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Copilotmrjf
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Fast-forward autoloop branches when ahead=0 instead of merging
Agent-Logs-Url: https://github.com/githubnext/tsessebe/sessions/fd8b9575-c039-4e3a-ad47-adf60b149480 Co-authored-by: mrjf <180956+mrjf@users.noreply.github.com>
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Lines changed: 91 additions & 6 deletions

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‎.github/workflows/autoloop.md‎

Lines changed: 28 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -378,11 +378,35 @@ Each run executes **one iteration for the single selected program**:
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- Program `build-tsb-pandas-typescript-migration` → branch `autoloop/build-tsb-pandas-typescript-migration`
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```bash
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git fetch origin
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git fetch origin main
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if git ls-remote --exit-code origin autoloop/{program-name}; then
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# Branch exists — check it out and merge the default branch
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git checkout -b autoloop/{program-name} origin/autoloop/{program-name}
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git merge origin/main --no-edit -m "Merge main into autoloop/{program-name}"
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# Branch exists — fetch it too so the ahead/behind counts below are
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# computed against up-to-date local copies of the remote tips.
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git fetch origin autoloop/{program-name}
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ahead=$(git rev-list --count origin/main..origin/autoloop/{program-name})
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behind=$(git rev-list --count origin/autoloop/{program-name}..origin/main)
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if [ "$ahead" = "0" ] && [ "$behind" != "0" ]; then
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# All of the branch's commits are already in main (typical case after a
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# successful merge of the previous iteration's PR). A merge here would
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# produce a noisy "Merge main into branch" commit that re-exposes every
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# historical file as a patch touch — the failure mode that triggers
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# gh-aw's E003 (>100 files) when a new PR is opened. Fast-forward the
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# canonical branch to main instead. This is lossless because ahead=0
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# proves every commit on the branch is already reachable from main.
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git checkout -B autoloop/{program-name} origin/main
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git push --force-with-lease origin autoloop/{program-name}
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elif [ "$ahead" != "0" ] && [ "$behind" != "0" ]; then
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# True divergence: branch has unique commits AND main has moved on.
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# Merge main into the branch so the iteration builds on the latest code.
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git checkout -B autoloop/{program-name} origin/autoloop/{program-name}
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git merge origin/main --no-edit -m "Merge main into autoloop/{program-name}"
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else
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# Already at main (ahead=0, behind=0) or only ahead of main (ahead>0,
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# behind=0). Nothing to merge — just check out the branch.
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git checkout -B autoloop/{program-name} origin/autoloop/{program-name}
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fi
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else
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# Branch does not exist — create it from the default branch
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git checkout -b autoloop/{program-name} origin/main

‎.github/workflows/sync-branches.lock.yml‎

Lines changed: 1 addition & 1 deletion
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‎.github/workflows/sync-branches.md‎

Lines changed: 62 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -82,7 +82,68 @@ steps:
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failed.append(branch)
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continue
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# Merge the default branch into the program branch
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# Determine whether the branch can be fast-forwarded to the default
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# branch (ahead=0) or has truly diverged and needs a merge.
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ahead_proc = subprocess.run(
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["git", "rev-list", "--count", f"origin/{default_branch}..origin/{branch}"],
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capture_output=True, text=True,
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)
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behind_proc = subprocess.run(
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["git", "rev-list", "--count", f"origin/{branch}..origin/{default_branch}"],
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capture_output=True, text=True,
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)
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if ahead_proc.returncode != 0 or behind_proc.returncode != 0:
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# Don't guess — a failed rev-list with empty stdout would
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# otherwise be parsed as 0 below and could trigger an
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# incorrect fast-forward that loses commits.
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print(f" Failed to compute ahead/behind for {branch}: "
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f"ahead.rc={ahead_proc.returncode} stderr={ahead_proc.stderr.strip()!r} "
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f"behind.rc={behind_proc.returncode} stderr={behind_proc.stderr.strip()!r}")
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failed.append(branch)
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continue
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try:
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ahead = int(ahead_proc.stdout.strip())
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behind = int(behind_proc.stdout.strip())
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except ValueError:
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print(f" Failed to parse ahead/behind counts for {branch}: "
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f"ahead={ahead_proc.stdout!r} behind={behind_proc.stdout!r}")
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failed.append(branch)
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continue
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if behind == 0:
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# Branch already contains every commit on the default branch.
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print(f" {branch} is already up to date with {default_branch} (ahead={ahead}, behind=0)")
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continue
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if ahead == 0:
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# Lossless fast-forward: every commit on the branch is already
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# reachable from the default branch (typical case once the
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# previous iteration's PR has been merged). A real merge here
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# would create a "Merge default into branch" commit that re-
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# exposes every historical file as a patch touch — the noise
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# that trips gh-aw's MAX_FILES limit when the next iteration
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# opens a new PR. Reset the branch to the default branch's HEAD
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# and force-push (with lease) instead.
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reset = subprocess.run(
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["git", "reset", "--hard", f"origin/{default_branch}"],
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capture_output=True, text=True,
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)
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if reset.returncode != 0:
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print(f" Failed to fast-forward {branch}: {reset.stderr}")
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failed.append(branch)
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continue
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push = subprocess.run(
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["git", "push", "--force-with-lease", "origin", branch],
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capture_output=True, text=True,
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)
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if push.returncode != 0:
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print(f" Failed to push fast-forward of {branch}: {push.stderr}")
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failed.append(branch)
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continue
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print(f" Fast-forwarded {branch} to {default_branch} (was behind by {behind})")
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continue
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# True divergence (ahead>0 and behind>0): merge the default branch in.
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merge = subprocess.run(
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["git", "merge", f"origin/{default_branch}", "--no-edit",
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"-m", f"Merge {default_branch} into {branch}"],

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