import QtQml

QtObject {
    function f(a: Main.Whatever) : int { return 1 }
    Component.onCompleted: console.log(f(1))
} 

The type annotation does not make sense. (I stumbled upon this while working on https://bugreports.qt.io/browse/QTBUG-135255) However, this code generates a dependency cycle warning at runtime and does not execute f.

qt.qml.typeresolution.cycle: Cyclic dependency detected between "qrc:/qt/qml/Truc/Main.qml" and "qrc:/qt/qml/Truc/Main.qml" 

Removing the type annotation or replacing it with int fixes the issue.

This does not reproduce in 6.8 or later.