Adding where clause already filled relax traits bounds in impl

[supersurviveur]

I tried this code:

trait Foo {
    type B;
}

struct A<T> {
    a: T
}

trait Bar<T> {
    fn bar(a: <A<T> as Foo>::B) {}
}

impl<T> Bar<T> for T
where
    A<T>: Foo
{
    fn bar(a: u32) {}
}

impl<T> Foo for A<T> {
    type B = u32;
}

I expected it to compile, but instead I get the error

error[E0053]: method `bar` has an incompatible type for trait
  --> src/main.rs:17:15
   |
17 |     fn bar(a: u32) {}
   |               ^^^ expected associated type, found `u32`
   |
note: type in trait
  --> src/main.rs:10:15
   |
10 |     fn bar(a: <A<T> as Foo>::B) {}
   |               ^^^^^^^^^^^^^^^^
   = note: expected signature `fn(<A<T> as Foo>::B)`
              found signature `fn(u32)`
help: change the parameter type to match the trait
   |
17 -     fn bar(a: u32) {}
17 +     fn bar(a: <A<T> as Foo>::B) {}

The error disappears when I remove the where clause in Bar implementation.
I expected both code to compile since the where clause should only add trait bounds, and A<T>::B is u32 in both cases.

rustc --version --verbose:

rustc 1.89.0-nightly (ce7e97f73 2025-05-11)
binary: rustc
commit-hash: ce7e97f7371af47e0786f74aa169f6ac9473ff4e
commit-date: 2025-05-11
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.4