MediaWiki\Logger\LoggerFactory implements a PSR-3 [0] compatible message
logging system.

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

The "Spi" in MediaWiki\Logger\Spi stands for "service provider interface". An
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
MediaWiki\Logger\LoggerFactory service to allow alternate PSR-3 logging
implementations to be easily integrated with MediaWiki.

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

The MediaWiki\Logger\LegacySpi class implements a service provider to generate
MediaWiki\Logger\LegacyLogger instances. The MediaWiki\Logger\LegacyLogger
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 MediaWiki\Logger\LegacySpi 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 MediaWiki\Logger\MonologSpi 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 MediaWiki\Logger\MonologSpi 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 ==
; MediaWiki\Logger\LoggerFactory
: Factory for Psr\Log\LoggerInterface loggers
; MediaWiki\Logger\Spi
: Service provider interface for MediaWiki\Logger\LoggerFactory
; MediaWiki\Logger\NullSpi
: MediaWiki\Logger\Spi for creating instances that discard all log events
; MediaWiki\Logger\LegacySpi
: Service provider for creating MediaWiki\Logger\LegacyLogger instances
; MediaWiki\Logger\LegacyLogger
: PSR-3 logger that mimics the historical output and configuration of wfDebug,
  wfErrorLog and other global logging functions.
; MediaWiki\Logger\MonologSpi
: MediaWiki\Logger\Spi for creating instances backed by the monolog logging library
; MediaWiki\Logger\Monolog\LegacyHandler
: Monolog handler that replicates the udp2log and file logging
  functionality of wfErrorLog()
; MediaWiki\Logger\Monolog\WikiProcessor
: 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 MediaWiki\Logger\LoggerFactory

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