Function makeLessWorker

packages/vite/src/node/plugins/css.ts:2775–2923

(
  environment: PartialEnvironment,
  resolvers: CSSAtImportResolvers,
  maxWorkers: number | undefined,
)

// #region Less
// .less
const makeLessWorker = (
  environment: PartialEnvironment,
  resolvers: CSSAtImportResolvers,
  maxWorkers: number | undefined,
) => {
  const skipRebaseUrls = (unquotedUrl: string, _rawUrl: string) => {
    // matches both
    // - interpolation: `url('@{foo}')`
    // - variable: `url(@foo)`
    return unquotedUrl[0] === '@'
  }

  const viteLessResolve = async (
    filename: string,
    dir: string,
    rootFile: string,
    mime: string | undefined,
  ) => {
    const resolved = await resolvers.less(
      environment,
      filename,
      // Less only exposes the importer's directory, not the file, so Vite can't
      // pass a real importer like CSS/Sass do. `resolve.tsconfigPaths` therefore
      // does not apply inside `.less` files. See the `resolve.tsconfigPaths` docs.
      path.join(dir, '*'),
    )
    if (!resolved) return undefined

    // don't rebase URLs in JavaScript plugins
    if (mime === 'application/javascript') {
      const file = path.resolve(resolved) // ensure os-specific flashes
      return { resolved: file }
    }

    const result = await rebaseUrls(
      environment,
      resolved,
      rootFile,
      resolvers.less,
      skipRebaseUrls,
    )
    return {
      resolved,
      contents: 'contents' in result ? result.contents : undefined,
    }
  }

  const worker = new WorkerWithFallback(
    async () => {
      const [fsp, path] = await Promise.all([
        import('node:fs/promises'),
        import('node:path'),
      ])

      let ViteLessManager: any
      const createViteLessPlugin = (
        less: typeof Less,
        rootFile: string,