Fix silent get_sources failure caused by SIGPIPE in git version check

speedrequested to merge
gitlab-community/gitlab-org/gitlab-runner:fix-sigpipe-in-if-git-version-is-at-least into main

What does this MR do?

Replaces head -n1 with sed -n '1p' in IfGitVersionIsAtLeast (shells/bash.go) to prevent SIGPIPE from silently aborting the get_sources script.

The IfGitVersionIsAtLeast function uses a sort ... | head -n1 pipeline to compare git versions. head -n1 closes the pipe after reading the first line, so sort receives SIGPIPE (exit code 141) when writing the second line. Under set -o pipefail + set -o errexit (enabled in the generated script), this SIGPIPE silently aborts the entire get_sources script:

  • The clone/fetch commands after the version check never execute.
  • The project directory is never created.
  • The next stage fails with No such file or directory.
  • The job fails with exit code 1 and no error output indicating the root cause.

This is intermittent (depends on kernel scheduling timing), so retries usually succeed. It is triggered when FF_USE_GIT_NATIVE_CLONE=true + GIT_STRATEGY=clone.

Replacing head -n1 with sed -n '1p' fixes this: sed reads all input without closing the pipe early, so sort never receives SIGPIPE and the exit code is 0. Single-line change.

Why was this MR needed?

CI jobs intermittently fail silently in the get_sources stage with exit code 1 and no error output, only when FF_USE_GIT_NATIVE_CLONE=true + GIT_STRATEGY=clone. The root cause is a SIGPIPE in the git version-check pipeline that, combined with pipefail + errexit + the : | eval wrapper, aborts the script without any error message. See #39680 (closed) for full root-cause analysis, reproduction steps, and evidence.

The head -n1 pipeline in IfGitVersionIsAtLeast has never been modified — the current main branch (shells/bash.go:304) still contains it, so all gitlab-runner versions are affected.

What's the best way to test this MR?

Unit test: Test_BashWriter_IfGitVersionIsAtLeast in shells/bash_test.go verifies the generated script uses sed -n '1p' instead of head -n1.

go test ./shells/ -run Test_BashWriter_IfGitVersionIsAtLeast -v

Reproduction: see the "Steps to reproduce" section in #39680 (closed). A minimal shell script reproduces the SIGPIPE trigger and verifies the fix:

  • Original (head -n1): 49 out of 50 iterations failed (exit code normalized to 1).
  • Fixed (sed -n '1p'): all 50 iterations succeeded.

What are the relevant issue numbers?

Closes #39680 (closed)

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