git-node: suggest -x and --autosquash for git rebase (#237)

- Suggest to add `-x "git node land --amend"` which will put
  `exec git node land --amend` on every picked commit.
- Suggest to add `--autosquash` if `fixup!` or `squash!` appears
  in the commit messages, which will add fixup or squash actions
  to corresponding commits if they match the autosquash rules.

Author: joyeecheung

lib/landing_session.js

@@ -3,7 +3,7 @@
 const path = require('path');
 
 const {
-  runAsync, runSync, forceRunAsync, exit
+  runAsync, runSync, forceRunAsync
 } = require('./run');
 const Session = require('./session');
 
@@ -46,17 +46,10 @@ class LandingSession extends Session {
     cli.ok(`Aborted \`git node land\` session in ${this.ncuDir}`);
   }
 
-  async apply() {
+  async downloadAndPatch() {
     const { cli, req, repo, owner, prid } = this;
 
-    if (!this.readyToApply()) {
-      cli.warn('This session can not proceed to apply patches, ' +
-        'run `git node land --abort`');
-      return;
-    }
-    await this.tryResetBranch();
-
-    // TODO: restore previously downloaded patches
+    // TODO(joyeecheung): restore previously downloaded patches
     cli.startSpinner(`Downloading patch for ${prid}`);
     const patch = await req.text(
       `https://github.com/${owner}/${repo}/pull/${prid}.patch`);
@@ -81,13 +74,42 @@ class LandingSession extends Session {
         ]);
       } else {
         cli.error('Failed to apply patches');
-        exit();
+        process.exit(1);
       }
     }
     cli.ok('Patches applied');
+    return patch;
+  }
 
-    this.startAmending();
-    if (/Subject: \[PATCH\]/.test(patch)) {
+  getRebaseSuggestion(subjects) {
+    const { upstream, branch } = this;
+    let command = `git rebase ${upstream}/${branch} -i`;
+    command += ' -x "git node land --amend"';
+
+    const squashes = subjects.filter(
+      line => line.includes('fixup!') || line.includes('squash!'));
+
+    if (squashes.length !== 0) {
+      command += ' --autosquash';
+    }
+
+    return command;
+  }
+
+  async suggestAfterPatch(patch) {
+    const { cli } = this;
+    const subjects = patch.match(/Subject: \[PATCH.*?\].*/g);
+    if (!subjects) {
+      cli.warn('Cannot get number of commits in the patch. ' +
+        'It seems to be malformed');
+      return;
+    }
+
+    // XXX(joyeecheung) we cannot guarantee that no one will put a subject
+    // line in the commit message but that seems unlikely (some deps update
+    // might do that).
+    if (subjects.length === 1) {
+      // assert(subjects[0].startsWith('Subject: [PATCH]'))
       const shouldAmend = await cli.prompt(
         'There is only one commit in this PR.\n' +
         'do you want to amend the commit message?');
@@ -101,20 +123,25 @@ class LandingSession extends Session {
       return this.final();
     }
 
-    const re = /Subject: \[PATCH 1\/(\d+)\]/;
-    const match = patch.match(re);
-    if (!match) {
-      cli.warn('Cannot get number of commits in the patch. ' +
-        'It seems to be malformed');
+    const suggestion = this.getRebaseSuggestion(subjects);
+
+    cli.log(`There are ${subjects.length} commits in the PR`);
+    cli.log('Please run the following command to complete landing\n\n' +
+            `$ ${suggestion}  # put "edit" on every commit that will stay`);
+  }
+
+  async apply() {
+    const { cli } = this;
+    if (!this.readyToApply()) {
+      cli.warn('This session can not proceed to apply patches, ' +
+        'run `git node land --abort`');
       return;
     }
-    const { upstream, branch } = this;
-    cli.log(
-      `There are ${match[1]} commits in the PR.\n` +
-      `Please run \`git rebase ${upstream}/${branch} -i\`, put "edit" on ` +
-      'every commit that\'s gonna stay and use `git node land --amend` to ' +
-      'amend the commit messages');
-    // TODO: do git rebase automatically?
+    await this.tryResetBranch();
+
+    const patch = await this.downloadAndPatch();
+    this.startAmending();
+    await this.suggestAfterPatch(patch);
   }
 
   getCurrentRev() {
@@ -166,17 +193,17 @@ class LandingSession extends Session {
     cli.log(`Please manually edit ${messageFile}, then run\n` +
       `\`git commit --amend -F ${messageFile}\` ` +
       'to finish amending the message');
-    return false;
+    process.exit(1);  // make it work with git rebase -x
   }
 
   async final() {
-    const { cli } = this;
+    const { cli, owner, repo, upstream, branch, prid } = this;
+
     if (!this.readyToFinal()) {  // check git rebase/am has been done
       cli.warn('Not yet ready to final');
       return;
-    }
-    const upstream = this.upstream;
-    const branch = this.branch;
+    };
+
     const notYetPushed = this.getNotYetPushedCommits();
     const notYetPushedVerbose = this.getNotYetPushedCommits(true);
     const validateCommand = path.join(
@@ -196,9 +223,11 @@ class LandingSession extends Session {
       const head = this.getUpstreamHead().slice(0, 7);
       willBeLanded = `${head}...${willBeLanded}`;
     }
+
     cli.log('To finish landing:');
     cli.log(`1. Run \`git push ${upstream} ${branch}\``);
-    cli.log(`2. Post in the PR: \`Landed in ${willBeLanded}\``);
+    const url = `https://github.com/${owner}/${repo}/pull/${prid}`;
+    cli.log(`2. Post in ${url}: \`Landed in ${willBeLanded}\``);
 
     const shouldClean = await cli.prompt('Clean up generated temporary files?');
     if (shouldClean) {

lib/session.js

@@ -79,6 +79,13 @@ class Session {
     });
   }
 
+  // TODO(joyeecheung): more states
+  // - STARTED (fetching metadata)
+  // - DOWNLOADING (downloading the patch)
+  // - PATCHING (git am)
+  // - AMENDING (git rebase or just amending messages)
+  // - DONE
+
   startApplying() {
     this.updateSession({
       state: APPLYING