Breaking change in macro_rules ty fragment parsing in version 1.68 #107796
Description
I tried this code:
macro_rules! impl_primitive {
($ty:ty) => { impl_primitive!(impl $ty);};
(impl $ty:ty) => { fn a(_: $ty) {} }
}
impl_primitive! { u8 }I expected to see this happen:
Macro is expanded to fn a(_: u8) {}
Instead, this happened:
On stable 1.67 it works as expected.
On beta 1.68 and nightly 1.69 it fails with the following error
error: expected a trait, found type
--> src/lib.rs:6:19
|
2 | ($ty:ty) => { impl_primitive!(impl $ty);};
| ------ while parsing argument for this `ty` macro fragment
...
6 | impl_primitive! { u8 }
| ^^
It is probably caused by ty fragment that now treats impl as a start of impl Trait type.
So makes sense. But breaks existing code :)