We switched on Maven timestamps in our log, since it's a handy way to check build times.
In Maven, this is done by editing conf/logging/simplelogger.properties and setting org.slf4j.simpleLogger.showDateTime=true
This results in compiler warnings like this:
( given that the date/time format is org.slf4j.simpleLogger.dateTimeFormat=HH:mm:ss.SSS )
Taking a look at the source code, it seems that JAVAC_WARNING_PATTERN does a full match of the line, which does not accept that something could exist before [WARNING] .
We use other parsers for Checkstyle, PMD etc. and they work fine.