feat: implement autorebase for PRs with multiple commits

components/git/land.js

@@ -47,6 +47,11 @@ const landOptions = {
     describe: 'Prevent adding Fixes and Refs information to commit metadata',
     default: false,
     type: 'boolean'
+  },
+  autorebase: {
+    describe: 'Automatically rebase branches with multiple commits',
+    default: false,
+    type: 'boolean'
   }
 };
 
@@ -165,7 +170,8 @@ 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, argv.skipRefs, cli);
     if (argv.backport) {
       const split = metadata.metadata.split('\n')[0];

lib/landing_session.js

@@ -16,15 +16,17 @@ 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;
   }
 
@@ -131,6 +133,17 @@ class LandingSession extends Session {
     return command;
   }
 
+  makeRebaseSuggestion(subjects) {
+    const suggestion = this.getRebaseSuggestion(subjects);
+    this.cli.log('Please run the following commands to complete landing\n\n' +
+      `$ ${suggestion}\n` +
+      '$ git node land --continue');
+  }
+
+  canAutomaticallyRebase(subjects) {
+    return subjects.every(line => !line.startsWith('squash!'));
+  }
+
   async validateLint() {
     // The linter is currently only run on non-Windows platforms.
     if (os.platform() === 'win32') {
@@ -168,14 +181,34 @@ class LandingSession extends Session {
       }
 
       return this.final();
+    } 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. ` +
+        'Attempting autorebase.');
+      const { upstream, branch } = this;
+      const assumeYes = this.cli.assumeYes ? '--yes' : '';
+      const msgAmend = `-x "git node land --amend ${assumeYes}"`;
+      try {
+        await forceRunAsync('git',
+          ['rebase', `${upstream}/${branch}`, '-i', '--autosquash', msgAmend],
+          {
+            ignoreFailure: false,
+            spawnArgs: {
+              shell: true,
+              env: { ...process.env, GIT_SEQUENCE_EDITOR: ':' }
+            }
+          });
+        return this.final();
+      } catch (e) {
+        await runAsync('git', ['rebase', '--abort']);
+        const count = subjects.length;
+        cli.log(`Couldn't rebase ${count} commits in the PR automatically`);
+        this.makeRebaseSuggestion(subjects);
+      }
+    } else {
+      this.makeRebaseSuggestion(subjects);
     }
-
-    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() {