Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

update test for inductive canonical cycles #106640

Merged
merged 1 commit into from
Jan 10, 2023
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
75 changes: 58 additions & 17 deletions src/test/ui/traits/solver-cycles/inductive-canonical-cycle.rs
Original file line number Diff line number Diff line change
@@ -1,28 +1,69 @@
// known-bug
// check-pass

// This test checks that we're correctly dealing with inductive cycles
// with canonical inference variables.

// This should compile but fails with the current solver.
//
// This checks that the new solver uses `Ambiguous` when hitting the
// inductive cycle here when proving `exists<^0, ^1> (): Trait<^0, ^1>`
// which requires proving `Trait<?1, ?0>` but that has the same
// canonical representation.
trait Trait<T, U> {}

impl<T, U> Trait<T, U> for ()
trait IsNotU32 {}
impl IsNotU32 for i32 {}
impl<T: IsNotU32, U> Trait<T, U> for () // impl 1
where
(): Trait<U, T>,
T: OtherTrait,
(): Trait<U, T>
{}

trait OtherTrait {}
impl OtherTrait for u32 {}
impl<T> Trait<u32, T> for () {} // impl 2

// If we now check whether `(): Trait<?0, ?1>` holds this has to
// result in ambiguity as both `for<T> (): Trait<u32, T>` and `(): Trait<i32, u32>`
// applies. The remainder of this test asserts that.

// If we were to error on inductive cycles with canonical inference variables
// this would be wrong:

fn require_trait<T, U>()
// (): Trait<?0, ?1>
// - impl 1
// - ?0: IsNotU32 // ambig
// - (): Trait<?1, ?0> // canonical cycle -> err
// - ERR
// - impl 2
// - OK ?0 == u32
//
// Result: OK ?0 == u32.

// (): Trait<i32, u32>
// - impl 1
// - i32: IsNotU32 // ok
// - (): Trait<u32, i32>
// - impl 1
// - u32: IsNotU32 // err
// - ERR
// - impl 2
// - OK
// - OK
// - impl 2 (trivial ERR)
//
// Result OK

// This would mean that `(): Trait<?0, ?1>` is not complete,
// which is unsound if we're in coherence.

fn implements_trait<T, U>() -> (T, U)
where
(): Trait<T, U>
{}
(): Trait<T, U>,
{
todo!()
}

// A hack to only constrain the infer vars after first checking
// the `(): Trait<_, _>`.
trait Constrain<T> {}
impl<T> Constrain<T> for T {}
fn constrain<T: Constrain<U>, U>(_: U) {}

fn main() {
require_trait::<_, _>();
//~^ ERROR overflow evaluating
let (x, y) = implements_trait::<_, _>();

constrain::<i32, _>(x);
constrain::<u32, _>(y);
}
26 changes: 0 additions & 26 deletions src/test/ui/traits/solver-cycles/inductive-canonical-cycle.stderr

This file was deleted.