Thread names have gone missing in stack overflow messages in Rust v1.89 (currently in beta). Reproduces on both Darwin and Linux.

I haven't bisected, but the culprit is almost certainly #140628. Nothing else has touched the stack overflow code path since Rust v1.88. cc @joboet @workingjubilee @RalfJung @Mark-Simulacrum as the reviewers of #140628.

Code

I tried this code:

fn main() {
    f()
}

fn f() {
    f();
}

I expected to see the thread name (main) included in the error message:

thread 'main' has overflowed its stack
fatal runtime error: stack overflow, aborting
Aborted

Instead, the thread is listed as <unknown>:

thread '<unknown>' has overflowed its stack
fatal runtime error: stack overflow, aborting
Aborted

Version it worked on

Works on the latest stable Rust (v1.88.0).

Version with regression

Broken in v1.89.0-beta.7. Tested on both Darwin and Linux.

rustc 1.89.0-beta.7 (4229c2e70 2025-07-25)
binary: rustc
commit-hash: 4229c2e708ce796c71747b7fa177ff4ef9aa794c
commit-date: 2025-07-25
host: aarch64-apple-darwin
release: 1.89.0-beta.7
LLVM version: 20.1.7

rustc 1.89.0-beta.7 (4229c2e70 2025-07-25)
binary: rustc
commit-hash: 4229c2e708ce796c71747b7fa177ff4ef9aa794c
commit-date: 2025-07-25
host: x86_64-unknown-linux-gnu
release: 1.89.0-beta.7
LLVM version: 20.1.7

@rustbot modify labels: +regression-from-stable-to-beta -regression-untriaged