[RFC] Allow arbitrary logger types #1736
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At the moment, all sites are tied to using the fast-logger `Logger` type for Yesod's logging functions, including `makeLogger` and `messageLoggerSource`. This represents an obstacle to logging through other libraries which are incompatible with the fast-logger API. This replaces the use of the concrete `Logger` type with an associated type family on the `Yesod` class which allows sites to use their choice of logger representation for Yesod's logging functions. The associated type family is declared in such a way that existing instances should work with no further effort. This commit introduces a change in semantics around how logging is shared between the Yesod site and the underlying WAI server - because WAI is still tied to fast-logger, it's not possible to have them share the logging config in general. Instead, the logger passed to WAI is the default stdout logger.
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Intended to fix #1735.
This is a possible solution to allowing Yesod to support basically any kind of logging library, using an associated type family for the logger representation.
I don't know whether or not the existence of
makeLoggerand the passing of the logger tomessageLoggerSourcestill make sense - a better design might simply be to rip them out entirely - but these changes should at least be backwards-compatible from an API standpoint.Issues
This introduces a wedge between a Yesod site and the WAI server it runs on. The default logging middlewares that Yesod sets up will only accept
Loggers, and since it's no longer possible to provide aLoggerfrom the site type, a new one has to be created just to log from the middleware. That's a change in semantics that might surprise users. Additionally, some parts of middleware logging (like the exception logging inwarp) still go through the Yesod site logger instead.