should_panic in doctests accepts crashes, aborts, std::process::exit

I tried this code:

/// ```should_panic
/// std::process::exit(1);
/// ```
fn f() {}

cargo test

I expected to see this happen: test fails.

Instead, this happened: test passes.

This also applies to explicit aborts, the process being killed by a signal, Miri aborting execution due to UB, etc. I've just found UB in my doctest that was accidentally hidden by this, and I only stumbled upon it because

WARNING: No rustdoc doctest environment variable provided so doctests will be run in the same process

happened when running under cross and apparently that affects how should_panic works.

This applies to both separate doctest binaries and edition 2024-style merged doctests.

Meta

rustc --version --verbose:

rustc 1.90.0-nightly (28f1c8079 2025-06-24)
binary: rustc
commit-hash: 28f1c807911c63f08d98e7b468cfcf15a441e34b
commit-date: 2025-06-24
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.7

@rustbot label +A-doctests +T-rustdoc

Use the reproducer in the issue as the entry point: run cargo test with the should_panic doctest containing std::process::exit(1), then compare the separate and merged doctest cases described in the report. Trace rustdoc's doctest handling; done means crashes, aborts, signals, and Miri UB are not accepted as should_panic successes while ordinary panics retain the expected behavior.