mirror of https://github.com/rust-lang/rust
55 lines
2.0 KiB
Rust
55 lines
2.0 KiB
Rust
//@ check-pass
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//@ revisions: old next
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//@[next] compile-flags: -Znext-solver
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// If we use canonical goals during trait solving we have to reevaluate
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// the root goal of a cycle until we hit a fixpoint.
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//
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// Here `main` has a goal `(?0, ?1): Trait` which is canonicalized to
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// `exists<^0, ^1> (^0, ^1): Trait`.
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//
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// - `exists<^0, ^1> (^0, ^1): Trait` -instantiate-> `(?0, ?1): Trait`
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// -`(?1, ?0): Trait` -canonicalize-> `exists<^0, ^1> (^0, ^1): Trait`
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// - COINDUCTIVE CYCLE OK (no constraints)
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// - `(): ConstrainToU32<?0>` -canonicalize-> `exists<^0> (): ConstrainToU32<^0>`
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// - OK (^0 = u32 -apply-> ?0 = u32)
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// - OK (?0 = u32 -canonicalize-> ^0 = u32)
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// - coinductive cycle with provisional result != final result, rerun
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//
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// - `exists<^0, ^1> (^0, ^1): Trait` -instantiate-> `(?0, ?1): Trait`
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// -`(?1, ?0): Trait` -canonicalize-> `exists<^0, ^1> (^0, ^1): Trait`
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// - COINDUCTIVE CYCLE OK (^0 = u32 -apply-> ?1 = u32)
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// - `(): ConstrainToU32<?0>` -canonicalize-> `exists<^0> (): ConstrainToU32<^0>`
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// - OK (^0 = u32 -apply-> ?1 = u32)
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// - OK (?0 = u32, ?1 = u32 -canonicalize-> ^0 = u32, ^1 = u32)
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// - coinductive cycle with provisional result != final result, rerun
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//
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// - `exists<^0, ^1> (^0, ^1): Trait` -instantiate-> `(?0, ?1): Trait`
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// -`(?1, ?0): Trait` -canonicalize-> `exists<^0, ^1> (^0, ^1): Trait`
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// - COINDUCTIVE CYCLE OK (^0 = u32, ^1 = u32 -apply-> ?1 = u32, ?0 = u32)
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// - `(): ConstrainToU32<?0>` -canonicalize-> `exists<^0> (): ConstrainToU32<^0>`
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// - OK (^0 = u32 -apply-> ?1 = u32)
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// - OK (?0 = u32, ?1 = u32 -canonicalize-> ^0 = u32, ^1 = u32)
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// - coinductive cycle with provisional result == final result, DONE
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#![feature(rustc_attrs)]
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#[rustc_coinductive]
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trait Trait {}
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impl<T, U> Trait for (T, U)
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where
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(U, T): Trait,
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(): ConstrainToU32<T>,
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{}
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trait ConstrainToU32<T> {}
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impl ConstrainToU32<u32> for () {}
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fn impls_trait<T, U>()
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where
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(T, U): Trait,
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{}
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fn main() {
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impls_trait::<_, _>();
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}
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