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

Named Psr\Log\LoggerInterface instances can be obtained from the
MWLoggerFactory::getInstance() static method. MWLoggerFactory expects a class
implementing the MWLoggerSpi interface to act as a factory for new
Psr\Log\LoggerInterface instances.

The "Spi" in MWLoggerSpi stands for "service provider interface". A SPI is
an 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 MWLoggerFactory service to allow
alternate PSR-3 logging implementations to be easily integrated with
MediaWiki.

The MWLoggerFactory::getInstance() static method is the means by which most
code acquires a Psr\Log\LoggerInterface instance. This in turn delegates
creation of Psr\Log\LoggerInterface 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 MWLoggerFactory::registerProvider method can be
called to inject an MWLoggerSpi instance into MWLoggerFactory 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
Psr\Log\LoggerInterface 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 ==
; MWLoggerFactory
: Factory for Psr\Log\LoggerInterface loggers
; MWLoggerSpi
: Service provider interface for MWLoggerFactory
; 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 MWLoggerFactory

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