Clean up QList(iterator, iterator)

Fold the two overloads into one, and distinguish the cases using
if constexpr. Do not overload QArrayOps::copyAppend(), to make it
clear which one is being used.

Change-Id: If6a894841aacb84ba190fb2209246f5f61034b42
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/tools/qarraydataops.h

@@ -917,18 +917,14 @@ public:
     // using Base::assign;
     // using Base::compare;
 
-    using Base::copyAppend;
-
     template<typename It>
-    void copyAppend(It b, It e, QtPrivate::IfIsForwardIterator<It> = true,
+    void appendIteratorRange(It b, It e, QtPrivate::IfIsForwardIterator<It> = true)
-                    QtPrivate::IfIsNotConvertible<It, const T *> = true,
-                    QtPrivate::IfIsNotConvertible<It, const T *> = true)
     {
         Q_ASSERT(this->isMutable() || b == e);
         Q_ASSERT(!this->isShared() || b == e);
-
         const qsizetype distance = std::distance(b, e);
         Q_ASSERT(distance >= 0 && distance <= this->allocatedCapacity() - this->size);
+        Q_UNUSED(distance);
 
         T *iter = this->end();
         for (; b != e; ++iter, ++b) {

src/corelib/tools/qlist.h

@@ -181,22 +181,25 @@ public:
             d->copyAppend(args.begin(), args.end());
         return *this;
     }
-    template <typename InputIterator, QtPrivate::IfIsForwardIterator<InputIterator> = true>
+    template <typename InputIterator, QtPrivate::IfIsInputIterator<InputIterator> = true>
     QList(InputIterator i1, InputIterator i2)
     {
-        const auto distance = std::distance(i1, i2);
+        if constexpr (!std::is_convertible_v<typename std::iterator_traits<Iterator>::iterator_category, std::forward_iterator_tag>) {
-        if (distance) {
+            std::copy(i1, i2, std::back_inserter(*this));
-            d = DataPointer(Data::allocate(distance));
+        } else {
-            d->copyAppend(i1, i2);
+            const auto distance = std::distance(i1, i2);
+            if (distance) {
+                d = DataPointer(Data::allocate(distance));
+                if constexpr (std::is_same_v<std::decay_t<InputIterator>, iterator> ||
+                              std::is_same_v<std::decay_t<InputIterator>, const_iterator>) {
+                    d->copyAppend(i1, i2);
+                } else {
+                    d->appendIteratorRange(i1, i2);
+               }
+            }
         }
     }
 
-    template <typename InputIterator, QtPrivate::IfIsNotForwardIterator<InputIterator> = true>
-    QList(InputIterator i1, InputIterator i2)
-    {
-        std::copy(i1, i2, std::back_inserter(*this));
-    }
-
     // This constructor is here for compatibility with QStringList in Qt 5, that has a QStringList(const QString &) constructor
     template<typename String, typename = std::enable_if_t<std::is_same_v<T, QString> && std::is_convertible_v<String, QString>>>
     inline explicit QList(const String &str)

tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp

@@ -1169,7 +1169,7 @@ void tst_QArrayData::arrayOpsExtra()
             auto copy = cloneArrayDataPointer(dataPointer, dataPointer.size);
             const size_t distance = std::distance(first, last);
 
-            dataPointer->copyAppend(first, last);
+            dataPointer->appendIteratorRange(first, last);
             QCOMPARE(size_t(dataPointer.size), originalSize + distance);
             size_t i = 0;
             for (; i < originalSize; ++i)