Implement QIcon::isNull support for QtSVG Icons

This was via a virtual hook in QIconEngine in Qt 5.7

This is especially useful for the SVG icon loader which returns no
availableSizes which means we currently have no way to tell if an icon
was loaded or not.

Change-Id: Ic14971f94213fb2309f29bd0daa0a1c387d4da3c
Reviewed-by: Kai Uwe Broulik <kde@privat.broulik.de>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

2 files changed, 9 insertions, 0 deletions

diff --git a/src/plugins/iconengines/svgiconengine/qsvgiconengine.cpp b/src/plugins/iconengines/svgiconengine/qsvgiconengine.cpp
index 53e9a57..0798e48 100644
--- a/src/plugins/iconengines/svgiconengine/qsvgiconengine.cpp
+++ b/src/plugins/iconengines/svgiconengine/qsvgiconengine.cpp
@@ -375,6 +375,14 @@ bool QSvgIconEngine::write(QDataStream &out) const
     return true;
 }
 
+void QSvgIconEngine::virtual_hook(int id, void *data)
+{
+    if (id == QIconEngine::IsNullHook) {
+        *reinterpret_cast<bool*>(data) = d->svgFiles.isEmpty() && !d->addedPixmaps;
+    }
+    QIconEngine::virtual_hook(id, data);
+}
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_SVGRENDERER
diff --git a/src/plugins/iconengines/svgiconengine/qsvgiconengine.h b/src/plugins/iconengines/svgiconengine/qsvgiconengine.h
index cf4f255..672828c 100644
--- a/src/plugins/iconengines/svgiconengine/qsvgiconengine.h
+++ b/src/plugins/iconengines/svgiconengine/qsvgiconengine.h
@@ -70,6 +70,7 @@ public:
     bool read(QDataStream &in) override;
     bool write(QDataStream &out) const override;
 
+    void virtual_hook(int id, void *data) override;
 private:
     QSharedDataPointer<QSvgIconEnginePrivate> d;
 };