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bpo-29097: Forego fold detection on windows for low timestamp values (GH-2385)

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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.
This commit is contained in:
Ammar Askar 2018-07-25 09:54:58 -07:00 • committed by Alexander Belopolsky
parent 74102c9a5f
commit 96d1e69a12
4 changed files with 34 additions and 2 deletions
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17
Modules/_datetimemodule.c
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@ -4625,7 +4625,22 @@ datetime_from_timet_and_us(PyObject *cls, TM_FUNC f, time_t timet, int us,
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,