From 6df9074a1a81c923bad70acbcd4a4b0d0e269322 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Wed, 10 Jan 2024 11:27:06 +0100
Subject: [PATCH] QWinTimeZonePrivate::availableTimeZoneIds(): cache result
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This follows up on commit d59e539b3a1252aa22783c4fdf1e22b35e5a4292,
doing the same for one of its callers. The mapping from windows IDs to
IANA ones is hard-coded (using CLDR-generated data), so the
(now unchanging) availableWindowsIds() list shall always map to the
same list of IANA IDs.

Pick-to: 6.6 6.5
Task-number: QTBUG-120682
Change-Id: I4d610c24110064236b375cab04cde90bbe07735f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
(cherry picked from commit 83871413636407f196c2ef7ca4e5b0a846c646ec)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/time/qtimezoneprivate_win.cpp | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/corelib/time/qtimezoneprivate_win.cpp b/src/corelib/time/qtimezoneprivate_win.cpp
index 82666407d2c..2502516810a 100644
--- a/src/corelib/time/qtimezoneprivate_win.cpp
+++ b/src/corelib/time/qtimezoneprivate_win.cpp
@@ -849,13 +849,16 @@ QByteArray QWinTimeZonePrivate::systemTimeZoneId() const
 
 QList<QByteArray> QWinTimeZonePrivate::availableTimeZoneIds() const
 {
-    QList<QByteArray> result;
-    const auto winIds = availableWindowsIds();
-    for (const QByteArray &winId : winIds)
-        result += windowsIdToIanaIds(winId);
-    std::sort(result.begin(), result.end());
-    result.erase(std::unique(result.begin(), result.end()), result.end());
-    return result;
+    static const QList<QByteArray> cache = [] {
+        QList<QByteArray> result;
+        const auto winIds = availableWindowsIds();
+        for (const QByteArray &winId : winIds)
+            result += windowsIdToIanaIds(winId);
+        std::sort(result.begin(), result.end());
+        result.erase(std::unique(result.begin(), result.end()), result.end());
+        return result;
+    }();
+    return cache;
 }
 
 QTimeZonePrivate::Data QWinTimeZonePrivate::ruleToData(const QWinTransitionRule &rule,