build: ensure that refs and shas for PRs only need to be requested once (#36207)

This is done by requesting the refs and shas for the PR when the
env.sh script is run.  Additionally, the env.sh script is now setup
to write all of the environment variables created to a cache file
and subsequent loads of the environment load the values from there.

The get-refs-and-shas-for-target.js script now also first attempts
to load the refs and shas from an environment variable before
falling back to requesting from github via the API.

PR Close #36207

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

@@ -6,6 +6,11 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+// NOTE: When invoked directly via node, this script will take the first positional
+// arguement as to be the PR number, and log out the ref and sha information in its
+// JSON format.  For other usages, the function to get the ref and sha information
+// may be imported by another script to be invoked.
+
 // This script uses `console` to print messages to the user.
 // tslint:disable:no-console
 
@@ -16,7 +21,18 @@ 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'}};
+  let options = {headers: {'User-Agent': 'angular'}};
+
+  // If a github token is present, use it for authorization.
+  const githubToken = process.env.TOKEN || process.env.GITHUB_TOKEN || '';
+  if (githubToken) {
+    options = {
+      headers: {
+        Authorization: `token ${githubToken}`,
+        ...options.headers,
+      }
+    };
+  }
 
   return new Promise((resolve, reject) => {
     https
@@ -54,9 +70,19 @@ async function requestDataFromGithub(url) {
         .on('error', (e) => { reject(e); });
   });
 }
+// clang-format off
+// clang keeps trying to put the function name on the next line.
+async function getRefsAndShasForTarget(prNumber, suppressLog) {
+  // clang-format on
+  // If the environment variable already contains the refs and shas, reuse them.
+  if (process.env['GITHUB_REFS_AND_SHAS']) {
+    suppressLog ||
+        console.info(`Retrieved refs and SHAs for PR ${prNumber} from environment variables.`);
+    return JSON.parse(process.env['GITHUB_REFS_AND_SHAS']);
+  }
 
-module.exports = async function getRefsAndShasForTarget(prNumber) {
-  console.log(`Getting refs and SHAs for PR ${prNumber} on angular/angular.`);
+  suppressLog ||
+      console.info(`Getting refs and SHAs for PR ${prNumber} on angular/angular from Github.`);
   const pullsUrl = `https://api.github.com/repos/angular/angular/pulls/${prNumber}`;
   const result = await requestDataFromGithub(pullsUrl);
 
@@ -84,6 +110,19 @@ module.exports = async function getRefsAndShasForTarget(prNumber) {
     latestShaOfTargetBranch: latestShaOfTargetBranch.trim(),
     latestShaOfPrBranch: latestShaOfPrBranch.trim(),
   };
-
   return output;
-};
+}
+
+// If the script is called directly, log the output of the refs and sha for the
+// requested PR.
+if (require.main === module) {
+  const run = async() => {
+    const prNumber = Number.parseInt(process.argv[2], 10);
+    if (!!prNumber) {
+      console.info(JSON.stringify(await getRefsAndShasForTarget(prNumber, true)));
+    }
+  };
+  run();
+}
+
+module.exports = getRefsAndShasForTarget;