Link Featured Images to Their Posts

// The image link repeats the title link, so it is hidden from screen readers and skipped by the Tab key.
$wpide_featured_link_open = function ( $post_id ) {
    return '<a href="' . esc_url( get_permalink( $post_id ) ) . '" class="wpide-featured-image-link" aria-hidden="true" tabindex="-1">';
};

$wpide_featured_link_skip = function ( $post_id ) {
    return ! $post_id || is_admin() || is_feed() || ( is_singular() && (int) $post_id === get_queried_object_id() );
};

// Classic themes: the_post_thumbnail() and get_the_post_thumbnail().
add_filter( 'post_thumbnail_html', function ( $html, $post_id ) use ( $wpide_featured_link_open, $wpide_featured_link_skip ) {
    if ( '' === trim( (string) $html ) || wp_is_block_theme() || false !== stripos( $html, '<a ' ) || $wpide_featured_link_skip( $post_id ) ) {
        return $html;
    }

    return $wpide_featured_link_open( $post_id ) . $html . '</a>';
}, 10, 2 );

// Block themes: the Featured Image block when "Link to post" is switched off.
add_filter( 'render_block_core/post-featured-image', function ( $content, $block, $instance = null ) use ( $wpide_featured_link_open, $wpide_featured_link_skip ) {
    $post_id = ( $instance instanceof WP_Block && ! empty( $instance->context['postId'] ) ) ? (int) $instance->context['postId'] : 0;

    if ( '' === trim( (string) $content ) || ! empty( $block['attrs']['isLink'] ) || false !== stripos( $content, '<a ' ) || $wpide_featured_link_skip( $post_id ) ) {
        return $content;
    }

    return preg_replace_callback( '/<img\b[^>]*>/i', function ( $match ) use ( $wpide_featured_link_open, $post_id ) {
        return $wpide_featured_link_open( $post_id ) . $match[0] . '</a>';
    }, $content, 1 );
}, 10, 3 );