diff options
Diffstat (limited to 'src/test/ui/associated-types/normalize-cycle-in-eval.rs')
-rw-r--r-- | src/test/ui/associated-types/normalize-cycle-in-eval.rs | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/src/test/ui/associated-types/normalize-cycle-in-eval.rs b/src/test/ui/associated-types/normalize-cycle-in-eval.rs new file mode 100644 index 000000000..dff4c9051 --- /dev/null +++ b/src/test/ui/associated-types/normalize-cycle-in-eval.rs @@ -0,0 +1,43 @@ +// regression test for #74868 + +// check-pass + +trait BoxedDsl<'a> { + type Output; +} + +impl<'a, T> BoxedDsl<'a> for T +where + T: BoxedDsl<'a>, +{ + type Output = <T as BoxedDsl<'a>>::Output; +} + +// Showing this trait is wf requires proving +// Self: HandleUpdate +// +// The impl below is a candidate for this projection, as well as the `Self: +// HandleUpdate` bound in the environment. +// We evaluate both candidates to see if we need to consider both applicable. +// Evaluating the impl candidate requires evaluating +// <T as BoxedDsl<'static>>::Output == () +// The above impl cause normalizing the above type normalize to itself. +// +// This previously compiled because we would generate a new region +// variable each time around the cycle, and evaluation would eventually return +// `EvaluatedToErr` from the `Self: Sized` in the impl, which would in turn +// leave the bound as the only candidate. +// +// #73452 changed this so that region variables are canonicalized when we +// normalize, which means that the projection cycle is detected before +// evaluation returns EvaluatedToErr. The cycle resulted in an error being +// emitted immediately, causing this to fail to compile. +// +// To fix this, normalization doesn't directly emit errors when it finds a +// cycle, instead letting the caller handle it. This restores the original +// behavior. +trait HandleUpdate {} + +impl<T> HandleUpdate for T where T: BoxedDsl<'static, Output = ()> {} + +fn main() {} |