-- in.cue --
a: 12
#Controller: settings: {
    controller: #Controller
}

-- out/eval --
Errors:
#Controller.settings.controller: structural cycle

Result:
(_|_){
  // [structural cycle]
  a: (int){ 12 }
  #Controller: (_|_){
    // [structural cycle]
    settings: (_|_){
      // [structural cycle]
      controller: (_|_){
        // [structural cycle] #Controller.settings.controller: structural cycle
        settings: (_|_){// {
          //   controller: 〈2;#Controller〉
          // }
        }
      }
    }
  }
}
-- out/compile --
--- in.cue
{
  a: 12
  #Controller: {
    settings: {
      controller: 〈2;#Controller〉
    }
  }
}