index.js

/**
 * 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
 * @format
 * @oncall react_native
 */

'use strict';

import type {BabelCoreOptions, BabelFileMetadata} from '@babel/core';

const {parseSync, transformFromAstSync} = require('@babel/core');
const nullthrows = require('nullthrows');

export type CustomTransformOptions = {
  [string]: mixed,
  __proto__: null,
  ...
};

export type TransformProfile = 'default' | 'hermes-stable' | 'hermes-canary';

type BabelTransformerOptions = $ReadOnly<{
  customTransformOptions?: CustomTransformOptions,
  dev: boolean,
  enableBabelRCLookup?: boolean,
  enableBabelRuntime: boolean | string,
  extendsBabelConfigPath?: string,
  experimentalImportSupport?: boolean,
  hermesParser?: boolean,
  hot: boolean,
  inlineRequires: boolean,
  nonInlinedRequires?: $ReadOnlyArray<string>,
  minify: boolean,
  unstable_disableES6Transforms?: boolean,
  platform: ?string,
  projectRoot: string,
  publicPath: string,
  unstable_transformProfile?: TransformProfile,
  globalPrefix: string,
  ...
}>;

export type BabelTransformerArgs = $ReadOnly<{
  filename: string,
  options: BabelTransformerOptions,
  plugins?: $PropertyType<BabelCoreOptions, 'plugins'>,
  src: string,
}>;

export type BabelFileFunctionMapMetadata = $ReadOnly<{
  names: $ReadOnlyArray<string>,
  mappings: string,
}>;

export type MetroBabelFileMetadata = {
  ...BabelFileMetadata,
  metro?: ?{
    functionMap?: ?BabelFileFunctionMapMetadata,
    ...
  },
  ...
};

export type BabelTransformer = {
  transform: BabelTransformerArgs => {
    ast: BabelNodeFile,
    // Deprecated, will be removed in a future breaking release. Function maps
    // will be generated by an input Babel plugin instead and written into
    // `metadata` - transformers don't need to return them explicitly.
    functionMap?: BabelFileFunctionMapMetadata,
    metadata?: MetroBabelFileMetadata,
    ...
  },
  getCacheKey?: () => string,
};

function transform({filename, options, plugins, src}: BabelTransformerArgs) {
  const OLD_BABEL_ENV = process.env.BABEL_ENV;
  process.env.BABEL_ENV = options.dev
    ? 'development'
    : process.env.BABEL_ENV || 'production';

  try {
    const babelConfig = {
      caller: {name: 'metro', bundler: 'metro', platform: options.platform},
      ast: true,
      babelrc: options.enableBabelRCLookup,
      code: false,
      cwd: options.projectRoot,
      highlightCode: true,
      filename,
      plugins,
      sourceType: 'module',

      // NOTE(EvanBacon): We split the parse/transform steps up to accommodate
      // Hermes parsing, but this defaults to cloning the AST which increases
      // the transformation time by a fair amount.
      // You get this behavior by default when using Babel's `transform` method directly.
      cloneInputAst: false,
    };
    const sourceAst = options.hermesParser
      ? require('hermes-parser').parse(src, {
          babel: true,
          sourceType: babelConfig.sourceType,
        })
      : parseSync(src, babelConfig);

    const transformResult = transformFromAstSync<MetroBabelFileMetadata>(
      sourceAst,
      src,
      babelConfig,
    );

    return {
      ast: nullthrows(transformResult.ast),
      metadata: transformResult.metadata,
    };
  } finally {
    if (OLD_BABEL_ENV) {
      process.env.BABEL_ENV = OLD_BABEL_ENV;
    }
  }
}

module.exports = ({
  transform,
}: BabelTransformer);