build: speed up golden testing by parallelizing

Speeds up golden testing by parallelizing. This got it down from
~85second of e.g. Material golden testing to 15seconds!t

Author: devversion

bazel/api-golden/BUILD.bazel

@@ -20,6 +20,7 @@ ts_project(
     deps = [
         "//bazel:node_modules/@microsoft/api-extractor",
         "//bazel:node_modules/@types/node",
+        "//bazel:node_modules/piscina",
         "//bazel:node_modules/typescript",
     ],
 )

bazel/api-golden/index_npm_packages.ts

@@ -12,6 +12,7 @@ import {normalizePathToPosix} from './path-normalize.js';
 import {readFileSync} from 'fs';
 import {testApiGolden} from './test_api_report.js';
 import * as fs from 'fs';
+import {Piscina} from 'piscina';
 
 /** Interface describing contents of a `package.json`. */
 export interface PackageJson {
@@ -40,11 +41,11 @@ async function main(
   const packageJsonPath = path.join(npmPackageDir, 'package.json');
   const packageJson = JSON.parse(readFileSync(packageJsonPath, 'utf8')) as PackageJson;
   const entryPoints = findEntryPointsWithinNpmPackage(npmPackageDir, packageJson);
-  const outdatedGoldens: string[] = [];
-
-  let allTestsSucceeding = true;
+  const worker = new Piscina<Parameters<typeof testApiGolden>, string>({
+    filename: path.resolve(__dirname, './test_api_report.js'),
+  });
 
-  for (const {subpath, typesEntryPointPath} of entryPoints) {
+  const processEntryPoint = async (subpath: string, typesEntryPointPath: string) => {
     // API extractor generates API reports as markdown files. For each types
     // entry-point we maintain a separate golden file. These golden files are
     // based on the name of the defining NodeJS exports subpath in the NPM package,
@@ -53,32 +54,54 @@ async function main(
     const goldenFilePath = path.join(goldenDir, goldenName);
     const moduleName = normalizePathToPosix(path.join(packageJson.name, subpath));
 
-    const actual = await testApiGolden(
+    const actual = await worker.run([
       typesEntryPointPath,
       stripExportPattern,
       typeNames,
       packageJsonPath,
       moduleName,
-    );
+    ]);
 
     if (actual === null) {
       console.error(`Could not generate API golden for subpath: "${subpath}". See errors above.`);
       process.exit(1);
     }
 
     if (approveGolden) {
-      fs.mkdirSync(path.dirname(goldenFilePath), {recursive: true});
-      fs.writeFileSync(goldenFilePath, actual, 'utf8');
+      await fs.promises.mkdir(path.dirname(goldenFilePath), {recursive: true});
+      await fs.promises.writeFile(goldenFilePath, actual, 'utf8');
     } else {
-      const expected = fs.readFileSync(goldenFilePath, 'utf8');
+      const expected = await fs.promises.readFile(goldenFilePath, 'utf8');
       if (actual !== expected) {
         // Keep track of outdated goldens for error message.
         outdatedGoldens.push(goldenName);
-        allTestsSucceeding = false;
+        return false;
       }
     }
+
+    return true;
+  };
+
+  const outdatedGoldens: string[] = [];
+  const tasks: Promise<boolean>[] = [];
+  // Process in batches. Otherwise we risk out of memory errors.
+  const batchSize = 10;
+
+  for (let i = 0; i < entryPoints.length; i += batchSize) {
+    const batchEntryPoints = entryPoints.slice(i, i + batchSize);
+
+    for (const {subpath, typesEntryPointPath} of batchEntryPoints) {
+      tasks.push(processEntryPoint(subpath, typesEntryPointPath));
+    }
+
+    // Wait for new batch.
+    await Promise.all(tasks);
   }
 
+  // Wait for final batch/retrieve all results.
+  const results = await Promise.all(tasks);
+  const allTestsSucceeding = results.every((r) => r === true);
+
   if (outdatedGoldens.length) {
     console.error(chalk.red(`The following goldens are outdated:`));
     outdatedGoldens.forEach((name) => console.info(`-  ${name}`));

bazel/api-golden/test_api_report.ts

@@ -55,7 +55,8 @@ export async function testApiGolden(
   customPackageName: string,
 ): Promise<string | null> {
   const tempDir =
-    process.env.TEST_TMPDIR ?? fs.mkdtempSync(path.join(os.tmpdir(), 'api-golden-rule'));
+    process.env.TEST_TMPDIR ??
+    (await fs.promises.mkdtemp(path.join(os.tmpdir(), 'api-golden-rule')));
   const rjsMode = process.env['RJS_MODE'] === 'true';
 
   let resolvedTypePackages: Awaited<ReturnType<typeof resolveTypePackages>> | null = null;
@@ -144,8 +145,8 @@ export async function testApiGolden(
   if (!result.succeeded) {
     return null;
   }
-  const reportOut = fs.readFileSync(reportTmpOutPath, 'utf8');
-  fs.rmSync(reportTmpOutPath);
+  const reportOut = await fs.promises.readFile(reportTmpOutPath, 'utf8');
+  await fs.promises.rm(reportTmpOutPath);
   return reportOut;
 }
 
@@ -167,7 +168,6 @@ async function processExtractorMessage(message: ExtractorMessage) {
   }
 }
 
-/** Resolves the `package.json` of the workspace executing this action. */
-function resolveWorkspacePackageJsonPath(): string {
-  return path.resolve(`./package.json`);
+export default function (args: Parameters<typeof testApiGolden>) {
+  return testApiGolden(...args);
 }

bazel/package.json

@@ -2,8 +2,9 @@
   "name": "@devinfra/bazel",
   "dependencies": {
     "@microsoft/api-extractor": "7.52.2",
-    "typescript": "5.8.2",
-    "@types/node": "22.14.0"
+    "@types/node": "22.14.0",
+    "piscina": "^4.9.2",
+    "typescript": "5.8.2"
   },
   "pnpm": {
     "onlyBuiltDependencies": []