Zone handling tweaks

* Handle a null DateTimeZone as we did before, by propagating the
  null. This is used to indicate an invalid zone in our Ruby Time
  logic.
* Provide a map of zone aliases to pick up the old three-letter
  zones. This helps but is not sufficient to handle all
  three-letter formats tested by specs and tests (e.g. "PDT").
* For fixed-offset zones, use the offset rather than the ID. This
  causes those zones to lose their ID, so "AST-3:00:00" becomes
  an unnamed ZoneOffset of "3:00:00". This leads to other failures
  when the ID and offset are both expected to propagate into Time.

core/src/main/java/org/jruby/RubyTime.java

@@ -175,7 +175,7 @@ public static ZoneId getZoneIdFromTZString(Ruby runtime, String zone) {
         ZoneId cachedZone = runtime.getZoneIdCache().get(zone);
         if (cachedZone != null) return cachedZone;
 
-        ZoneId dtz = JodaConverters.jodaToJavaTimeZone(parseTZString(runtime, zone));
+        ZoneId dtz = JodaConverters.jodaToJavaTimeZone(getTimeZoneFromTZString(runtime, zone));
         runtime.getZoneIdCache().put(zone, dtz);
         return dtz;
     }
@@ -359,7 +359,11 @@ public static ZoneId getZoneIdFromUtcOffset(ThreadContext context, IRubyObject a
         ZoneId cachedZone = runtime.getZoneIdCache().get(strOffset);
         if (cachedZone != null) return cachedZone;
 
-        ZoneId zone = JodaConverters.jodaToJavaTimeZone(getTimeZoneFromUtcOffset(context, arg));
+        DateTimeZone dtz = getTimeZoneFromUtcOffset(context, arg);
+
+        if (dtz == null) return null;
+
+        ZoneId zone = JodaConverters.jodaToJavaTimeZone(dtz);
 
         runtime.getZoneIdCache().put(strOffset, zone);
 

core/src/main/java/org/jruby/util/time/JodaConverters.java

@@ -1,5 +1,9 @@
 package org.jruby.util.time;
 
+import org.joda.time.tz.FixedDateTimeZone;
+
+import java.time.ZoneId;
+
 /**
  * The JodaConverters class contains static methods for org.joda.time.* and java.time.* conversion.
  *
@@ -194,7 +198,9 @@ public static org.joda.time.Instant javaToJodaInstant( java.time.Instant instant
 	 * @return Java 8 ZoneId
 	 */
 	public static java.time.ZoneId jodaToJavaTimeZone( org.joda.time.DateTimeZone timeZone ) {
-		return java.time.ZoneId.of( timeZone.getID() );
+		return timeZone.isFixed() ?
+				java.time.ZoneOffset.ofTotalSeconds(timeZone.toTimeZone().getRawOffset() / 1000) :
+				java.time.ZoneId.of( timeZone.getID(), ZoneId.SHORT_IDS );
 	}
 
 	/**