Add filter to allow filtering of the must-use plugins list in the admin

[nateallen]

Currently, the Must-Use plugin list in the WordPress admin only shows files that end in .php, and there is no way to filter this list. This is a problem because we use a single autoloader that allows us to add plugins to mu-plugins without needing to create a separate PHP file for each one.

As a result, the Must-Use plugin list appears like this:

Admins have no way of knowing which must-use plugins are actually installed.

If there was a filter, we could remove mu-loader.php from the list and add each plugin individually, like this:

<?php
function custom_mu_plugin_filter( $mu_plugins ) {
        unset( $mu_plugins['mu-loader.php'] );

        $directories = glob( WPMU_PLUGIN_DIR . '/*', GLOB_ONLYDIR );

        foreach ( $directories as $directory ) {
                $plugin_file = $directory . '/' . basename( $directory ) . '.php';

                $mu_plugins[ $plugin_file ] = get_plugin_data( $plugin_file );
        }

        return $mu_plugins;
}
add_filter( 'mu_plugins', 'custom_mu_plugin_filter' );

Which would result in:

There are probably other uses for this filter, like hiding a must-use plugin from the list that you don't want clients/users seeing.

Adds a new filter called mu_plugins that allows the filtering of the must-use plugins array.

Trac ticket: https://core.trac.wordpress.org/ticket/57278

[fischfood]

Test Report

This report confirms that the indicated patch addresses the enhancement.
Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/3728

Environment

OS: macOS 12.4
PHP: 8.0.0+2
WordPress: 6.1.1
Browsers: Brave v1.46.134, Safari 15.5
Theme: Twenty Twenty-Two

Steps

• Added a single file plugin to the mu-plugins directory (visible)
• Added Akismet Anti-Spam and Jetpack to the mu-plugins directory (not visible)
• Added the above filter to my theme

Results

After adding the example 'custom_mu_plugin_filter' to my theme, instead of just seeing my standalone single file plugin, I am now able to see the two directory based plugins as well

[mukesh27]

Thanks @nateallen, Left one nit-pick document changes feedback on PR.

Can you please add unit tests for the new filter?

get_mu_plugins() introduce in version to 3.0

[peterwilsoncc]

Instead of a filter for mu-plugins, I think a general purpose filter for items displayed in the plugin list table could be of more use here.

This would allow developers to show/hide plugins in each category on an as needs basis.

[SergeyBiryukov]

Replying to peterwilsoncc:

Instead of a filter for mu-plugins, I think a general purpose filter for items displayed in the plugin list table could be of more use here.

I tend to agree, this seems more flexible in the long run.

[audrasjb]

Also, I'm unsure about the name of the filter in the proposed PR, maybe it's too general. Adding _list` would clarify that it is filtering the list items.

[nateallen]

Thanks everyone for the suggestions! I implemented the change as a filter for all of the plugins instead of just must-use plugins.

The filter is added right before the totals get calculated. This ensures accuracy of the plugin count even if the filter is used for adding or removing plugins.

I also added a test for the filter.

[costdev]

As the PR still needs to be tested and we're releasing 6.2 Beta 1 today, I'm going to move this to Future Release.

P.S. There are some failures on the PR, but they don't appear to be related to the patch, I think?

Additional props: @mukesh27

[nateallen]

The failures with the PR were caused by null being passed to strlen in class-wp-plugins-list-table.php, which results in a TypeError in PHP 8. I added an isset check before calling strlen which fixes that issue.

Here are testing instructions for the new plugins_list filter:

To reproduce the issue:

1. Add a normal plugin to the mu-plugins directory (like Jetpack)
2. Add the mu-loader.php file to the mu-plugins directory. See code at the bottom of this comment
3. In the admin, go to Plugins > Installed Plugins and click on the "Must-Use" link
4. Observe that the mu-loader.php is listed, but the plugin is not

To test the fix:

1. Apply the patch attached to this ticket.
2. Ensure a plugin and mu-loader.php are in mu-plugins as before
3. Use the new plugins_list filter to add the plugin to the list. See example code at the bottom of this comment.
4. In the admin, go to Plugins > Installed Plugins and click on the "Must-Use" link
5. Observe that the plugin is now listed and mu-loader.php is removed

---

Code used for testing:

The must-use autoloader example
Save this code to an mu-loader.php file in your mu-plugins directory

<?php
require_once ABSPATH . 'wp-admin/includes/plugin.php';

foreach ( glob( WPMU_PLUGIN_DIR . '/*/*.php' ) as $file ) {
        $plugin_data = get_plugin_data( $file, false, false );

        if ( empty( $plugin_data['Name'] ) ) {
                continue;
        }

        include_once $file;
}

Using the new plugins_list filter
Place this code in your theme's functions.php file

<?php
function custom_mu_plugin_filter( $mu_plugins ) {
        unset( $mu_plugins['mustuse']['mu-loader.php'] );

        foreach ( glob( WPMU_PLUGIN_DIR . '/*/*.php' ) as $file ) {
                $plugin_data = get_plugin_data( $file, false, false );

                if ( empty( $plugin_data['Name'] ) ) {
                        continue;
                }

                $mu_plugins['mustuse'][ basename( $file ) ] = $plugin_data;
        }

        return $mu_plugins;
}
add_filter( 'plugins_list', 'custom_mu_plugin_filter' );

[SergeyBiryukov]

Related: #58055

[ecorica]

Test Report

This report validates that the indicated patch addresses the issue.

Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/3728

Environment

• OS: macOS 13.3.1
• Web Server: Nginx
• PHP: 7.4.33
• WordPress: 6.3-alpha-55505-src
• Browser: Google Chrome 112.0.5615.121
• Theme: Twenty Twenty-Three
• Active Plugins:
  • Jetpack 12.0

Actual Results

✅ After following the steps of @nateallen I confirm that the jetpack plugin appears in the list of "Must use" plugins and that the mu-loader.php does not appear in the list.

[ecorica]

Screenshot after testing PR 3728

[zunaid321]

Report

This report confirms that the suggested patch fixes the problem.
Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/3728

Environment

• OS: Windows 11 (22H2)
• Web Server: nginx/1.23.4
• PHP: 7.4.33
• WordPress: 6.3-alpha-55505-src
• Browsers: Chrome Version 113.0.5672.126 (Official Build) (64-bit)
• Theme: Twenty Twenty-Three

Steps:

• Added the file: mu-loader.php with the mentioned code to the mu-plugins directory.
• Added Jetpack to the mu-plugins directory
• Added the above filter code to functions.php of my current theme.

Results

I was able to replicate the feature as mentioned in this ticket.

[zunaid321]

Feature Working For Ticket #57278