Support client mu-plugins

[joshbetz]

• Mount mu-plugins as vip-mu-plugins or something less confusing.
• Include all PHP files in this directory on muplugins_loaded

https://github.com/WordPress/WordPress/blob/703d5bdc8deb17781e9c6d8f0dd7e2c6b6353885/wp-settings.php#L210-L223

Can we do this without breaking the muplugins_loaded hook? How early is add_action available? Can we add a hook before mu-plugins are loaded and include them there?

[nickdaugherty]

The trick is bootstrapping. WP core will include files in mu-plugins automatically, but there isn't a way for us to tell WP to include files from another folder.

Probably the only way to do it is to have clients include a 000-vip-init.php file in their own mu-plugins in every repo that bootstraps the Go plugins.

[joshbetz]

We could hijack wp_get_mu_plugins() to load a file which itself loads our mu-plugins and the clients' mu-plugins by manipulating WPMU_PLUGIN_DIR.

https://github.com/WordPress/WordPress/blob/703d5bdc8deb17781e9c6d8f0dd7e2c6b6353885/wp-settings.php#L210-L213 https://github.com/WordPress/WordPress/blob/703d5bdc8deb17781e9c6d8f0dd7e2c6b6353885/wp-includes/load.php#L525-L539

This gets very much in the realm of vipd.

[mjangda]

Possible simpler option:

• Add a client-mu-plugins folder (or something similar to vip-skeleton).
• Add whatever to vipd to make sure that folder ^^ gets included in containers.
• Add a zzz-client-mu-plugins.php that just loads files from client-mu-plugins the same waywp_get_mu_plugins` does.

The trade-off is that client mu-plugins load later (although, still before muplugins_loaded) but I think that's okay.

[joshbetz]

We could probably even call it mu-plugins in the vip-skeleton repo and map it as client-mu-plugins in the container, although that may be too confusing.