main.go

func (s *server) run() error {
  // do things
  widget, err := widgetClient.Foo("abc")
  if err != nil {
    // QUESTION: what should the top of the stack be (what line)?
    optionallyLogStackAtDebugLogLevel(err)
    // other error handling
  }
}

func (c *WidgetGRPCClient) Foo(s string) (Widget, error) {
  response, err := c.grpcClient.Foo(context.Background(), &proto.FooRequest{S: s})
  if err != nil {
    return nil, convertGRPCError(err)
  }
  // ...
}

func (s *WidgetGRPCServer) Foo(ctx context.Context, req *proto.FooRequest) (*proto.FooResponse, error) {
  widget, err := s.widgetImpl.Foo(req.S)
  if err != nil {
    return nil, toGRPCError(err)
  }
  // ...
}

func (w *widgetImpl) Foo(s string) (Widget, error) {
  // do stuff
  // oh no, an error!
  return nil, newBadWidgetError()
}