code: func (g *genProtoIDL) Filter(c *generator.Context, t *types.Type) bool {
  	tagVals := types.ExtractCommentTags("+", t.CommentLines)["protobuf"]
  	if tagVals != nil {
  		if tagVals[0] == "false" {
  			// Type specified "false".
  			return false
  		}
  		if tagVals[0] == "true" {
  			// Type specified "true".
  			return true
  		}
  		klog.Fatalf(`Comment tag "protobuf" must be true or false, found: %q`, tagVals[0])
  	}
  	if !g.generateAll {
  		// We're not generating everything.
  		return false
  	}
  	seen := map[*types.Type]bool{}
  	ok := isProtoable(seen, t)
  	return ok
  }
docs: // Filter ignores types that are identified as not exportable.