Function merge

packages/cli/src/internal/options.ts:2022–2036

(
  map1: HashMap.HashMap<string, ReadonlyArray<string>>,
  map2: ReadonlyArray<[string, ReadonlyArray<string>]>
)

 * Sums the list associated with the same key.
 */
const merge = (
  map1: HashMap.HashMap<string, ReadonlyArray<string>>,
  map2: ReadonlyArray<[string, ReadonlyArray<string>]>
): HashMap.HashMap<string, ReadonlyArray<string>> => {
  if (Arr.isNonEmptyReadonlyArray(map2)) {
    const head = Arr.headNonEmpty(map2)
    const tail = Arr.tailNonEmpty(map2)
    const newMap = Option.match(HashMap.get(map1, head[0]), {
      onNone: () => HashMap.set(map1, head[0], head[1]),
      onSome: (elems) => HashMap.set(map1, head[0], Arr.appendAll(elems, head[1]))
    })
    return merge(newMap, tail)
  }
  return map1
}

// =============================================================================
// Completion Internals