id: go-prefer-string-builder
valid:
  - |
    func build(parts []string) string {
        var b strings.Builder
        for _, p := range parts {
            b.WriteString(p)
        }
        return b.String()
    }
invalid:
  - |
    func concat(a string, b string) string {
        a = a + b
        return a
    }
  - |
    func appendSuffix(s string) string {
        s += "suffix"
        return s
    }