QPermission: fight template bloat in data()

Extract the type-independent code into an out-of-line data_impl()
private method, leaving data() containing only the
QMetaType::fromType<T>() call as well as T copy- and
default-constructor calls.

As a drive-by, use categorized logging (consistency with the rest of
the permissions code) and printf-style qWarning() (expands to less
code).

Change-Id: Ie23b83cb3fc537c9cff15f853ceee2888bf63124
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 66235481043d85e4f51a216cf2ad3bb895ea7842)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qpermissions.cpp

@@ -257,6 +257,22 @@ Q_LOGGING_CATEGORY(lcPermissions, "qt.permissions", QtWarningMsg);
     Returns the type of the permission.
 */
 
+/*
+    \internal
+*/
+const void *QPermission::data(QMetaType requestedType) const
+{
+    const auto actualType = type();
+    if (requestedType != actualType) {
+        qCWarning(lcPermissions, "Cannot convert from %s to %s",
+                  actualType.name(), requestedType.name());
+        return nullptr;
+    }
+    return m_data.data();
+}
+
+
+
 #define QT_DEFINE_PERMISSION_SPECIAL_FUNCTIONS(ClassName) \
     ClassName::ClassName() : d(new ClassName##Private) {} \
     ClassName::ClassName(const ClassName &other) noexcept = default; \

src/corelib/kernel/qpermissions.h

@@ -61,13 +61,10 @@ public:
     template <typename T, std::enable_if_t<is_permission<T>::value, bool> = true>
     T data() const
     {
-        auto requestedType = QMetaType::fromType<T>();
-        if (type() != requestedType) {
-            qWarning() << "Can not convert from" << type().name()
-                       << "to" << requestedType.name();
+        if (auto p = data(QMetaType::fromType<T>()))
+            return *static_cast<const T *>(p);
+        else
             return T{};
-        }
-        return m_data.value<T>();
     }
 #endif
 
@@ -76,6 +73,8 @@ public:
 #endif
 
 private:
+    Q_CORE_EXPORT const void *data(QMetaType id) const;
+
     Qt::PermissionStatus m_status = Qt::PermissionStatus::Undetermined;
     QVariant m_data;