feat (vuejs#102): tag PRs using alert blocks (vuejs#107)

* chore: tag PRs using alert blocks

* fix: typo

* fix: run only for PR

* fix: use origin/master as base branch

* fix: fetch origin/master branch

* fix: label PRs with review-alert-box

Author: znck

.github/workflows/pr.yaml

@@ -0,0 +1,33 @@
+name: CI
+
+on: [pull_request]
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  tag-alert-blocks:
+    name: Tag alert blocks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - run: |
+          git fetch --no-tags --prune --depth=1 origin +refs/heads/master:refs/remotes/origin/master
+      - uses: actions/github-script@v1
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            const path = require('path')
+            const { isUsingAlertBlock } = require(path.resolve(process.cwd(), 'scripts/tag-alert-blocks.js'))
+
+            isUsingAlertBlock().then(ok => {
+              if (ok) {
+                github.issues.addLabels({
+                  issue_number: context.issue.number,
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  labels: ['review-alert-box']
+                })
+              }
+            })

scripts/tag-alert-blocks.js

@@ -0,0 +1,42 @@
+#!/usr/bin/env node
+
+const { exec } = require('child_process')
+
+/**
+ * Execute a command and return stdout as string.
+ * @param {string} command
+ * @returns {Promise<string>}
+ */
+function run(command) {
+  return new Promise((resolve, reject) => {
+    exec(command, { encoding: 'utf-8' }, (error, stdout) =>
+      error ? reject(error) : resolve(stdout)
+    )
+  })
+}
+
+const ALERT_BLOCK = /^\+\s*:::\s?(\w+)/m
+
+async function isUsingAlertBlock(base = 'origin/master') {
+  const result = await run(`git diff --name-only ${base}`)
+  const files = (
+    await Promise.all(
+      result
+        .trim()
+        .split(/\r?\n/)
+        .map(file =>
+          run(`git diff ${base} -- ${file}`)
+            .then(diff => ALERT_BLOCK.test(diff))
+            .then(usesAlertBlock => (usesAlertBlock ? file : ''))
+        )
+    )
+  ).filter(Boolean)
+
+  if (files.length) {
+    return true
+  }
+
+  return false
+}
+
+module.exports = { isUsingAlertBlock }