[core] Don't force a remote when listing prettier changes (#18794)

package.json

@@ -37,7 +37,7 @@
     "test:karma": "cross-env NODE_ENV=test karma start test/karma.conf.js",
     "test:regressions": "webpack --config test/regressions/webpack.config.js && rimraf test/regressions/screenshots/chrome/* && vrtest run --config test/vrtest.config.js --record",
     "test:umd": "node packages/material-ui/test/umd/run.js",
-    "test:unit": "cross-env NODE_ENV=test mocha 'packages/**/*.test.js' 'docs/**/*.test.js' --exclude '**/node_modules/**'",
+    "test:unit": "cross-env NODE_ENV=test mocha 'packages/**/*.test.js' 'docs/**/*.test.js' 'scripts/**/*.test.js' --exclude '**/node_modules/**'",
     "test:watch": "yarn test:unit --watch",
     "typescript": "lerna run typescript --parallel"
   },

scripts/listChangedFiles.js

@@ -27,7 +27,8 @@ async function execGitCmd(args) {
 }
 
 async function listChangedFiles() {
-  const mergeBase = await execGitCmd(['rev-parse', 'origin/master']);
+  const comparedBranch = process.env.CIRCLECI ? 'origin/master' : 'master';
+  const mergeBase = await execGitCmd(['rev-parse', comparedBranch]);
   const gitDiff = await execGitCmd(['diff', '--name-only', mergeBase]);
   const gitLs = await execGitCmd(['ls-files', '--others', '--exclude-standard']);
   return new Set([...gitDiff, ...gitLs]);

scripts/listChangedFiles.test.js

@@ -0,0 +1,23 @@
+const listChangedFiles = require('./listChangedFiles');
+const fs = require('fs');
+const rimraf = require('rimraf');
+const { promisify } = require('util');
+const { assert } = require('chai');
+
+const writeFileAsync = promisify(fs.writeFile);
+const rimrafAsync = promisify(rimraf);
+
+describe('listChangedFiles', () => {
+  it('should detect changes', async () => {
+    const changesBefore = await listChangedFiles();
+    const testFile = 'someTestFile.js';
+    try {
+      await writeFileAsync(testFile, 'console.log("hello");');
+      const changesAfterAdd = await listChangedFiles();
+      const addedFiles = Array.from(changesAfterAdd).filter(file => !changesBefore.has(file));
+      assert.deepEqual(addedFiles, [testFile]);
+    } finally {
+      await rimrafAsync(testFile);
+    }
+  });
+});