Consider importing mu-plugins directories

[danielbachhuber]

We currently ignore mu-plugins directories in our import workflow. We should consider properly importing them.

[wojtekn]

From https://developer.wordpress.org/advanced-administration/plugins/mu-plugins/:

[...] For web hosts, mu-plugins are commonly used to add support for host-specific features, especially those where their absence could break the site.

It makes sense to treat those as host-specific features. Studio puts different polyfills there, and any host or local app could do the same.

@danielbachhuber how this addition would help you?

[danielbachhuber]

@wojtekn I'm not sure I agree with that description. I think mu-plugins can often be use for site-specific code.

[wojtekn]

@danielbachhuber Now Playground supports loading polyfill my-plugins from Playground-specific directory (/internal/shared/mu-plugins), so they won't clutter WordPress WP Admin: https://github.com/WordPress/wordpress-playground/blob/b81c81d9636989acfcbb7102e618ee840072b958/packages/playground/wordpress/src/index.ts#L17

We could move our polyfills there and support importing and exporting the default mu-plugins/ directory. Users who don't want them can always delete them manually after the import.

[danielbachhuber]

@wojtekn Nice!