feat: /roller update-branch command

src/index.ts

@@ -4,8 +4,9 @@ import { handleNodeCheck } from './node-handler.js';
 import { handleChromiumCheck } from './chromium-handler.js';
 import { handleBuildImagesCheck } from './build-images-handler.js';
 import { handleBuildImagesChromiumDepsCheck } from './build-images-chromium-deps-handler.js';
-import { REPOS, ROLL_TARGETS } from './constants.js';
+import { REPOS, ROLLER_BOT_LOGIN, ROLL_TARGETS } from './constants.js';
 import { isAuthorizedElectronRepoUser } from './utils/is-authorized-user.js';
+import { updatePRBranch } from './utils/update-pr-branch.js';
 
 const handler = (robot: Probot) => {
   robot.on('pull_request.closed', async (context) => {
@@ -63,11 +64,6 @@ const handler = (robot: Probot) => {
     const d = debug('roller/github:issue_comment.created');
     const { issue, comment } = context.payload;
 
-    const match = comment.body.match(/^\/roll (main|\d+-x-y)$/);
-    if (!match || !match[1]) {
-      return;
-    }
-
     // Roll commands perform privileged actions against electron/electron, so only
     // honor them when issued from that repository. This prevents permissions on
     // unrelated repos where this app is installed from authorizing a roll.
@@ -94,6 +90,34 @@ const handler = (robot: Probot) => {
       return;
     }
 
+    // Maintainer command to update the branch with the latest changes from its base branch
+    if (/^\/roller update-branch$/.test(comment.body)) {
+      const { data: pr } = await context.octokit.rest.pulls.get(
+        context.repo({ pull_number: issue.number }),
+      );
+
+      // Ensure the PR was actually created by roller before updating it.
+      if (pr.user?.login !== ROLLER_BOT_LOGIN) {
+        d(`#${issue.number} was not created by roller - skipping update-branch`);
+        await context.octokit.rest.issues.createComment(
+          context.repo({
+            issue_number: issue.number,
+            body: 'This PR was not created by roller and cannot be updated via this command.',
+          }),
+        );
+        return;
+      }
+
+      d(`Updating the branch for #${issue.number}`);
+      await updatePRBranch(context, pr);
+      return;
+    }
+
+    const match = comment.body.match(/^\/roll (main|\d+-x-y)$/);
+    if (!match || !match[1]) {
+      return;
+    }
+
     const branch = match[1];
     const isNodePR = issue.title.startsWith(`chore: bump ${ROLL_TARGETS.node.name}`);
     const isChromiumPR = issue.title.startsWith(`chore: bump ${ROLL_TARGETS.chromium.name}`);

src/types.ts

@@ -1,5 +1,6 @@
 import { RestEndpointMethodTypes } from '@octokit/rest';
 
+export type PullsGetResponseItem = RestEndpointMethodTypes['pulls']['get']['response']['data'];
 export type PullsListResponseItem = RestEndpointMethodTypes['pulls']['list']['response']['data'][0];
 export type ReposListBranchesResponseItem =
   RestEndpointMethodTypes['repos']['listBranches']['response']['data'][0];

src/utils/update-pr-branch.ts

@@ -0,0 +1,60 @@
+import debug from 'debug';
+import type { Context } from 'probot';
+
+import type { PullsGetResponseItem } from '../types.js';
+
+/**
+ * Updates a pull request's branch by merging the latest changes from its base
+ * branch into it. This is the same operation as the "Update branch" button in
+ * the GitHub UI and is used to re-trigger CI on stale roller PRs.
+ */
+export async function updatePRBranch(
+  context: Context<'issue_comment.created'>,
+  pr: PullsGetResponseItem,
+): Promise<void> {
+  const d = debug('roller/github:updatePRBranch()');
+
+  d(`Updating #${pr.number} by merging the latest changes from "${pr.base.ref}"`);
+
+  // Don't use the REBASE update method, as it would create unverified commits.
+  const mutation = `mutation UpdatePullRequestBranch($pullRequestId: ID!, $expectedHeadOid: GitObjectID!) {
+    updatePullRequestBranch(input: {
+      pullRequestId: $pullRequestId,
+      expectedHeadOid: $expectedHeadOid,
+      updateMethod: MERGE
+    }) {
+      pullRequest {
+        number
+      }
+    }
+  }`;
+
+  try {
+    await context.octokit.graphql(mutation, {
+      pullRequestId: pr.node_id,
+      expectedHeadOid: pr.head.sha,
+    });
+  } catch (error) {
+    d(`Failed to update branch for #${pr.number}`, error);
+
+    const isConflict = (error as Error)?.message?.includes('merge conflict between base and head');
+
+    await context.octokit.rest.issues.createComment(
+      context.repo({
+        issue_number: pr.number,
+        body: isConflict
+          ? `This branch could not be updated because there is a merge conflict with \`${pr.base.ref}\`. Please resolve the conflict manually.`
+          : `I was unable to update this branch with the latest changes from \`${pr.base.ref}\`. Please update it manually.`,
+      }),
+    );
+
+    return;
+  }
+
+  await context.octokit.rest.issues.createComment(
+    context.repo({
+      issue_number: pr.number,
+      body: `This branch has been updated with the latest changes from \`${pr.base.ref}\`.`,
+    }),
+  );
+}

tests/fixtures/issue_comment_update_branch.created.json

@@ -0,0 +1,36 @@
+{
+  "name": "issue_comment",
+  "payload": {
+    "action": "created",
+    "issue": {
+      "url": "https://api.github.com/repos/electron/electron/pull/0",
+      "html_url": "https://github.com/electron/electron/pull/0",
+      "number": 0,
+      "title": "chore: bump chromium to 1.2.3.4",
+      "user": {
+        "login": "dsanders11"
+      },
+      "body": "Bump the version of Chromium to 1.2.3.4.",
+      "pull_request": {}
+    },
+    "comment": {
+      "url": "https://api.github.com/repos/electron/electron/pulls/comments/0",
+      "html_url": "https://github.com/electron/electron/pulls/0#issuecomment-0",
+      "id": 0,
+      "user": {
+        "login": "dsanders11"
+      },
+      "body": "/roller update-branch"
+    },
+    "repository": {
+      "name": "electron",
+      "full_name": "electron/electron",
+      "owner": {
+        "login": "electron"
+      }
+    },
+    "installation": {
+      "id": 12345
+    }
+  }
+}

tests/index.spec.ts

@@ -4,17 +4,44 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 import handler from '../src/index.js';
 import { handleChromiumCheck } from '../src/chromium-handler.js';
+import { ROLLER_BOT_LOGIN } from '../src/constants.js';
 import { handleNodeCheck } from '../src/node-handler.js';
 import { isAuthorizedElectronRepoUser } from '../src/utils/is-authorized-user.js';
+import { updatePRBranch } from '../src/utils/update-pr-branch.js';
 
 import issueCommentRollCreatedEvent from './fixtures/issue_comment_roll.created.json' with { type: 'json' };
+import issueCommentUpdateBranchCreatedEvent from './fixtures/issue_comment_update_branch.created.json' with { type: 'json' };
 
 vi.mock('../src/chromium-handler.js');
 vi.mock('../src/node-handler.js');
 vi.mock('../src/utils/is-authorized-user.js');
+vi.mock('../src/utils/update-pr-branch.js');
 
 const GH_API = 'https://api.github.com';
 
+const MOCK_PR = {
+  merged: true,
+  head: {
+    sha: '6dcb09b5b57875f334f61aebed695e2e4193db5e',
+  },
+  base: {
+    ref: 'main',
+    repo: {
+      default_branch: 'main',
+    },
+  },
+  labels: [
+    {
+      url: 'my_cool_url',
+      name: 'target/X-X-X',
+      color: 'fc2929',
+    },
+  ],
+  user: {
+    login: ROLLER_BOT_LOGIN,
+  },
+};
+
 describe('roller', () => {
   describe('issue_comment.created event', () => {
     let probot: Probot;
@@ -103,5 +130,43 @@ describe('roller', () => {
       expect(handleChromiumCheck).not.toHaveBeenCalled();
       expect(handleNodeCheck).not.toHaveBeenCalled();
     });
+
+    it('triggers a branch update on `/roller update-branch` comment', async () => {
+      vi.mocked(isAuthorizedElectronRepoUser).mockResolvedValue(true);
+
+      nock(GH_API).persist().get('/repos/electron/electron/pulls/0').reply(200, MOCK_PR);
+
+      await probot.receive(
+        issueCommentUpdateBranchCreatedEvent as Parameters<typeof probot.receive>[0],
+      );
+
+      expect(updatePRBranch).toHaveBeenCalled();
+    });
+
+    it('does not trigger a branch update on `/roller update-branch` comment when roller is not the author', async () => {
+      vi.mocked(isAuthorizedElectronRepoUser).mockResolvedValue(true);
+
+      nock(GH_API)
+        .persist()
+        .get('/repos/electron/electron/pulls/0')
+        .reply(200, { ...MOCK_PR, user: { login: 'someone-else' } });
+
+      let comment: string | undefined;
+      nock(GH_API)
+        .post('/repos/electron/electron/issues/0/comments', ({ body }) => {
+          comment = body;
+          return true;
+        })
+        .reply(200);
+
+      await probot.receive(
+        issueCommentUpdateBranchCreatedEvent as Parameters<typeof probot.receive>[0],
+      );
+
+      expect(updatePRBranch).not.toHaveBeenCalled();
+      expect(comment).toEqual(
+        'This PR was not created by roller and cannot be updated via this command.',
+      );
+    });
   });
 });