Document new DST fallback rules.

Fix time change in Eastern Europe (not 3:00 but 4:00 local time)
[Bug 2207436]

3 files changed, 27 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 51f4989..796d294 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-12-12  Jan Nijtmans  <nijtmans@users.sf.net>
+
+	* doc/clock.n:  Document new DST fallback rules.
+	* library/clock.tcl (ProcessPosixTimeZone): Fix time change
+	in Eastern Europe (not 3:00 but 4:00 local time) [Bug 2207436]
+
 2008-12-12  Donal K. Fellows  <dkf@users.sf.net>
 
 	* generic/tclZlib.c, unix/configure.in: Added stubs to use when the
@@ -62,7 +68,7 @@
 
 	* library/clock.tcl (ProcessPosixTimeZone): Fallback to European time
 	zone DST rules, when the timezone is between 0 and -12. [Bug 2207436]
-	* tests/clock.test (clock-64.[12]): Test cases for [Bug 2207436]
+	* tests/clock.test (clock-52.[23]): Test cases for [Bug 2207436]
 	
 2008-12-11  Donal K. Fellows  <dkf@users.sf.net>
 
diff --git a/doc/clock.n b/doc/clock.n
index 60042be..f4c3805 100644
--- a/doc/clock.n
+++ b/doc/clock.n
@@ -805,6 +805,23 @@ environment variable will be recognized.  The specification
 may be found at
 \fIhttp://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html\fR.
 .PP
+If the Posix time zone string contains a DST (Daylight Savings Time)
+part, but doesn't contain a rule stating when DST starts or ends,
+then default rules are used. For Timezones with an offset between 0
+and +12, the current European/Russian rules are used, otherwise the
+current US rules are used. In Europe (offset +0 to +2) the switch
+to summertime is done each last Sunday in March at 1:00 GMT, and
+the switch back is each last Sunday in October at 2:00 GMT. In
+Russia (offset +3 to +12), the switch dates are the same, only
+the switch to summertime is at 2:00 local time, and the switch
+back is at 3:00 local time in all time zones. The US switch to
+summertime takes place each second Sunday in March at 2:00 local
+time, and the switch back is each first Sunday in November at
+3:00 local time. These default rules mean that in all European,
+Russian and US (or compatible) time zones, DST calculations will
+be correct for dates in 2007 and later, unless in the future the
+rules change again.
+.PP
 Any other time zone string is processed by prefixing a colon and attempting
 to use it as a location name, as above.
 .SH "LOCALIZATION"
diff --git a/library/clock.tcl b/library/clock.tcl
index bfac4e6..d972955 100644
--- a/library/clock.tcl
+++ b/library/clock.tcl
@@ -13,7 +13,7 @@
 # See the file "license.terms" for information on usage and redistribution
 # of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 #
-# RCS: @(#) $Id: clock.tcl,v 1.50 2008/12/11 14:01:59 nijtmans Exp $
+# RCS: @(#) $Id: clock.tcl,v 1.51 2008/12/12 17:42:52 nijtmans Exp $
 #
 #----------------------------------------------------------------------
 
@@ -3891,7 +3891,7 @@ proc ::tcl::clock::ProcessPosixTimeZone { z } {
 	 && [dict get $z startMonth] eq {} } {
 	if {($stdHours>=0) && ($stdHours<=12)} {
 	    dict set z startWeekOfMonth 5
-	    if {$stdHours>1} {
+	    if {$stdHours>2} {
 		dict set z startHours 2
 	    } else {
 		dict set z startHours [expr {$stdHours+1}]
@@ -3910,7 +3910,7 @@ proc ::tcl::clock::ProcessPosixTimeZone { z } {
 	if {($stdHours>=0) && ($stdHours<=12)} {
 	    dict set z endMonth 10
 	    dict set z endWeekOfMonth 5
-	    if {$stdHours>1} {
+	    if {$stdHours>2} {
 		dict set z endHours 3
 	    } else {
 		dict set z endHours [expr {$stdHours+2}]