sds / overcommit / 27295850158

92%

master: 91%

push

github

Make hook context input reads thread-safe (#882)

## Summary

This fixes a small race in `HookContext::Base#input_string`.

Hook contexts currently cache stdin lazily with `@input_string ||=
@input.read`. Since hooks are parallelized by default, two hooks sharing
the same context can race during that first read. For hook types that
receive real data on stdin, such as `pre-push`, one hook can consume the
stream while another reads EOF and caches an empty string.

If that happens, helpers like `pushed_refs` can silently see no refs
even though Git did provide them.

## Changes

- Add a mutex around the first `input_string` read so the stream is
consumed once.
- Keep the cached string shared by all callers after the initial read.
- Add a spec that forces a concurrent read attempt without relying on
flaky timing.

This follows up on #881.

## Verification

Focused checks pass locally:

```sh
bundle exec rspec spec/overcommit/hook_context/base_spec.rb
bundle exec rubocop lib/overcommit/hook_context/base.rb spec/overcommit/hook_context/base_spec.rb
bundle exec overcommit --run
```

I also ran the full spec suite. It still has a few unrelated failures
around git alias amendment detection on my machine, but this change's
focused spec passes.

5 of 5 new or added lines in 1 file covered. (100.0%)

3278 of 3578 relevant lines covered (91.62%)

3025.45 hits per line