Bad error messages

[weiznich]

👋

As part of my rust foundation project grant I will work on ways to improve error messages generated by trait heavy crates. I just want to reach out to collect examples of potential bad error messages emitted by rustc due to the (mis-) usage of axum. I would be happy to hear about such cases here or as PR to this repo

[jplatte]

The worst ones definitely are when you try to register a route handler, but it doesn't implement the Handler trait for some reason. We have a macro attribute that you can apply to the handler function to get a better error message: axum_macros::debug_handler. For a list of cases where a function doesn't implement this trait, and the correponding output from debug_handler, see its trybuild fail tests. I think the error message without debug_handler is always pretty much the same – just "the trait Handler<...> is not implemented for ..." without any more detail.