Must add project's own source directory to cpp.includePaths in order to get new QML type registration to work

I'm trying out the new QML import support (QBS-1531):

https://github.com/mitchcurtis/slate/commit/26344781ffaf1006445b76adefd0e8e01ec03bf4#diff-0b0ebc8a92a44b173a51df2ce749a742

A .cpp file is generated as expected:

/home/mitch/dev/slate-qt_dev_debug_no_asan-Debug/Debug_qt_dev_d_750558401e966ce4/lib.9d062baf/slate_qmltyperegistrations.cpp

but the first include from my project in that file cannot be found:

#include <QtQml/qqml.h>
#include <QtQml/qqmlmoduleregistration.h>

#include <animationplayback.h> // <===
...

From looking at the change, I can see where the *_qmltyperegistrations file is created:

https://codereview.qt-project.org/c/qbs/qbs/+/293160/3/share/qbs/module-providers/Qt/templates/qml.qbs#84

but I don't see where it's included as part of the project's sources. In qmake, it seems to be done here:

https://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/qmltyperegistrar/qmltypes.prf#n77

Adding the project's own source directory to cpp.includePaths fixes it:

    cpp.includePaths: [
        product.sourceDirectory + "/3rdparty",
        "."
    ]

However, I don't think this is necessary with qmake, so I wonder if it should be necessary with qbs.