Merge markdown.config when extending existing config

[sevenc-nanashi]

Is your feature request related to a problem? Please describe.

I'm trying to create two plugins, which extends markdown feature.
And I'm trying to merge those two and my config, using extends like { extends: { extends: myPlugin1, ...myPlugin2 }, ...myPlugin3 }.

But I noticed that this solution does not work well because myPlugin1's markdown.config is replaced with myPlugin2's markdown.config.

Describe the solution you'd like

Merge markdown.config properly.
I'm using this mergeConfigs helper for now:

function mergeConfigs(
  ...configs: Omit<UserConfig<DefaultTheme.Config>, "extends">[]
): UserConfig<DefaultTheme.Config> {
  return configs.slice(1).reduce((merged, config) => {
    return {
      ...config,
      markdown: {
        config(md) {
          merged.markdown?.config?.(md);
          config.markdown?.config?.(md);
        },
      },
      extends: merged,
    };
  }, configs[0]);
}

Describe alternatives you've considered

None.

Additional context

Also it would be good if there's mergeConfigs by default.

Validations

• Follow our Code of Conduct
• Read the docs.
• Read the Contributing Guidelines.
• Check that there isn't already an issue that asks for the same feature to avoid creating a duplicate.