Fix changeset checker (#5100)

Author: hsubox76

.github/workflows/check-changeset.yml

@@ -2,6 +2,10 @@ name: Check Changeset
 
 on: pull_request
 
+env:
+  GITHUB_PULL_REQUEST_HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+  GITHUB_PULL_REQUEST_BASE_SHA: ${{ github.event.pull_request.base.sha }}
+
 jobs:
   check_changeset:
     name: Check changeset vs changed files

scripts/check_changeset.ts

@@ -25,6 +25,9 @@ import fs from 'mz/fs';
 const root = resolve(__dirname, '..');
 const git = simpleGit(root);
 
+const baseRef = process.env.GITHUB_PULL_REQUEST_BASE_SHA || 'master';
+const headRef = process.env.GITHUB_PULL_REQUEST_HEAD_SHA || 'HEAD';
+
 // Version bump text converted to rankable numbers.
 const bumpRank: Record<string, number> = {
   'patch': 0,
@@ -65,7 +68,7 @@ async function getDiffData(): Promise<{
   changedPackages: Set<string>;
   changesetFile: string;
 } | null> {
-  const diff = await git.diff(['--name-only', 'origin/master...HEAD']);
+  const diff = await git.diff(['--name-only', `${baseRef}...${headRef}`]);
   const changedFiles = diff.split('\n');
   let changesetFile = '';
   const changedPackages = new Set<string>();
@@ -120,7 +123,7 @@ async function parseChangesetFile(changesetFile: string) {
 async function main() {
   const errors = [];
   try {
-    await exec('yarn changeset status');
+    await exec(`yarn changeset status --since ${baseRef}`);
     console.log(`::set-output name=BLOCKING_FAILURE::false`);
   } catch (e) {
     if (e.message.match('No changesets present')) {
@@ -173,9 +176,8 @@ async function main() {
 
       // Check for packages with a minor or major bump where 'firebase' hasn't been
       // bumped high enough or at all.
-      const { highestBump, bumpText, bumpPackage } = getHighestBump(
-        changesetPackages
-      );
+      const { highestBump, bumpText, bumpPackage } =
+        getHighestBump(changesetPackages);
       if (highestBump > bumpRank.patch) {
         if (changesetPackages['firebase'] == null) {
           errors.push(