deprecated-admin-notices.php

<?php
/**
 * Plugin Name: Deprecated admin_notices
 * Description: Disable PHP Deprecated notices and display in admin_notices
 * Author: Weston Ruter, XWP
 */

call_user_func( function() {

	error_reporting( error_reporting() ^ E_DEPRECATED );

	$deprecated_notices = array();

	set_error_handler(
		function( $errno, $errstr, $errfile, $errline, $errcontext ) use ( &$deprecated_notices ) {
			$deprecated_notices[] = compact( 'errno', 'errstr', 'errfile', 'errline', 'errcontext' );
		},
		E_USER_DEPRECATED
	);

	add_action( 'admin_notices', function() use ( $deprecated_notices ) {
		if ( empty( $deprecated_notices ) ) {
			return;
		}
		?>
		<div class="error">
			<details>
				<summary>Alert: There are <?php echo count( $deprecated_notices ) ?> deprecation notices are suppressed.</summary>
				<ul>
					<?php foreach ( $deprecated_notices as $deprecated_notice ) : ?>
						<li><code><?php echo esc_html( wp_json_encode( $deprecated_notice ) ); ?></code></li>
					<?php endforeach; ?>
				</ul>
			</details>
		</div>
		<?php
	} );
} );