Add SC2337: warn about grep early exit in pipelines under pipefail

[mclasmeier]

Adds a new linter rule about using grep -q in combination with set -o pipefail

When set -o pipefail is active and grep -q (or --quiet) appears as a non-first command in a pipeline, the upstream command may receive SIGPIPE because grep -q exits immediately upon finding a match. This causes the pipeline to report a non-zero exit status under pipefail.

The check covers grep, egrep, and fgrep variants. It does not warn when grep -q reads from a file directly or is the first command in the pipeline.

Please note, my Haskell skills have become a bit rusty -- did this together with Claude.
Is there anything missing for this contribution?

[e-kwsm]

This gives false positive to

grep -e -q  # search "-q"

Also, there are other cases where SIGPIPE is sent:

• grep -m 𝑛 -e 𝑝𝑎𝑡
• head
• sed’s quit e.g. sed -n -e '/𝑝𝑎𝑡/{p;q;}'
• nawk’s exit e.g. nawk '$0 ~ /𝑝𝑎𝑡/ { print; exit; }'

[mclasmeier]

@e-kwsm Hi, thanks for the review.
Regarding the other cases (head, sed, etc.), I would consider this out of scope for this PR?
Are you generally positive about this contribution, once false positives are addressed?

[mclasmeier]

@e-kwsm I have pushed a commit addressing the false positives by using getOpts instead.

[e-kwsm]

The following non-POSIX options are not covered:

• grep -m 𝑛 -e pat (GNU and BSD)
• grep -L -e pat (GNU sends SIGPIPE, while BSD does not)

[e-kwsm]

Regarding the other cases (head, sed, etc.), I would consider this out of scope for this PR?

So SC2337 covers grep only, and SC2338? should deal with head?

[mclasmeier]

@e-kwsm Updated to also detect grep -m n and grep -L.
Indeed, I would leave other tools such as head, for other PRs.

[e-kwsm]

This will fix #665.