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