Implement a callback function for DatetimeRotatingFileLogger.

[fredrikekre]

This allows passing a callback that is called with the previous file whenever the logger rotates the backing file. Example callback to compress the logfile:

callback(nt) = run(`gzip $(nt.file)`)

[fredrikekre]

On second thought,

function callback(file::String)
    # do stuff
end

is probably enough. The directory you can get from dirname(file) and if you need the datformat for some more elaborate handling you can just use that from the "outside" since the general pattern would be something like

using Logging, LoggingExtras

const pattern = raw"yyyy-mm-dd.\l\o\g"

function callback(file)
    # do something with `file` and global `pattern`
end

logger = DatetimeFileRotatingLogger(dir, pattern; callback=callback)

[oxinabox]

Nice.
this is useful and make a lot of sense as a thing to have.

Some fairly minor comments. but basically looks good.

[oxinabox]

Hmm why is CI failing here, saying it was only rotated once?
https://github.com/oxinabox/LoggingExtras.jl/pull/42/checks#step:6:41

[fredrikekre]

Yea I was just discussing this with @staticfloat and basically allowing to rotate for so small time-scales is not very robust. Our idea (which is implemented in the last commit) is to just error for sub-minute resolution. I think this is fine since I believe in real life one wouldn't use this for sub-day resolution, possibly hour-level. Thoughts?

[oxinabox]

Yeah could do.
For testing purposes now should we increase the sleep?

Or use Mocking.jl / SimpleMock.jl to mock the call to now()?

[fredrikekre]

Yea the sleeping now should have ~5 seconds of margin

[fredrikekre]

Thanks