Issue #10941: Fix imaplib.Internaldate2tuple to produce correct result near

the DST transition.  Patch by Joe Peterson.

2 files changed, 38 insertions, 2 deletions

diff --git a/Lib/test/support.py b/Lib/test/support.py
index a1ab09c..a7d0833 100644
--- a/Lib/test/support.py
+++ b/Lib/test/support.py
@@ -57,7 +57,7 @@ __all__ = [
     "get_attribute", "swap_item", "swap_attr", "requires_IEEE_754",
     "TestHandler", "Matcher", "can_symlink", "skip_unless_symlink",
     "import_fresh_module", "requires_zlib", "PIPE_MAX_SIZE", "failfast",
-    "anticipate_failure"
+    "anticipate_failure", "run_with_tz"
     ]
 
 class Error(Exception):
@@ -1100,6 +1100,35 @@ def run_with_locale(catstr, *locales):
     return decorator
 
 #=======================================================================
+# Decorator for running a function in a specific timezone, correctly
+# resetting it afterwards.
+
+def run_with_tz(tz):
+    def decorator(func):
+        def inner(*args, **kwds):
+            if 'TZ' in os.environ:
+                orig_tz = os.environ['TZ']
+            else:
+                orig_tz = None
+            os.environ['TZ'] = tz
+            time.tzset()
+
+            # now run the function, resetting the tz on exceptions
+            try:
+                return func(*args, **kwds)
+            finally:
+                if orig_tz == None:
+                    del os.environ['TZ']
+                else:
+                    os.environ['TZ'] = orig_tz
+                time.tzset()
+
+        inner.__name__ = func.__name__
+        inner.__doc__ = func.__doc__
+        return inner
+    return decorator
+
+#=======================================================================
 # Big-memory-test support. Separate from 'resources' because memory use
 # should be configurable.
 
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index c4c7ecc..50b2da1 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -11,7 +11,7 @@ import socketserver
 import time
 import calendar
 
-from test.support import reap_threads, verbose, transient_internet
+from test.support import reap_threads, verbose, transient_internet, run_with_tz
 import unittest
 
 try:
@@ -36,6 +36,13 @@ class TestImaplib(unittest.TestCase):
             b'25 (INTERNALDATE "31-Dec-1999 12:30:00 -1130")')
         self.assertEqual(time.mktime(tt), t0)
 
+    @run_with_tz('MST+07MDT,M4.1.0,M10.5.0')
+    def test_Internaldate2tuple_issue10941(self):
+        self.assertNotEqual(imaplib.Internaldate2tuple(
+            b'25 (INTERNALDATE "02-Apr-2000 02:30:00 +0000")'),
+                            imaplib.Internaldate2tuple(
+            b'25 (INTERNALDATE "02-Apr-2000 03:30:00 +0000")'))
+
     def test_that_Time2Internaldate_returns_a_result(self):
         # We can check only that it successfully produces a result,
         # not the correctness of the result itself, since the result