feat(cli): prompt user when landing PR with several commits

And add an option to abort the session if trying to land more than one
commit.

Refs: nodejs/node#40436

components/git/land.js

@@ -46,6 +46,12 @@ const landActions = {
       'other commit messages',
     default: false,
     type: 'boolean'
+  },
+  oneCommitMax: {
+    describe: 'When run in conjunction with the --yes and --autorebase ' +
+      'options, will abort the session if trying to land more than one commit',
+    default: false,
+    type: 'boolean'
   }
 };
 

lib/landing_session.js

@@ -22,14 +22,17 @@ const LINT_RESULTS = {
 };
 
 class LandingSession extends Session {
-  constructor(cli, req, dir,
-    { prid, backport, lint, autorebase, fixupAll, checkCI } = {}) {
+  constructor(cli, req, dir, {
+    prid, backport, lint, autorebase, fixupAll,
+    checkCI, oneCommitMax
+  } = {}) {
     super(cli, dir, prid);
     this.req = req;
     this.backport = backport;
     this.lint = lint;
     this.autorebase = autorebase;
     this.fixupAll = fixupAll;
+    this.oneCommitMax = oneCommitMax;
     this.expectedCommitShas = [];
     this.checkCI = !!checkCI;
   }
@@ -40,6 +43,7 @@ class LandingSession extends Session {
     args.lint = this.lint;
     args.autorebase = this.autorebase;
     args.fixupAll = this.fixupAll;
+    args.oneCommitMax = this.oneCommitMax;
     return args;
   }
 
@@ -349,7 +353,9 @@ class LandingSession extends Session {
   }
 
   async final() {
-    const { cli, owner, repo, upstream, branch, prid } = this;
+    const {
+      cli, owner, repo, upstream, branch, prid, oneCommitMax
+    } = this;
 
     // Check that git rebase/am has been completed.
     if (!this.readyToFinal()) {
@@ -360,6 +366,20 @@ class LandingSession extends Session {
     };
 
     const stray = this.getStrayCommits();
+    if (stray.length > 1) {
+      const forceLand = await cli.prompt(
+        'There are more than one commit in the PR. ' +
+        'Do you still want to land it?',
+        { defaultAnswer: !oneCommitMax });
+
+      if (!forceLand) {
+        cli.info(
+          'Use --fixupAll option, squash the PR manually or land the PR from ' +
+          'the command line.'
+        );
+        process.exit(1);
+      }
+    }
     const strayVerbose = this.getStrayCommits(true);
     const validateCommand = path.join(
       __dirname,