[skip ci] Add API to run benchmarks in Fantom (facebook#48452)

Summary:

Changelog: [internal]

Implements a basic API to run benchmarks with Fantom (using `tinybench` under the hood):

```
import {benchmark} from 'react-native/fantom';

benchmark
  .suite('Suite name', {
    // options
  })
  .add(
    'Test name',
    () => {
      // code to benchmark
    },
    {
      beforeAll: () => {},
      beforeEach: () => {},
      afterEach: () => {},
      afterAll: () => {},
    },
  )
  .verify(results => {
    // check results and throw an error if the expectations fail
  });
```

Features:
* Print benchmark results in the console as a table.
* It opts into optimized builds automatically
* Verifies that optimized build is used (unless manually opting out of the check via `disableOptimizedBuildCheck`).
* Supports verification of results (making expectations and making the test fail if the benchmark doesn't meet some expectations).

Reviewed By: rshest

Differential Revision: D66926183

packages/react-native-fantom/runner/getFantomTestConfig.js

@@ -46,6 +46,8 @@ const DEFAULT_MODE: FantomTestConfigMode =
 
 const FANTOM_FLAG_FORMAT = /^(\w+):(\w+)$/;
 
+const FANTOM_BENCHMARK_SUITE_RE = /\nbenchmark(\s*)\.suite\(/g;
+
 /**
  * Extracts the Fantom configuration from the test file, specified as part of
  * the docblock comment. E.g.:
@@ -69,7 +71,9 @@ const FANTOM_FLAG_FORMAT = /^(\w+):(\w+)$/;
 export default function getFantomTestConfig(
   testPath: string,
 ): FantomTestConfig {
-  const docblock = extract(fs.readFileSync(testPath, 'utf8'));
+  const testContents = fs.readFileSync(testPath, 'utf8');
+
+  const docblock = extract(testContents);
   const pragmas = parse(docblock) as DocblockPragmas;
 
   const config: FantomTestConfig = {
@@ -102,6 +106,10 @@ export default function getFantomTestConfig(
       default:
         throw new Error(`Invalid Fantom mode: ${mode}`);
     }
+  } else {
+    if (FANTOM_BENCHMARK_SUITE_RE.test(testContents)) {
+      config.mode = FantomTestConfigMode.Optimized;
+    }
   }
 
   const maybeRawFlagConfig = pragmas.fantom_flags;

packages/react-native-fantom/src/Benchmark.js

@@ -0,0 +1,99 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+import nullthrows from 'nullthrows';
+import NativeCPUTime from 'react-native/src/private/specs/modules/NativeCPUTime';
+import {
+  Bench,
+  type BenchOptions,
+  type FnOptions,
+  type TaskResult,
+} from 'tinybench';
+
+type SuiteOptions = $ReadOnly<{
+  ...Pick<
+    BenchOptions,
+    'iterations' | 'time' | 'warmup' | 'warmupIterations' | 'warmupTime',
+  >,
+  disableOptimizedBuildCheck?: boolean,
+}>;
+
+type SuiteResults = Array<$ReadOnly<TaskResult>>;
+
+interface SuiteAPI {
+  add(name: string, fn: () => void, options?: FnOptions): SuiteAPI;
+  verify(fn: (results: SuiteResults) => void): SuiteAPI;
+}
+
+export function suite(
+  suiteName: string,
+  suiteOptions?: ?SuiteOptions,
+): SuiteAPI {
+  const {disableOptimizedBuildCheck, ...benchOptions} = suiteOptions ?? {};
+
+  const bench = new Bench({
+    ...benchOptions,
+    name: suiteName,
+    throws: true,
+    now: () => NativeCPUTime.getCPUTimeNanos() / 1000000,
+  });
+
+  const verifyFns = [];
+
+  global.it(suiteName, () => {
+    if (bench.tasks.length === 0) {
+      throw new Error('No benchmark tests defined');
+    }
+
+    bench.runSync();
+
+    printBenchmarkResults(bench);
+
+    for (const verify of verifyFns) {
+      verify(bench.results);
+    }
+
+    if (!NativeCPUTime.hasAccurateCPUTimeNanosForBenchmarks()) {
+      throw new Error(
+        '`NativeCPUTime` module does not provide accurate CPU time information in this environment. Please run the benchmarks in an environment where it does.',
+      );
+    }
+
+    if (__DEV__ && disableOptimizedBuildCheck !== true) {
+      throw new Error('Benchmarks should not be run in development mode');
+    }
+  });
+
+  const suiteAPI = {
+    add(name: string, fn: () => void, options?: FnOptions): SuiteAPI {
+      bench.add(name, fn, options);
+      return suiteAPI;
+    },
+    verify(fn: (results: SuiteResults) => void): SuiteAPI {
+      verifyFns.push(fn);
+      return suiteAPI;
+    },
+  };
+
+  return suiteAPI;
+}
+
+function printBenchmarkResults(bench: Bench) {
+  const longestTaskNameLength = bench.tasks.reduce(
+    (maxLength, task) => Math.max(maxLength, task.name.length),
+    0,
+  );
+  const separatorWidth = 121 + longestTaskNameLength - 'Task name'.length;
+
+  console.log('-'.repeat(separatorWidth));
+  console.log(bench.name);
+  console.table(nullthrows(bench.table()));
+  console.log('-'.repeat(separatorWidth) + '\n');
+}

packages/react-native-fantom/src/index.js

@@ -14,6 +14,7 @@ import type {
 } from './getFantomRenderedOutput';
 import type {MixedElement} from 'react';
 
+import * as Benchmark from './Benchmark';
 import getFantomRenderedOutput from './getFantomRenderedOutput';
 import ReactFabric from 'react-native/Libraries/Renderer/shims/ReactFabric';
 import NativeFantom from 'react-native/src/private/specs/modules/NativeFantom';
@@ -63,7 +64,7 @@ class Root {
       this.#hasRendered = true;
     }
 
-    ReactFabric.render(element, this.#surfaceId, () => {}, true);
+    ReactFabric.render(element, this.#surfaceId, null, true);
   }
 
   getMountingLogs(): Array<string> {
@@ -137,3 +138,69 @@ export function runWorkLoop(): void {
 export function createRoot(rootConfig?: RootConfig): Root {
   return new Root(rootConfig);
 }
+
+export const benchmark = Benchmark;
+
+/**
+ * Quick and dirty polyfills required by tinybench.
+ */
+
+if (typeof global.Event === 'undefined') {
+  global.Event = class Event {
+    constructor() {}
+  };
+} else {
+  console.warn(
+    'The global Event class is already defined. If this API is already defined by React Native, you might want to remove this logic.',
+  );
+}
+
+if (typeof global.EventTarget === 'undefined') {
+  global.EventTarget = class EventTarget {
+    listeners: $FlowFixMe;
+
+    constructor() {
+      this.listeners = {};
+    }
+
+    addEventListener(type: string, cb: () => void) {
+      if (!(type in this.listeners)) {
+        this.listeners[type] = [];
+      }
+      this.listeners[type].push(cb);
+    }
+
+    removeEventListener(type: string, cb: () => void): void {
+      if (!(type in this.listeners)) {
+        return;
+      }
+      let handlers = this.listeners[type];
+      for (let i in handlers) {
+        if (cb === handlers[i]) {
+          handlers.splice(i, 1);
+          return;
+        }
+      }
+    }
+
+    dispatchEvent(type: string, event: Event) {
+      if (!(type in this.listeners)) {
+        return;
+      }
+      let handlers = this.listeners[type];
+      for (let i in handlers) {
+        handlers[i].call(this, event);
+      }
+    }
+
+    clearEventListeners() {
+      for (let i in this.listeners) {
+        delete this.listeners[i];
+      }
+    }
+  };
+} else {
+  console.warn(
+    'The global Event class is already defined. If this API is already defined by React Native, you might want to remove this logic.',
+  );
+}