📝 Provide detailed reproduction steps (if any)

1. Setup a project with TypeScript + Yarn PnP (default strict mode)
2. Create a plugin file along the lines of

import {Plugin} from 'ckeditor5';

export default class FooUI extends Plugin {
  init() {
    this.editor.ui.componentFactory.add('addFoo', (locale) => {
      ...
  }
}

3. Run tsc to check types

✔️ Expected result

The type of this.editor.ui to be resolved correctly, so that consequently the type of locale in the componentFactory.add call can be inferred.

❌ Actual result

The type of this.editor.ui.componentFactory is marked as any yielding an error Parameter 'locale' implicitly has an 'any' type.ts(7006).

❓ Possible solution

This issue only appears with Yarn PnP mode, as the import import type { EditorUI } from '@ckeditor/ckeditor5-ui'; within the ckeditor5-core cannot be resolved, since the package is not listed as dependency in ckeditor5-core. To make this resolvable, the @ckeditor/ckeditor5-ui should be listed as dependency, peerDependency or optional peerDependency in the ckeditor5-core, with the last one probably being the best option.

Manual workarounds:

• import the type EditorUI and manually cast with (this.editor.ui as EditorUI)
• use pnpMode: loose or non-pnp mode with Yarn
• patch the (optional) peer dependency within your own project by adding the following to .yarnrc.yml:

packageExtensions:
  # See https://github.com/ckeditor/ckeditor5/issues/17213
  "@ckeditor/ckeditor5-core@*":
    peerDependencies:
      "@ckeditor/ckeditor5-ui": "*"
    peerDependenciesMeta:
      "@ckeditor/ckeditor5-ui":
        optional: true

📃 Other details

• Browser: N/A
• OS: N/A
• First affected CKEditor version: 42.0.0 (possibly earlier); edit: still observed on 43.2.0
• Installed CKEditor plugins: N/A

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