mirror of https://github.com/rust-lang/rust
36 lines
1010 B
Rust
36 lines
1010 B
Rust
//@ compile-flags: -Znext-solver
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// Proving `W<?0>: Trait` instantiates `?0` with `(W<?1>, W<?2>)` and then
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// proves `W<?1>: Trait` and `W<?2>: Trait`, resulting in a coinductive cycle.
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//
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// Proving coinductive cycles runs until we reach a fixpoint. However, after
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// computing `try_evaluate_added_goals` in the second fixpoint iteration, the
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// self type already has a depth equal to the number of steps. This results
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// in enormous constraints, causing the canonicalizer to hang without ever
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// reaching the recursion limit. We currently avoid that by erasing the constraints
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// from overflow.
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//
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// This previously caused a hang in the trait solver, see
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// https://github.com/rust-lang/trait-system-refactor-initiative/issues/13.
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#![feature(rustc_attrs)]
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#[rustc_coinductive]
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trait Trait {}
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struct W<T>(T);
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impl<T, U> Trait for W<(W<T>, W<U>)>
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where
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W<T>: Trait,
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W<U>: Trait,
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{
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}
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fn impls<T: Trait>() {}
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fn main() {
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impls::<W<_>>();
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//~^ ERROR overflow evaluating the requirement
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}
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