Fails to backport clean cherry-picks

[silverwind]

go-gitea/gitea#27503 is a clean cherry-pick against both 1.21 and 1.20, but the bot failed for unknown reasons. Here's how I do it, maybe the bot tries it differently?

git checkout release/v1.21
git reset --hard origin/release/v1.21
git checkout -b backport-27503-21
git cherry-pick 08efeb5
git push silverwind backport-27503-21

[yardenshoham]

Logs:

2023-10-08T03:13:30.426 app[148ed433fe9d08] ams [info] Synced PR #27503
2023-10-08T03:13:35.518 app[148ed433fe9d08] ams [info] Set commit status in "Fix mermaid flowchart margin issue" (#27503)
2023-10-08T03:20:16.010 app[148ed433fe9d08] ams [info] Parsing #27503
2023-10-08T03:20:16.125 app[148ed433fe9d08] ams [info] Locked issue #25798
2023-10-08T03:20:16.389 app[148ed433fe9d08] ams [info] Set milestone 1.22 for PR #27503
2023-10-08T03:20:16.575 app[148ed433fe9d08] ams [info] Cherry-picking #27503
2023-10-08T03:20:17.338 app[148ed433fe9d08] ams [info] Added comment to #27503
2023-10-08T03:20:18.328 app[148ed433fe9d08] ams [info] Parsing #27503
2023-10-08T03:20:18.760 app[148ed433fe9d08] ams [info] Cherry-picking #27503
2023-10-08T03:20:19.645 app[148ed433fe9d08] ams [info] Added comment to #27503
2023-10-08T03:20:28.105 app[148ed433fe9d08] ams [info] Removed reviewed/wait-merge from "Fix mermaid flowchart margin issue" (#27503)

[silverwind]

Is it using ./contrib/backport? When I try that, it fails:

$ go run ./contrib/backport --version v1.21 --no-push 27503
* Backporting 27503 to origin/release/v1.21 as backport-27503-v1.21
* `git fetch origin main`

* `git fetch origin release/v1.21`

* Current branch is main
* Branch backport-27503-v1.21 already exists. Checking it out...
* Attempting git cherry-pick 08efeb5cdc22d21b5ef12cc540727594a22062d1
git cherry-pick 08efeb5cdc22d21b5ef12cc540727594a22062d1 failed:
On branch backport-27503-v1.21
Your branch and 'origin/release/v1.21' have diverged,
and have 137 and 73 different commits each, respectively.

You are currently cherry-picking commit 08efeb5cdc.
  (all conflicts fixed: run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

nothing to commit (use -u to show untracked files)

Unable to backport: git cherry-pick 08efeb5cdc22d21b5ef12cc540727594a22062d1 failed: exit status 1

I've now made a simple bash script that works, but it also does not amend either:

backport() {
  if [ $# -eq 0 ]; then; echo "backport PR VER"; return 1; fi
  PR="$1"
  VER="$2"

  git checkout "release/v$VER"
  git reset --hard "origin/release/v$VER"
  git branch -D "backport-$PR-$VER"
  git checkout -b "backport-$PR-$VER"
  HASH="$(curl -sH "X-GitHub-Api-Version: 2022-11-28" "https://api.github.com/repos/go-gitea/gitea/pulls/$PR" | jq -r .merge_commit_sha)"
  git cherry-pick "$HASH"
}

[silverwind]

go-gitea/gitea#27501 was also clean cherry-pick which I backported with this bash script now.

[silverwind]

Contributed the script in go-gitea/gitea#27519.

[yardenshoham]

How it backports

gitea-backporter/src/git.ts

Lines 44 to 92 in aab91a4

	export const cherryPickPr = async (
	commitHash: string,
	prNumber: number,
	giteaMajorMinorVersion: string,
	): Promise<boolean> => {
	// fetch the upstream main branch
	await cmd.run("git", {
	cwd: "gitea",
	args: ["fetch", "upstream", "main"],
	});
	// fetch the upstream release branch
	await cmd.run("git", {
	cwd: "gitea",
	args: ["fetch", "upstream", `release/v${giteaMajorMinorVersion}`],
	});
	// create the backport branch from the upstream release branch
	await cmd.run("git", {
	cwd: "gitea",
	args: [
	"checkout",
	`upstream/release/v${giteaMajorMinorVersion}`,
	"-b",
	getPrBranchName(prNumber, giteaMajorMinorVersion),
	],
	});
	// cherry-pick the PR
	const cherryPickStatus = await cmd.run("git", {
	cwd: "gitea",
	args: ["cherry-pick", commitHash],
	});
	if (!cherryPickStatus.success) {
	await cmd.run("git", {
	cwd: "gitea",
	args: ["cherry-pick", "--abort"],
	});
	return false;
	}
	// push the branch to the fork
	await cmd.run("git", {
	cwd: "gitea",
	args: ["push", "origin", getPrBranchName(prNumber, giteaMajorMinorVersion)],
	});
	return true;
	};

[silverwind]

Why does the log not show any error?

[silverwind]

Maybe this if branch should log or throw the error?

gitea-backporter/src/git.ts

Lines 78 to 84 in aab91a4

	if (!cherryPickStatus.success) {
	await cmd.run("git", {
	cwd: "gitea",
	args: ["cherry-pick", "--abort"],
	});
	return false;
	}

I would make it throw an error on any command failure, much better than returning false and not knowing why it failed.

[silverwind]

Overall I think the bot should make use of https://github.com/go-gitea/gitea/tree/main/contrib/backport, so that the backporting mechanism can be tested locally in the repo as well. Likely that script needs a few adjustments as mention in the PR.

Edit: go-gitea/gitea#27520 will make that script much less error-prone.

[silverwind]

After go-gitea/gitea#27520, we could make the backporter use this script to cherry-pick. Imho, is is much better to having something that can be ran and debugged locally and we will only have one way to apply backports instead of two.

[silverwind]

go-gitea/gitea#27752 likely another case of a 1-line change not being backported.

[silverwind]

Another case: go-gitea/gitea#29106 (comment)

This is what I did locally and it worked fine:

git checkout release/v1.21
git reset --hard origin/release/v1.21
git checkout -b backport-29106-29111
git cherry-pick 9c39f85
git cherry-pick c7a21cb
git push silverwind backport-29106-29111

Maybe we could add some debug info in a <details> block in the bot comment to show what it did and where it failed to get to the root of this problem.

[yardenshoham]

Sure, send a PR, I will review it

[silverwind]

I think the bot currently can not successfully do any backport onto release/v1.21. I assume once we cut release/v1.22 it will be able to again for unknown reason. I think I've seen this pattern already in the last two releases. At some point in the target branch history, it just can't do it anymore.