formatPatch

formatPatch(result: DiffResult, options?: DiffPatchOptions): string

interface DiffPatchOptions {
  context?: number; // 3
  before?: string; // 'before'
  after?: string; // 'after'
}

String formatPatch(DiffResult result, [DiffPatchOptions? options]);

class DiffPatchOptions {
  const DiffPatchOptions({this.context = 3, this.before = 'before', this.after = 'after'});
}

A comparison written out as a unified diff. context is how many unchanged lines are kept either side of a change, and before and after are the two names written into the header.

It returns an empty string for two documents that are the same. parsePatch reads one back.