Remove qtypetraits.h's contents altogether

So that QFlags can use an (un)signed int matching the
underlying type as identified by the compiler and not by us.

Requires fixing a few warnings about sign conversion due to
QFlags misusages in qtbase that were either plain wrong, or
were relying on the enum being backed by an (un)signed int
when it wasn't.

Keep qtypetraits.h in the source tree in order to prevent
source breaks if some downstream #includes it (note however
that it did not contain any public API).

Change-Id: Ib3a92b98db7031e793a088fb2a3b306eff4d7a3c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 12 insertions, 52 deletions

diff --git a/src/corelib/global/qflags.h b/src/corelib/global/qflags.h
index b871c90c9d..89a0ae9083 100644
--- a/src/corelib/global/qflags.h
+++ b/src/corelib/global/qflags.h
@@ -42,13 +42,12 @@
 #ifndef QFLAGS_H
 #define QFLAGS_H
 
-#include <QtCore/qtypeinfo.h>
-#include <QtCore/qtypetraits.h>
-
 #ifdef Q_COMPILER_INITIALIZER_LISTS
 #include <initializer_list>
 #endif
 
+#include <type_traits>
+
 QT_BEGIN_NAMESPACE
 
 class QFlag
@@ -94,6 +93,8 @@ class QFlags
     Q_STATIC_ASSERT_X((sizeof(Enum) <= sizeof(int)),
                       "QFlags uses an int as storage, so an enum with underlying "
                       "long long will overflow.");
+    Q_STATIC_ASSERT_X((std::is_enum<Enum>::value), "QFlags is only usable on enumeration types.");
+
     struct Private;
     typedef int (Private::*Zero);
 public:
@@ -103,7 +104,7 @@ public:
     typedef int Int;
 #else
     typedef typename std::conditional<
-            QtPrivate::QIsUnsignedEnum<Enum>::value,
+            std::is_unsigned<typename std::underlying_type<Enum>::type>::value,
             unsigned int,
             signed int
         >::type Int;
diff --git a/src/corelib/global/qtypetraits.h b/src/corelib/global/qtypetraits.h
index 9773db919b..35e407e2de 100644
--- a/src/corelib/global/qtypetraits.h
+++ b/src/corelib/global/qtypetraits.h
@@ -37,6 +37,12 @@
 **
 ****************************************************************************/
 
+// ### Qt 6: remove this header
+//
+// This header is deliberately empty. Although it did not contain any public API,
+// it was accidentally made public in Qt 5. So: do not remove it for the moment
+// being, to prevent #include breaks in downstreams.
+
 #include "QtCore/qglobal.h"
 
 #ifndef QTYPETRAITS_H
@@ -44,53 +50,6 @@
 
 QT_BEGIN_NAMESPACE
 
-namespace QtPrivate {
-
-//
-// Define QIsUnsignedEnum, QIsSignedEnum -
-// std::is_signed, std::is_unsigned does not work for enum's
-//
-
-// a metafunction to invert an integral_constant:
-template <typename T>
-struct not_
-    : std::integral_constant<bool, !T::value> {};
-
-// Checks whether a type is unsigned (T must be convertible to unsigned int):
-template <typename T>
-struct QIsUnsignedEnum
-    : std::integral_constant<bool, (T(0) < T(-1))> {};
-
-// Checks whether a type is signed (T must be convertible to int):
-template <typename T>
-struct QIsSignedEnum
-    : not_< QIsUnsignedEnum<T> > {};
-
-Q_STATIC_ASSERT(( QIsUnsignedEnum<quint8>::value));
-Q_STATIC_ASSERT((!QIsUnsignedEnum<qint8>::value));
-
-Q_STATIC_ASSERT((!QIsSignedEnum<quint8>::value));
-Q_STATIC_ASSERT(( QIsSignedEnum<qint8>::value));
-
-Q_STATIC_ASSERT(( QIsUnsignedEnum<quint16>::value));
-Q_STATIC_ASSERT((!QIsUnsignedEnum<qint16>::value));
-
-Q_STATIC_ASSERT((!QIsSignedEnum<quint16>::value));
-Q_STATIC_ASSERT(( QIsSignedEnum<qint16>::value));
-
-Q_STATIC_ASSERT(( QIsUnsignedEnum<quint32>::value));
-Q_STATIC_ASSERT((!QIsUnsignedEnum<qint32>::value));
-
-Q_STATIC_ASSERT((!QIsSignedEnum<quint32>::value));
-Q_STATIC_ASSERT(( QIsSignedEnum<qint32>::value));
-
-Q_STATIC_ASSERT(( QIsUnsignedEnum<quint64>::value));
-Q_STATIC_ASSERT((!QIsUnsignedEnum<qint64>::value));
-
-Q_STATIC_ASSERT((!QIsSignedEnum<quint64>::value));
-Q_STATIC_ASSERT(( QIsSignedEnum<qint64>::value));
-
-} // namespace QtPrivate
-
 QT_END_NAMESPACE
+
 #endif  // QTYPETRAITS_H