Provide diagnostic information when plugin loading fails.

[plexus]

A follow-up to #35 / #42. Currently when a plugin isn't found, this is what it looks like

It would be good if we could give the user some kind of indication of what might be going wrong.

[AndreaCrotti]

Would it not be enough to print out the list of available plugins in these cases?
That should hopefully clarify what they are doing wrong automatically.

[plexus]

Any namespace on the classpath could potentially be a plugin, so that's not really feasible.

[noorfathima11]

Can this be assigned to me?

[plexus]

That would be great @noorfathima11 , thanks for looking into this. You'll find the code in kaocha.plugin. What happens there is two things

First we try to load the plugin namespace based on the plugin name. How it does this depends on what kind of name the plugin has.

If it's a namespaced (qualified) keyword like :foo.bar/baz then we try to first load foo.bar.baz, and if that doesn't succeed then we try to load foo.bar.

If it's a simple keyword that contains a period then we load the corresponding namespace, so :foo.bar.baz -> (require 'foo.bar.baz). If there is no period in the name, e.g. :notifier, then we consider the plugin to be under kaocha.plugin, so we (require 'kaocha.plugin.notifier) (that last bit is new, I've been wanting to do that forever, code coming to master today).

This namespace loading completely ignores all errors, it really doesn't care if it finds a namespace or not, it proceeds regardless.

The namespace that we try to load is expected to contain a (defmethod kaocha.plugin/-register :the-plugin-name ...). (or a (defplugin ...), which really does the same thing). After trying to load the namespace, we call -register, and this is the point where you get the error message you see above. It's printed in the :default implementation of -register, so it's what you get if no specific -register has been defined for the plugin.

So to give better diagnostics this code is going to have to become smarter. try-load-third-party-namespaces should return information about which namespaces we tried to load, and which one of them actually loaded. The default version of -register should not throw immediately, but it should return a special value so that the caller knows that the default was called.

In register (without the -) we now get all the information we need to generate a proper error message. We can check if the default version of -register got called, and if so print out a message saying which files we attempted to load, and which ones did or did not load.

For example:

ERROR: Failed loading plugin :foo.bar.baz, no such namespace foo.bar.baz.
ERROR: Failed loading plugin :foo.bar/baz, no such namespace foo.bar or foo.bar/baz.
ERROR: Failed loading plugin :foo.bar/baz, loaded namespace foo.bar, but no definition of kaocha.plugin/-register found for :foo.bar/baz.

I hope that makes sense... let me know if you have any questions!

[plexus]

Hi @noorfathima11 , I've unassigned you so others can take this up if they want you. Do let me know if you still want to try your hand at this or other issues.

[alysbrooks]

Fixed by #181