ci: move determineTargetRefAndSha to a new file for reusability (#35035)

PR Close #35035

tools/utils/get-refs-and-shas-for-target.js

@@ -0,0 +1,85 @@
+/**
+ * @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
+ */
+
+const https = require('https');
+const util = require('util');
+const child_process = require('child_process');
+const exec = util.promisify(child_process.exec);
+
+async function requestDataFromGithub(url) {
+  // GitHub requires a user agent: https://developer.github.com/v3/#user-agent-required
+  const options = {headers: {'User-Agent': 'angular'}};
+
+  return new Promise((resolve, reject) => {
+    https
+        .get(
+            url, options,
+            (res) => {
+              const {statusCode} = res;
+              const contentType = res.headers['content-type'];
+              let rawData = '';
+
+              res.on('data', (chunk) => { rawData += chunk; });
+              res.on('end', () => {
+                let error;
+                if (statusCode !== 200) {
+                  error = new Error(
+                      `Request Failed.\nStatus Code: ${statusCode}.\nResponse: ${rawData}`);
+                } else if (!/^application\/json/.test(contentType)) {
+                  error = new Error(
+                      'Invalid content-type.\n' +
+                      `Expected application/json but received ${contentType}`);
+                }
+
+                if (error) {
+                  reject(error);
+                  return;
+                }
+
+                try {
+                  resolve(JSON.parse(rawData));
+                } catch (e) {
+                  reject(e);
+                }
+              });
+            })
+        .on('error', (e) => { reject(e); });
+  });
+}
+
+module.exports = async function getRefsAndShasForTarget(prNumber) {
+  console.log(`Getting refs and SHAs for PR ${prNumber} on angular/angular.`);
+  const pullsUrl = `https://api.github.com/repos/angular/angular/pulls/${prNumber}`;
+  const result = await requestDataFromGithub(pullsUrl);
+
+  // Ensure the base ref is up to date
+  await exec(`git fetch origin ${result.base.ref}`);
+
+  // The sha of the latest commit on the target branch.
+  const {stdout: latestShaOfTargetBranch} = await exec(`git rev-parse origin/${result.base.ref}`);
+  // The sha of the latest commit on the PR.
+  const {stdout: latestShaOfPrBranch} = await exec(`git rev-parse HEAD`);
+  // The first common SHA in the history of the target branch and the latest commit in the PR.
+  const {stdout: commonAncestorSha} =
+      await exec(`git merge-base origin/${result.base.ref} ${latestShaOfPrBranch}`);
+
+  return {
+    base: {
+      ref: result.base.ref.trim(),
+      sha: result.base.sha.trim(),
+    },
+    head: {
+      ref: result.head.ref.trim(),
+      sha: result.head.sha.trim()
+    },
+    commonAncestorSha: commonAncestorSha.trim(),
+    latestShaOfTargetBranch: latestShaOfTargetBranch.trim(),
+    latestShaOfPrBranch: latestShaOfPrBranch.trim(),
+  }
+
+}