feat: The BOT

.dockerignore

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+node_modules
+.env

.env.example

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+# GitHub App ID
+APP_ID=
+WEBHOOK_SECRET=CAFFCF94-2B07-4EBC-BEC8-646CBE46FBA5
+PRIVATE_KEY=
+PORT=8080
+LOG_LEVEL=debug

.gitignore

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+node_modules
+.env

Dockerfile

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+FROM livingdocs/node:12.0
+
+COPY package.json /app/
+RUN npm install --production && npm cache clean -f
+COPY . /app/
+ENV PORT 8080
+EXPOSE 8080
+CMD ["node", "/app/index.js"]

app.yml

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+default_events:
+- issue_comment
+- pull_request_review_comment
+
+default_permissions:
+  contents: write
+  issues: write
+  pull_requests: write

backport.js

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+const cherryPick = require('./cherry-pick')
+
+module.exports = async function (context, targetBase) {
+  const pr = await getPullRequest(context)
+  const reviewers = await getReviewers(context)
+  reviewers.push(pr.user.login)
+
+  const token = await getToken(context.payload.installation.id)
+  const targetBranch = await cherryPick(context, pr, targetBase, token)
+  const backport = await createPullRequest(context, pr, targetBase, targetBranch)
+  await requestReviewers(context, backport.data.number, reviewers)
+
+  return backport
+}
+
+// Obtain token to push to this repo
+let cached
+const githubAuth = require('github-app')({
+  id: process.env.APP_ID,
+  cert: process.env.PRIVATE_KEY ?
+    process.env.PRIVATE_KEY :
+    (process.env.PRIVATE_KEY_FILE && require('fs').readFileSync(process.env.PRIVATE_KEY_FILE))
+})
+
+async function getToken (installationId) {
+  if (cached && Date.parse(cached.expires_at) > (Date.now() + 1000 * 60)) return cached.token
+  const token = await githubAuth.createToken(installationId)
+  cached = token.data
+  return cached.token
+}
+
+async function createPullRequest (context, origPR, targetBase, targetBranch) {
+  return context.github.pullRequests.create(context.repo({
+    title: `${origPR.title} [${targetBase}] `,
+    head: targetBranch,
+    base: targetBase,
+    body: `Backport of #${origPR.number}\n\n${origPR.body}`
+  }))
+}
+
+async function getPullRequest (context) {
+  if (context.payload.pull_request) return context.payload.pull_request
+  const pullRequest = await context.github.pullRequests.get(context.issue())
+  return pullRequest.data
+}
+
+async function getReviewers (context) {
+  const reviewers = await context.github.pullRequests.listReviews(context.issue())
+  const rewiewRequests = await context.github.pullRequests.listReviewRequests(context.issue())
+  const reviewerIds = reviewers.data.map(reviewer => reviewer.user.login)
+  const reviewerRequestedIds = rewiewRequests.data.users.map(reviewer => reviewer.login)
+  return [...reviewerIds, ...reviewerRequestedIds]
+}
+
+async function requestReviewers (context, prId, reviewers) {
+  return context.github.pullRequests.createReviewRequest(context.repo({
+    number: prId,
+    reviewers: reviewers
+  }))
+}

cherry-pick.js

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+const path = require('path')
+const tmp = require('os').tmpdir()
+const fs = require('fs-extra')
+const execFile = require('util').promisify(require('child_process').execFile)
+
+function createGit (dir, context) {
+  function exec (file, args = [], options) {
+    context.log.debug(file, ...args)
+    return execFile(file, args, {cwd: dir, ...options})
+  }
+  function git (args, options) { return exec('/usr/bin/git', args, options) }
+  function child (subdir) { return createGit(path.join(dir, subdir), context) }
+  exec.git = git
+  exec.child = child
+  exec.exec = exec
+  exec.path = dir
+  return exec
+}
+
+async function getWorktree (slug, context, token) {
+  const dir = path.join(tmp, 'backport', slug)
+  const worktree = createGit(dir, context)
+  try {
+    await fs.stat(path.join(worktree.path, '.git'))
+  } catch (err) {
+    if (err.code !== 'ENOENT') throw err
+    await fs.mkdir(worktree.path, {recursive: true})
+    await worktree.git(['clone', '--bare', `https://x-access-token:${token}@github.com/${slug}.git`, '.git'])
+    await worktree.git(['update-ref', '--no-deref', 'HEAD', 'HEAD^{commit}'])
+    await fs.appendFile(path.join(worktree.path, '.git/config'), '        fetch = +refs/heads/*:refs/remotes/origin/*')
+
+    // Setup config
+    await worktree.git(['config', '--local', 'user.email', '[email protected]'])
+    await worktree.git(['config', '--local', 'user.name', 'Machine User'])
+    await worktree.git(['config', '--local', 'commit.gpgsign', 'false'])
+  }
+  return worktree
+}
+
+module.exports = async function (context, pr, targetBase, token) {
+  const slug = `${context.repo().owner}/${context.repo().repo}`
+  const worktree = await getWorktree(slug, context, token)
+  const targetBranch = 'backport/' + pr.number + '/' + targetBase
+  const targetDir = `${Date.now()}-${targetBranch}`
+  const branch = worktree.child(targetDir)
+
+  try {
+    // Fetch and create branch
+    await worktree.git(['fetch', 'origin', targetBase, pr.head.ref])
+    await worktree.git(['worktree', 'add', '-b', targetDir, targetDir, pr.head.ref])
+
+    // Rebase the branch onto the new base and push
+    await branch.git(['rebase', '--onto', targetBase, pr.base.sha])
+    await branch.git(['push', 'origin', `${targetDir}:${targetBranch}`])
+    return targetBranch
+  } catch (err) {
+    throw err
+  } finally {
+    try {
+      await worktree.git(['worktree', 'remove', '--force', targetDir])
+    } catch {}
+  }
+}

index.js

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+const {Probot} = require('probot')
+const backport = require('./backport')
+
+Probot.run(backportApp)
+
+async function backportApp (app) {
+  async function handler (context) {
+    const issue = context.payload.issue || context.payload.pull_request
+    const comment = context.payload.comment
+    if (!issue.html_url.endsWith(`pull/${issue.number}`)) return
+
+    const targetBranch = matchComment(comment.body)
+    if (!targetBranch) return
+
+    try {
+      await updateComment(context, `🕑 ${comment.body}`)
+      await backport(context, targetBranch)
+      await updateComment(context, `🎉 ${comment.body}`)
+    } catch (err) {
+      context.log.warn(`Backport to ${targetBranch} failed`, err)
+      return updateComment(context, [
+        `💥 ${comment.body}`,
+        '',
+        `The backport to ${targetBranch} failed.`,
+        `Please do this backport manually.`,
+        '```js',
+        err.stack,
+        '```'
+      ].join('\n'))
+    }
+  }
+
+  app.on('pull_request_review_comment.created', handler)
+  app.on('issue_comment.created', handler)
+}
+
+async function updateComment (context, body) {
+  const comment = context.payload.comment
+  const resource = comment.pull_request_review_id ? context.github.pulls : context.github.issues;
+  return resource.updateComment(context.issue({comment_id: comment.id, body}))
+}
+
+const commandRegexp = /^ *\/backport ([a-zA-Z0-9\/\-._]+) *([a-zA-Z0-9\/\-._]+)?$/im
+function matchComment (comment) {
+  return commandRegexp.exec(comment.trim()) && RegExp.$1
+}