Add caller_depth arg

[jwittkoski]

Adds an optional argument caller_depth to the psgix.logger anonymous sub so that callers can add additional layers of caller_depth to Log4perl output that is using Plack::Middleware::Log4perl PatternLayout config values which include the file or line number (like %F, %l and %L).

Without the ability to have the caller additionally adjust the caller depth, a psgix.logger using Log4perl always shows the immediate caller and not (necessarily) the "original" caller.

For example, when using Dancer::Logger::PSGI, the Dancer logging keywords have three additional calling layers so the %F, %l and %L placeholders point to Dancer/Logger/PSGI.pm instead of the "original" caller.

Originally I addressed this problem by using local and adjusting $Log::Log4perl::caller_depth in Dancer::Logger::PSGI which works. However, because psgix.logger is an anonymous sub, the caller to psgix.logger (Dancer::Logger::PSGI in this case) doesn't doesn't know whether the currently configured Plack logger is Log4perl or something else (like Log::Dispatch) and therefore whether $Log::Log4perl::caller_depth is even available.

Of course, to get this all to work Dancer::Logger::PSGI would also have to be modified to set the caller_depth argument when calling psgix.logger.

Perhaps there is a cleaner way to address this problem? Dancer::Logger::PSGI could just check whether Logger::Log4perl is loaded and set $Log::Log4perl::caller_depth only in that case.

[coveralls]

Coverage increased (+0.01%) when pulling 6d5b781 on jwittkoski:caller_depth_adjust into cf3e3db on plack:master.

[coveralls]

Coverage increased (+0.01%) when pulling da59a75 on jwittkoski:caller_depth_adjust into 2dcdf47 on plack:master.

[jwittkoski]

I also looked at using Log4perl's wrapper_register but similar to using Log::Log4perl::caller_depth it requires the "downstream" caller to determine whether Log::Log4perl is in use which might be problematic.

Adding this optional caller_depth argument to Plack::Middleware::Log4perl allows "downstream" callers to specify the additional caller depth without knowing or caring which middleware logging module is currently in use. If the current middleware doesn't use or need it it will be silently ignored.