title: Go "cannot find package"
body: <p>I have a public repository <a href="https://github.com/zhksoftGo/Packet" rel="nofollow noreferrer">https://github.com/zhksoftGo/Packet</a>. I have put some common go files in it.
  Currently, there are two.</p>
  <pre><code> Packet.go under github.com/zhksoftGo/Packet
   TypeDefineCactus.go under github.com/zhksoftGo/Packet/protocol/Cactus/
  </code></pre>
  <p>I meet trouble at importing one of them.</p>
  <pre><code>import &quot;github.com/zhksoftGo/Packet&quot;   // works fine
  import &quot;github.com/zhksoftGo/Packet/protocol/Cactus&quot; // &quot;cannot find package&quot;
  </code></pre>
  <p>//referer project .mod file:</p>
  <pre><code>module github.com/zhksoftGo/SnowWolf
  
  go 1.15
  
  require (
      github.com/gookit/slog v0.1.3
      github.com/panjf2000/gnet v1.4.2
      github.com/smartystreets/goconvey v1.6.4 // indirect
      github.com/zhksoftGo/Packet v0.0.0-20210320131229-5311a044e61f
      gopkg.in/ini.v1 v1.62.0
  )
  </code></pre>
  <p>I have already set GO111MODULE=on. Could somebody help on this?</p>