Plugin submenu first item has strange behaviors

[MikeHansenMe]

When testing the current version of trunk I found that any plugins that add menu items have strange behaviours. The first item has the same hover effects as top level even though it is in the submenu. To reproduce install Jetpack on trunk.

The lines that seem to have changed in trunk are:

- <li class="wp-first-item">
	<a class="wp-first-item" href="admin.php?page=jetpack">Jetpack</a>

+ <li class="wp-first-item menu-top toplevel_page_jetpack">
	<a class="wp-first-item menu-top toplevel_page_jetpack" href="admin.php?page=jetpack">Jetpack</a>

[MikeHansenMe]

Jetpack on 391

[MikeHansenMe]

Jetpack on trunk

[MikeHansenMe]

another effected plugin

[MikeHansenMe]

It looks like plugins that use CPTs are not effected. Only when add_menu_page is used.

[MikeHansenMe]

Related #28583

[SergeyBiryukov]

Confirmed. It's hard to see the difference on these screenshots, here's a larger one: 28936.png​.

I don't think reverting [28778]/[29083] is the best fix here, let's see if there's another way.

[SergeyBiryukov]

Caused by add_submenu_page() copying the parent item, including classes:
tags/3.9.1/src/wp-admin/includes/plugin.php#L1122​.

I think we can just skip adding custom classes for the first submenu item, see 28936.2.diff​.

[SergeyBiryukov]

A better fix would probably be to avoid copying classes in add_submenu_page(). See 28936.3.diff​.

[MikeHansenMe]

Just tested 28936.3.diff and it works great.

[SergeyBiryukov]

In 29326:

In add_submenu_page(), avoid inadvertently copying classes of a menu item to the first submenu item.

fixes #28936.