QBitArray: replace the member operator~ with a hidden friend

Which takes the array to be inverted by value, so we get free move
semantics and allowing us to perform the negation in-place.

[ChangeLog][Potentially Source-Incompatible Changes] The bitwise AND,
OR, XOR, and NOT operator functions on QBitArray are now hidden
friends. This may cause source-incompatibility in unusual coding styles
(like 'array.operator~()') or with classes that have a casting 'operator
QBitArray()'.

Change-Id: I85b3fc2dd45c4693be13fffd1795ba1fbaf23769
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/compat/removed_api.cpp

@@ -618,6 +618,13 @@ QStringView QXmlStreamAttributes::value(QLatin1StringView qualifiedName) const
 
 #if QT_CORE_REMOVED_SINCE(6, 7)
 
+#include "qbitarray.h"
+
+QBitArray QBitArray::operator~() const
+{
+    return QBitArray(*this).inverted_inplace();
+}
+
 #include "qbytearray.h"
 
 QByteArray QByteArray::left(qsizetype len)  const

src/corelib/tools/qbitarray.cpp

@@ -583,8 +583,9 @@ QBitArray &QBitArray::operator^=(const QBitArray &other)
 }
 
 /*!
-    Returns a bit array that contains the inverted bits of this bit
-    array.
+    \fn QBitArray QBitArray::operator~(QBitArray a)
+    Returns a bit array that contains the inverted bits of the bit
+    array \a a.
 
     Example:
     \snippet code/src_corelib_tools_qbitarray.cpp 11
@@ -592,12 +593,19 @@ QBitArray &QBitArray::operator^=(const QBitArray &other)
     \sa operator&(), operator|(), operator^()
 */
 
-QBitArray QBitArray::operator~() const
+Q_NEVER_INLINE QBitArray QBitArray::inverted_inplace() &&
 {
     qsizetype n = d.size();
-    QBitArray result(QByteArrayData(n, n));
-    const uchar *src = reinterpret_cast<const uchar *>(data_ptr().data());
-    uchar *dst = reinterpret_cast<uchar *>(result.data_ptr().data());
+    uchar *dst = reinterpret_cast<uchar *>(data_ptr().data());
+    const uchar *src = dst;
+    QBitArray result([&] {
+        if (d.isDetached() || n == 0)
+            return std::move(d.data_ptr());     // invert in-place
+
+        QByteArrayData tmp(n, n);
+        dst = reinterpret_cast<uchar *>(tmp.data());
+        return tmp;
+    }());
 
     uchar bitdiff = 8;
     if (n)

src/corelib/tools/qbitarray.h

@@ -16,6 +16,8 @@ class Q_CORE_EXPORT QBitArray
     friend Q_CORE_EXPORT QDataStream &operator>>(QDataStream &, QBitArray &);
 #endif
     friend Q_CORE_EXPORT size_t qHash(const QBitArray &key, size_t seed) noexcept;
+    friend QBitArray operator~(QBitArray a)
+    { return std::move(a).inverted_inplace(); }
     QByteArray d;
 
     QBitArray(QByteArrayData &&dd) : d(std::move(dd)) {}
@@ -32,6 +34,8 @@ class Q_CORE_EXPORT QBitArray
         return R{ ba.d[1 + byteIdx], uchar(1U << bitIdx) };
     }
 
+    QBitArray inverted_inplace() &&;
+
 public:
     inline QBitArray() noexcept {}
     explicit QBitArray(qsizetype size, bool val = false);
@@ -78,7 +82,9 @@ public:
     QBitArray &operator&=(const QBitArray &);
     QBitArray &operator|=(const QBitArray &);
     QBitArray &operator^=(const QBitArray &);
+#if QT_CORE_REMOVED_SINCE(6, 7)
     QBitArray operator~() const;
+#endif
 
     inline bool operator==(const QBitArray &other) const { return d == other.d; }
     inline bool operator!=(const QBitArray &other) const { return d != other.d; }

tests/auto/corelib/tools/qbitarray/tst_qbitarray.cpp

@@ -454,6 +454,7 @@ void tst_QBitArray::operator_neg()
     input = ~input;
 
     QCOMPARE(input, res);
+    QCOMPARE(~~input, res);     // performs two in-place negations
 }
 
 void tst_QBitArray::datastream_data()