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add test from chalk#788 for new solver
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lcnr committed Aug 8, 2023
1 parent bf62436 commit 95d1f6b
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46 changes: 46 additions & 0 deletions tests/ui/traits/new-solver/cycles/inductive-not-on-stack.rs
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// compile-flags: -Ztrait-solver=next
#![feature(rustc_attrs, trivial_bounds)]

// We have to be careful here:
//
// We either have the provisional result of `A -> B -> A` on the
// stack, which is a fully coinductive cycle. Accessing the
// provisional result for `B` as part of the `A -> C -> B -> A` cycle
// has to make sure we don't just use the result of `A -> B -> A` as the
// new cycle is inductive.
//
// Alternatively, if we have `A -> C -> A` first, then `A -> B -> A` has
// a purely inductive stack, so something could also go wrong here.

#[rustc_coinductive]
trait A {}
#[rustc_coinductive]
trait B {}
trait C {}

impl<T: B + C> A for T {}
impl<T: A> B for T {}
impl<T: B> C for T {}

fn impls_a<T: A>() {}

// The same test with reordered where clauses to make sure we're actually testing anything.
#[rustc_coinductive]
trait AR {}
#[rustc_coinductive]
trait BR {}
trait CR {}

impl<T: CR + BR> AR for T {}
impl<T: AR> BR for T {}
impl<T: BR> CR for T {}

fn impls_ar<T: AR>() {}

fn main() {
impls_a::<()>();
//~^ ERROR overflow evaluating the requirement `(): A`

impls_ar::<()>();
//~^ ERROR overflow evaluating the requirement `(): AR`
}
29 changes: 29 additions & 0 deletions tests/ui/traits/new-solver/cycles/inductive-not-on-stack.stderr
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error[E0275]: overflow evaluating the requirement `(): A`
--> $DIR/inductive-not-on-stack.rs:41:5
|
LL | impls_a::<()>();
| ^^^^^^^^^^^^^
|
= help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_not_on_stack`)
note: required by a bound in `impls_a`
--> $DIR/inductive-not-on-stack.rs:25:15
|
LL | fn impls_a<T: A>() {}
| ^ required by this bound in `impls_a`

error[E0275]: overflow evaluating the requirement `(): AR`
--> $DIR/inductive-not-on-stack.rs:44:5
|
LL | impls_ar::<()>();
| ^^^^^^^^^^^^^^
|
= help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_not_on_stack`)
note: required by a bound in `impls_ar`
--> $DIR/inductive-not-on-stack.rs:38:16
|
LL | fn impls_ar<T: AR>() {}
| ^^ required by this bound in `impls_ar`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0275`.

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