Rollup merge of #106640 - lcnr:update-test, r=jackh726
update test for inductive canonical cycles the previous test always resulted in a cycle 😅 cc https://github.com/rust-lang/chalk/pull/787. I checked with #102713 and this is the only test which fails with that PR. r? ``@jackh726``
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2 changed files with 58 additions and 43 deletions
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// known-bug
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// check-pass
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// This test checks that we're correctly dealing with inductive cycles
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// with canonical inference variables.
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// This should compile but fails with the current solver.
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//
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// This checks that the new solver uses `Ambiguous` when hitting the
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// inductive cycle here when proving `exists<^0, ^1> (): Trait<^0, ^1>`
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// which requires proving `Trait<?1, ?0>` but that has the same
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// canonical representation.
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trait Trait<T, U> {}
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trait Trait<T, U> {}
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impl<T, U> Trait<T, U> for ()
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trait IsNotU32 {}
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impl IsNotU32 for i32 {}
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impl<T: IsNotU32, U> Trait<T, U> for () // impl 1
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where
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where
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(): Trait<U, T>,
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(): Trait<U, T>
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T: OtherTrait,
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{}
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{}
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trait OtherTrait {}
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impl<T> Trait<u32, T> for () {} // impl 2
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impl OtherTrait for u32 {}
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fn require_trait<T, U>()
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// If we now check whether `(): Trait<?0, ?1>` holds this has to
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// result in ambiguity as both `for<T> (): Trait<u32, T>` and `(): Trait<i32, u32>`
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// applies. The remainder of this test asserts that.
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// If we were to error on inductive cycles with canonical inference variables
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// this would be wrong:
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// (): Trait<?0, ?1>
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// - impl 1
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// - ?0: IsNotU32 // ambig
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// - (): Trait<?1, ?0> // canonical cycle -> err
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// - ERR
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// - impl 2
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// - OK ?0 == u32
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//
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// Result: OK ?0 == u32.
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// (): Trait<i32, u32>
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// - impl 1
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// - i32: IsNotU32 // ok
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// - (): Trait<u32, i32>
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// - impl 1
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// - u32: IsNotU32 // err
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// - ERR
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// - impl 2
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// - OK
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// - OK
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// - impl 2 (trivial ERR)
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//
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// Result OK
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// This would mean that `(): Trait<?0, ?1>` is not complete,
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// which is unsound if we're in coherence.
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fn implements_trait<T, U>() -> (T, U)
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where
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where
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(): Trait<T, U>
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(): Trait<T, U>,
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{}
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{
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todo!()
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}
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// A hack to only constrain the infer vars after first checking
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// the `(): Trait<_, _>`.
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trait Constrain<T> {}
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impl<T> Constrain<T> for T {}
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fn constrain<T: Constrain<U>, U>(_: U) {}
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fn main() {
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fn main() {
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require_trait::<_, _>();
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let (x, y) = implements_trait::<_, _>();
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//~^ ERROR overflow evaluating
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constrain::<i32, _>(x);
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constrain::<u32, _>(y);
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}
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}
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@ -1,26 +0,0 @@
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error[E0275]: overflow evaluating the requirement `_: Sized`
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--> $DIR/inductive-canonical-cycle.rs:26:5
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LL | require_trait::<_, _>();
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| ^^^^^^^^^^^^^^^^^^^^^
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= help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_canonical_cycle`)
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note: required for `()` to implement `Trait<_, _>`
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--> $DIR/inductive-canonical-cycle.rs:11:12
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LL | impl<T, U> Trait<T, U> for ()
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| ^^^^^^^^^^^ ^^
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= note: 128 redundant requirements hidden
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= note: required for `()` to implement `Trait<_, _>`
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note: required by a bound in `require_trait`
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--> $DIR/inductive-canonical-cycle.rs:22:9
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LL | fn require_trait<T, U>()
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| ------------- required by a bound in this
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LL | where
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LL | (): Trait<T, U>
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| ^^^^^^^^^^^ required by this bound in `require_trait`
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error: aborting due to previous error
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For more information about this error, try `rustc --explain E0275`.
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