ci: rebase PRs on target branch

.appveyor.yml

@@ -9,6 +9,13 @@ skip_branch_with_pr: true
 
 install:
   - ps: Install-Product node $env:nodejs_version
+  - ps: |
+      if (Test-Path env:APPVEYOR_PULL_REQUEST_NUMBER) {
+        # user is required for rebase.	
+        git config user.name "angular-ci"	
+        git config user.email "angular-ci"
+        # Rebase on target branch.
+        node tools\rebase-pr.js angular/angular-cli $env:APPVEYOR_PULL_REQUEST_NUMBER }
   # --network-timeout is a workaround for https://github.com/yarnpkg/yarn/issues/6221
   - yarn --frozen-lockfile --network-timeout=500000
   - yarn webdriver-update

.circleci/config.yml

@@ -25,26 +25,19 @@ anchor_1: &defaults
   docker:
     - image: *docker_image
 
-# After checkout, rebase on top of master.
-# Similar to travis behavior, but not quite the same.
-# See https://discuss.circleci.com/t/1662
+# After checkout, rebase on top of target branch.
 anchor_2: &post_checkout
   run:
-    name: Post checkout step
+    name: Rebase PR on target branch
     command: >
       if [[ -n "${CIRCLE_PR_NUMBER}" ]]; then
-        # Fetch the head and merge commits for this PR.
-        git fetch origin +refs/pull/$CIRCLE_PR_NUMBER/head:pr/$CIRCLE_PR_NUMBER/head
-        git fetch origin +refs/pull/$CIRCLE_PR_NUMBER/merge:pr/$CIRCLE_PR_NUMBER/merge
-        # Checkout the merged PR for testing as CircleCI will just use the PR head otherwise.
-        git checkout -qf pr/$CIRCLE_PR_NUMBER/merge
-        # Reset the merge commit into its PR head.
-        git reset pr/$CIRCLE_PR_NUMBER/head
-        # Commit the merge changes into the head of the PR.
-        # This way we keep the last commit message.
-        git config user.name "angular-ci"
-        git config user.email "angular-ci"
-        git commit . --amend --no-edit
+        # User is required for rebase.
+        git config user.name "angular-ci"	
+        git config user.email "angular-ci"      
+        # Rebase PR on top of target branch.
+        node tools/rebase-pr.js angular/angular-cli ${CIRCLE_PR_NUMBER}
+      else
+        echo "This build is not over a PR, nothing to do."
       fi
 anchor_3: &restore_cache
   restore_cache:

tools/rebase-pr.js

@@ -0,0 +1,92 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+ // tslint:disable:no-console
+// ** IMPORTANT **
+// This script cannot use external dependencies because it needs to run before they are installed.
+
+const util = require('util');
+const https = require('https');
+const child_process = require('child_process');
+const exec = util.promisify(child_process.exec);
+
+function determineTargetBranch(repository, prNumber) {
+  const pullsUrl = `https://api.github.com/repos/${repository}/pulls/${prNumber}`;
+  // GitHub requires a user agent: https://developer.github.com/v3/#user-agent-required
+  const options = { headers: { 'User-Agent': repository } };
+
+  return new Promise((resolve, reject) => {
+    https.get(pullsUrl, options, (res) => {
+      const { statusCode } = res;
+      const contentType = res.headers['content-type'];
+
+      let error;
+      if (statusCode !== 200) {
+        error = new Error(`Request Failed.\nStatus Code: ${statusCode}.\nResponse: ${res}.\n' +`);
+      } else if (!/^application\/json/.test(contentType)) {
+        error = new Error('Invalid content-type.\n' +
+          `Expected application/json but received ${contentType}`);
+      }
+      if (error) {
+        reject(error);
+        res.resume();
+        return;
+      }
+
+      res.setEncoding('utf8');
+      let rawData = '';
+      res.on('data', (chunk) => { rawData += chunk; });
+      res.on('end', () => {
+        try {
+          const parsedData = JSON.parse(rawData);
+          resolve(parsedData['base']['ref']);
+        } catch (e) {
+          reject(e);
+        }
+      });
+    }).on('error', (e) => {
+      reject(e);
+    });
+  });
+}
+
+if (process.argv.length != 4) {
+  console.error(`This script requires the GitHub repository and PR number as arguments.`);
+  console.error(`Example: node scripts/rebase-pr.js angular/angular 123`);
+  process.exitCode = 1;
+  return;
+}
+
+const repository = process.argv[2];
+const prNumber = process.argv[3];
+let targetBranch;
+
+
+return Promise.resolve()
+  .then(() => {
+    console.log(`Determining target branch for PR ${prNumber} on ${repository}.`);
+    return determineTargetBranch(repository, prNumber);
+  })
+  .then(target => {
+    targetBranch = target;
+    console.log(`Target branch is ${targetBranch}.`);
+  })
+  .then(() => {
+    console.log(`Fetching ${targetBranch} from origin.`);
+    return exec(`git fetch origin ${targetBranch}`);
+  })
+  .then(target => {
+    console.log(`Rebasing current branch on ${targetBranch}.`);
+    return exec(`git rebase origin/${targetBranch}`);
+  })
+  .then(() => console.log('Rebase successfull.'))
+  .catch(err => {
+    console.log('Failed to rebase on top or target branch.\n');
+    console.error(err);
+    process.exitCode = 1;
+  });