URI::Generic#merge

# File tmp/rubies/ruby-3.1.3/lib/uri/generic.rb, line 1099
def merge(oth)
  rel = parser.__send__(:convert_to_uri, oth)

  if rel.absolute?
    #raise BadURIError, "both URI are absolute" if absolute?
    # hmm... should return oth for usability?
    return rel
  end

  unless self.absolute?
    raise BadURIError, "both URI are relative"
  end

  base = self.dup

  authority = rel.userinfo || rel.host || rel.port

  # RFC2396, Section 5.2, 2)
  if (rel.path.nil? || rel.path.empty?) && !authority && !rel.query
    base.fragment=(rel.fragment) if rel.fragment
    return base
  end

  base.query = nil
  base.fragment=(nil)

  # RFC2396, Section 5.2, 4)
  if !authority
    base.set_path(merge_path(base.path, rel.path)) if base.path && rel.path
  else
    # RFC2396, Section 5.2, 4)
    base.set_path(rel.path) if rel.path
  end

  # RFC2396, Section 5.2, 7)
  base.set_userinfo(rel.userinfo) if rel.userinfo
  base.set_host(rel.host)         if rel.host
  base.set_port(rel.port)         if rel.port
  base.query = rel.query       if rel.query
  base.fragment=(rel.fragment) if rel.fragment

  return base
end