fix: ensure git found on trop runner

Aptfile

@@ -0,0 +1,2 @@
+# Heroku-24 stack doesn't include git by default.
+git-all

app.json

@@ -11,15 +11,14 @@
       "required": true
     }
   },
-  "formation": {
-  },
-  "addons": [
-
-  ],
+  "formation": {},
+  "addons": [],
   "buildpacks": [
     {
       "url": "heroku/nodejs"
+    }, {
+      "url": "heroku-community/apt"
     }
   ],
-  "stack": "heroku-22"
+  "stack": "heroku-24"
 }

src/index.ts

@@ -370,7 +370,7 @@ const probotHandler: ApplicationFunction = async (robot, { getRouter }) => {
       'pull_request.unlabeled',
       'pull_request.synchronize',
     ],
-    async (context) => {
+    async (context: WebHookPRContext) => {
       const pr = context.payload.pull_request;
 
       if (pr.base.ref !== pr.base.repo.default_branch) {
@@ -423,7 +423,7 @@ const probotHandler: ApplicationFunction = async (robot, { getRouter }) => {
   );
 
   // Backport pull requests to labeled targets when PR is merged.
-  robot.on('pull_request.closed', async (context: WebHookPRContext) => {
+  robot.on('pull_request.closed', async (context) => {
     const { pull_request: pr } = context.payload;
 
     const oldPRNumbers = getPRNumbersFromPRBody(pr, true);
@@ -471,7 +471,7 @@ const probotHandler: ApplicationFunction = async (robot, { getRouter }) => {
   const TROP_COMMAND_PREFIX = '/trop ';
 
   // Manually trigger backporting process on trigger comment phrase.
-  robot.on('issue_comment.created', async (context: WebHookIssueContext) => {
+  robot.on('issue_comment.created', async (context) => {
     const { issue, comment } = context.payload;
 
     const isPullRequest = (i: { number: number; html_url: string }) =>

src/utils.ts

@@ -1,5 +1,6 @@
 import fetch from 'node-fetch';
 import * as fs from 'fs-extra';
+import { execSync } from 'child_process';
 import Queue from 'queue';
 import simpleGit from 'simple-git';
 
@@ -29,7 +30,7 @@ import {
   WebHookPR,
   WebHookRepoContext,
 } from './types';
-import { Context, Probot } from 'probot';
+import { Probot } from 'probot';
 
 const { parse: parseDiff } = require('what-the-diff');
 
@@ -475,6 +476,17 @@ export const backportImpl = async (
     }
   }
 
+  const gitExists = execSync('which git').toString().trim();
+  if (/git not found/.test(gitExists)) {
+    await context.octokit.issues.createComment(
+      context.repo({
+        body: `Git not found - unable to proceed with backporting to ${targetBranch}`,
+        issue_number: pr.number,
+      }),
+    );
+    return;
+  }
+
   const base = pr.base;
   const slug = `${base.repo.owner.login}/${base.repo.name}`;
   const bp = `backport from PR #${pr.number} to "${targetBranch}"`;