async transformFile()

in packages/metro/src/DeltaBundler/Transformer.js [66:147]

• 63 lines of code
• 5 McCabe index (conditional complexity)

  async transformFile(
    filePath: string,
    transformerOptions: TransformOptions,
  ): Promise<TransformResultWithSource<>> {
    const cache = this._cache;

    const {
      customTransformOptions,
      dev,
      experimentalImportSupport,
      hot,
      inlinePlatform,
      inlineRequires,
      minify,
      nonInlinedRequires,
      platform,
      runtimeBytecodeVersion,
      type,
      unstable_disableES6Transforms,
      unstable_transformProfile,
      ...extra
    } = transformerOptions;

    for (const key in extra) {
      // $FlowFixMe[cannot-resolve-name]
      if (hasOwnProperty.call(extra, key)) {
        throw new Error(
          'Extra keys detected: ' + Object.keys(extra).join(', '),
        );
      }
    }

    const localPath = path.relative(this._config.projectRoot, filePath);

    const partialKey = stableHash([
      // This is the hash related to the global Bundler config.
      this._baseHash,

      // Path.
      localPath,

      customTransformOptions,
      dev,
      experimentalImportSupport,
      hot,
      inlinePlatform,
      inlineRequires,
      minify,
      nonInlinedRequires,
      platform,
      runtimeBytecodeVersion,
      type,
      unstable_disableES6Transforms,
      unstable_transformProfile,
    ]);

    const sha1 = this._getSha1(filePath);
    let fullKey = Buffer.concat([partialKey, Buffer.from(sha1, 'hex')]);
    const result = await cache.get(fullKey);

    // A valid result from the cache is used directly; otherwise we call into
    // the transformer to computed the corresponding result.
    const data = result
      ? {result, sha1}
      : await this._workerFarm.transform(localPath, transformerOptions);

    // Only re-compute the full key if the SHA-1 changed. This is because
    // references are used by the cache implementation in a weak map to keep
    // track of the cache that returned the result.
    if (sha1 !== data.sha1) {
      fullKey = Buffer.concat([partialKey, Buffer.from(data.sha1, 'hex')]);
    }

    cache.set(fullKey, data.result);

    return {
      ...data.result,
      getSource(): Buffer {
        return fs.readFileSync(filePath);
      },
    };
  }