Hi!

In FileRotationLogger.swift the function rotateFiles() fails at line 109 during the following instruction:

try FileManager.default.moveItem(at: fileURL, to: archivedFileURL)

This happens because in Formatter.swift the function dateFormatter(_:, locale:, dateFormat:, timeZone:) creates a timestamp that includes colons (:) which the file system does not like.

One potential solution is changing the dateFormat in line 13 of Formatter.swift from "yyyy-MM-dd'T'HH:mm:ss.SSSZZZZZ" to "yyyy-MM-dd'T'HH-mm-ss.SSS". This removes the explicit colons in the original date format string, as well as an implicit colon which is added by ZZZZZ which expands to an HH:MM style presentation of the timezone.

You might also consider reducing the complexity of this string further, since I'd argue if a detailed timestamp is necessary then it can be placed inside the log file, rather than in the file name.

One alternative could be to structure like this:

myLog.log
myLog.log.1
myLog.log.2

This proposal would simplify the implementation of the rest of the rotateFiles method that is concerned with removing old archived files.