[PATCH] wrong timezone offset if DST rules changed this year (issue2511)

[Dmitry Panov]

# HG changeset patch
# User Dmitry Panov <dop at itoolabs.com>
# Date 1321144166 0
# Node ID ca83bd6d909c1ad6b325262ad008c9567e83b036
# Parent  1bb0a5b02da9ef3505bfb4ac02b2d51cf220220f
makedate: wrong timezone offset if DST rules changed this year (issue2511)

Python's time module sets timezone and altzone based on UTC offsets of
two dates: first and middle day of the current year. This approach doesn't
work on a year when DST rules change.

For example Russia abandoned winter time this year, so the correct UTC 
offset
should be +4 now, but time.timezone returns 3 hours difference because 
that's
what it was on 01.01.2011.

Related python issue: http://bugs.python.org/issue1647654

diff -r 1bb0a5b02da9 -r ca83bd6d909c mercurial/util.py
--- a/mercurial/util.py Thu Nov 10 17:06:30 2011 -0600
+++ b/mercurial/util.py Sun Nov 13 00:29:26 2011 +0000
@@ -16,7 +16,7 @@
  from i18n import _
  import error, osutil, encoding
  import errno, re, shutil, sys, tempfile, traceback
-import os, time, calendar, textwrap, signal
+import os, time, datetime, calendar, textwrap, signal
  import imp, socket, urllib

  if os.name == 'nt':
@@ -899,16 +899,14 @@
          yield s

  def makedate():
-    lt = time.localtime()
-    if lt[8] == 1 and time.daylight:
-        tz = time.altzone
-    else:
-        tz = time.timezone
-    t = time.mktime(lt)
-    if t < 0:
+    ct = time.time()
+    if ct < 0:
          hint = _("check your clock")
-        raise Abort(_("negative timestamp: %d") % t, hint=hint)
-    return t, tz
+        raise Abort(_("negative timestamp: %d") % ct, hint=hint)
+    delta = datetime.datetime.utcfromtimestamp(ct) - \
+       datetime.datetime.fromtimestamp(ct)
+    tz = delta.days * 86400 + delta.seconds
+    return ct, tz

  def datestr(date=None, format='%a %b %d %H:%M:%S %Y %1%2'):
      """represent a (unixtime, offset) tuple as a localized time.

-- 
Best regards,

  Dmitry Panov
  Chief Technology Officer
  Itoolabs.