On 01/18/2018 01:36 PM, Meno Hochschild wrote:
I also suspect that this is another problem (not yet tested): Java would start with v2018a to report Irish Summer Time (IST) in winter and GMT in summer when it comes to formatting the Irish zone Europe/Dublin.
Yes, it sounds quite plausible that Java/OpenJDK would somehow translate "IST" to "Irish Summer Time" in Europe/Dublin. This assumption has been incorrect for quite some time, as for many years tzdata's Europe/Dublin has used "IST" to stand for "Irish Standard Time" for some timestamps (notably, between 1968 and 1971). Unfortunately the tzdata format does not allow this assumption to be stated in the data; it's only in comments. If the Java/OpenJDK model does not allow the same abbreviation ("IST" in this case) to mean different things at different times in the same location, that would be a shortcoming in the model regardless of whether the Irish data moves to timestamps with negative DST offsets. Java/OpenJDK is a different project from tzcode, and it has always supported a superset-of-a-subset of what tzcode supports. For example, Java (at least, Oracle's version of Java) does not support POSIX-format TZ settings; on the other hand, Java supports long names like "Pacific Standard Time" that tzcode does not. With that in mind, it would be understandable if Java/OpenJDK decides not to support negative DST offsets; it would be just one more thing in the list of things that tzcode has but Java lacks. If that happens, it should be possible for Java-based readers of tzdata source files to automatically translate negative DST offsets into positive ones (switching abbreviations of course), as I think Stephen Colebourne suggested. It's also possible that all things considered it would be better if Java supported negative DST offsets -- but that's not our call to make. We can give the Java folks some time to prepare for this by backing out the Irish changes for now. We can bring the changes back in the not-too-distant future, and in the meantime the Java folks can test their fixes on 2018b.