Adding a breadcrumb logger

[Cawllec]

Additions

• Adds a logger to track events output to a logger to breadcrumbs
• BugsnagLogger can be assigned to any interface that uses a Logger, such as ActiveRecord::Base.logger or Mongoid::Loggable.logger
• Breadcrumb logging threshold can be set during initialisation or at any point afterwards
• MultiLogger accepts an array of loggers on creation and will output to each of them on message receipt, allowing user to attach other loggers alongside BugsnagLogger

Discussion

• Considering changing name to BreadcrumbLogger to be more explicit about functionality
• I created this as a separate PR to the breadcrumbs PR to avoid splitting focus. I think the breadcrumb feature should be completed before this

TODO

• Needs tests added
• Needs examples/documenting

[Cawllec]

Tests are now added as well as a few updates

[snmaynard]

I dont think we should implement this. We can recommend another one if we want, but its out of the scope of our lib imo

[snmaynard]

we can call this logger and put it in the bugsnag module if we get rid of multi

[snmaynard]

We havent inherited from logger which is potentially a better idea. I looked at some things. Found log4r which might be a good thing to use? We could also instead build an appender? http://www.rubydoc.info/gems/logging/Logging/Appenders

That way we dont have to even worry about multi loggers. I havent looked into this deeply at all however!

[Cawllec]

I'll subclass Appender for the same goal in a different branch. If we'd prefer that I'll close this one out

[Cawllec]

Hmm, I didn't notice when I last checked that Appenders doesn't belong to Stdlib. Personally I'd prefer to implement an stdlib solution with examples for other common third parties. I can remove multi-logger and re-tool Bugsnag-Logger into just Logger.

[kattrali]

There's two sets of users here that we can support:

• folks using the stdlib logger
• folks using other loggers (e.g. logging and log4r gems)

For the first group, the simplest solution seems to be subclassing Logger, since it already provides log levels and filtering by level. In that case the implementation only needs to map levels to severities and make breacrumbs/reports from the log() method when its invoked.

For the folks using something other than the stdlib Logger, the logging gem seems to be the most used and maintained, as log4r hasn't seen a release in the last 7ish years. We'd need an appender for this and a check that the Logging class exists to activate it. The appender and the stdlib Logger subclass could share the same logic, potentially, depending on what an appender needs to do.

[Cawllec]

stdlib includes a LogDevice which seems to be equivalent to an Appender in the Logging lib. I think targeting these two and allow users to configure the actual logger may be the best solution.

• Edit -
  LogDevice doesn't seem to support being handed log - levels, making it a non-starter. I'll do what you suggested above @kattrali

[Cawllec]

I think we're in favour of #375 more than this, so I'll close this for now.