impl block on a type defined with type_alias_impl_trait can conflict with other unrelated impl #139583
Description
I tried this code:
#![feature(type_alias_impl_trait)] use std::any::TypeId; pub trait Trait {} impl<T: ?Sized> Trait for T {} pub trait Other {} macro_rules! mymac { () => {{ struct S; type Foo = impl Trait; let x: Foo = S; println!("{:?}", TypeId::of::<Foo>()); impl Foo { fn foo() -> () {} } impl Other for Foo {} }}; } fn main() { mymac!(); mymac!(); }I expected to see this happen: compiles without error
Instead, this happened:
error[E0119]: conflicting implementations of trait `Other` for type `main::Foo` --> src/main.rs:19:9 | 19 | impl Other for Foo {} | ^^^^^^^^^^^^^^^^^^ | | | first implementation here | conflicting implementation for `main::Foo` ... 25 | mymac!(); | -------- in this macro invocation | = note: this error originates in the macro `mymac` (in Nightly builds, run with -Z macro-backtrace for more info) Meta
Rust nightly version on the playground as of 9th of April 2025.