Max Gekk created SPARK-57488:
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Summary: checkout-pr.sh review helper aborts with bash "unbound
variable" on the no-force checkout path under bash 3.2
Key: SPARK-57488
URL: https://issues.apache.org/jira/browse/SPARK-57488
Project: Spark
Issue Type: Bug
Components: Project Infra
Affects Versions: 5.0.0
Reporter: Max Gekk
h3. Summary
The {{checkout-pr.sh}} helper used by the spark-dev PR-review tooling aborts
with {{force_args[@]: unbound variable}} whenever it takes the no-force
checkout path. That path is *always* taken for self-PRs (and for any external
PR before a force is needed), so self-PR review is consistently broken on
macOS. The caller misreports the crash as a {{branch-diverged}} stop (exit 11),
so a clean branch that is already at the PR head looks as if it has diverged.
h3. Environment
* macOS, where {{/usr/bin/env bash}} resolves to {{/bin/bash}} = GNU bash
*3.2.57* (Apple's stock version).
* Triggered via the PR setup/checkout step of the review tooling.
h3. Steps to reproduce
# On macOS (bash 3.2), check out your own open PR locally so the branch is
already at the PR head.
# Run the review checkout step against that PR.
h3. Expected
Checkout is a no-op (branch already at head); setup exits 0 and proceeds.
h3. Actual
{noformat}
checkout-pr.sh: line 63: force_args[@]: unbound variable
branch-diverged: local branch <name> could not be fast-forwarded to the PR head
...
{noformat}
Setup exits 11 (branch-diverged), halting the review even though the working
tree is clean and HEAD exactly matches the PR head_sha.
h3. Root cause
The helper builds an optional force flag in an array:
{code:bash}
local force_args=()
[[ "$1" == "1" ]] && force_args=(-f)
gh pr checkout ... "${force_args[@]}"
{code}
Under {{set -euo pipefail}}, *bash 3.2 treats expansion of an empty array*
({{"${force_args[@]}"}}) *as an unbound variable* and aborts -- a bug fixed in
bash 4.4+. On the no-force path the array is empty, so the command never runs.
h3. Fix
Use the {{set -u}}-safe expansion idiom, which yields nothing when the array is
empty and the quoted elements otherwise:
{code:bash}
gh pr checkout "${PR_NUMBER}" -R "${OWNER}/${REPO}"
${force_args[@]+"${force_args[@]}"} 2>&1
{code}
h3. Test gap
The script's self-test stubs out the checkout function entirely, so it never
exercises the real argv assembly -- which is why this shipped green. A
regression test should stub the {{gh}} binary instead of the function so the
empty-array expansion runs under {{set -u}}.
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