ci/github-script/lint-commits: confirm Git names/emails are present

Prevents issues reported on Matrix by Jujutsu users,
caused by people omitting these fields.

ci/github-script/get-pr-commit-details.js

@@ -2,6 +2,17 @@
 const { promisify } = require('node:util')
 const execFile = promisify(require('node:child_process').execFile)
 
+/**
+ * @typedef {{
+ *  subject: string,
+ *  sha: string,
+ *  author: { name: string, email: string },
+ *  committer: { name: string, email: string}
+ *  changedPaths: string[],
+ *  changedPathSegments: Set<string>,
+ * }} Commit
+ */
+
 /**
  * @param {{
  *  args: string[]
@@ -34,12 +45,7 @@ async function runGit({ args, repoPath, core, quiet }) {
  *  repoPath?: string,
  * }} GetCommitMessagesForPRProps
  *
- * @returns {Promise<{
- *  subject: string,
- *  sha: string,
- *  changedPaths: string[],
- *  changedPathSegments: Set<string>,
- * }[]>}
+ * @returns {Promise<Commit[]>}
  */
 async function getCommitDetailsForPR({ core, pr, repoPath }) {
   await runGit({
@@ -70,17 +76,25 @@ async function getCommitDetailsForPR({ core, pr, repoPath }) {
 
   return Promise.all(
     shas.map(async (sha) => {
-      // Subject first, then a blank line, then filenames.
+      // Subject, author name, author email, committer name, committer email (all tab-seperated)
+      // then a blank line, then filenames.
       const result = (
         await runGit({
-          args: ['log', '--format=%s', '--name-only', '-1', sha],
+          args: [
+            'log',
+            '--format=%s\t%aN\t%aE\t%cN\t%cE',
+            '--name-only',
+            '-1',
+            sha,
+          ],
           repoPath,
           core,
           quiet: true,
         })
       ).stdout.split('\n')
 
-      const subject = result[0]
+      const [subject, authorName, authorEmail, committerName, committerEmail] =
+        result[0].split('\t')
 
       const changedPaths = result.slice(2, -1)
 
@@ -91,6 +105,8 @@ async function getCommitDetailsForPR({ core, pr, repoPath }) {
       return {
         sha,
         subject,
+        author: { name: authorName, email: authorEmail },
+        committer: { name: committerName, email: committerEmail },
         changedPaths,
         changedPathSegments,
       }

ci/github-script/lint-commits.js

@@ -2,15 +2,17 @@
 const { classify } = require('../supportedBranches.js')
 const { getCommitDetailsForPR } = require('./get-pr-commit-details.js')
 
+/** @typedef {import('./get-pr-commit-details.js').Commit} Commit */
+
 /**
  * @param {{
  *  github: InstanceType<import('@actions/github/lib/utils').GitHub>,
- *  context: import('@actions/github/lib/context').Context,
+ *  context: typeof import('@actions/github').context,
  *  core: import('@actions/core'),
  *  repoPath?: string,
- * }} CheckCommitMessagesProps
+ * }} LintCommitsProps
  */
-async function checkCommitMessages({ github, context, core, repoPath }) {
+async function lintCommits({ github, context, core, repoPath }) {
   // This check should only be run when we have the pull_request context.
   const pull_number = context.payload.pull_request?.number
   if (!pull_number) {
@@ -48,6 +50,17 @@ async function checkCommitMessages({ github, context, core, repoPath }) {
 
   const commits = await getCommitDetailsForPR({ core, pr, repoPath })
 
+  await checkCommitMessages({ commits, core })
+  await checkCommitMetadata({ commits, core })
+}
+
+/**
+ * @param {{
+ *  commits: Commit[],
+ *  core: import('@actions/core'),
+ * }} CheckCommitMessagesProps
+ */
+async function checkCommitMessages({ commits, core }) {
   const failures = new Set()
 
   const conventionalCommitTypes = [
@@ -152,4 +165,59 @@ async function checkCommitMessages({ github, context, core, repoPath }) {
   }
 }
 
-module.exports = checkCommitMessages
+/**
+ * @param {{
+ *  commits: Commit[],
+ *  core: import('@actions/core'),
+ * }} CheckGitFieldsProps
+ */
+async function checkCommitMetadata({ commits, core }) {
+  const failures = new Set()
+
+  /** @type {(s: string) => boolean} */
+  const isEmail = (s) => /^.+@.*$/.test(s)
+
+  for (const commit of commits) {
+    if (!commit.author.name) {
+      core.error(`Commit ${commit.sha} author's name field is missing`)
+      failures.add(commit.sha)
+    }
+
+    if (!commit.author.email || !isEmail(commit.author.email)) {
+      core.error(
+        `Commit ${commit.sha} author's email field is missing or invalid`,
+      )
+      failures.add(commit.sha)
+    }
+
+    if (!commit.committer.name) {
+      core.error(`Commit ${commit.sha} committer's name field is missing`)
+      failures.add(commit.sha)
+    }
+
+    if (!commit.committer.email || !isEmail(commit.committer.email)) {
+      core.error(
+        `Commit ${commit.sha} committer's email field is missing or invalid`,
+      )
+      failures.add(commit.sha)
+    }
+
+    if (!failures.has(commit.sha)) {
+      core.info(
+        `Commit ${commit.sha}'s git fields passed our automated checks!`,
+      )
+    }
+  }
+
+  if (failures.size !== 0) {
+    core.error(
+      'Please add the missing commit fields. ' +
+        'You can use the noreply email address generated for you by GitHub ' +
+        '(https://docs.github.com/en/account-and-profile/reference/email-addresses-reference#your-noreply-email-address) ' +
+        "if you'd like.",
+    )
+    core.setFailed('Committers: merging is discouraged.')
+  }
+}
+
+module.exports = lintCommits