bpo-29097: Forego fold detection on windows for low timestamp values (GH-2385) (GH-8466)
On Windows, passing a negative value to local results in an OSError because localtime_s on Windows does not support negative timestamps. Unfortunately this means that fold detection for timestamps between 0 and max_fold_seconds will result in this OSError since we subtract max_fold_seconds from the timestamp to detect a fold. However, since we know there haven't been any folds in the interval [0, max_fold_seconds) in any timezone, we can hackily just forego fold detection for this time range on Windows.
(cherry picked from commit 96d1e69a12ed8ab80203277e1abdaf573457a964)
Co-authored-by: Ammar Askar <ammar_askar@hotmail.com>
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 0a3856c..20d2d25 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -4625,7 +4625,22 @@
second = Py_MIN(59, tm.tm_sec);
/* local timezone requires to compute fold */
- if (tzinfo == Py_None && f == _PyTime_localtime) {
+ if (tzinfo == Py_None && f == _PyTime_localtime
+ /* On Windows, passing a negative value to local results
+ * in an OSError because localtime_s on Windows does
+ * not support negative timestamps. Unfortunately this
+ * means that fold detection for time values between
+ * 0 and max_fold_seconds will result in an identical
+ * error since we subtract max_fold_seconds to detect a
+ * fold. However, since we know there haven't been any
+ * folds in the interval [0, max_fold_seconds) in any
+ * timezone, we can hackily just forego fold detection
+ * for this time range.
+ */
+#ifdef MS_WINDOWS
+ && (timet - max_fold_seconds > 0)
+#endif
+ ) {
long long probe_seconds, result_seconds, transition;
result_seconds = utc_to_seconds(year, month, day,