Is there a way to list all used/unused WP templates?

I’m working to optimize a site that I’ve recently taken management of, and it appears to me that there are a fair few unused templates. I want to remove all the unused and redundant template files so that we can focus our developments on those templates we do support, however there are 100+ pages and posts on this site, so I can’t just do a spot check, I need a robust query.

I’ve established how to query which page template is being called from joining wp_posts and wp_postmeta, and I’ve sussed out which post formats are being used by querying wp_posts and wp_terms via wp_term_relationships BUT… this still doesn’t seem to tell me whether the index.php is ever used (and I don’t think it is).

I’m probably missing something obvious, but is there a way to see which of the normal WordPress theme files are actually being called? OR is it that I have all the information already and ‘index.php’ just isn’t being used.

Any help would be much appreciated!

Thanks

Here’s a rough function I use to handle this, it should work well for anyone out there wanting to do this quick and easy. Add this this your functions.php file and then visit your site with ?template_report added onto the URL to display a report for every custom theme template.

It’s rough, I’d suggest commenting/uncommenting the add_action call when you want to use it.

/**
 * Theme Template Usage Report
 *
 * Displays a data dump to show you the pages in your WordPress
 * site that are using custom theme templates.
 */
function theme_template_usage_report( $file = false ) {
    if ( ! isset( $_GET['template_report'] ) ) return;

    $templates = wp_get_theme()->get_page_templates();
    $report = array();

    echo '<h1>Page Template Usage Report</h1>';
    echo "<p>This report will show you any pages in your WordPress site that are using one of your theme's custom templates.</p>";

    foreach ( $templates as $file => $name ) {
        $q = new WP_Query( array(
            'post_type' => 'page',
            'posts_per_page' => -1,
            'meta_query' => array( array(
                'key' => '_wp_page_template',
                'value' => $file
            ) )
        ) );

        $page_count = sizeof( $q->posts );

        if ( $page_count > 0 ) {
            echo '<p style="color:green">' . $file . ': <strong>' . sizeof( $q->posts ) . '</strong> pages are using this template:</p>';
            echo "<ul>";
            foreach ( $q->posts as $p ) {
                echo '<li><a href="' . get_permalink( $p, false ) . '">' . $p->post_title . '</a></li>';
            }
            echo "</ul>";
        } else {
            echo '<p style="color:red">' . $file . ': <strong>0</strong> pages are using this template, you should be able to safely delete it from your theme.</p>';
        }

        foreach ( $q->posts as $p ) {
            $report[$file][$p->ID] = $p->post_title;
        }
    }

    exit;
}
add_action( 'wp', 'theme_template_usage_report' );

The output looks like this: