ci/github-script/lint-commits: support PRs with over 250 commits

We want to be able to check python-updates.

.github/workflows/lint.yml

@@ -136,10 +136,8 @@ jobs:
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
-          persist-credentials: false
+          persist-credentials: true # Needed to run git fetch for large PRs.
           path: trusted
-          sparse-checkout: |
-            ci/github-script
       - name: Check commit messages
         uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
         with:
@@ -150,4 +148,5 @@ jobs:
               github,
               context,
               core,
+              repoPath: 'trusted',
             })

ci/github-script/lint-commits.js

@@ -1,14 +1,37 @@
 // @ts-check
 const { classify } = require('../supportedBranches.js')
+const { promisify } = require('node:util')
+const execFile = promisify(require('node:child_process').execFile)
+
+/**
+ * @param {{
+ *  args: string[]
+ *  core: import('@actions/core'),
+ *  quiet?: boolean,
+ *  repoPath?: string,
+ * }} RunGitProps
+ */
+async function runGit({ args, repoPath, core, quiet }) {
+  if (repoPath) {
+    args = ['-C', repoPath, ...args]
+  }
+
+  if (!quiet) {
+    core.info(`About to run \`git ${args.map((s) => `'${s}'`).join(' ')}\``)
+  }
+
+  return await execFile('git', args)
+}
 
 /**
  * @param {{
  *  github: InstanceType<import('@actions/github/lib/utils').GitHub>,
- *  context: import('@actions/github/lib/context').Context
- *  core: import('@actions/core')
+ *  context: import('@actions/github/lib/context').Context,
+ *  core: import('@actions/core'),
+ *  repoPath?: string,
  * }} CheckCommitMessagesProps
  */
-async function checkCommitMessages({ github, context, core }) {
+async function checkCommitMessages({ 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) {
@@ -42,15 +65,70 @@ async function checkCommitMessages({ github, context, core }) {
     return
   }
 
-  const commits = await github.paginate(github.rest.pulls.listCommits, {
-    ...context.repo,
-    pull_number,
-  })
+  /**
+   * GitHub's API will return a maximum of 250 commits.
+   * We will use it if we can, but fall back to using git locally.
+   * This type is used to abstract over the differences between the two.
+   * @type {{
+   *  message: string,
+   *  sha: string,
+   * }[]}
+   */
+  let commits
+
+  if (pr.commits < 250) {
+    commits = (
+      await github.paginate(github.rest.pulls.listCommits, {
+        ...context.repo,
+        pull_number,
+      })
+    ).map((commit) => ({ message: commit.commit.message, sha: commit.sha }))
+  } else {
+    await runGit({
+      args: ['fetch', `--depth=1`, 'origin', pr.base.sha],
+      repoPath,
+      core,
+    })
+    await runGit({
+      args: ['fetch', `--depth=${pr.commits + 1}`, 'origin', pr.head.sha],
+      repoPath,
+      core,
+    })
+
+    const shas = (
+      await runGit({
+        args: [
+          'rev-list',
+          `--max-count=${pr.commits}`,
+          `${pr.base.sha}..${pr.head.sha}`,
+        ],
+        repoPath,
+        core,
+      })
+    ).stdout
+      .split('\n')
+      .map((s) => s.trim())
+      .filter(Boolean)
+
+    commits = await Promise.all(
+      shas.map(async (sha) => ({
+        sha,
+        message: (
+          await runGit({
+            args: ['log', '--format=%s', '-1', sha],
+            repoPath,
+            core,
+            quiet: true,
+          })
+        ).stdout,
+      })),
+    )
+  }
 
   const failures = new Set()
 
   for (const commit of commits) {
-    const message = commit.commit.message
+    const message = commit.message
     const firstLine = message.split('\n')[0]
 
     const logMsgStart = `Commit ${commit.sha}'s message's subject ("${firstLine}")`