QVariant::fromValue<T>: require T to be copy constructible

In Qt 5, QVariant::fromValue<T> would not compile unless
Q_DECLARE_METATYPE(T) was used, and Q_DECLARE_METATYPE(T) would lead to
a compile error if T were not copy constructible.
In Qt 6, we do not require Q_DECLARE_METATYPE before using fromValue,
and QMetaType itself works with non-copy constructible types just fine.
However, QVariant still requires it, thus we need to now enforce this in
fromValue itself.

Change-Id: Ib6964a438d8c46033dd3a037b9d871de2b42e175
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/corelib/kernel/qvariant.h b/src/corelib/kernel/qvariant.h
index 8c3a27e3ca..b7d347a61e 100644
--- a/src/corelib/kernel/qvariant.h
+++ b/src/corelib/kernel/qvariant.h
@@ -392,7 +392,12 @@ class Q_CORE_EXPORT QVariant
     }
 
     template<typename T>
+#ifndef Q_CLANG_QDOC
+    static inline auto fromValue(const T &value) ->
+    std::enable_if_t<std::is_copy_constructible_v<T>, QVariant>
+#else
     static inline QVariant fromValue(const T &value)
+#endif
     {
         return QVariant(QMetaType::fromType<T>(), std::addressof(value));
     }