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Fix backport bot failing with 'fatal: bad object' on squash merges #2907

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Fix backport bot failing with 'fatal: bad object' on squash merges #2907

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65 changes: 53 additions & 12 deletions .github/scripts/backport.js
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Original file line number Diff line number Diff line change
Expand Up @@ -43,13 +43,52 @@ if (commits.length === 0) {
}

core.info(`Backporting PR #${prNumber}: "${prTitle}"`);
core.info(`Commits to cherry-pick: ${commits.length}`);
commits.forEach((commit, index) => {
core.info(` ${index + 1}. ${commit.sha.substring(0, 7)} - ${commit.commit.message.split('\n')[0]}`);
});

const { execSync } = require('child_process');

// A squash or rebase merge rewrites the head commits listCommits returns, and GitHub
// deletes the head branch, so cherry-pick what actually landed on the base branch.
const baseRef = pullRequest.base.ref;
const mergeSha = pullRequest.merge_commit_sha;
execSync(`git fetch origin +refs/heads/${baseRef}:refs/remotes/origin/${baseRef}`, { stdio: 'inherit' });

// Exit 1 = not an ancestor, 128 = not in the clone; both mean unusable.
const isOnBase = (sha) => {
try {
execSync(`git merge-base --is-ancestor ${sha} refs/remotes/origin/${baseRef}`, { stdio: 'pipe' });
return true;
} catch (e) {
return false;
}
};

let picks = commits.map(c => ({ sha: c.sha, subject: c.commit.message.split('\n')[0] }));
let pickError = null;

if (!picks.every(p => isOnBase(p.sha))) {
if (!mergeSha || !isOnBase(mergeSha)) {
pickError = `PR #${prNumber} is not on \`${baseRef}\`, and neither is merge_commit_sha \`${mergeSha || 'none'}\`. Please cherry-pick manually.`;
} else {
// A rebase replays every commit and preserves subjects, leaving merge_commit_sha as
// the tip of the range. A squash lands one commit, whose subject differs.
const landed = execSync(`git log --format='%H %s' -n ${picks.length} ${mergeSha}`, { encoding: 'utf-8' })
.trim().split('\n').reverse()
.map(l => ({ sha: l.split(' ')[0], subject: l.slice(l.indexOf(' ') + 1) }));
const matched = landed.filter(c => picks.some(p => p.subject === c.subject)).length;
if (matched && matched !== picks.length) {
pickError = `PR #${prNumber} looks rebase-merged, but only ${matched} of its ${picks.length} commits are on \`${baseRef}\`. Please cherry-pick manually.`;
} else {
picks = matched ? landed : [landed[landed.length - 1]];
core.info(`PR was ${matched ? 'rebase' : 'squash'}-merged - cherry-picking from ${baseRef}`);
}
}
}

core.info(`Commits to cherry-pick: ${picks.length}`);
picks.forEach((pick, index) => {
core.info(` ${index + 1}. ${pick.sha.substring(0, 7)} - ${pick.subject}`);
});

const results = [];

for (const targetBranch of branches) {
Expand All @@ -58,17 +97,19 @@ for (const targetBranch of branches) {
core.info(`========================================`);
const backportBranch = `backport-${prNumber}-to-${targetBranch}`;
try {
if (pickError) {
throw new Error(pickError);
}
// Create/reset backport branch from target release branch
core.info(`Creating/resetting branch ${backportBranch} from ${targetBranch}`);
execSync(`git fetch origin ${targetBranch}:${targetBranch}`, { stdio: 'inherit' });
execSync(`git checkout -B ${backportBranch} ${targetBranch}`, { stdio: 'inherit' });
// Cherry-pick each commit from the PR
let hasConflicts = false;
for (let i = 0; i < commits.length; i++) {
const commit = commits[i];
const commitSha = commit.sha;
const commitMessage = commit.commit.message.split('\n')[0];
core.info(`Cherry-picking commit ${i + 1}/${commits.length}: ${commitSha.substring(0, 7)} - ${commitMessage}`);
for (let i = 0; i < picks.length; i++) {
const commitSha = picks[i].sha;
const commitMessage = picks[i].subject;
core.info(`Cherry-picking commit ${i + 1}/${picks.length}: ${commitSha.substring(0, 7)} - ${commitMessage}`);
try {
execSync(`git cherry-pick -m 1 -x ${commitSha}`, {
encoding: 'utf-8',
Expand Down Expand Up @@ -112,7 +153,7 @@ for (const targetBranch of branches) {
const existingPR = existingPRs.length > 0 ? existingPRs[0] : null;

// Create pull request
const commitList = commits.map(c => `- \`${c.sha.substring(0, 7)}\` ${c.commit.message.split('\n')[0]}`).join('\n');
const commitList = picks.map(p => `- \`${p.sha.substring(0, 7)}\` ${p.subject}`).join('\n');

// Build PR body based on conflict status
let prBody = `🤖 **Automated backport of #${prNumber} to \`${targetBranch}\`**\n\n`;
Expand All @@ -123,7 +164,7 @@ for (const targetBranch of branches) {
Original PR: #${prNumber}
Original Author: @${prAuthor}

**Cherry-picked commits (${commits.length}):**
**Cherry-picked commits (${picks.length}):**
${commitList}

**Next Steps:**
Expand Down Expand Up @@ -151,7 +192,7 @@ git push --force-with-lease origin ${backportBranch}
Original PR: #${prNumber}
Original Author: @${prAuthor}

**Cherry-picked commits (${commits.length}):**
**Cherry-picked commits (${picks.length}):**
${commitList}

This backport was automatically created by the backport bot.`;
Expand Down
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