Admin submenu issue with PHP not detecting two strings as equal

Question

I am adding a submenu page as follows:

add_submenu_page( $slug, __('Categories','acs'), __('Categories','acs'), $cap, 'edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group' );

But the submenu does not display as active when selected.

So after wondering... I went into WP Core and added a var dump at wp-amdin/menu-header.php

Right where the check is made, to add the .current CSS classname.

var_dump($submenu_file);
var_dump($sub_item[2]);

And... the output is a mystery:

string(77) "edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group"
string(73) "edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group"

Same string, different length!

Of course it must be some encoding game, but I'm using phpStorm with encoding set to UTF-8.

I don't know how to get over this, help will be appreciated.

Answer 1

string(77) "edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group"
string(73) "edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group"

Same string, different length!

No, they're not the same string — if you had viewed the raw/server-generated HTML source, or used this instead of the var_dump($submenu_file);:

echo '<pre>'; var_dump($submenu_file, $sub_item[2]); echo '</pre>';

Then you would have seen the correct string which uses & instead of just &:

string(77) "edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group"

So that means, your (sub-)menu slug (the 5th parameter for add_submenu_page()) needs to use the ampersand's HTML entity, i.e. &, like so:

add_submenu_page( $slug, __('Categories','acs'), __('Categories','acs'), $cap, // wrapped for brevity
    'edit-tags.php?taxonomy=acs-field-group-category&post_type=acs-field-group' ); // ← use &

That way, the submenu would be active when the submenu page is loaded.

And actually, you can see a core example here in wp-admin/edit-tags.php (WordPress v6.0.1), which implies that $submenu_file (the submenu slug) expects & to be used.

_{PS: Remember to restore the original wp-admin/menu-header.php file — remove your "hack"/modifications.}