[slf4j-user] Fail Silently on NOP implementation

[Joachim Durchholz]

Am 28.04.2016 um 22:15 schrieb Phillip Lord:
>
> This is not true. My library has around 70 dependencies, some of which I
> have never heard of. As the recent debacle with left-pad and NPM has
> shown, very few people are consciously aware of all their dependencies.

I agree with your sentiment that one shouldn't need to bother that much 
about indirect dependencies; I think logging has become because it's a 
cross-cutting concern, just like the availability of stdout and whether 
it's a tty or a pipe.

Now if you're writing a library you should never bother with logging 
configuration. Maybe make sure it doesn't clutter your unit-testing 
output, but that's more cosmetic than anything else.

If, on the other hand, you're writing an application, you definitely 
need to configure logging.
The good news is that the NOP logger message you are seeing is just a 
misconfiguration. I don't know who's responsible; you need to check 
direct and indirect dependencies and see what libraries are pulling in a 
backend, and exclude dependencies (many libraries are misguided in that 
they declare a dependency on a logging backend, and you need to exclude 
that).
Dependency sanitizing is something that you need to do, occasionally, 
even if you shouldn't have to if everybody were doing things right.

> Yes, although these do not equate to the artifacts. slf4j-api is
> actually the API and the NOP logger.

Last time I looked these were different libraries. I dimly recall that 
slf4j-api didn't even pull in any logger as a dependency; it certainly 
shouldn't, though it's possible that it does just to be able to simply 
output messages in case of misconfiguration - which is what I assume you 
are seeing.

Anyway - did the SLF4J artifacts change their composition or their 
dependencies?

> If not, I will just include slf4j-nop directly and leave it at that.

 From the keywords I have seen, you're getting messages because you have 
more than one logging backend in your classpath, slf4j-nop and something 
else. Including slf4j-nop will not change anything about that.

I'm just guessing about details though; let us know how things worked 
out for you.