From 45bf63676d7dc74bfefb1a9c949c132de91538a7 Mon Sep 17 00:00:00 2001
From: Dennis Oberst <dennis.oberst@qt.io>
Date: Wed, 16 Aug 2023 18:25:41 +0200
Subject: [PATCH] QArrayDataPointer: remove Q_CHECK_PTR in assign(it, it) again

This commit reverts 2d77051f9dfd11ae292ad4bac2f28c5f7a0e7f83.

When requesting an allocation of size 0, we will actually get
a nullptr.

 qarraydata.cpp:
    ~~~
    if (capacity == 0) {
        *dptr = nullptr;
        return nullptr;
    }

This will let the Q_CHECK_PTR trigger falsely. Such an occurrence was
initially detected during the cmake_automoc_parser build-step.

Found-by: Marc Mutz <marc.mutz@qt.io>
Task-number: QTBUG-106196
Change-Id: Icb68c5dd518c9623119a61d5c4fdcff43dc4ac5d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 3db9ef358da817480d6f4c055d85a6aa7be17991)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/tools/qarraydatapointer.h        |  2 --
 tests/auto/corelib/tools/qlist/tst_qlist.cpp | 20 ++++++++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index 258e7b7446b..a77db21c99b 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -327,12 +327,10 @@ public:
             const qsizetype n = std::distance(first, last);
             if (needsDetach() || n > constAllocatedCapacity()) {
                 QArrayDataPointer allocated(Data::allocate(detachCapacity(n)));
-                Q_CHECK_PTR(allocated.data());
                 swap(allocated);
             }
         } else if (needsDetach()) {
             QArrayDataPointer allocated(Data::allocate(allocatedCapacity()));
-            Q_CHECK_PTR(allocated.data());
             swap(allocated);
             // We don't want to copy data that we know we'll overwrite
         }
diff --git a/tests/auto/corelib/tools/qlist/tst_qlist.cpp b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
index afced64b42c..2b910e2a8ee 100644
--- a/tests/auto/corelib/tools/qlist/tst_qlist.cpp
+++ b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
@@ -231,6 +231,7 @@ private slots:
     void appendCustom() const { append<Custom>(); }
     void appendRvalue() const;
     void appendList() const;
+    void assignEmpty() const;
     void assignInt() const { assign<int>(); }
     void assignMovable() const { assign<Movable>(); }
     void assignCustom() const { assign<Custom>(); }
@@ -762,6 +763,25 @@ void tst_QList::append() const
     }
 }
 
+void tst_QList::assignEmpty() const
+{
+    // Test that the realloc branch in assign(it, it) doesn't crash.
+    using T = int;
+    QList<T> list;
+    QList<T> ref1 = list;
+    QVERIFY(list.d.needsDetach());
+    list.assign(list.begin(), list.begin());
+
+#if !defined Q_OS_QNX // QNX has problems with the empty istream_iterator
+    auto empty = std::istream_iterator<T>{};
+    list.squeeze();
+    QCOMPARE_EQ(list.capacity(), 0);
+    ref1 = list;
+    QVERIFY(list.d.needsDetach());
+    list.assign(empty, empty);
+#endif
+}
+
 template <typename T>
 void tst_QList::assign() const
 {