Seems like we already have this. MWExceptionHandler already installs an error handler which logs to the "error" channel.

Maybe we're just missing routing? I don't see it in $wmgMonologChannels

Yes, in theory this should be already happening but doesn't. (Or maybe doesn't some of the time, not sure.)

If it was only a routing issue, I'd expect the error to not show up anywhere. If ends up in HHVM, then it's probably not caught.

Strike that, the handler actually passes the error on:

// This handler is for logging only. Return false will instruct PHP
// to continue regular handling.
return false;

@bd808 do you know why we do that? Is that to make fatalmonitor work?

In T158270#3039715, @Tgr wrote:

Strike that, the handler actually passes the error on:

// This handler is for logging only. Return false will instruct PHP
// to continue regular handling.
return false;

@bd808 do you know why we do that? Is that to make fatalmonitor work?

We do that because it's the correct way for a default set_error_handler() to function. If we swallowed the errors there without returning false then $php_errormsg would not be populated and all errors would be handled as though the @ suppression operator was applied to every line in the codebase.

In T158270#3039702, @tstarling wrote:

Maybe we're just missing routing? I don't see it in $wmgMonologChannels

See T45086#787151. The channel is too noisy to log on WMF's production servers.

This whole ticket is really a duplicate of T45086: Capture PHP warnings with stacktraces in MediaWiki and save to logstash.

@bd808 sorry, I seem to have a really short memory when it comes to logging :) Now I remember having talked about this in T154112.