Unresolved field with trait with single implementation

[lnicola]

We still don't resolve x.

type Alias<T> = T;

trait Trait<T> {
    type Assoc;
}

struct Foo;
struct Bar {
    x: i32,
}

impl Trait<()> for Foo {
    type Assoc = Bar;
}

fn main() {
    Alias::<<Foo as Trait<_>>::Assoc> { x: 10 };
}

Originally posted by @lnicola in #17651 (comment)

[ShoyuVanilla]

├─114ms DEBUG Ok, solution=Unique(Canonical { value: ConstrainedSubst { subst: [?0 := 0<[]>, ?1 := Bar<[]>], constraints: [] }, binders: [] }), priority=High
└─┐with_priorities domain_goal=AliasEq(<Foo<[]> as Trait<^0.0>>::Assoc = ^0.1), a=Unique(Canonical { value: ConstrainedSubst { subst: [?0 := ^0.0, ?1 := Trait::Assoc<[?0 := Foo<[]>, ?1 := ^0.0]>], constraints: [] }, binders: [U0 with kind type] }), prio_a=Low, b=Unique(Canonical { value: ConstrainedSubst { subst: [?0 := 0<[]>, ?1 := Bar<[]>], constraints: [] }, binders: [] }), prio_b=High
  ├─  0ms DEBUG combine Unique; substitution [?0 := 0<[]>, ?1 := Bar<[]>] with Unique; for<?U0> { substitution [?0 := ^0.0, ?1 := Trait::Assoc<[?0 := Foo<[]>, ?1 := ^0.0]>] }
  ├─  0ms DEBUG combined result, result=(Ambig(Unknown), High)

Not have been looking into this much, but it seems like chalk combines the solution(_ = () in Trait<_>) with for<?U0> { substitution [?0 := ^0.0, ?1 := Trait::Assoc<[?0 := Foo<[]>, ?1 := ^0.0]>] and returns ambiguous, resulting in type inference failure 🤔

I'll test on chalk with simplified input

[ShoyuVanilla]

rust-lang/chalk#816

[ChayimFriedman2]

Works now.