From 04419c2852463e9f0e25e108dd3300a29cd885f8 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Fri, 8 Oct 2021 13:20:28 +0200
Subject: [PATCH] Set tm_isdst = -1 before calling mktime()

Leaving it set to 0 will cause mktime() to interpret other fields as
in standard time, potentially "correcting" them and tm_isdst to
represent the equivalent moment in daylight-saving time. Set it to -1
to tell mktime() to let the system work out whether the time is
standard or daylight-saving.

Change-Id: Id33d4cb0afdb14f236ca5ce04cf605610a30d712
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/time/qdatetime.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/corelib/time/qdatetime.cpp b/src/corelib/time/qdatetime.cpp
index 0d836fa9367..f8b9724604e 100644
--- a/src/corelib/time/qdatetime.cpp
+++ b/src/corelib/time/qdatetime.cpp
@@ -2726,6 +2726,7 @@ static auto computeSystemMillisRange()
         local.tm_year = tmYearFromQYear(1901);
         local.tm_mon = 11;
         local.tm_mday = 15; // A day and a bit after the start of 32-bit time_t:
+        local.tm_isdst = -1;
         return R{qMkTime(&local) == -1 ? 0 : msecsMin, msecsMax, false, false};
     } else {
         const struct { int year; qint64 millis; } starts[] = {
@@ -2754,6 +2755,7 @@ static auto computeSystemMillisRange()
             local.tm_mday = 31;
             local.tm_hour = 23;
             local.tm_min = local.tm_sec = 59;
+            local.tm_isdst = -1;
             if (qMkTime(&local) != -1) {
                 stop = c.millis;
                 break;
@@ -2766,6 +2768,7 @@ static auto computeSystemMillisRange()
             local.tm_year = tmYearFromQYear(c.year);
             local.tm_mon = 1;
             local.tm_mday = 1;
+            local.tm_isdst = -1;
             if (qMkTime(&local) != -1)
                 return R{c.millis, stop, startMin, stopMax};
             startMin = false;