-- in.cue --
#Def: {
    "@type": string
}

-- out/TestGenerateOpenAPI/out.json --
{
   "openapi": "3.0.0",
   "info": {
      "title": "Generated by cue.",
      "version": "no version"
   },
   "paths": {},
   "components": {
      "schemas": {
         "Def": {
            "type": "object",
            "required": [
               "@type"
            ],
            "properties": {
               "@type": {
                  "type": "string"
               }
            }
         }
      }
   }
}