display trace/warning messages

[daniel-sampliner]

Fixes issue #128.

[daniel-sampliner]

I'm a definitely a complete novice to Haskell, so I won't deny this PR carries the stench of a copy-and-paste hack job. No offense taken if this is rejected in favor of a cleaner solution.

[maralorn]

Don’t worry. Thank you for looking into this. And I am glad that you learned a bit of Haskell along the way. :D

I will look into it as soon as I got the time.

[maralorn]

The Haskell code looks quite fine to me. Only question is what is operationally the "correct" solution. Does it make sense to special case messages prepended with "trace"? Are there other similar messages which we should also display?

[daniel-sampliner]

Does it make sense to special case messages prepended with "trace"? Are there other similar messages which we should also display?

Yeah I was concerned about the same. I was hoping that these kind of messages would have a unique level in the json logs (or any other concrete signature), but unfortunately that doesn't appear to be the case.

That being said, is it possible to print messages to the console outside of builtins.trace (or throwing an error, but I think we can safely say errors are already covered by nom)? There isn't anything like printf, so I imagine any kind of abstractions in nixos modules and the various lib.traceX are all eventually going to call builtins.trace?

[maralorn]

Thank you. This is an improvement as is.

[viperML]

Could we get a new release tag that includes this PR? Or maybe something else blocking on master?

[maralorn]

There is a test failing on the main branch and I haven’t had the patience to look into it.
Also I want to fine tune and improve the trace display a bit before I release it.
So this might take a bit, sorry.

[viperML]

No problem, just wanted to know about that 🙂