Hang in trait resolution with recursive blanket impl for slices

This issue was discovered by a fuzzer that generates code by adding a trait bound（T: Set）. The compiler hangs indefinitely (consuming high CPU) when compiling the following code.

I tried this code:

trait Set<T> {
    fn contains(&self, _: T) -> bool;
    fn set(&mut self, _: T);
}
impl<'a, T: Set, S> Set<&'a [T]> for S
where
    T: Copy,
    S: Set<T>,
{
    fn contains(&self, bits: &[T]) -> bool {
        bits.iter().all(|&bit| self.contains(bit))
    }
    fn set(&mut self, bits: &[T]) {
        for &bit in bits {
            self.set(bit)
        }
    }
}
fn main() {
    let bits: &[_] = &[0, 1];
    0.contains(bits);
}

I expected to see this happen: The compiler should terminate. It should emit a compilation error

Instead, this happened: The rustc process hangs indefinitely, consuming high CPU.

Meta

rustc --version --verbose:

rustc 1.94.0-nightly (e29fcf45e 2026-01-04)
binary: rustc
commit-hash: e29fcf45e4ae686d77b490bf07320f0d3a2cf35f
commit-date: 2026-01-04
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.8

Compiler hang

Start by compiling the provided recursive blanket-impl example with the reported nightly rustc version and confirm that trait resolution hangs. Investigate the compiler's trait-resolution handling for this case, then add coverage that ensures compilation terminates with an error rather than consuming high CPU.