Function formatPatchToDiscardChanges

app/src/lib/patch-formatter.ts:251–335

(
  filePath: string,
  diff: ITextDiff,
  selection: DiffSelection
)

 * @param selection  A selection of lines from the diff object that we want to discard.
 */
export function formatPatchToDiscardChanges(
  filePath: string,
  diff: ITextDiff,
  selection: DiffSelection
): string | null {
  let patch = ''

  diff.hunks.forEach((hunk, hunkIndex) => {
    let hunkBuf = ''

    let oldCount = 0
    let newCount = 0

    let anyAdditionsOrDeletions = false

    hunk.lines.forEach((line, lineIndex) => {
      const absoluteIndex = hunk.unifiedDiffStart + lineIndex

      // We write our own hunk headers
      if (line.type === DiffLineType.Hunk) {
        return
      }

      // Context lines can always be let through, they will
      // never appear for new files.
      if (line.type === DiffLineType.Context) {
        hunkBuf += `${line.text}\n`
        oldCount++
        newCount++
      } else if (selection.isSelected(absoluteIndex)) {
        // Reverse the change (if it was an added line, treat it as removed and vice versa).
        if (line.type === DiffLineType.Add) {
          hunkBuf += `-${line.text.substring(1)}\n`
          newCount++
        } else if (line.type === DiffLineType.Delete) {
          hunkBuf += `+${line.text.substring(1)}\n`
          oldCount++
        } else {
          assertNever(line.type, `Unsupported line type ${line.type}`)
        }

        anyAdditionsOrDeletions = true
      } else {
        if (line.type === DiffLineType.Add) {
          // An unselected added line will stay in the file after discarding the changes,
          // so we just print it untouched on the diff.
          oldCount++
          newCount++
          hunkBuf += ` ${line.text.substring(1)}\n`
        } else if (line.type === DiffLineType.Delete) {
          // An unselected removed line has no impact on this patch since it's not
          // found on the current working copy of the file, so we can ignore it.
          return
        } else {
          // Guarantee that we've covered all the line types.
          assertNever(line.type, `Unsupported line type ${line.type}`)
        }
      }