The compiler fails to see recursion bug

Code

use core::fmt::{self, Display, Formatter};

enum E {
    A,
    B,
}

impl Display for E {

    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        match self {
            Self::A => write!(f, "A"),
            other => other.fmt(f),
        }
    }

}

fn main() {
    println!("{}", E::A);
    println!("{}", E::B);
}

Current output

No warning

Desired output

No response

Rationale and extra context

The compiler fails to see the recursion bug in Display implementation of E, at branch other => other.fmt(f),

When you run it, only E::A is printed out. The program recurses when it tries to print E::B.

Other cases

Rust Version

rustc 1.98.0-nightly (3daae5e42 2026-06-14)
binary: rustc
commit-hash: 3daae5e42ec9ba435212987331af1b7b8634fa90
commit-date: 2026-06-14
host: x86_64-unknown-linux-gnu
release: 1.98.0-nightly
LLVM version: 22.1.6

Anything else?

No response

Start by compiling the Rust reproducer with rustc 1.98.0-nightly and tracing how the compiler handles the recursive other.fmt(f) call in the Display implementation. Determine the intended diagnostic for this recursion and add or update the relevant compiler test once the responsible subsystem is identified.