bpo-37552: Skip failing tests in strptime/strftime with UCRT version 17763.615 (#14460)

A bug in MSVC UCRT version 17763.615 (which has been fixed in newer versions) is causing test failures in some strptime/strftime tests when the default code page is c65001. This change selectively skips the tests affected by this.

Lib/test/support/__init__.py

@@ -14,6 +14,7 @@ import gc
 import glob
 import importlib
 import importlib.util
+import locale
 import logging.handlers
 import nntplib
 import os
@@ -92,7 +93,7 @@ __all__ = [
     "bigmemtest", "bigaddrspacetest", "cpython_only", "get_attribute",
     "requires_IEEE_754", "skip_unless_xattr", "requires_zlib",
     "anticipate_failure", "load_package_tests", "detect_api_mismatch",
-    "check__all__", "skip_unless_bind_unix_socket",
+    "check__all__", "skip_unless_bind_unix_socket", "skip_if_buggy_ucrt_strfptime",
     "ignore_warnings",
     # sys
     "is_jython", "is_android", "check_impl_detail", "unix_shell",
@@ -2501,6 +2502,27 @@ def skip_unless_symlink(test):
     msg = "Requires functional symlink implementation"
     return test if ok else unittest.skip(msg)(test)
 
+_buggy_ucrt = None
+def skip_if_buggy_ucrt_strfptime(test):
+    """
+    Skip decorator for tests that use buggy strptime/strftime
+
+    If the UCRT bugs are present time.localtime().tm_zone will be
+    an empty string, otherwise we assume the UCRT bugs are fixed
+
+    See bpo-37552 [Windows] strptime/strftime return invalid
+    results with UCRT version 17763.615
+    """
+    global _buggy_ucrt
+    if _buggy_ucrt is None:
+        if(sys.platform == 'win32' and
+                locale.getdefaultlocale()[1]  == 'cp65001' and
+                time.localtime().tm_zone == ''):
+            _buggy_ucrt = True
+        else:
+            _buggy_ucrt = False
+    return unittest.skip("buggy MSVC UCRT strptime/strftime")(test) if _buggy_ucrt else test
+
 class PythonSymlink:
     """Creates a symlink for the current Python executable"""
     def __init__(self, link=None):

Lib/test/test_strptime.py

@@ -7,6 +7,7 @@ import re
 import os
 import sys
 from test import support
+from test.support import skip_if_buggy_ucrt_strfptime
 from datetime import date as datetime_date
 
 import _strptime
@@ -135,6 +136,7 @@ class TimeRETests(unittest.TestCase):
                       "%s does not have re characters escaped properly" %
                       pattern_string)
 
+    @skip_if_buggy_ucrt_strfptime
     def test_compile(self):
         # Check that compiled regex is correct
         found = self.time_re.compile(r"%A").match(self.locale_time.f_weekday[6])
@@ -365,6 +367,7 @@ class StrptimeTests(unittest.TestCase):
             _strptime._strptime("-01:3030", "%z")
         self.assertEqual("Inconsistent use of : in -01:3030", str(err.exception))
 
+    @skip_if_buggy_ucrt_strfptime
     def test_timezone(self):
         # Test timezone directives.
         # When gmtime() is used with %Z, entire result of strftime() is empty.
@@ -489,6 +492,7 @@ class CalculationTests(unittest.TestCase):
     def setUp(self):
         self.time_tuple = time.gmtime()
 
+    @skip_if_buggy_ucrt_strfptime
     def test_julian_calculation(self):
         # Make sure that when Julian is missing that it is calculated
         format_string = "%Y %m %d %H %M %S %w %Z"
@@ -498,6 +502,7 @@ class CalculationTests(unittest.TestCase):
                         "Calculation of tm_yday failed; %s != %s" %
                          (result.tm_yday, self.time_tuple.tm_yday))
 
+    @skip_if_buggy_ucrt_strfptime
     def test_gregorian_calculation(self):
         # Test that Gregorian date can be calculated from Julian day
         format_string = "%Y %H %M %S %w %j %Z"
@@ -512,6 +517,7 @@ class CalculationTests(unittest.TestCase):
                           self.time_tuple.tm_year, self.time_tuple.tm_mon,
                           self.time_tuple.tm_mday))
 
+    @skip_if_buggy_ucrt_strfptime
     def test_day_of_week_calculation(self):
         # Test that the day of the week is calculated as needed
         format_string = "%Y %m %d %H %S %j %Z"

Lib/test/test_time.py

@@ -14,6 +14,7 @@ try:
 except ImportError:
     _testcapi = None
 
+from test.support import skip_if_buggy_ucrt_strfptime
 
 # Max year is only limited by the size of C int.
 SIZEOF_INT = sysconfig.get_config_var('SIZEOF_INT') or 4
@@ -250,6 +251,7 @@ class TimeTestCase(unittest.TestCase):
             result = time.strftime("%Y %m %d %H %M %S %w %j", (2000,)+(0,)*8)
         self.assertEqual(expected, result)
 
+    @skip_if_buggy_ucrt_strfptime
     def test_strptime(self):
         # Should be able to go round-trip from strftime to strptime without
         # raising an exception.
@@ -672,6 +674,7 @@ class TestStrftime4dyear(_TestStrftimeYear, _Test4dYear, unittest.TestCase):
 
 
 class TestPytime(unittest.TestCase):
+    @skip_if_buggy_ucrt_strfptime
     @unittest.skipUnless(time._STRUCT_TM_ITEMS == 11, "needs tm_zone support")
     def test_localtime_timezone(self):