Try Clazy fix-its

clazy is a compiler plugin which allows clang to understand Qt
semantics. You get more than 50 Qt related compiler warnings, ranging
from unneeded memory allocations to misusage of API, including fix-its
for automatic refactoring.

https://invent.kde.org/sdk/clazy

sources/editor/ui/polygoneditor.cpp

@@ -76,7 +76,8 @@ void PolygonEditor::setUpChangeConnections()
 
 void PolygonEditor::disconnectChangeConnections()
 {
-	for (QMetaObject::Connection c : m_change_connections) {
+	for (const QMetaObject::Connection& c : std::as_const(m_change_connections))
+	{
 		disconnect(c);
 	}
 	 m_change_connections.clear();