Provide more hints for UndefinedFunctionError in case there is a behaviour

[michalmuskala]

If there's a behaviour declared on a module that expects a particular function and we get an UndefinedFunctionError on that function - the blame callback should add information about this.

The information about behaviours is available in the return of the module_info/1 function and the information about callbacks of a particular behaviour is available in the return of the behaviour_info/1 function.

[dnsbty]

I would love to help with this one if no one has picked it up by this afternoon.

[michalmuskala]

Please, go ahead 🙂

[dnsbty]

Any ideas on what those hints should actually say? I think I've got some basic ideas on this so I'll try to get a first pass on a PR up in a couple minutes

[josevalim]

I am really not sure what is the benefit here. We already warn it at compile time, so why do we need an extra information on runtime? It can even be confusing. What if we missing function is not in a module that I own? Users may think that this is something they have to fix it but they aren't really the ones to blame. So what is the use case here? :)

[michalmuskala]

I think even a very brief information required by the behaviour foo would be beneficial. It's really not a lot of work to get this information and it might be useful to understand why this function was called in the first place.

Similarly we also warn at compile-time for undefined functions with xref, yet we also implement the runtime blaming for this - it just gives more information right there when you encounter the error.

And as will all exceptions we blame today - they call can appear not in your code. That does not change the fact that understanding why something is happening, regardless if you can fix it immediately or not, is helpful.

[josevalim]

Closing in favor of #8517

[josevalim]

Thanks for expanding @michalmuskala !