QML-defined singletons require a qmldir to be "found". If one imports a local directory containing a file marked with the singleton pragma, and attempts to use it, i.e:

main.qml:

import "stuff"

Item {
    Component.onCompleted: console.log(StuffThing.foo)
}

stuff/StuffThing.qml:

import QtQuick 2.6
pragma Singleton

Item {
    property int foo
}

... will fail with an (unhelpful) ReferenceError: StuffThing is not defined, until one creates a qmldir mentioning the singleton.

I think we should do one or more of the following:

• Remove the qmldir requirement (better compatibility with non-singleton type resolution)
• Document the qmldir requirement more clearly
• See if we can improve the error reporting for this case, so it is clearer that singleton types require resolution here (might be hard).