Elixir: Logger and dialyzer

Created on 6 Apr 2016 · 5Comments · Source: elixir-lang/elixir

Elixir version (elixir -v): Elixir 1.2.4
Operating system: OS X 10.11.4

When configured to check unmatched returns, dialyzer complains about each usage of Logger: Expression produces a value of type 'ok' | {'error',_}, but this value is unmatched.
It's possible to overcome this problem by typing :ok = Logger.info "....", but it's cumbersome.

Static analysis is the key for a robust system ("failing fast" doesn't mean to have a badly written code :-)). On the one hand I don't want to deactivate this warning, but on the other hand keeping it means that I will possibly miss an important error among all warnings reported for usages of Logger.

Maybe something simple as Logger.info! could do the trick?

Source

ahamez

All 5 comments

The slippery slope with regard to ! is that you may (and _often_ I would add) want to just log and don't care if it fails or goes well. :ok = Logger.info(...) has a specific semantic: it will fail with a MatchError if Logger.info/2 returns {:error, _}. For this reason, we can't just go our merry way and change all Logger calls to match :ok, as this is not the semantics they currently have.

I think the dialyzer warning can be solved without changing the semantics by doing this:

_ = Logger.info(...)

whatyouhide on 6 Apr 2016

Yes, indeed it works, but between :ok = Logger.info and _ = Logger.info, there's not so much difference (although the first one can fail). But it still feels awkward, just for logging, no ?

ahamez on 6 Apr 2016

👍1

@ahamez I feel like failing or not failing is quite a huge difference! :) I don't think crashing the process if logging fails is an acceptable behaviour in many (if not most) applications.

whatyouhide on 6 Apr 2016

If you are using dialyzer, then you should explicitly handle its requirements. That's going to be preferable than hiding the warnings behind Logger.info!, specially because, as @whatyouhide side, you likely want to use _ = Logger.info.