QFlags: use unsigned int when the enum's underlying is unsigned

Replace storage and operator int() return types with unsigned int
if the enum is unsigned.

This fixes a number of exisiting warnings, in particular with
Qt::MouseButton under GCC.

Change-Id: Ia12d36212329aec3e9d62a5fbd38809a6c2b36d0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

dist/changes-5.0.0

@@ -62,6 +62,11 @@ information about a particular change.
 
 - qIsDetached<> has been removed without replacement.
 
+- The return type of QFlags<Enum>::operator int() now matches the Enum's underlying
+  type in signedness instead of always being 'int'. This was done in order to allow
+  QFlags over enums whose underlying type is unsigned (Qt::MouseButton is one such
+  enum).
+
 - QMetaType:
   * QMetaType::construct() has been renamed to QMetaType::create().
   * QMetaType::unregisterType() has been removed.

src/corelib/global/qflags.h

@@ -44,6 +44,7 @@
 
 #include <QtCore/qglobal.h>
 #include <QtCore/qtypeinfo.h>
+#include <QtCore/qtypetraits.h>
 
 QT_BEGIN_HEADER
 
@@ -82,11 +83,18 @@ class QFlags
                       "long long would overflow. Qt 5.1 will have support for 64bit enums.");
     struct Private;
     typedef int (Private::*Zero);
-    int i;
 public:
+#ifndef qdoc
+    typedef typename QtPrivate::if_<
+            QtPrivate::is_unsigned<Enum>::value,
+            unsigned int,
+            signed int
+        >::type Int;
+#endif
     typedef Enum enum_type;
     // compiler-generated copy/move ctor/assignment operators are fine!
 #ifdef qdoc
+    typedef int Int; // the real typedef above is too complex for qdoc
     inline QFlags(const QFlags &other);
     inline QFlags &operator=(const QFlags &other);
 #endif
@@ -101,7 +109,7 @@ public:
     inline QFlags &operator^=(QFlags f) { i ^= f.i; return *this; }
     inline QFlags &operator^=(Enum f) { i ^= f; return *this; }
 
-    Q_DECL_CONSTEXPR  inline operator int() const { return i; }
+    Q_DECL_CONSTEXPR  inline operator Int() const { return i; }
 
     Q_DECL_CONSTEXPR inline QFlags operator|(QFlags f) const { return QFlags(Enum(i | f.i)); }
     Q_DECL_CONSTEXPR inline QFlags operator|(Enum f) const { return QFlags(Enum(i | f)); }
@@ -114,7 +122,9 @@ public:
 
     Q_DECL_CONSTEXPR inline bool operator!() const { return !i; }
 
-    Q_DECL_CONSTEXPR inline bool testFlag(Enum f) const { return (i & f) == f && (f != 0 || i == int(f) ); }
+    Q_DECL_CONSTEXPR inline bool testFlag(Enum f) const { return (i & f) == f && (f != 0 || i == Int(f) ); }
+private:
+    Int i;
 };
 
 #define Q_DECLARE_FLAGS(Flags, Enum)\

src/corelib/global/qglobal.cpp

@@ -171,6 +171,15 @@ Q_CORE_EXPORT void *qMemSet(void *dest, int c, size_t n);
     \sa QFlag
 */
 
+/*!
+    \typedef QFlags::Int
+    \since 5.0
+
+    Typedef for the integer type used for storage as well as for
+    implicit conversion. Either \c int or \c{unsigned int}, depending
+    on whether the enum's underlying type is signed or unsigned.
+*/
+
 /*!
     \typedef QFlags::enum_type
 
@@ -261,9 +270,11 @@ Q_CORE_EXPORT void *qMemSet(void *dest, int c, size_t n);
 */
 
 /*!
-    \fn QFlags::operator int() const
+    \fn QFlags::operator Int() const
 
     Returns the value stored in the QFlags object as an integer.
+
+    \sa Int
 */
 
 /*!

tests/auto/corelib/global/qflags/tst_qflags.cpp

@@ -48,6 +48,7 @@ private slots:
     void testFlagZeroFlag() const;
     void testFlagMultiBits() const;
     void constExpr();
+    void signedness();
 };
 
 void tst_QFlags::testFlag() const
@@ -123,10 +124,23 @@ void tst_QFlags::constExpr()
 #endif
 }
 
+void tst_QFlags::signedness()
+{
+    // these are all 'true' on GCC, but since the std says the
+    // underlying type is implementation-defined, we need to allow for
+    // a different signedness, so we only check that the relative
+    // signedness of the types matches:
+    Q_STATIC_ASSERT((QtPrivate::is_unsigned<Qt::MouseButton>::value ==
+                     QtPrivate::is_unsigned<Qt::MouseButtons::Int>::value));
+
+    Q_STATIC_ASSERT((QtPrivate::is_signed<Qt::AlignmentFlag>::value ==
+                     QtPrivate::is_signed<Qt::Alignment::Int>::value));
+}
+
 // (statically) check QTypeInfo for QFlags instantiations:
 enum MyEnum { Zero, One, Two, Four=4 };
-Q_DECLARE_FLAGS( MyFlags, MyEnum );
-Q_DECLARE_OPERATORS_FOR_FLAGS( MyFlags );
+Q_DECLARE_FLAGS( MyFlags, MyEnum )
+Q_DECLARE_OPERATORS_FOR_FLAGS( MyFlags )
 
 Q_STATIC_ASSERT( !QTypeInfo<MyFlags>::isComplex );
 Q_STATIC_ASSERT( !QTypeInfo<MyFlags>::isStatic );