From abf8d5a6714d78d30bb0d666adc439fa700644d5 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Tue, 4 Jun 2024 17:54:05 +0200
Subject: [PATCH] Use QByteArrayView lists of IANA IDs before working out which
 we have

The QTZP::availableTimeZoneIds() overloads taking a territory or
offset to select on were building a list of QBAs, allocating copies of
static data to do so, and then taking their intersection with the
no-parameter overload. Since the latter is of QBAs and the
intersection code used its begin() and end() for the first pair of
parameters to std::intersection(), from which the results are drawn,
we can use a QBAV list for the second pair of parameters (with whose
range the first pair's range is intersected), thanks to QBAV entries
in the list being comparable with QBA.

This saves allocating copies of the static data, when we can make do
with simply building a list of views of that data.

Belatedly picking to 6.8 as a prerequisite of a later change.

Change-Id: I42de4a91273e23fb394f9ae7a86f7f3fadf95be3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 67fb5dcfcd1bac5d5b30723a4ebba84acda58902)
Reviewed-by: Mate Barany <mate.barany@qt.io>
---
 src/corelib/time/qtimezoneprivate.cpp | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/corelib/time/qtimezoneprivate.cpp b/src/corelib/time/qtimezoneprivate.cpp
index 5e50ce6dbab..99f443aa0e9 100644
--- a/src/corelib/time/qtimezoneprivate.cpp
+++ b/src/corelib/time/qtimezoneprivate.cpp
@@ -613,7 +613,8 @@ QList<QByteArray> QTimeZonePrivate::availableTimeZoneIds() const
     return QList<QByteArray>();
 }
 
-static QList<QByteArray> selectAvailable(QList<QByteArray>&& desired, const QList<QByteArray>& all)
+static QList<QByteArray> selectAvailable(QList<QByteArrayView> &&desired,
+                                         const QList<QByteArray> &all)
 {
     std::sort(desired.begin(), desired.end());
     const auto newEnd = std::unique(desired.begin(), desired.end());
@@ -628,13 +629,13 @@ static QList<QByteArray> selectAvailable(QList<QByteArray>&& desired, const QLis
 QList<QByteArray> QTimeZonePrivate::availableTimeZoneIds(QLocale::Territory territory) const
 {
     // Default fall-back mode, use the zoneTable to find Region of know Zones
-    QList<QByteArray> regions;
+    QList<QByteArrayView> regions;
 
     // First get all Zones in the Zones table belonging to the Region
     for (const ZoneData &data : zoneDataTable) {
         if (data.territory == territory) {
             for (auto l1 : data.ids())
-                regions << QByteArray(l1.data(), l1.size());
+                regions << QByteArrayView(l1.data(), l1.size());
         }
     }
     return selectAvailable(std::move(regions), availableTimeZoneIds());
@@ -642,16 +643,16 @@ QList<QByteArray> QTimeZonePrivate::availableTimeZoneIds(QLocale::Territory terr
 
 QList<QByteArray> QTimeZonePrivate::availableTimeZoneIds(int offsetFromUtc) const
 {
-    // Default fall-back mode, use the zoneTable to find Offset of know Zones
-    QList<QByteArray> offsets;
-    // First get all Zones in the table using the Offset
+    // Default fall-back mode: use the zoneTable to find offsets of know zones.
+    QList<QByteArrayView> offsets;
+    // First get all Zones in the table using the given offset:
     for (const WindowsData &winData : windowsDataTable) {
         if (winData.offsetFromUtc == offsetFromUtc) {
             for (auto data = zoneStartForWindowsId(winData.windowsIdKey);
                  data != std::end(zoneDataTable) && data->windowsIdKey == winData.windowsIdKey;
                  ++data) {
                 for (auto l1 : data->ids())
-                    offsets << QByteArray(l1.data(), l1.size());
+                    offsets << QByteArrayView(l1.data(), l1.size());
             }
         }
     }