| //@ run-pass |
| // Regression test for #31299. This was generating an overflow error |
| // because of eager normalization: |
| // |
| // proving `M: Sized` requires |
| // - proving `PtrBack<Vec<M>>: Sized` requires |
| // - normalizing `Vec<<Vec<M> as Front>::Back>>: Sized` requires |
| // - proving `Vec<M>: Front` requires |
| // - `M: Sized` <-- cycle! |
| // |
| // If we skip the normalization step, though, everything goes fine. |
| // |
| // This could be fixed by implementing lazy normalization everywhere. |
| // |
| // However, we want this to work before then. For that, when checking |
| // whether a type is Sized we only check that the tails are Sized. As |
| // PtrBack does not have a tail, we don't need to normalize anything |
| // and this compiles |
| |
| trait Front { |
| type Back; |
| } |
| |
| impl<T> Front for Vec<T> { |
| type Back = Vec<T>; |
| } |
| |
| struct PtrBack<T: Front>(#[allow(dead_code)] Vec<T::Back>); |
| |
| struct M(#[allow(dead_code)] PtrBack<Vec<M>>); |
| |
| #[allow(unused_must_use)] |
| fn main() { |
| std::mem::size_of::<M>(); |
| } |
