Function preprocessCSS

packages/vite/src/node/plugins/css.ts:1840–1866

(
  code: string,
  filename: string,
  config: ResolvedConfig,
)

 * @experimental
 */
export async function preprocessCSS(
  code: string,
  filename: string,
  config: ResolvedConfig,
): Promise<PreprocessCSSResult> {
  let workerController = preprocessorWorkerControllerCache.get(config)

  if (!workerController) {
    // if workerController doesn't exist, create a workerController that always uses fake workers
    // because fake workers doesn't require calling `.close` unlike real workers
    alwaysFakeWorkerWorkerControllerCache ||=
      createPreprocessorWorkerController(0)
    workerController = alwaysFakeWorkerWorkerControllerCache
  }

  // `preprocessCSS` is hardcoded to use the client environment.
  // Since CSS is usually only consumed by the client, and the server builds need to match
  // the client asset chunk name to deduplicate the link reference, this may be fine in most
  // cases. We should revisit in the future if there's a case to preprocess CSS based on a
  // different environment instance.
  const environment: PartialEnvironment = new PartialEnvironment(
    'client',
    config,
  )

  return await compileCSS(environment, filename, code, workerController)
}

export async function formatPostcssSourceMap(
  rawMap: ExistingRawSourceMap,