+ * Returns the canonical URL for a post.
+ *
+ * When the post is the same as the current requested page the function will handle the
+ * pagination arguments too.
+ *
+ * @since 4.6.0
+ *
+ * @param int|WP_Post $post Optional. Post ID or object. Default is global `$post`.
+ * @return string|false The canonical URL, or false if the post does not exist or has not
+ * been published yet.
+ */
+function wp_get_canonical_url( $post = null ) {
+ $post = get_post( $post );
+
+ if ( ! $post ) {
+ return false;
+ }
+
+ if ( 'publish' !== $post->post_status ) {
+ return false;
+ }
+
+ $canonical_url = get_permalink( $post );
+
+ // If a canonical is being generated for the current page, make sure it has pagination if needed.
+ if ( $post->ID === get_queried_object_id() ) {
+ $page = get_query_var( 'page', 0 );
+ if ( $page >= 2 ) {
+ if ( '' == get_option( 'permalink_structure' ) ) {
+ $canonical_url = add_query_arg( 'page', $page, $canonical_url );
+ } else {
+ $canonical_url = trailingslashit( $canonical_url ) . user_trailingslashit( $page, 'single_paged' );
+ }
+ }
+
+ $cpage = get_query_var( 'cpage', 0 );
+ if ( $cpage ) {
+ $canonical_url = get_comments_pagenum_link( $cpage );
+ }
+ }
+
+ /**
+ * Filters the canonical URL for a post.
+ *
+ * @since 4.6.0
+ *
+ * @param string $string The post's canonical URL.
+ * @param WP_Post $post Post object.
+ */
+ return apply_filters( 'get_canonical_url', $canonical_url, $post );
+}
+
+/**
+ * Outputs rel=canonical for singular queries.