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ci(promote): make promotion idempotent and immutable-safe #3

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GeekTrainer merged 2 commits into from
Aug 26, 2026
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ci(promote): make promotion idempotent and immutable-safe #3

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ci(promote): make promotion idempotent and immutable-safe
GeekTrainer Aug 26, 2026
2545213
ci(promote): fail fast on fetch errors instead of swallowing them
GeekTrainer Aug 26, 2026
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36 changes: 30 additions & 6 deletions .github/workflows/promote-branches.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,10 @@ jobs:
FROM: ${{ github.event.inputs.from_module }}
run: |
set -euo pipefail
# Make current remote alias tips available so we only move a learner branch when
# its content actually changed -- avoids gratuitously rewriting unchanged public
# start-of-module-* branches to new commit shas on every promotion.
git fetch --no-tags origin "refs/heads/start-of-module-*:refs/remotes/origin/start-of-module-*" || true
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REFSPECS=()
for start in $(node -e "console.log(JSON.parse(process.env.BRANCHES).join(' '))"); do
# start = start-of-module-NN ; module = NN-1
Expand All @@ -92,23 +96,43 @@ jobs:
fi
staged="regen/${DID}/${start}"
sha="$(git rev-parse "$staged")"
# Mutable alias (force — it moves) + immutable version tag (must NOT already exist).
staged_tree="$(git rev-parse "${staged}^{tree}")"

# Mutable alias: move it only when the built content differs from what the branch
# already points at (or the branch does not exist yet). Force, because promotion
# rebuilds commits (new commit shas even for identical trees).
cur_tree="$(git rev-parse --verify --quiet "refs/remotes/origin/${start}^{tree}" 2>/dev/null || true)"
if [ "$cur_tree" != "$staged_tree" ]; then
REFSPECS+=("+${sha}:refs/heads/${start}")
echo "alias ${start}: content changed -> ${staged_tree:0:12} (move)"
else
echo "alias ${start}: unchanged (${staged_tree:0:12}); leaving in place."
fi

# Immutable version tag: cut exactly once. Never overwrite an existing tag (that
# is what "immutable" means); skip it so re-running promotion is idempotent
# instead of aborting the whole job.
tag="acc-${VERSION}/${start}"
if git rev-parse --verify --quiet "refs/tags/${tag}" >/dev/null; then
echo "ERROR: immutable tag ${tag} already exists; refusing to overwrite." >&2
exit 1
echo "tag ${tag}: already exists; leaving unchanged."
else
REFSPECS+=("${sha}:refs/tags/${tag}")
echo "tag ${tag}: creating at ${sha:0:12}."
fi
REFSPECS+=("+${sha}:refs/heads/${start}")
REFSPECS+=("${sha}:refs/tags/${tag}")
done
if [ "${#REFSPECS[@]}" -eq 0 ]; then
echo "No refs to promote." >&2; exit 1
echo "Nothing to promote: all aliases current and all version tags present."
echo "changed=false" >> "$GITHUB_OUTPUT"
: > /tmp/refspecs.txt
exit 0
fi
echo "changed=true" >> "$GITHUB_OUTPUT"
printf '%s\n' "${REFSPECS[@]}"
# persist for next step
printf '%s\n' "${REFSPECS[@]}" > /tmp/refspecs.txt

- name: Atomic push (all aliases + tags, or nothing)
if: steps.refs.outputs.changed == 'true'
run: |
set -euo pipefail
mapfile -t REFSPECS < /tmp/refspecs.txt
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