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
Pick-to: 6.6
Change-Id: Icb68c5dd518c9623119a61d5c4fdcff43dc4ac5d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/auto/corelib/tools/qlist/tst_qlist.cpp b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
index 06ae1c4fb8..743028351c 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>(); }
@@ -759,6 +760,25 @@ 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
 {