Contradictory error message: trait is simultaneously implemented and not

[Kyuuhachi]

The following code gives somewhat contradictory error message:

trait A {}
struct B;

impl A for B where B: A {}
impl A for B where B: A {}

fn main() {
    let a: &dyn A = &B;
}

error[E0277]: the trait bound `B: A` is not satisfied
 --> src/lib.rs:4:20
  |
4 | impl A for B where B: A {}
  |                    ^^^^ the trait `A` is not implemented for `B`
  |
  = help: the trait `A` is implemented for `B`
  = help: see issue #48214

^^^^ the trait `A` is not implemented for `B`
help: the trait `A` is implemented for `B`

???

Including only one of the impl lines produces a more reasonable overflow evaluating the requirement `B: A` instead.

This happens both on stable 1.65.0, beta 1.66.0-beta.2 (2022-11-20 004070), and nightly 1.67.0-nightly (2022-11-28 2585bc).

Nightly suggests adding #![feature(trivial_bounds)], but the contradictory error message still exists with that (however pointed at the dyn rather than the impls).

[Kyuuhachi]

Sorry, this should be tagged diagnostic, not bug. Don't know how to change that.

[lukas-code]

@rustbot label -C-bug +A-diagnostics +A-traits +T-compiler +D-confusing