You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: reg_test.go
    path of file: ./repos/gitkube/vendor/golang.org/x/text/collate
    
    the code of the file until where you have to start completion: // Copyright 2012 The Go Authors. All ri
    
func parseUCA(builder *build.Builder) {
	r := gen.OpenUnicodeFile("UCA", "", "allkeys.txt")
	defer r.Close()
	input := bufio.NewReader(r)
	colelem := regexp.MustCompile(`\[([.*])([0-9A-F.]+)\]`)
	for i := 1; true; i++ {
		l, prefix, err := input.ReadLine()
		if err == io.EOF {
			break
		}
		Error(err)
		line := string(l)
		if prefix {
			log.Fatalf("%d: buffer overflow", i)
		}
		if len(line) == 0 || line[0] == '#' {
			continue
		}
		if line[0] == '@' {
			if strings.HasPrefix(line[1:], "version ") {
				if v := strings.Split(line[1:], " ")[1]; v != gen.UnicodeVersion() {
					log.Fatalf("incompatible version %s; want %s", v, gen.UnicodeVersion())
				}
			}
		} else {
			// parse entries
			part := strings.Split(line, " ; ")
			if len(part) != 2 {
				log.Fatalf("%d: production rule without ';': %v", i, line)
			}
			lhs := []rune{}
			for _, v := range strings.Split(part[0], " ") {
				if v != "" {
					lhs = append(lhs, rune(convHex(i, v)))
				}
			}
			vars := []int{}
			rhs := [][]int{}
			for i, m := range colelem.FindAllStringSubmatch(part[1], -1) {
				if m[1] == "*" {
					vars = append(vars, i)
				}
				elem := []int{}
				for _, h := range strings.Split(m[2], ".") {
					elem = append(elem, convHex(i, h))
				}
				rhs = append(rhs, elem)
			}
			builder.Add(lhs, rhs, vars)
		}
	}
}