Comment # 3 on bug 1228131 from Fabian Vogt

-DVERBOSE_QML_COMPILER=TRUE shows the cause:

Warning: PromptDialog.qml:11:1: Warnings occurred while importing module
"org.kde.kirigami": [import]
import org.kde.kirigami as Kirigami
^^^^^^
---
Warning: QML types file does not exist:
/home/fabian/kderepos/kirigami/build2/bin/org/kde/kirigami/Kirigami.qmltypes
[import]
Warning: QtQuick.Controls uses optional imports which are not supported. Some
types might not be found. [import]
Warning: QML types file does not exist:
/home/fabian/kderepos/kirigami/build2/bin/org/kde/kirigami/primitives/KirigamiPrimitives.qmltypes
[import]
Warning: QML types file does not exist:
/home/fabian/kderepos/kirigami/build2/bin/org/kde/kirigami/delegates/KirigamiDelegates.qmltypes
[import]

And various similar other cases. So this is yet another instance of
https://bugreports.qt.io/browse/QTBUG-121643, which unfortunately does not have
a satisfying resolution so far. Declaring all dependencies manually is a lot of
work and too fragile, we need some automatic way.