QList: add STL-style assign()

Implemented assign() methods for QList to align with the criteria of
std::vector, addressing the previously missing functionality.

Reference:
https://en.cppreference.com/w/cpp/container/vector/assign

[ChangeLog][QtCore][QList] Added assign().

Fixes: QTBUG-106196
Change-Id: I5df8689c020dafde68d2cd7d09c769744fa8f137
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 69 insertions, 0 deletions

diff --git a/tests/auto/corelib/tools/containerapisymmetry/tst_containerapisymmetry.cpp b/tests/auto/corelib/tools/containerapisymmetry/tst_containerapisymmetry.cpp
index f3909cd4e8..24f5dba17e 100644
--- a/tests/auto/corelib/tools/containerapisymmetry/tst_containerapisymmetry.cpp
+++ b/tests/auto/corelib/tools/containerapisymmetry/tst_containerapisymmetry.cpp
@@ -338,6 +338,7 @@ private:
 private Q_SLOTS:
     void assign_std_vector() { assign_impl<std::vector<int>>(); };
     void assign_QVarLengthArray() { assign_impl<QVarLengthArray<int, 4>>(); };
+    void assign_QList() { assign_impl<QList<int>>(); }
 
 private:
     template <typename Container>
@@ -802,6 +803,10 @@ void tst_ContainerApiSymmetry::assign_impl() const
         iter.assign(8, tData);
         c.assign(iter.begin(), iter.end());
         CHECK(c, tData, c.size(), S(8), c.capacity(), std::max(oldCapacity, S(8)));
+
+        c.assign(iter.begin(), iter.begin());
+        QCOMPARE_EQ(c.size(), S(0));
+        QCOMPARE_EQ(c.capacity(), std::max(oldCapacity, S(8)));
     }
     {
         // range version for input iterator
diff --git a/tests/auto/corelib/tools/qlist/tst_qlist.cpp b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
index 482079b0fe..050bb80ab1 100644
--- a/tests/auto/corelib/tools/qlist/tst_qlist.cpp
+++ b/tests/auto/corelib/tools/qlist/tst_qlist.cpp
@@ -231,6 +231,9 @@ private slots:
     void appendCustom() const { append<Custom>(); }
     void appendRvalue() const;
     void appendList() const;
+    void assignInt() const { assign<int>(); }
+    void assignMovable() const { assign<Movable>(); }
+    void assignCustom() const { assign<Custom>(); }
     void at() const;
     void capacityInt() const { capacity<int>(); }
     void capacityMovable() const { capacity<Movable>(); }
@@ -396,6 +399,7 @@ private:
     template<typename T> void testAssignment() const;
     template<typename T> void add() const;
     template<typename T> void append() const;
+    template<typename T> void assign() const;
     template<typename T> void assignFromInitializerList() const;
     template<typename T> void capacity() const;
     template<typename T> void clear() const;
@@ -750,6 +754,66 @@ void tst_QList::append() const
     }
 }
 
+template <typename T>
+void tst_QList::assign() const
+{
+    TST_QLIST_CHECK_LEAKS(T)
+    {
+        QList<T> myvec;
+        myvec.assign(2, T_FOO);
+        QVERIFY(myvec.isDetached());
+        QCOMPARE(myvec, QList<T>() << T_FOO << T_FOO);
+
+        QList<T> myvecCopy = myvec;
+        QVERIFY(!myvec.isDetached());
+        QVERIFY(!myvecCopy.isDetached());
+        QVERIFY(myvec.isSharedWith(myvecCopy));
+        QVERIFY(myvecCopy.isSharedWith(myvec));
+
+        myvec.assign(3, T_BAR);
+        QCOMPARE(myvec, QList<T>() << T_BAR << T_BAR << T_BAR);
+        QVERIFY(myvec.isDetached());
+        QVERIFY(myvecCopy.isDetached());
+        QVERIFY(!myvec.isSharedWith(myvecCopy));
+        QVERIFY(!myvecCopy.isSharedWith(myvec));
+    }
+    {
+        QList<T> myvec;
+        myvec.assign(4, T_FOO);
+        QVERIFY(myvec.isDetached());
+        QCOMPARE(myvec, QList<T>() << T_FOO << T_FOO << T_FOO << T_FOO);
+
+        QList<T> myvecCopy = myvec;
+        QVERIFY(!myvec.isDetached());
+        QVERIFY(!myvecCopy.isDetached());
+        QVERIFY(myvec.isSharedWith(myvecCopy));
+        QVERIFY(myvecCopy.isSharedWith(myvec));
+
+        myvecCopy.assign(myvec.begin(), myvec.begin() + 2);
+        QVERIFY(myvec.isDetached());
+        QVERIFY(myvecCopy.isDetached());
+        QVERIFY(!myvec.isSharedWith(myvecCopy));
+        QVERIFY(!myvecCopy.isSharedWith(myvec));
+        QCOMPARE(myvecCopy, QList<T>() << T_FOO << T_FOO);
+    }
+    {
+        // Test the prepend optimization.
+        QList<T> withFreeSpaceAtBegin(16, T_FOO);
+        // try at most 100 times to create freeSpaceAtBegin():
+        for (int i = 0; i < 100 && !withFreeSpaceAtBegin.d.freeSpaceAtBegin(); ++i)
+             withFreeSpaceAtBegin.prepend(T_FOO);
+        QCOMPARE_GT(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 0);
+        const auto oldData = withFreeSpaceAtBegin.constData();
+        std::vector<T> v(withFreeSpaceAtBegin.capacity(), T_BAR);
+        withFreeSpaceAtBegin.assign(v.begin(), v.end());
+        QCOMPARE_EQ(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 0);
+        // TODO: Check for equality after the prepend optimization
+        // the following test checks that we didn't reallocate, but re-used the prepend buffer
+        QEXPECT_FAIL("","Use of freeSpaceAtBegin() isn't, yet, implemented", Continue);
+        QVERIFY(QtPrivate::q_points_into_range(oldData, withFreeSpaceAtBegin));
+    }
+}
+
 void tst_QList::appendRvalue() const
 {
     QList<QString> v;