Not possible to extend on top of built-in editors via LIT

[bielu]

Which Umbraco version are you using? (Please write the exact version, example: 10.1.0)

14 and 15

Bug summary

I tried to built custom editors which extend on built-in ones, but it fails, because types are not exported, so the extending is impossible.
Example code:

import { html, customElement, property } from "@umbraco-cms/backoffice/external/lit";
// @ts-ignore
import {UmbPropertyEditorUiElement} from "@umbraco-cms/backoffice/dist-cms/packages/core/extension-registry";
import UmbPropertyEditorUINumberElement
  from "@umbraco-cms/backoffice/dist-cms/packages/property-editors/number/property-editor-ui-number.element";

/**
 * An example element.
 *
 * @slot - This element has a slot
 * @csspart button - The button
 */
@customElement('test-element')
export class Test extends UmbPropertyEditorUINumberElement implements UmbPropertyEditorUiElement{
  @property({ type: String })
  public value = "";

  render() {
    return html`I'm a property editor!  3 3`;
  }
}

Specifics

No response

Steps to reproduce

1. build new library package
2. install backoffice
3. try to compile example above

Expected result / actual result

I would expect to be able to extend on top of elements built-in in umbraco backoffice (especially property editors).

[github-actions]

Hi there @bielu!

Firstly, a big thank you for raising this issue. Every piece of feedback we receive helps us to make Umbraco better.

We really appreciate your patience while we wait for our team to have a look at this but we wanted to let you know that we see this and share with you the plan for what comes next.

• We'll assess whether this issue relates to something that has already been fixed in a later version of the release that it has been raised for.
• If it's a bug, is it related to a release that we are actively supporting or is it related to a release that's in the end-of-life or security-only phase?
• We'll replicate the issue to ensure that the problem is as described.
• We'll decide whether the behavior is an issue or if the behavior is intended.

We wish we could work with everyone directly and assess your issue immediately but we're in the fortunate position of having lots of contributions to work with and only a few humans who are able to do it. We are making progress though and in the meantime, we will keep you in the loop and let you know when we have any questions.

Thanks, from your friendly Umbraco GitHub bot 🤖 🙂