gh-123681: Check NORMALIZE_CENTURY behavior at runtime; require C99

Lib/_pydatetime.py

@@ -213,17 +213,6 @@ def _need_normalize_century():
  _normalize_century = True
  return _normalize_century
 
-_supports_c99 = None
-def _can_support_c99():
- global _supports_c99
- if _supports_c99 is None:
- try:
- _supports_c99 = (
- _time.strftime("%F", (1900, 1, 1, 0, 0, 0, 0, 1, 0)) == "1900-01-01")
- except ValueError:
- _supports_c99 = False
- return _supports_c99
-
 # Correctly substitute for %z and %Z escapes in strftime formats.
 def _wrap_strftime(object, format, timetuple):
  # Don't call utcoffset() or tzname() unless actually needed.
@@ -283,7 +272,7 @@ def _wrap_strftime(object, format, timetuple):
  newformat.append(Zreplace)
  # Note that datetime(1000, 1, 1).strftime('%G') == '1000' so
  # year 1000 for %G can go on the fast path.
- elif ((ch in 'YG' or ch in 'FC' and _can_support_c99()) and
+ elif ((ch in 'YG' or ch in 'FC') and
  object.year < 1000 and _need_normalize_century()):
  if ch == 'G':
  year = int(_time.strftime("%G", timetuple))

Lib/test/datetimetester.py

@@ -1807,7 +1807,7 @@ def test_bool(self):
  self.assertTrue(self.theclass.min)
  self.assertTrue(self.theclass.max)
 
- def test_strftime_y2k(self):
+ def check_strftime_y2k(self, specifier):
  # Test that years less than 1000 are 0-padded; note that the beginning
  # of an ISO 8601 year may fall in an ISO week of the year before, and
  # therefore needs an offset of -1 when formatting with '%G'.
@@ -1821,22 +1821,28 @@ def test_strftime_y2k(self):
  (1000, 0),
  (1970, 0),
  )
- specifiers = 'YG'
- if _time.strftime('%F', (1900, 1, 1, 0, 0, 0, 0, 1, 0)) == '1900-01-01':
- specifiers += 'FC'
  for year, g_offset in dataset:
- for specifier in specifiers:
- with self.subTest(year=year, specifier=specifier):
- d = self.theclass(year, 1, 1)
- if specifier == 'G':
- year += g_offset
- if specifier == 'C':
- expected = f"{year // 100:02d}"
- else:
- expected = f"{year:04d}"
- if specifier == 'F':
- expected += f"-01-01"
- self.assertEqual(d.strftime(f"%{specifier}"), expected)
+ with self.subTest(year=year, specifier=specifier):
+ d = self.theclass(year, 1, 1)
+ if specifier == 'G':
+ year += g_offset
+ if specifier == 'C':
+ expected = f"{year // 100:02d}"
+ else:
+ expected = f"{year:04d}"
+ if specifier == 'F':
+ expected += f"-01-01"
+ self.assertEqual(d.strftime(f"%{specifier}"), expected)
+
+ def test_strftime_y2k(self):
+ self.check_strftime_y2k('Y')
+ self.check_strftime_y2k('G')
+
+ def test_strftime_y2k_c99(self):
+ # CPython requires C11; specifiers new in C99 must work.
+ # (Other implementations may want to disable this test.)
+ self.check_strftime_y2k('F')
+ self.check_strftime_y2k('C')
 
  def test_replace(self):
  cls = self.theclass

Misc/NEWS.d/next/Build/2025-01-03-13-02-06.gh-issue-123681.gQ67nK.rst

@@ -0,0 +1,3 @@
+Check the ``strftime()`` behavior at runtime instead of at the compile time
+to support cross-compiling.
+Remove the internal macro ``_Py_NORMALIZE_CENTURY``.

Modules/_datetimemodule.c

@@ -1760,6 +1760,24 @@ format_utcoffset(char *buf, size_t buflen, const char *sep,
  return 0;
 }
 
+/* Check whether year with century should be normalized for strftime. */
+inline static int
+normalize_century(void)
+{
+ static int cache = -1;
+ if (cache < 0){
+ char year[5];
+ struct tm date ={
+ .tm_year = -1801,
+ .tm_mon = 0,
+ .tm_mday = 1
+ };
+ cache = (strftime(year, sizeof(year), "%Y", &date) &&
+ strcmp(year, "0099") != 0);
+ }
+ return cache;
+}
+
 static PyObject *
 make_somezreplacement(PyObject *object, char *sep, PyObject *tzinfoarg)
 {
@@ -1931,10 +1949,9 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
  }
  replacement = freplacement;
  }
-#ifdef _Py_NORMALIZE_CENTURY
- else if (ch == 'Y' || ch == 'G'
- || ch == 'F' || ch == 'C'
- ){
+ else if (normalize_century()
+ && (ch == 'Y' || ch == 'G' || ch == 'F' || ch == 'C'))
+{
  /* 0-pad year with century as necessary */
  PyObject *item = PySequence_GetItem(timetuple, 0);
  if (item == NULL){
@@ -1985,7 +2002,6 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
  }
  continue;
  }
-#endif
  else{
  /* percent followed by something else */
  continue;

Tools/c-analyzer/cpython/ignored.tsv

@@ -228,6 +228,7 @@ Modules/_datetimemodule.c datetime_isoformat specs -
 Modules/_datetimemodule.c parse_hh_mm_ss_ff correction -
 Modules/_datetimemodule.c time_isoformat specs -
 Modules/_datetimemodule.c - capi_types -
+Modules/_datetimemodule.c normalize_century cache -
 Modules/_decimal/_decimal.c - cond_map_template -
 Modules/_decimal/_decimal.c - dec_signal_string -
 Modules/_decimal/_decimal.c - dflt_ctx -

configure.ac

@@ -6800,57 +6800,6 @@ then
  [Define if you have struct stat.st_mtimensec])
 fi
 
-AC_CACHE_CHECK([whether year with century should be normalized for strftime], [ac_cv_normalize_century], [
-AC_RUN_IFELSE([AC_LANG_SOURCE([[
-#include <time.h>
-#include <string.h>
-
-int main(void)
-{
- char year[5];
- struct tm date ={
- .tm_year = -1801,
- .tm_mon = 0,
- .tm_mday = 1
- };
- if (strftime(year, sizeof(year), "%Y", &date) && !strcmp(year, "0099")){
- return 1;
- }
- return 0;
-}
-]])],
-[ac_cv_normalize_century=yes],
-[ac_cv_normalize_century=no],
-[ac_cv_normalize_century=yes])])
-if test "$ac_cv_normalize_century" = yes
-then
- AC_DEFINE([_Py_NORMALIZE_CENTURY], [1],
- [Define if year with century should be normalized for strftime.])
-fi
-
-AC_CACHE_CHECK([whether C99-compatible strftime specifiers are supported], [ac_cv_strftime_c99_support], [
-AC_RUN_IFELSE([AC_LANG_SOURCE([[
-#include <time.h>
-#include <string.h>
-
-int main(void)
-{
- char full_date[11];
- struct tm date ={
- .tm_year = 0,
- .tm_mon = 0,
- .tm_mday = 1
- };
- if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "1900-01-01")){
- return 0;
- }
- return 1;
-}
-]])],
-[ac_cv_strftime_c99_support=yes],
-[AC_MSG_ERROR([Python requires C99-compatible strftime specifiers])],
-[ac_cv_strftime_c99_support=])])
-
 dnl check for ncursesw/ncurses and panelw/panel
 dnl NOTE: old curses is not detected.
 dnl have_curses=[no, yes]

pyconfig.h.in

@@ -2023,9 +2023,6 @@
 /* HACL* library can compile SIMD256 implementations */
 #undef _Py_HACL_CAN_COMPILE_VEC256
 
-/* Define if year with century should be normalized for strftime. */
-#undef _Py_NORMALIZE_CENTURY
-
 /* Define to force use of thread-safe errno, h_errno, and other functions */
 #undef _REENTRANT