From 6535b6d5f3db3e3afbb9f011207399a16b1dc961 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Mon, 28 Oct 2024 19:21:13 +0100
Subject: [PATCH] QList: fix std::to_address(QList::iterator) on older
 compilers

Need to enable element_type unconditionally, to direct the default
std::pointer_traits::to_address to fall back to operator->().

[ChangeLog][QtCore][QList] Fixed std::to_address() on QList::iterator
on older compilers.

Fixes: QTBUG-130643
Change-Id: I521f327933c51ca87c511a7741b2dce65094032b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit b8c879f273533d87f52dbc8e9d2f9b3b3566cd60)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/tools/qlist.h                    |  4 ++--
 tests/auto/corelib/tools/qlist/tst_qlist.cpp | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 6f98ef4d5bb..60c48d30e58 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -120,8 +120,8 @@ public:
         using value_type = T;
 #ifdef QT_COMPILER_HAS_LWG3346
         using iterator_concept = std::contiguous_iterator_tag;
-        using element_type = value_type;
 #endif
+        using element_type = value_type;
         using iterator_category = std::random_access_iterator_tag;
         using pointer = T *;
         using reference = T &;
@@ -190,8 +190,8 @@ public:
         using value_type = T;
 #ifdef QT_COMPILER_HAS_LWG3346
         using iterator_concept = std::contiguous_iterator_tag;
-        using element_type = const value_type;
 #endif
+        using element_type = const value_type;
         using iterator_category = std::random_access_iterator_tag;
         using pointer = const T *;
         using reference = const T &;
diff --git a/tests/auto/corelib/tools/qlist/tst_qlist.cpp b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
index d879467da37..9ebfd7aee05 100644
--- a/tests/auto/corelib/tools/qlist/tst_qlist.cpp
+++ b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
@@ -15,6 +15,7 @@
 #include <qlist.h>
 
 #include <cstdio>
+#include <QtCore/q20memory.h>
 
 #ifdef QT_COMPILER_HAS_LWG3346
 #  if __has_include(<concepts>)
@@ -340,6 +341,7 @@ private slots:
     void swapInt() const { swap<int>(); }
     void swapMovable() const { swap<Movable>(); }
     void swapCustom() const { swap<Custom>(); }
+    void toAddress() const;
     void toList() const;
 #if QT_VERSION < QT_VERSION_CHECK(6,0,0)
     void fromStdVector() const;
@@ -2935,6 +2937,23 @@ void tst_QList::startsWith() const
     QVERIFY(myvec.startsWith(1));
 }
 
+void tst_QList::toAddress() const
+{
+    // Annoyingly, QList::iterator is a class; make sure std::to_address works on them
+    QList<int> l = {1, 2, 3, 4, 5};
+    auto check = [&](auto b, auto e) {
+        QCOMPARE_EQ(q20::to_address(b), l.data());
+        QCOMPARE_EQ(q20::to_address(e), l.data() + l.size());
+    };
+    // begin QTBUG-130643
+    check(l.begin(), l.end());
+    check(l.cbegin(), l.cend());
+    // end QTBUG-130643
+    // for reverse_iterator, account for the off-by-one to its ::base():
+    check(l.rend() - 1, l.rbegin() - 1);
+    check(l.crend() - 1, l.crbegin() - 1);
+}
+
 template<typename T>
 void tst_QList::swap() const
 {