Function combineSourcemaps

packages/vite/src/node/utils.ts:857–911

(
  filename: string,
  sourcemapList: Array<DecodedSourceMap | RawSourceMap>,
)

 * Note that the length of sourcemapList must be 2.
 */
export function combineSourcemaps(
  filename: string,
  sourcemapList: Array<DecodedSourceMap | RawSourceMap>,
): RawSourceMap {
  if (
    sourcemapList.length === 0 ||
    sourcemapList.every((m) => m.sources.length === 0)
  ) {
    return { ...nullSourceMap }
  }

  // hack for parse broken with normalized absolute paths on windows (C:/path/to/something).
  // escape them to linux like paths
  // also avoid mutation here to prevent breaking plugin's using cache to generate sourcemaps like vue (see #7442)
  sourcemapList = sourcemapList.map((sourcemap) => {
    const newSourcemaps = { ...sourcemap }
    newSourcemaps.sources = sourcemap.sources.map((source) =>
      source ? escapeToLinuxLikePath(source) : null,
    )
    if (sourcemap.sourceRoot) {
      newSourcemaps.sourceRoot = escapeToLinuxLikePath(sourcemap.sourceRoot)
    }
    return newSourcemaps
  })
  const escapedFilename = escapeToLinuxLikePath(filename)

  // We don't declare type here so we can convert/fake/map as RawSourceMap
  let map //: SourceMap
  let mapIndex = 1
  const useArrayInterface =
    sourcemapList.slice(0, -1).find((m) => m.sources.length !== 1) === undefined
  if (useArrayInterface) {
    map = remapping(sourcemapList, () => null)
  } else {
    map = remapping(sourcemapList[0], function loader(sourcefile) {
      // this line assumes that the length of the sourcemapList is 2
      if (sourcefile === escapedFilename && sourcemapList[mapIndex]) {
        return sourcemapList[mapIndex++]
      } else {
        return null
      }
    })
  }
  if (!map.file) {
    delete map.file
  }

  // unescape the previous hack
  map.sources = map.sources.map((source) =>
    source ? unescapeToLinuxLikePath(source) : source,
  )
  map.file = filename

  return map as RawSourceMap
}

export function unique<T>(arr: T[]): T[] {
  return Array.from(new Set(arr))