Make QtWidgets wizard work with namespaced Qt

Fixes: QTCREATORBUG-19590
Change-Id: Ic003b2b1f580d9a6708e144b690c4cee8d94ff69
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

share/qtcreator/templates/wizards/projects/qtwidgetsapplication/widget.h

@@ -10,7 +10,13 @@
 %{JS: Cpp.openNamespaces('%{Class}')}\
 @if %{GenerateForm}
 
+@if ! %{JS: Cpp.hasNamespaces('%{Class}')}
+QT_BEGIN_NAMESPACE
+@endif
 namespace Ui { class %{CN}; }
+@if ! %{JS: Cpp.hasNamespaces('%{Class}')}
+QT_END_NAMESPACE
+@endif
 @endif
 
 class %{CN} : public %{BaseClass}

src/plugins/cpptools/cpptoolsjsextension.cpp

@@ -60,6 +60,11 @@ QStringList CppToolsJsExtension::namespaces(const QString &klass) const
     return result;
 }
 
+bool CppToolsJsExtension::hasNamespaces(const QString &klass) const
+{
+    return !namespaces(klass).empty();
+}
+
 QString CppToolsJsExtension::className(const QString &klass) const
 {
     QStringList result = parts(klass);

src/plugins/cpptools/cpptoolsjsextension.h

@@ -47,6 +47,7 @@ public:
 
     // Work with classes:
     Q_INVOKABLE QStringList namespaces(const QString &klass) const;
+    Q_INVOKABLE bool hasNamespaces(const QString &klass) const;
     Q_INVOKABLE QString className(const QString &klass) const;
     // Fix the filename casing as configured in C++/File Naming:
     Q_INVOKABLE QString classToFileName(const QString &klass,