gh-123681: Check the strftime() behavior at runtime instead of at the compile time

It is needed to support cross-compiling.
Remove macros Py_NORMALIZE_CENTURY and Py_STRFTIME_C99_SUPPORT.

Author: serhiy-storchaka

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 macros Py_NORMALIZE_CENTURY and
+Py_STRFTIME_C99_SUPPORT.

Modules/_datetimemodule.c

@@ -1740,6 +1740,42 @@ 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 _normalize_century = -1;
+    if (_normalize_century < 0) {
+        char year[5];
+        struct tm date = {
+            .tm_year = -1801,
+            .tm_mon = 0,
+            .tm_mday = 1
+        };
+        _normalize_century = (strftime(year, sizeof(year), "%Y", &date) &&
+                              strcmp(year, "0099") != 0);
+    }
+    return _normalize_century;
+}
+
+/* Check whether C99-specific strftime specifiers are supported. */
+inline static int
+strftime_c99_support(void)
+{
+    static int _strftime_c99_support = -1;
+    if (_strftime_c99_support < 0) {
+        char full_date[11];
+        struct tm date = {
+            .tm_year = 0,
+            .tm_mon = 0,
+            .tm_mday = 1
+        };
+        _strftime_c99_support = (strftime(full_date, sizeof(full_date), "%F", &date) &&
+                                 strcmp(full_date, "1900-01-01") == 0);
+    }
+    return _strftime_c99_support;
+}
+
 static PyObject *
 make_somezreplacement(PyObject *object, char *sep, PyObject *tzinfoarg)
 {
@@ -1910,12 +1946,9 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             }
             replacement = freplacement;
         }
-#ifdef Py_NORMALIZE_CENTURY
-        else if (ch == 'Y' || ch == 'G'
-#ifdef Py_STRFTIME_C99_SUPPORT
-                 || ch == 'F' || ch == 'C'
-#endif
-        ) {
+        else if (normalize_century() && (ch == 'Y' || ch == 'G' ||
+                 (strftime_c99_support() && (ch == 'F' || ch == 'C'))))
+        {
             /* 0-pad year with century as necessary */
             PyObject *item = PySequence_GetItem(timetuple, 0);
             if (item == NULL) {
@@ -1952,15 +1985,11 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
              * +6 to accommodate dashes, 2-digit month and day for %F. */
             char buf[SIZEOF_LONG * 5 / 2 + 2 + 6];
             Py_ssize_t n = PyOS_snprintf(buf, sizeof(buf),
-#ifdef Py_STRFTIME_C99_SUPPORT
                                       ch == 'F' ? "%04ld-%%m-%%d" :
-#endif
                                       "%04ld", year_long);
-#ifdef Py_STRFTIME_C99_SUPPORT
             if (ch == 'C') {
                 n -= 2;
             }
-#endif
             if (_PyUnicodeWriter_WriteSubstring(&writer, format, start, end) < 0) {
                 goto Error;
             }
@@ -1970,7 +1999,6 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             }
             continue;
         }
-#endif
         else {
             /* percent followed by something else */
             continue;

configure

@@ -6644,62 +6644,6 @@ 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 "$ac_cv_normalize_century" = yes
-then
-  AC_DEFINE([Py_NORMALIZE_CENTURY], [1],
-  [Define if year with century should be normalized for strftime.])
-fi
-
-AC_CACHE_CHECK([whether C99-specific strftime specifiers are supported], [ac_cv_strftime_c99_support], [
-AC_RUN_IFELSE([AC_LANG_SOURCE([[
-#include <time.h>
-#include <string.h>
-
-int main(void)
-{
-  char full_date[11];
-  struct tm date = {
-    .tm_year = 0,
-    .tm_mon = 0,
-    .tm_mday = 1
-  };
-  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "1900-01-01")) {
-    return 0;
-  }
-  return 1;
-}
-]])],
-[ac_cv_strftime_c99_support=yes],
-[ac_cv_strftime_c99_support=no],
-[ac_cv_strftime_c99_support=no])])
-if test "$ac_cv_strftime_c99_support" = yes
-then
-  AC_DEFINE([Py_STRFTIME_C99_SUPPORT], [1],
-  [Define if C99-specific strftime specifiers are supported.])
-fi
-
 dnl check for ncursesw/ncurses and panelw/panel
 dnl NOTE: old curses is not detected.
 dnl have_curses=[no, yes]

configure.ac

@@ -1706,18 +1706,12 @@
 /* Defined if _Complex C type is available. */
 #undef Py_HAVE_C_COMPLEX
 
-/* Define if year with century should be normalized for strftime. */
-#undef Py_NORMALIZE_CENTURY
-
 /* Define if rl_startup_hook takes arguments */
 #undef Py_RL_STARTUP_HOOK_TAKES_ARGS
 
 /* Define if you want to enable internal statistics gathering. */
 #undef Py_STATS
 
-/* Define if C99-specific strftime specifiers are supported. */
-#undef Py_STRFTIME_C99_SUPPORT
-
 /* The version of SunOS/Solaris as reported by `uname -r' without the dot. */
 #undef Py_SUNOS_VERSION