Conflicting implementations with unresolved associated types

Code

trait A {
    type B: A<B = Self::B>;
}
struct C;
trait X<T> { }
impl<T: A<B = T>> X<T> for C { }

struct D<T>(T);
impl<T: A<B = T>> A for D<T> {
    //type B = T; // tastcase 1: this is fine
    type B = T::B; // testcase 2: this causes an error even though it's the same!
}
impl<T: A<B = T>> X<D<T>> for C { }

Current output

error[E0119]: conflicting implementations of trait `X<D<_>>` for type `C`
  --> src/main.rs:13:1
   |
 6 | impl<T: A<B = T>> X<T> for C { }
   | ---------------------------- first implementation here
...
13 | impl<T: A<B = T>> X<D<T>> for C { }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `C`

For more information about this error, try `rustc --explain E0119`.

Desired output

warn[E....]: using an indirect reference to a fixed associated type
  --> src/main.rs:11:13
   |
   |     type B = T::B; // testcase 2: this causes an error even though it's the same!
   |              ^^^^
note: the associated type is fixed here
 --> src/main.rs:9:10
  |
9 | impl<T: A<B = T>> A for D<T> {
  |           ^^^^^
note: consider using the value of the associated type directly
 --> src/main.rs:11:13
   |
11 |     type B = T; // testcase 2: this causes an error even though it's the same!
   |              +
error[E0119]: conflicting implementations of trait `X<D<_>>` for type `C`
  --> src/main.rs:13:1
   |
 6 | impl<T: A<B = T>> X<T> for C { }
   | ---------------------------- first implementation here
...
13 | impl<T: A<B = T>> X<D<T>> for C { }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `C`

For more information about this error, try `rustc --explain E0119`.

Rationale and extra context

I expected both testcases 1, 2 to work fine, as it's trivial for the rustcompiler to look up what T::B is in this case, however instead it required me to explicitly specify T. This would not have been a problem, if the compiler would have told me, that that is the problem. Instead the compiler tells me that there is conflicting implementations. I would therefore expect to either have both cases working (which doesn't add any real functionallity afaict) or have a compiler warning, which tells me that I specified a type which is known, but can not be automatically resolved (which would probably make my code cleaner in this case).

Other cases

Rust Version

rustc 1.91.0-nightly (a1208bf76 2025-09-03)
binary: rustc
commit-hash: a1208bf765ba783ee4ebdc4c29ab0a0c215806ef
commit-date: 2025-09-03
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.0

Anything else?

No response

Reproduce the example in src/main.rs with the reported rustc 1.91.0-nightly version, comparing the two associated-type implementations and the resulting E0119 diagnostic. Trace the compiler's handling of the fixed associated type; done when the valid case is accepted or the diagnostic clearly explains the unresolved indirect reference.