The signals of IProjectBuilder cannot be connected. I think the class must be derived from QObject. STEPS TO REPRODUCE void TestView::built(KDevelop::ProjectBaseItem*); void TestView::addTestSuite(ITestSuite* suite) { auto builder = suite->project()->buildSystemManager()->builder(); connect(builder, &KDevelop::IProjectBuilder::built, this, &TestView::built); OBSERVED RESULT In file included from /usr/include/x86_64-linux-gnu/qt5/QtGui/qkeysequence.h:45, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/qaction.h:44, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/QAction:1, from /home/twollgam/projects/TestBrowser/src/testview.h:3, from /home/twollgam/projects/TestBrowser/src/testview.cpp:1: /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs.h: In instantiation of ‘struct QtPrivate::HasQ_OBJECT_Macro<KDevelop::IProjectBuilder>’: /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:235:9: required from ‘static QMetaObject::Connection QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const typename QtPrivate::FunctionPointer<Func2>::Object*, Func2, Qt::ConnectionType) [with Func1 = void (KDevelop::IProjectBuilder::*)(KDevelop::ProjectBaseItem*); Func2 = void (TestView::*)(KDevelop::ProjectBaseItem*); typename QtPrivate::FunctionPointer<Func>::Object = KDevelop::IProjectBuilder; typename QtPrivate::FunctionPointer<Func2>::Object = TestView]’ /home/twollgam/projects/TestBrowser/src/testview.cpp:529:79: required from here /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs.h:622:37: error: ‘qt_metacall’ is not a member of ‘KDevelop::IProjectBuilder’ 622 | enum { Value = sizeof(test(&Object::qt_metacall)) == sizeof(int) }; | ^~~~~~~~~~~~~~~~~~~~ In file included from /usr/include/x86_64-linux-gnu/qt5/QtGui/qtguiglobal.h:43, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/qtwidgetsglobal.h:43, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/qaction.h:43, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/QAction:1, from /home/twollgam/projects/TestBrowser/src/testview.h:3, from /home/twollgam/projects/TestBrowser/src/testview.cpp:1: /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h: In instantiation of ‘static QMetaObject::Connection QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const typename QtPrivate::FunctionPointer<Func2>::Object*, Func2, Qt::ConnectionType) [with Func1 = void (KDevelop::IProjectBuilder::*)(KDevelop::ProjectBaseItem*); Func2 = void (TestView::*)(KDevelop::ProjectBaseItem*); typename QtPrivate::FunctionPointer<Func>::Object = KDevelop::IProjectBuilder; typename QtPrivate::FunctionPointer<Func2>::Object = TestView]’: /home/twollgam/projects/TestBrowser/src/testview.cpp:529:79: required from here /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:235:9: error: static assertion failed: No Q_OBJECT in the class with the signal 235 | Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value, | ^~~~~~~~~~~~~~~~~ In file included from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/qwidget.h:45, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/qaction.h:46, from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/QAction:1, from /home/twollgam/projects/TestBrowser/src/testview.h:3, from /home/twollgam/projects/TestBrowser/src/testview.cpp:1: /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:254:42: error: ‘staticMetaObject’ is not a member of ‘QtPrivate::FunctionPointer<void (KDevelop::IProjectBuilder::*)(KDevelop::ProjectBaseItem*)>::Object’ {aka ‘KDevelop::IProjectBuilder’} 254 | type, types, &SignalType::Object::staticMetaObject); EXPECTED RESULT No compile errors. ADDITIONAL INFORMATION class KDEVPLATFORMPROJECT_EXPORT IProjectBuilder : public QObject { Q_OBJECT public:
you have to use oldschool Qt4-like connections on interfaces, or a concrete ProjectBuilder instance. The error is not in our code - is it? from /home/twollgam/projects/TestBrowser/src/testview.h:3, I'll close this issue. If you want to do something about it, we are happy to review your cleanup patches on gitlab. Thanks!