Clean up constructors for "statics" in QString and QByteArray

There were two constuctors offering essentially the same functionality.
One taking the QStatic*Data<N> struct, the other what essentially
amounts to a pointer wrapper of that struct. The former was dropped and
the latter untemplatized and kept, as that is the most generic and
widely applicable. The template parameter in the wrapper was not very
useful as it essentially duplicated information that already maintained
in the struct, and there were no consistency checks to ensure they were
in sync.

In this case, using a wrapper is preferred over the use of naked
pointers both as a way to make explicit the transfer of ownership as
well as to avoid unintended conversions. By using the reference count
(even if only by calling deref() in the destructor), QByteArray and
QString must own their Data pointers.

Const qualification was dropped from the member variable in these
wrappers as it causes some compilers to emit warnings on the lack of
constructors, and because it isn't needed there.

To otherwise reduce noise, QStatic*Data<N> gained a member function to
directly access the const_cast'ed naked pointer. This plays nicely with
the above constructor. Its use also allows us to do further changes in
the QStatic*Data structs with fewer changes in remaining code. The
function has an assert on isStatic(), to ensure it is not inadvertently
used with data that requires ref-count operations.

With this change, the need for the private constructor taking a naked
Q*Data pointer is obviated and that was dropped too.

In updating QStringBuilder's QConcatenable specializations I noticed
they were broken (using data, instead of data()), so a test was added to
avoid this happening again in the future.

An unnecessary ref-count increment in QByteArray::clear was also
dropped.

Change-Id: I9b92fbaae726ab9807837e83d0d19812bf7db5ab
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

5 files changed, 95 insertions, 69 deletions

diff --git a/src/corelib/tools/qbytearray.cpp b/src/corelib/tools/qbytearray.cpp
index 574153fdaf..71244e0eab 100644
--- a/src/corelib/tools/qbytearray.cpp
+++ b/src/corelib/tools/qbytearray.cpp
@@ -584,7 +584,10 @@ QByteArray qUncompress(const uchar* data, int nbytes)
             d->offset = sizeof(QByteArrayData);
             d->data()[len] = 0;
 
-            return QByteArray(d.take(), 0, 0);
+            {
+                QByteArrayDataPtr dataPtr = { d.take() };
+                return QByteArray(dataPtr);
+            }
 
         case Z_MEM_ERROR:
             qWarning("qUncompress: Z_MEM_ERROR: Not enough memory");
@@ -912,9 +915,9 @@ QByteArray &QByteArray::operator=(const char *str)
 {
     Data *x;
     if (!str) {
-        x = const_cast<Data *>(&shared_null.ba);
+        x = shared_null.data_ptr();
     } else if (!*str) {
-        x = const_cast<Data *>(&shared_empty.ba);
+        x = shared_empty.data_ptr();
     } else {
         int len = strlen(str);
         if (d->ref.isShared() || len > int(d->alloc) || (len < d->size && len < int(d->alloc) >> 1))
@@ -1320,12 +1323,12 @@ void QByteArray::chop(int n)
 QByteArray::QByteArray(const char *data, int size)
 {
     if (!data) {
-        d = const_cast<Data *>(&shared_null.ba);
+        d = shared_null.data_ptr();
     } else {
         if (size < 0)
             size = strlen(data);
         if (!size) {
-            d = const_cast<Data *>(&shared_empty.ba);
+            d = shared_empty.data_ptr();
         } else {
             d = static_cast<Data *>(malloc(sizeof(Data) + size + 1));
             Q_CHECK_PTR(d);
@@ -1350,7 +1353,7 @@ QByteArray::QByteArray(const char *data, int size)
 QByteArray::QByteArray(int size, char ch)
 {
     if (size <= 0) {
-        d = const_cast<Data *>(&shared_empty.ba);
+        d = shared_empty.data_ptr();
     } else {
         d = static_cast<Data *>(malloc(sizeof(Data) + size + 1));
         Q_CHECK_PTR(d);
@@ -1406,7 +1409,7 @@ void QByteArray::resize(int size)
     }
 
     if (size == 0 && !d->capacityReserved) {
-        Data *x = const_cast<Data *>(&shared_empty.ba);
+        Data *x = shared_empty.data_ptr();
         if (!d->ref.deref())
             free(d);
         d = x;
@@ -2728,8 +2731,7 @@ void QByteArray::clear()
 {
     if (!d->ref.deref())
         free(d);
-    d = const_cast<Data *>(&shared_null.ba);
-    d->ref.ref();
+    d = shared_null.data_ptr();
 }
 
 #if !defined(QT_NO_DATASTREAM) || (defined(QT_BOOTSTRAPPED) && !defined(QT_BUILD_QMAKE))
@@ -3171,7 +3173,8 @@ QByteArray QByteArray::trimmed() const
     }
     int l = end - start + 1;
     if (l <= 0) {
-        return QByteArray(const_cast<Data *>(&shared_empty.ba), 0, 0);
+        QByteArrayDataPtr empty = { shared_empty.data_ptr() };
+        return QByteArray(empty);
     }
     return QByteArray(s+start, l);
 }
@@ -3878,9 +3881,9 @@ QByteArray QByteArray::fromRawData(const char *data, int size)
 {
     Data *x;
     if (!data) {
-        x = const_cast<Data *>(&shared_null.ba);
+        x = shared_null.data_ptr();
     } else if (!size) {
-        x = const_cast<Data *>(&shared_empty.ba);
+        x = shared_empty.data_ptr();
     } else {
         x = static_cast<Data *>(malloc(sizeof(Data) + 1));
         Q_CHECK_PTR(x);
@@ -3890,7 +3893,8 @@ QByteArray QByteArray::fromRawData(const char *data, int size)
         x->capacityReserved = false;
         x->offset = data - reinterpret_cast<char *>(x);
     }
-    return QByteArray(x, 0, 0);
+    QByteArrayDataPtr dataPtr = { x };
+    return QByteArray(dataPtr);
 }
 
 /*!
diff --git a/src/corelib/tools/qbytearray.h b/src/corelib/tools/qbytearray.h
index 31fa462ca4..2065c8fe91 100644
--- a/src/corelib/tools/qbytearray.h
+++ b/src/corelib/tools/qbytearray.h
@@ -136,21 +136,31 @@ template<int N> struct QStaticByteArrayData
 {
     QByteArrayData ba;
     char data[N + 1];
+
+    QByteArrayData *data_ptr() const
+    {
+        Q_ASSERT(ba.ref.isStatic());
+        return const_cast<QByteArrayData *>(&ba);
+    }
 };
 
-template<int N> struct QStaticByteArrayDataPtr
+struct QByteArrayDataPtr
 {
-    const QStaticByteArrayData<N> *ptr;
+    QByteArrayData *ptr;
 };
 
 
 #if defined(Q_COMPILER_LAMBDA)
-#  define QByteArrayLiteral(str) ([]() -> QStaticByteArrayDataPtr<sizeof(str) - 1> { \
+
+#  define QByteArrayLiteral(str) \
+    ([]() -> QByteArrayDataPtr { \
         enum { Size = sizeof(str) - 1 }; \
         static const QStaticByteArrayData<Size> qbytearray_literal = \
         { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, sizeof(QByteArrayData) }, str }; \
-        QStaticByteArrayDataPtr<Size> holder = { &qbytearray_literal }; \
-    return holder; }())
+        QByteArrayDataPtr holder = { qbytearray_literal.data_ptr() }; \
+        return holder; \
+    }()) \
+    /**/
 
 #elif defined(Q_CC_GNU)
 // We need to create a QByteArrayData in the .rodata section of memory
@@ -162,8 +172,11 @@ template<int N> struct QStaticByteArrayDataPtr
         enum { Size = sizeof(str) - 1 }; \
         static const QStaticByteArrayData<Size> qbytearray_literal = \
         { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, sizeof(QByteArrayData) }, str }; \
-        QStaticByteArrayDataPtr<Size> holder = { &qbytearray_literal }; \
-        holder; })
+        QByteArrayDataPtr holder = { qbytearray_literal.data_ptr() }; \
+        holder; \
+    }) \
+    /**/
+
 #endif
 
 #ifndef QByteArrayLiteral
@@ -377,19 +390,13 @@ public:
     int length() const { return d->size; }
     bool isNull() const;
 
-    template <int n>
-    inline QByteArray(const QStaticByteArrayData<n> &dd)
-        : d(const_cast<QByteArrayData *>(&dd.ba)) {}
-    template <int N>
-    Q_DECL_CONSTEXPR inline QByteArray(QStaticByteArrayDataPtr<N> dd)
-        : d(const_cast<QByteArrayData *>(&dd.ptr->ba)) {}
+    Q_DECL_CONSTEXPR inline QByteArray(QByteArrayDataPtr dd) : d(dd.ptr) {}
 
 private:
     operator QNoImplicitBoolCast() const;
     static const QStaticByteArrayData<1> shared_null;
     static const QStaticByteArrayData<1> shared_empty;
     Data *d;
-    QByteArray(Data *dd, int /*dummy*/, int /*dummy*/) : d(dd) {}
     void realloc(int alloc);
     void expand(int i);
     QByteArray nulTerminated() const;
@@ -402,7 +409,7 @@ public:
     inline DataPtr &data_ptr() { return d; }
 };
 
-inline QByteArray::QByteArray(): d(const_cast<Data *>(&shared_null.ba)) { }
+inline QByteArray::QByteArray(): d(shared_null.data_ptr()) { }
 inline QByteArray::~QByteArray() { if (!d->ref.deref()) free(d); }
 inline int QByteArray::size() const
 { return d->size; }
diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index bb66fdbdec..3bd2deee66 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -1050,7 +1050,7 @@ int QString::toUcs4_helper(const ushort *uc, int length, uint *out)
 QString::QString(const QChar *unicode, int size)
 {
    if (!unicode) {
-        d = const_cast<Data *>(&shared_null.str);
+        d = shared_null.data_ptr();
     } else {
         if (size < 0) {
             size = 0;
@@ -1058,7 +1058,7 @@ QString::QString(const QChar *unicode, int size)
                 ++size;
         }
         if (!size) {
-            d = const_cast<Data *>(&shared_empty.str);
+            d = shared_empty.data_ptr();
         } else {
             d = (Data*) ::malloc(sizeof(Data)+(size+1)*sizeof(QChar));
             Q_CHECK_PTR(d);
@@ -1082,7 +1082,7 @@ QString::QString(const QChar *unicode, int size)
 QString::QString(int size, QChar ch)
 {
    if (size <= 0) {
-        d = const_cast<Data *>(&shared_empty.str);
+        d = shared_empty.data_ptr();
     } else {
         d = (Data*) ::malloc(sizeof(Data)+(size+1)*sizeof(QChar));
         Q_CHECK_PTR(d);
@@ -1240,7 +1240,7 @@ void QString::resize(int size)
     }
 
     if (size == 0 && !d->capacityReserved) {
-        Data *x = const_cast<Data *>(&shared_empty.str);
+        Data *x = shared_empty.data_ptr();
         if (!d->ref.deref())
             QString::free(d);
         d = x;
@@ -4064,9 +4064,9 @@ QString::Data *QString::fromLatin1_helper(const char *str, int size)
 {
     Data *d;
     if (!str) {
-        d = const_cast<Data *>(&shared_null.str);
+        d = shared_null.data_ptr();
     } else if (size == 0 || (!*str && size < 0)) {
-        d = const_cast<Data *>(&shared_empty.str);
+        d = shared_empty.data_ptr();
     } else {
         if (size < 0)
             size = qstrlen(str);
@@ -4141,8 +4141,10 @@ QString QString::fromLocal8Bit_helper(const char *str, int size)
 {
     if (!str)
         return QString();
-    if (size == 0 || (!*str && size < 0))
-        return QString(shared_empty);
+    if (size == 0 || (!*str && size < 0)) {
+        QStringDataPtr empty = { shared_empty.data_ptr() };
+        return QString(empty);
+    }
 #if !defined(QT_NO_TEXTCODEC)
     if (size < 0)
         size = qstrlen(str);
@@ -4309,7 +4311,8 @@ QString QString::simplified() const
             break;
         if (++from == fromEnd) {
             // All-whitespace string
-            return QString(shared_empty);
+            QStringDataPtr empty = { shared_empty.data_ptr() };
+            return QString(empty);
         }
     }
     // This loop needs no underflow check, as we already determined that
@@ -4403,7 +4406,8 @@ QString QString::trimmed() const
     }
     int l = end - start + 1;
     if (l <= 0) {
-        return QString(shared_empty);
+        QStringDataPtr empty = { shared_empty.data_ptr() };
+        return QString(empty);
     }
     return QString(s + start, l);
 }
@@ -7436,9 +7440,9 @@ QString QString::fromRawData(const QChar *unicode, int size)
 {
     Data *x;
     if (!unicode) {
-        x = const_cast<Data *>(&shared_null.str);
+        x = shared_null.data_ptr();
     } else if (!size) {
-        x = const_cast<Data *>(&shared_empty.str);
+        x = shared_empty.data_ptr();
     } else {
         x = static_cast<Data *>(::malloc(sizeof(Data) + sizeof(ushort)));
         Q_CHECK_PTR(x);
@@ -7448,7 +7452,8 @@ QString QString::fromRawData(const QChar *unicode, int size)
         x->capacityReserved = false;
         x->offset = reinterpret_cast<const char *>(unicode) - reinterpret_cast<char *>(x);
     }
-    return QString(x, 0);
+    QStringDataPtr dataPtr = { x };
+    return QString(dataPtr);
 }
 
 /*!
diff --git a/src/corelib/tools/qstring.h b/src/corelib/tools/qstring.h
index 4f241e72e2..50796a9e29 100644
--- a/src/corelib/tools/qstring.h
+++ b/src/corelib/tools/qstring.h
@@ -113,12 +113,16 @@ Q_STATIC_ASSERT_X(sizeof(qunicodechar) == 2,
 #ifndef QT_NO_UNICODE_LITERAL
 #  define QT_UNICODE_LITERAL(str) QT_UNICODE_LITERAL_II(str)
 # if defined(Q_COMPILER_LAMBDA)
-#  define QStringLiteral(str) ([]() -> QStaticStringDataPtr<sizeof(QT_UNICODE_LITERAL(str))/2 - 1> { \
+
+#  define QStringLiteral(str) \
+    ([]() -> QStringDataPtr { \
         enum { Size = sizeof(QT_UNICODE_LITERAL(str))/2 - 1 }; \
         static const QStaticStringData<Size> qstring_literal = \
         { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, sizeof(QStringData) }, QT_UNICODE_LITERAL(str) }; \
-        QStaticStringDataPtr<Size> holder = { &qstring_literal }; \
-    return holder; }())
+        QStringDataPtr holder = { qstring_literal.data_ptr() }; \
+        return holder; \
+    }()) \
+    /**/
 
 # elif defined(Q_CC_GNU)
 // We need to create a QStringData in the .rodata section of memory
@@ -130,8 +134,11 @@ Q_STATIC_ASSERT_X(sizeof(qunicodechar) == 2,
         enum { Size = sizeof(QT_UNICODE_LITERAL(str))/2 - 1 }; \
         static const QStaticStringData<Size> qstring_literal = \
         { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, sizeof(QStringData) }, QT_UNICODE_LITERAL(str) }; \
-        QStaticStringDataPtr<Size> holder = { &qstring_literal }; \
-        holder; })
+        QStringDataPtr holder = { qstring_literal.data_ptr() }; \
+        holder; \
+    }) \
+    /**/
+
 # endif
 #endif // QT_NO_UNICODE_LITERAL
 
@@ -147,12 +154,17 @@ struct QStaticStringData
 {
     QStringData str;
     qunicodechar data[N + 1];
+
+    QStringData *data_ptr() const
+    {
+        Q_ASSERT(str.ref.isStatic());
+        return const_cast<QStringData *>(&str);
+    }
 };
 
-template <int N>
-struct QStaticStringDataPtr
+struct QStringDataPtr
 {
-    const QStaticStringData<N> *ptr;
+    QStringData *ptr;
 };
 
 class Q_CORE_EXPORT QString
@@ -421,11 +433,13 @@ public:
     // note - this are all inline so we can benefit from strlen() compile time optimizations
     static inline QString fromAscii(const char *str, int size = -1)
     {
-        return QString(fromAscii_helper(str, (str && size == -1) ? int(strlen(str)) : size), 0);
+        QStringDataPtr dataPtr = { fromAscii_helper(str, (str && size == -1) ? int(strlen(str)) : size) };
+        return QString(dataPtr);
     }
     static inline QString fromLatin1(const char *str, int size = -1)
     {
-        return QString(fromLatin1_helper(str, (str && size == -1) ? int(strlen(str)) : size), 0);
+        QStringDataPtr dataPtr = { fromLatin1_helper(str, (str && size == -1) ? int(strlen(str)) : size) };
+        return QString(dataPtr);
     }
     static inline QString fromUtf8(const char *str, int size = -1)
     {
@@ -600,7 +614,7 @@ public:
     // compatibility
     struct Null { };
     static const Null null;
-    inline QString(const Null &): d(const_cast<Data *>(&shared_null.str)) {}
+    inline QString(const Null &): d(shared_null.data_ptr()) {}
     inline QString &operator=(const Null &) { *this = QString(); return *this; }
     inline bool isNull() const { return d == &shared_null.str; }
 
@@ -609,10 +623,7 @@ public:
     bool isRightToLeft() const;
 
     QString(int size, Qt::Initialization);
-    template <int n>
-    inline QString(const QStaticStringData<n> &dd) : d(const_cast<QStringData *>(&dd.str)) {}
-    template <int N>
-    Q_DECL_CONSTEXPR inline QString(QStaticStringDataPtr<N> dd) : d(const_cast<QStringData *>(&dd.ptr->str)) {}
+    Q_DECL_CONSTEXPR inline QString(QStringDataPtr dd) : d(dd.ptr) {}
 
 private:
 #if defined(QT_NO_CAST_FROM_ASCII) && !defined(Q_NO_DECLARED_NOT_DEFINED)
@@ -627,7 +638,6 @@ private:
     static const QStaticStringData<1> shared_null;
     static const QStaticStringData<1> shared_empty;
     Data *d;
-    inline QString(Data *dd, int /*dummy*/) : d(dd) {}
 
     static int grow(int);
     static void free(Data *);
@@ -888,7 +898,7 @@ inline void QCharRef::setRow(uchar arow) { QChar(*this).setRow(arow); }
 inline void QCharRef::setCell(uchar acell) { QChar(*this).setCell(acell); }
 
 
-inline QString::QString() : d(const_cast<Data *>(&shared_null.str)) {}
+inline QString::QString() : d(shared_null.data_ptr()) {}
 inline QString::~QString() { if (!d->ref.deref()) free(d); }
 
 inline void QString::reserve(int asize)
diff --git a/src/corelib/tools/qstringbuilder.h b/src/corelib/tools/qstringbuilder.h
index 0b85e590cd..9a1fd6949b 100644
--- a/src/corelib/tools/qstringbuilder.h
+++ b/src/corelib/tools/qstringbuilder.h
@@ -253,16 +253,16 @@ template <> struct QConcatenable<QString> : private QAbstractConcatenable
     }
 };
 
-template <int N> struct QConcatenable<QStaticStringDataPtr<N> > : private QAbstractConcatenable
+template <> struct QConcatenable<QStringDataPtr> : private QAbstractConcatenable
 {
-    typedef QStaticStringDataPtr<N> type;
+    typedef QStringDataPtr type;
     typedef QString ConvertTo;
     enum { ExactSize = true };
-    static int size(const type &) { return N; }
+    static int size(const type &a) { return a.ptr->size; }
     static inline void appendTo(const type &a, QChar *&out)
     {
-        memcpy(out, reinterpret_cast<const char*>(a.ptr->data), sizeof(QChar) * N);
-        out += N;
+        memcpy(out, reinterpret_cast<const char*>(a.ptr->data()), sizeof(QChar) * a.ptr->size);
+        out += a.ptr->size;
     }
 };
 
@@ -358,22 +358,22 @@ template <> struct QConcatenable<QByteArray> : private QAbstractConcatenable
     }
 };
 
-template <int N> struct QConcatenable<QStaticByteArrayDataPtr<N> > : private QAbstractConcatenable
+template <> struct QConcatenable<QByteArrayDataPtr> : private QAbstractConcatenable
 {
-    typedef QStaticByteArrayDataPtr<N> type;
+    typedef QByteArrayDataPtr type;
     typedef QByteArray ConvertTo;
     enum { ExactSize = false };
-    static int size(const type &) { return N; }
+    static int size(const type &ba) { return ba.ptr->size; }
 #ifndef QT_NO_CAST_FROM_ASCII
     static inline QT_ASCII_CAST_WARN void appendTo(const type &a, QChar *&out)
     {
-        QAbstractConcatenable::convertFromAscii(a.ptr->data, N, out);
+        QAbstractConcatenable::convertFromAscii(a.ptr->data(), a.ptr->size, out);
     }
 #endif
     static inline void appendTo(const type &ba, char *&out)
     {
-        ::memcpy(out, ba.ptr->data, N);
-        out += N;
+        ::memcpy(out, ba.ptr->data(), ba.ptr->size);
+        out += ba.ptr->size;
     }
 };