MWLogger implements a PSR-3 [0] compatible message logging system.

The MWLogger class is actually a thin wrapper around any PSR-3 LoggerInterface
implementation. Named MWLogger instances can be obtained from the
MWLogger::getInstance() static method. MWLogger expects a class implementing
the MWLoggerSpi interface to act as a factory for new MWLogger instances.

The "Spi" in MWLoggerSpi stands for "service provider interface". An SPI is
a API intended to be implemented or extended by a third party. This software
design pattern is intended to enable framework extension and replaceable
components. It is specifically used in the MWLogger service to allow alternate
PSR-3 logging implementations to be easily integrated with MediaWiki.

The MWLogger::getInstance() static method is the means by which most code
acquires an MWLogger instance. This in turn delegates creation of MWLogger
instances to a class implementing the MWLoggerSpi service provider interface.

The service provider interface allows the backend logging library to be
implemented in multiple ways. The $wgMWLoggerDefaultSpi global provides the
classname of the default MWLoggerSpi implementation to be loaded at runtime.
This can either be the name of a class implementing the MWLoggerSpi with
a zero argument constructor or a callable that will return an MWLoggerSpi
instance. Alternately the MWLogger::registerProvider method can be called
to inject an MWLoggerSpi instance into MWLogger and bypass the use of this
configuration variable.

The MWLoggerLegacySpi class implements a service provider to generate
MWLoggerLegacyLogger instances. The MWLoggerLegacyLogger class implements the
PSR-3 logger interface and provides output and configuration equivalent to the
historic logging output of wfDebug, wfDebugLog, wfLogDBError and wfErrorLog.
The MWLoggerLegacySpi class is the default service provider configured in
DefaultSettings.php. It's usage should be transparent for users who are not
ready or do not wish to switch to a alternate logging platform.

The MWLoggerMonologSpi class implements a service provider to generate
MWLogger instances that use the Monolog [1] logging library. See the PHP docs
(or source) for MWLoggerMonologSpi for details on the configuration of this
provider. The default configuration installs a null handler that will silently
discard all logging events. The documentation provided by the class describes
a more feature rich logging configuration.

== Classes ==
; MWLogger
: PSR-3 compatible logger that wraps any \Psr\Log\LoggerInterface
  implementation
; MWLoggerSpi
: Service provider interface for MWLogger factories
; MWLoggerNullSpi
: MWLoggerSpi for creating instances that discard all log events
; MWLoggerLegacySpi
: Service provider for creating MWLoggerLegacyLogger instances
; MWLoggerLegacyLogger
: PSR-3 logger that mimics the historical output and configuration of wfDebug,
  wfErrorLog and other global logging functions.
; MWLoggerMonologSpi
: MWLoggerSpi for creating instances backed by the monolog logging library
; MwLoggerMonologHandler
: Monolog handler that replicates the udp2log and file logging
  functionality of wfErrorLog()
; MwLoggerMonologProcessor
: Monolog log processer that adds host: wfHostname() and wiki: wfWikiID()
  to all records

== Globals ==
; $wgMWLoggerDefaultSpi
: Specification for creating the default service provider interface to use
  with MWLogger

[0]: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-3-logger-interface.md
[1]: https://github.com/Seldaek/monolog