicates. `meta` comes closest, but excludes `true` and `false`. By fixing that, this change makes it easier to write declarative macros that parse `cfg` or `cfg_attr` invocations, for example https://github.com/rust-lang/rust/pull/146281/.

@rustbot label T-lang needs-fcp A-attributes A-cfg A-macros

2026-03-21 00:42:47 +01:00

..

src

Rollup merge of #146961 - Jules-Bertholet:expr-cfg, r=JonathanBrouwer

2026-03-21 00:42:47 +01:00

Cargo.toml

Convert to inline diagnostics in rustc_expand

2026-02-04 16:16:16 +01:00