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Cycle detected when using associated type bounds in super trait #65913
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When we write: trait B: A<T: B> {} this is equivalent to: trait B
where
Self: A<T: B>
{} which is equivalent to: trait B
where
Self: A,
<Self as A>::T: B,
{} This results in an error: error[E0277]: the trait bound `<<Self as A>::T as A>::T: B` is not satisfied One might think that this should compile because What is curious here is that rather than getting the error message about "not satisfied", we are getting a cycle error. cc @alexreg @nikomatsakis @tmandry |
I wonder if the supertraits query is including the associated type bound - AFAIK it should only include the bounds specified on |
@eddyb I know that was a problem previously, though I introduced a filter in relevant places to combat it. We may need to introduce a filter in another place. |
This issues still happens, are there any updates on fixes? |
As of #110512, this is no longer a cycle error, and the code above errors with:
The fact that this still errors is a somewhat unfortunate side-effect of #65913 (comment), since the Fixing this in a way that doesn't cause the compiler to overflow generating an infinite nested set of |
This now hangs on nightly (not only the sugared form but also the desugared one) with both the old and the new solver. @rustbot label I-hang E-needs-bisection |
Regressed in #112629 (git-revert: hang → errors). CC @compiler-errors |
Prevent cycle in implied predicates computation Makes rust-lang#65913 from hang -> fail. I believe fail is the correct state for this test to remain for the long term.
Rollup merge of rust-lang#121409 - compiler-errors:atb-cycle, r=cjgillot Prevent cycle in implied predicates computation Makes rust-lang#65913 from hang -> fail. I believe fail is the correct state for this test to remain for the long term.
I don't believe this will ever be made to compile. A cycle error IMO is the correct state for this. Diagnostics could perhaps be improved, but they would need to explain some details about how supertrait bound elaboration works. |
I don't know if this is a bug or expected behaviour. But I'm encountering the following error when compiling the following code.
But if I merge the traits
A
andB
into the traitC
it works.I think the first example should work as good as the second since the trait
C
is only split into two traitsA
andB
with same functionality.The text was updated successfully, but these errors were encountered: