e9182f195b
make `cfg_select` a builtin macro tracking issue: https://github.com/rust-lang/rust/issues/115585 This parses mostly the same as the `macro cfg_select` version, except: 1. wrapping in double brackets is no longer supported (or needed): `cfg_select {{ /* ... */ }}` is now rejected. 2. in an expression context, the rhs is no longer wrapped in a block, so that this now works: ```rust fn main() { println!(cfg_select! { unix => { "foo" } _ => { "bar" } }); } ``` 3. a single wildcard rule is now supported: `cfg_select { _ => 1 }` now works I've also added an error if none of the rules evaluate to true, and warnings for any arms that follow the `_` wildcard rule. cc `@traviscross` if I'm missing any feature that should/should not be included r? `@petrochenkov` for the macro logic details
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