PropertyGroups on bpy.types.KeyMapItem

Archive Python API
1

I had a random idea for an addon today and it revolves around being able to store custom properties on individual keymap items- but a PointerProperty to a PropertyGroup doesn’t seem to work with keymap items. Anyone have any experience with this and know a way around it (or, to satisfy my own curiosity- what makes a PointerProperty work with any other type of object I put one on).

As an example- this script works (taken from the 2.80 docs for PropertyGroup):

import bpy


class MaterialSettings(bpy.types.PropertyGroup):
    my_int: bpy.props.IntProperty()
    my_float: bpy.props.FloatProperty()
    my_string: bpy.props.StringProperty()


bpy.utils.register_class(MaterialSettings)

bpy.types.Material.my_settings = bpy.props.PointerProperty(type=MaterialSettings)

# test the new settings work
material = bpy.data.materials[0]

material.my_settings.my_int = 5
material.my_settings.my_float = 3.0
material.my_settings.my_string = "Foo"

but this script throws an exception saying ‘tuple’ has no attribute ‘my_int’:

import bpy


class KeymapItemSettings(bpy.types.PropertyGroup):
    my_int: bpy.props.IntProperty()
    my_float: bpy.props.FloatProperty()
    my_string: bpy.props.StringProperty()


bpy.utils.register_class(KeymapItemSettings)

bpy.types.KeyMapItem.my_settings = bpy.props.PointerProperty(type=KeymapItemSettings)

# test the new settings work
kmi = bpy.context.window_manager.keyconfigs.addon.keymaps[0].keymap_items[0]

kmi.my_settings.my_int = 5
kmi.my_settings.my_float = 3.0
kmi.my_settings.my_string = "Foo"
2

Python itself completely rejects even your first example for me, unless I am messing something else up. It only accepts fieldName: FieldType = fieldValue, e.g.: my_int: bpy.types.IntProperty = bpy.props.IntProperty(). (Also getting “has no attribute”-error otherwise.)
Edit: Apparantly it does work with the bpy.types.XXXProperty()-functions. Not sure why though. If I use a function of my own it fails, even if it annotates the return type. Is there more Python magic I am missing?