Static rustc_ap_rustc_lint_defs::builtin::COHERENCE_LEAK_CHECK

pub static COHERENCE_LEAK_CHECK: &Lint

The coherence_leak_check lint detects conflicting implementations of a trait that are only distinguished by the old leak-check code.

Example

trait SomeTrait { }
impl SomeTrait for for<'a> fn(&'a u8) { }
impl<'a> SomeTrait for fn(&'a u8) { }

{{produces}}

Explanation

In the past, the compiler would accept trait implementations for identical functions that differed only in where the lifetime binder appeared. Due to a change in the borrow checker implementation to fix several bugs, this is no longer allowed. However, since this affects existing code, this is a future-incompatible lint to transition this to a hard error in the future.

Code relying on this pattern should introduce “newtypes”, like struct Foo(for<'a> fn(&'a u8)).

See issue #56105 for more details.