while (index < mappings.size) {
    val mapping = mappings[index]
    val type = canonicalizeType(mapping.type)
    val mappedTo = mapping.mappedTo

    var unionWith: Mapping = mapping
    index++

    while (index < mappings.size) {
      val next = mappings[index]

      if (type != canonicalizeType(next.type)) break
      if (type == TYPE_MAPPED && mappedTo != next.mappedTo) break