Multisite: "No importers are available" error message shown to site admins, but not to network admins

[thomaswm]

Steps to reproduce:

• Consider one site in a WordPress multisite install.
• Verify that the "WordPress Importer" plugin is installed in the network, but disabled on this specific site.
• Log in as a site administrator.
• Click on "Tools" and "Import".
• You'll see the message "No importers are available."

If, however, you open the same screen as a network admin, WordPress will show a link "Run importer". If you click it, WP will activate the "WordPress Importer" plugin and proceed with the import process.

This inconsistency is confusing to users. It does not really make sense because both site admins and network admins have the necessary capabilities to activate the importer plugin (provided that it is installed).

[thomaswm]

It seems that lines 33ff. in wp-admin/import.php are responsible for this behaviour:

if ( current_user_can( 'install_plugins' ) ) {
        // List of popular importer plugins from the WordPress.org API.
        $popular_importers = wp_get_popular_importers();
} else {
        $popular_importers = array();
}

Site administrators do not have the install_plugins capability, but they do have the activate_plugins capability, which is sufficient if the specific importer plugin is already installed.

[vhmarkgmailcom]

This problem still exists in 4.8.1

[vhmarkgmailcom]

This would be a good first bug fix

[vhmarkgmailcom]

Due to this same problem, the WordPress importer is also not available to network admins if you've disallowed plugin updates in wp-config.php

define('DISALLOW_FILE_MODS', 1);

[vhmarkgmailcom]

This is still an issue in v 5.5. Proposed a patch at ​https://github.com/WordPress/wordpress-develop/pull/794