title: Intellij does not recognize Scala List operator
body: <p>Here is the intellij warning :</p>
  
  <p><img src="https://i.stack.imgur.com/MamMc.png" alt="enter image description here"></p>
  
  <p>When overing "::" Intellij display this message : Cannot resolve symbol ::</p>
  
  <p>I have scala + sbt plugins correctly installed.</p>
  
  <p>How can i fix this error ?</p>