Say hello to Q_NAMESPACE

Q_NAMESPACE is useful to add Q_ENUM_NS/Q_ENUMS, Q_FLAG_NS/Q_FLAGS and
Q_CLASSINFO to a namespace.

[ChangeLog] Added Q_NAMESPACE which can be used to add Q_ENUM_NS/
Q_ENUMS, Q_FLAG_NS/Q_FLAGS and Q_CLASSINFO to a namespace

Task-number: QTBUG-54981
Change-Id: Ic61b972794063e77134681fb347d6c4acddcdb44
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

2 files changed, 70 insertions, 2 deletions

diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 26c3ce2443..e901d8cefa 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -4248,7 +4248,7 @@ QDebug operator<<(QDebug dbg, const QObject *o)
 
     This macro registers an enum type with the meta-object system.
     It must be placed after the enum declaration in a class that has the Q_OBJECT or the
-    Q_GADGET macro.
+    Q_GADGET macro. For namespaces use \l Q_ENUM_NS instead.
 
     For example:
 
@@ -4275,7 +4275,7 @@ QDebug operator<<(QDebug dbg, const QObject *o)
     This macro registers a single \l{QFlags}{flags type} with the
     meta-object system. It is typically used in a class definition to declare
     that values of a given enum can be used as flags and combined using the
-    bitwise OR operator.
+    bitwise OR operator. For namespaces use \l Q_FLAG_NS instead.
 
     The macro must be placed after the enum declaration.
 
@@ -4294,6 +4294,48 @@ QDebug operator<<(QDebug dbg, const QObject *o)
     \sa {Qt's Property System}
 */
 
+/*!
+    \macro Q_ENUM_NS(...)
+    \since 5.8
+
+    This macro registers an enum type with the meta-object system.
+    It must be placed after the enum declaration in a namespace that
+    has the Q_NAMESPACE macro. It is the same as \l Q_ENUM but in a
+    namespace.
+
+    Enumerations that are declared with Q_ENUM_NS have their QMetaEnum
+    registered in the enclosing QMetaObject. You can also use
+    QMetaEnum::fromType() to get the QMetaEnum.
+
+    Registered enumerations are automatically registered also to the Qt meta
+    type system, making them known to QMetaType without the need to use
+    Q_DECLARE_METATYPE(). This will enable useful features; for example, if
+    used in a QVariant, you can convert them to strings. Likewise, passing them
+    to QDebug will print out their names.
+
+    \sa {Qt's Property System}
+*/
+
+
+/*!
+    \macro Q_FLAG_NS(...)
+    \since 5.8
+
+    This macro registers a single \l{QFlags}{flags type} with the
+    meta-object system. It is used in a namespace that has the
+    Q_NAMESPACE macro, to declare that values of a given enum can be
+    used as flags and combined using the bitwise OR operator.
+    It is the same as \l Q_FLAG but in a namespace.
+
+    The macro must be placed after the enum declaration.
+
+    \note The Q_FLAG_NS macro takes care of registering individual flag
+    values with the meta-object system, so it is unnecessary to use
+    Q_ENUM_NS() in addition to this macro.
+
+    \sa {Qt's Property System}
+*/
+
 
 /*!
     \macro Q_OBJECT
@@ -4335,6 +4377,21 @@ QDebug operator<<(QDebug dbg, const QObject *o)
 */
 
 /*!
+    \macro Q_NAMESPACE
+    \since 5.8
+
+    The Q_NAMESPACE macro can be used to add QMetaObject capabilities
+    to a namespace.
+
+    Q_NAMESPACEs can have Q_CLASSINFO, Q_ENUM_NS, Q_FLAG_NS, but they
+    cannot have Q_ENUM, Q_FLAG, Q_PROPERTY, Q_INVOKABLE, signals nor slots.
+
+    Q_NAMESPACE makes an external variable, \c{staticMetaObject}, available.
+    \c{staticMetaObject} is of type QMetaObject and provides access to the
+    enums declared with Q_ENUM_NS/Q_FLAG_NS.
+*/
+
+/*!
     \macro Q_SIGNALS
     \relates QObject
 
diff --git a/src/corelib/kernel/qobjectdefs.h b/src/corelib/kernel/qobjectdefs.h
index 3660d1c0e1..7ed6088d3b 100644
--- a/src/corelib/kernel/qobjectdefs.h
+++ b/src/corelib/kernel/qobjectdefs.h
@@ -124,6 +124,11 @@ class QString;
     friend Q_DECL_CONSTEXPR const char *qt_getEnumName(ENUM) Q_DECL_NOEXCEPT { return #ENUM; }
 #define Q_ENUM(x) Q_ENUMS(x) Q_ENUM_IMPL(x)
 #define Q_FLAG(x) Q_FLAGS(x) Q_ENUM_IMPL(x)
+#define Q_ENUM_NS_IMPL(ENUM) \
+    inline Q_DECL_CONSTEXPR const QMetaObject *qt_getEnumMetaObject(ENUM) Q_DECL_NOEXCEPT { return &staticMetaObject; } \
+    inline Q_DECL_CONSTEXPR const char *qt_getEnumName(ENUM) Q_DECL_NOEXCEPT { return #ENUM; }
+#define Q_ENUM_NS(x) Q_ENUMS(x) Q_ENUM_NS_IMPL(x)
+#define Q_FLAG_NS(x) Q_FLAGS(x) Q_ENUM_NS_IMPL(x)
 #define Q_SCRIPTABLE QT_ANNOTATE_FUNCTION(qt_scriptable)
 #define Q_INVOKABLE  QT_ANNOTATE_FUNCTION(qt_invokable)
 #define Q_SIGNAL QT_ANNOTATE_FUNCTION(qt_signal)
@@ -227,6 +232,12 @@ private: \
     QT_WARNING_POP \
     QT_ANNOTATE_CLASS(qt_qgadget, "") \
     /*end*/
+
+#define Q_NAMESPACE \
+    extern const QMetaObject staticMetaObject; \
+    QT_ANNOTATE_CLASS(qt_qnamespace, "") \
+    /*end*/
+
 #endif // QT_NO_META_MACROS
 
 #else // Q_MOC_RUN