Add "noflow" entry point mode to react-native

Summary: Reference impl for react-native-community/discussions-and-proposals#949 (exporting, then abandoning).

Differential Revision: D82653038

Author: huntie

.gitignore

@@ -174,8 +174,13 @@ fix_*.patch
 /private/react-native-fantom/.out/
 /private/react-native-fantom/tester/build/
 
-# [Experimental] Generated TS type definitions
-/packages/**/types_generated/
+# JS build output
+/packages/*/dist/
+/packages/*/dist_noflow/
+/packages/debugger-shell/build/
+
+# Generated TS type definitions
+/packages/*/types_generated/
 
 # Python
 __pycache__/

packages/react-native/package.json

@@ -31,11 +31,13 @@
   "exports": {
     ".": {
       "react-native-strict-api": "./types_generated/index.d.ts",
+      "react-native-noflow": "./dist_noflow/index.js",
       "types": "./types/index.d.ts",
       "default": "./index.js"
     },
     "./*": {
       "react-native-strict-api": null,
+      "react-native-noflow": "./dist_noflow/*.js",
       "types": "./*.d.ts",
       "default": "./*.js"
     },
@@ -75,6 +77,7 @@
   "files": [
     "build.gradle.kts",
     "cli.js",
+    "dist_noflow",
     "flow",
     "gradle.properties",
     "gradle/libs.versions.toml",

packages/virtualized-lists/package.json

@@ -22,16 +22,19 @@
   "exports": {
     ".": {
       "react-native-strict-api": "./types_generated/index.d.ts",
+      "react-native-noflow": "./dist_noflow/index.js",
       "types": "./index.d.ts",
       "default": "./index.js"
     },
     "./*": {
       "types": null,
+      "react-native-noflow": "./dist_noflow/*.js",
       "default": "./*.js"
     },
     "./package.json": "./package.json"
   },
   "files": [
+    "dist_noflow",
     "index.js",
     "index.d.ts",
     "Lists",

scripts/build/babel/noflow.config.js

@@ -0,0 +1,26 @@
+/**
+ * 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
+ */
+
+// A config which strips and transforms Flow features, to be received by either
+// Flow/JS compatible Babel presets.
+
+// IMPORTANT: We've given no public guarantee that we will preserve this
+// transform. The app/frameworks requirement is still to apply all of
+// @react-native/babel-preset.
+
+import type {BabelCoreOptions} from '@babel/core';
+
+const config: BabelCoreOptions = {
+  sourceMaps: true,
+  presets: [require.resolve('@babel/preset-flow')],
+  plugins: [require.resolve('babel-plugin-syntax-hermes-parser')],
+};
+
+module.exports = config;

scripts/build/build.js

@@ -10,6 +10,10 @@
 
 require('../shared/babelRegister').registerForScript();
 
+/*::
+import type {BuildOptions} from './config';
+*/
+
 const {PACKAGES_DIR, REPO_ROOT} = require('../shared/consts');
 const {
   buildConfig,
@@ -30,8 +34,9 @@ const {parseArgs, styleText} = require('util');
 
 const SRC_DIR = 'src';
 const BUILD_DIR = 'dist';
+const NOFLOW_BUILD_DIR = 'dist_noflow';
 const JS_FILES_PATTERN = '**/*.js';
-const IGNORE_PATTERN = '**/__{tests,mocks,fixtures}__/**';
+const IGNORE_PATTERN = '**/__{tests,mocks,fixtures,flowtests}__/**';
 
 const config = {
   allowPositionals: true,
@@ -77,6 +82,13 @@ async function build() {
 
   let ok = true;
   for (const packageName of packagesToBuild) {
+    const {target} = getBuildOptions(packageName);
+
+    if (target === 'noflow') {
+      await buildNoFlowTarget(packageName);
+      continue;
+    }
+
     await buildPackage(packageName, prepack);
   }
 
@@ -163,8 +175,9 @@ async function buildFile(
 ) {
   const {silent = false} = options;
   const packageName = getPackageName(file);
-  const buildPath = getBuildPath(file);
-  const {emitFlowDefs, emitTypeScriptDefs} = getBuildOptions(packageName);
+  const buildOptions = getBuildOptions(packageName);
+  const {emitFlowDefs, emitTypeScriptDefs} = buildOptions;
+  const buildPath = getBuildPath(file, buildOptions);
 
   const logResult = ({copied, desc} /*: {copied: boolean, desc?: string} */) =>
     silent ||
@@ -226,6 +239,87 @@ async function buildFile(
   logResult({copied: true});
 }
 
+async function buildNoFlowTarget(packageName /*: string */) {
+  try {
+    const buildOptions = getBuildOptions(packageName);
+    const {srcOverride} = buildOptions;
+
+    process.stdout.write(
+      `${packageName} ${styleText('yellow', '(noflow)')} ${styleText('dim', '.').repeat(63 - packageName.length)} `,
+    );
+
+    const files = glob.sync(
+      path.resolve(
+        PACKAGES_DIR,
+        packageName,
+        ...(srcOverride != null
+          ? ['{', srcOverride, '}']
+          : [SRC_DIR, '**/*.js']),
+      ),
+      {
+        nodir: true,
+        ignore: [IGNORE_PATTERN],
+      },
+    );
+
+    for (const file of files) {
+      const filePath = path.normalize(file);
+      const buildPath = getBuildPath(filePath, buildOptions);
+      const prettierConfig = {parser: 'babel'};
+      const source = await fs.readFile(file, 'utf-8');
+
+      await fs.mkdir(path.dirname(buildPath), {recursive: true});
+
+      // If file contains `@noflow`, copy only
+      if (/@noflow/.test(source)) {
+        await fs.copyFile(file, buildPath);
+        continue;
+      }
+
+      // Apply Flow transforms
+      const babelResult = await babel.transformFileAsync(
+        filePath,
+        getBabelConfig(packageName),
+      );
+      const transformed = await prettier.format(
+        babelResult.code,
+        /* $FlowFixMe[incompatible-type] Natural Inference rollout. See
+         * https://fburl.com/workplace/6291gfvu */
+        prettierConfig,
+      );
+
+      // Write transformed file with source map comment
+      const relativeSourcePath = path.relative(
+        path.dirname(buildPath),
+        filePath,
+      );
+      const sourceMapComment = `\n//# sourceMappingURL=${path.basename(buildPath)}.map`;
+      await fs.writeFile(buildPath, transformed + sourceMapComment);
+
+      // Write source map file
+      if (babelResult.map) {
+        const sourceMapPath = buildPath + '.map';
+        const sourceMap = {
+          ...babelResult.map,
+          sources: [relativeSourcePath],
+        };
+        await fs.writeFile(sourceMapPath, JSON.stringify(sourceMap, null, 2));
+      }
+    }
+
+    process.stdout.write(
+      styleText(['reset', 'inverse', 'bold', 'green'], ' DONE '),
+    );
+  } catch (e) {
+    process.stdout.write(
+      styleText(['reset', 'inverse', 'bold', 'red'], ' FAIL ') + '\n',
+    );
+    throw e;
+  } finally {
+    process.stdout.write('\n');
+  }
+}
+
 /*::
 type PackageJson = {
   name: string,
@@ -356,13 +450,19 @@ function getPackageName(file /*: string */) /*: string */ {
   return path.relative(PACKAGES_DIR, file).split(path.sep)[0];
 }
 
-function getBuildPath(file /*: string */) /*: string */ {
+function getBuildPath(
+  file /*: string */,
+  {srcOverride, target} /*: BuildOptions */,
+) /*: string */ {
   const packageDir = path.join(PACKAGES_DIR, getPackageName(file));
 
   return path.join(
     packageDir,
     file
-      .replace(path.join(packageDir, SRC_DIR), BUILD_DIR)
+      .replace(
+        path.join(packageDir, srcOverride ? '' : SRC_DIR),
+        target === 'noflow' ? NOFLOW_BUILD_DIR : BUILD_DIR,
+      )
       .replace('.flow.js', '.js'),
   );
 }

scripts/build/config.js

@@ -14,13 +14,24 @@ const {ModuleResolutionKind} = require('typescript');
 
 export type BuildOptions = Readonly<{
   // The target runtime to compile for.
-  target: 'node',
+  target:
+    | 'node'
+    // A special compile target aligning with the "react-native-noflow" exports
+    // condition. This entry point allows compatible native parsers (e.g. Bun
+    // and SWC) to consume React Native without Flow types. Output will be stored
+    // in `dist_noflow/`.
+    | 'noflow',
 
   // Whether to emit Flow definition files (.js.flow) (default: true).
   emitFlowDefs?: boolean,
 
   // Whether to emit TypeScript definition files (.d.ts) (default: false).
   emitTypeScriptDefs?: boolean,
+
+  // Source dir glob override (default: 'src/**/*'). This is intended to provide
+  // compatibility for the react-native package only. This setting is ignored
+  // unless using the 'noflow' compile target.
+  srcOverride?: string | null,
 }>;
 
 export type BuildConfig = Readonly<{
@@ -57,16 +68,25 @@ const buildConfig: BuildConfig = {
       emitTypeScriptDefs: true,
       target: 'node',
     },
+    'react-native': {
+      srcOverride: 'Libraries/**/*.js,src/**/*.js,index.js',
+      target: 'noflow',
+    },
     'react-native-compatibility-check': {
       emitTypeScriptDefs: true,
       target: 'node',
     },
+    'virtualized-lists': {
+      srcOverride: 'Lists/**/*.js,Utilities/**/*.js,index.js',
+      target: 'noflow',
+    },
   },
 };
 
 const defaultBuildOptions = {
   emitFlowDefs: true,
   emitTypeScriptDefs: false,
+  srcOverride: null,
 };
 
 function getBuildOptions(
@@ -86,6 +106,8 @@ function getBabelConfig(
   switch (target) {
     case 'node':
       return require('./babel/node.config.js');
+    case 'noflow':
+      return require('./babel/noflow.config.js');
   }
 }