Changes

This PR fixes an issue where rendering Astro components as Markdoc tags and nodes when configured using the extends property would lead to an error (Unable to render [object Object]. No valid renderer was found for this file extension.).

This would prevent for example Starlight users to have a configuration like this:

export default defineMarkdocConfig({
  extends: [starlightMarkdoc()]
  tags: {
    custom: { render: component('./src/components/Custom.astro') },
  },
});

The issue was that when creating the component configs for used tags and nodes, the user-defined Markdoc config was used instead of the computed one that also contains the merged configurations from the extends property.

Testing

I mostly duplicated the existing test/fixtures/render-with-components fixture and its associated test/render-components.test.js tests and created a fixture where the configuration is done using extends.

Docs

This is a bug fix for a feature that does not have a specific documentation or example.