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// Test case from Chalk.
// Make sure that we make sure that we don't allow arbitrary bounds to be
// proven when a bound and a where clause of an associated type are the same.
#![feature(trivial_bounds)]
trait Print {
fn print();
}
trait Foo {
type Item: Sized where <Self as Foo>::Item: Sized;
}
struct Number { }
impl Foo for Number {
// Well-formedness checks require that the following
// goal is true:
// ```
// if (str: Sized) { # if the where clauses hold
// str: Sized # then the bound on the associated type hold
// }
// ```
// which it is :)
type Item = str where str: Sized;
//~^ ERROR overflow evaluating the requirement `<Number as Foo>::Item == _`
}
struct OnlySized<T> where T: Sized { f: T }
impl<T> Print for OnlySized<T> {
fn print() {
println!("{}", std::mem::size_of::<T>());
}
}
trait Bar {
type Assoc: Print;
}
impl<T> Bar for T where T: Foo {
// This is not ok, we need to prove `wf(<T as Foo>::Item)`, which requires
// knowing that `<T as Foo>::Item: Sized` to satisfy the where clause. We
// can use the bound on `Foo::Item` for this, but that requires
// `wf(<T as Foo>::Item)`, which is an invalid cycle.
type Assoc = OnlySized<<T as Foo>::Item>;
}
fn foo<T: Print>() {
T::print() // oops, in fact `T = OnlySized<str>` which is ill-formed
}
fn bar<T: Bar>() {
// we have `FromEnv(T: Bar)` hence
// `<T as Bar>::Assoc` is well-formed and
// `Implemented(<T as Bar>::Assoc: Print)` hold
foo::<<T as Bar>::Assoc>()
}
fn main() {
bar::<Number>()
}
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