PHP Warning: Undefined array key 1 wp-admin\menu-header.php on line 202

[pras.88in]

i get the above warning when i use php version 8.1.6 in iis server,for php7.427 the code works , am using wordpress 6.0.1 released on jul 12 2022, am unable to fix it , kindly support , i get this error after succesfull login as admimistrator in plugin.php page , and other admin pages.

[sabernhardt]

Hi and welcome to Trac!

If you want site support, the support forums would be a better place to ask:
​https://wordpress.org/support/forums/

However, I'll leave this ticket open for now. The undefined key is the user capability needed to display a sub-menu item in the side admin menu, and maybe the condition needs to check whether the key is set/non-empty before using current_user_can().

Check for non-empty array key 1 before using it with current_user_can() to avoid PHP warning

Trac ticket: https://core.trac.wordpress.org/ticket/56254

[desrosj]

Adding needs-unit-tests since some were requested in the PR.

[hellofromTonya]

The code in the foreach was introduced in [8691] over 15 years ago:

// 0 = menu_title, 1 = capability, 2 = menu_slug, 3 = page_title, 4 = classes.
foreach ( $submenu_items as $sub_key => $sub_item ) {
   if ( ! current_user_can( $sub_item[1] ) ) {

I wonder: Why would the capability element be missing in the $sub_item?

Adding defensive code before attempting to access it is good, but can hide a potential problem. I'm hesitant to move forward with ​the patch without first understanding the root cause.

Seems this code is expecting the format identified which includes the capability element being at index 1.

I'm wondering ..

• Should sub items always be an array with element 1 as the capability?
• Are there checks or set up of the array structure where the menu is created, i.e. executing before the above code runs?
• If yes, then this is likely a plugin or theme doing it wrong?

The answers will take investigation.

@pras88in more information is needed for contributors like me to investigate:

• Can you share the steps of how to reproduce the issue?

• Can you share the backtrace call stack given with the PHP error? Copy and paste the full error message here.

• After deactivating all of the plugins, does the issue go away? If yes, then one or more of the plugins is the issue. You can reactivate each plugin one-by-one to discover which is causing the problem. Then report the issue to the plugin author.

[hellofromTonya]

Is this issue an incompatibility with PHP 8.1?

I don't think there's enough information to know if this is an issue in Core. Thus, I'm not adding the php-compatibility focus to list it in exclusions of PHP 8.1 compatibility.