feat: implement autorebase for PRs with multiple commits

Author: lundibundi

components/git/land.js

@@ -42,6 +42,11 @@ const landOptions = {
     describe: 'Land a backport PR onto a staging branch',
     default: false,
     type: 'boolean'
+  },
+  autorebase: {
+    describe: 'Automatically rebase branches with multiple commits',
+    default: false,
+    type: 'boolean'
   }
 };
 
@@ -159,7 +164,8 @@ async function main(state, argv, cli, req, dir) {
       cli.log('run `git node land --abort` before starting a new session');
       return;
     }
-    session = new LandingSession(cli, req, dir, argv.prid, argv.backport);
+    session = new LandingSession(cli, req, dir, argv.prid, argv.backport,
+      argv.autorebase);
     const metadata = await getMetadata(session.argv, cli);
     if (argv.backport) {
       const split = metadata.metadata.split('\n')[0];

lib/landing_session.js

@@ -15,15 +15,17 @@ const { shortSha } = require('./utils');
 const isWindows = process.platform === 'win32';
 
 class LandingSession extends Session {
-  constructor(cli, req, dir, prid, backport) {
+  constructor(cli, req, dir, prid, backport, autorebase) {
     super(cli, dir, prid);
     this.req = req;
     this.backport = backport;
+    this.autorebase = autorebase;
   }
 
   get argv() {
     const args = super.argv;
     args.backport = this.backport;
+    args.autorebase = this.autorebase;
     return args;
   }
 
@@ -130,6 +132,10 @@ class LandingSession extends Session {
     return command;
   }
 
+  canAutomaticallyRebase(subjects) {
+    return subjects.every(line => !line.startsWith('squash!'));
+  }
+
   async suggestAfterPatch(patch) {
     const { cli } = this;
     const subjects = patch.match(/Subject: \[PATCH.*?\].*/g);
@@ -155,14 +161,28 @@ class LandingSession extends Session {
         return;
       }
       return this.final();
-    }
-
-    const suggestion = this.getRebaseSuggestion(subjects);
-
-    cli.log(`There are ${subjects.length} commits in the PR`);
-    cli.log('Please run the following commands to complete landing\n\n' +
-            `$ ${suggestion}\n` +
+    } else if (this.autorebase && this.canAutomaticallyRebase(subjects)) {
+      // Run git rebase in interactive mode with autosquash but without editor
+      // so that it will perform everything automatically.
+      cli.log(`There are ${subjects.length} commits in the PR. ` +
+        'Attempring autorebase.');
+      const { upstream, branch } = this;
+      const msgAmend = '-x "git-node land --amend"';
+      await runAsync('git',
+        ['rebase', `${upstream}/${branch}`, '-i', '--autosquash', msgAmend],
+        {
+          spawnArgs: {
+            shell: true,
+            env: { ...process.env, GIT_SEQUENCE_EDITOR: ':' }
+          }
+        });
+    } else {
+      const suggestion = this.getRebaseSuggestion(subjects);
+      cli.log(`There are ${subjects.length} commits in the PR`);
+      cli.log('Please run the following commands to complete landing\n\n' +
+        `$ ${suggestion}\n` +
             '$ git node land --continue');
+    }
   }
 
   async apply() {