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// Regression test for #30225, which was an ICE that would trigger as
// a result of a poor interaction between trait result caching and
// type inference. Specifically, at that time, unification could cause
// unrelated type variables to become instantiated, if subtyping
// relationships existed. These relationships are now propagated
// through obligations and hence everything works out fine.
trait Foo<U,V> : Sized {
fn foo(self, u: Option<U>, v: Option<V>) {}
}
struct A;
struct B;
impl Foo<A, B> for () {} // impl A
impl Foo<u32, u32> for u32 {} // impl B, creating ambiguity
fn toxic() {
// cache the resolution <() as Foo<$0,$1>> = impl A
let u = None;
let v = None;
Foo::foo((), u, v);
}
fn bomb() {
let mut u = None; // type is Option<$0>
let mut v = None; // type is Option<$1>
let mut x = None; // type is Option<$2>
Foo::foo(x.unwrap(),u,v); // register <$2 as Foo<$0, $1>>
u = v; // mark $0 and $1 in a subtype relationship
//~^ ERROR mismatched types
x = Some(()); // set $2 = (), allowing impl selection
// to proceed for <() as Foo<$0, $1>> = impl A.
// kaboom, this *used* to trigge an ICE
}
fn main() {}
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