Add filter for attributes on menu item links

[simonwheatley]

I find myself needing to change the attributes of the link element of each menu item to add some classes. Currently I can do this by extending and substituting Walker_Nav_Menu, but that the start_el method I replace is fairly long and I'm nervous of changes to core breaking my kit in the future. Much better to be able to hook a filter, IMO.

I propose a new nav_menu_a_attributes filter in the start_el method of Walker_Nav_Menu, as per the attached patch.

In the patch I've also changed the way the attributes are built up within start_el so they work with a named array, as it is easier for plugin authors to then parse the attributes as an array than if they are passed a long string of HTML attributes. Hope that makes sense.

Looks good to me.

Keeping relatively as succinct as before.

I like this. Would be nice to get this in.

16738.diff​ refreshes @simonwheatley's patch and makes an effort to keep the format more succinct like it was originally.

Perhaps nav_menu_link_attributes is a better name, for consistency with *_posts_link_attributes and *_comments_link_attributes.

Replying to SergeyBiryukov:

Perhaps nav_menu_link_attributes is a better name, for consistency with *_posts_link_attributes and *_comments_link_attributes.

+1 for consistency in naming :) Updated the patch.

If a plugin adds $atts['class'] = 'class="my-menu-link"', adding a second class may be a non-trivial task.

I guess it would be easier to modify the attributes if the array values were the actual attribute values rather than key-value pairs: 16738.3.diff​.

16738.3.diff works for me.

In 23565:

Add a filter for attributes on menu item links. props simonwheatley, DrewAPicture, SergeyBiryukov, nacin. fixes #16738.