Source

File: wp-includes/class-wp-customize-nav-menus.php

public function load_available_items_query( $type = 'post_type', $object = 'page', $page = 0 ) {
		$items = array();

		if ( 'post_type' === $type ) {
			$post_type = get_post_type_object( $object );
			if ( ! $post_type ) {
				return new WP_Error( 'nav_menus_invalid_post_type' );
			}

			/*
			 * If we're dealing with pages, let's prioritize the Front Page,
			 * Posts Page and Privacy Policy Page at the top of the list.
			 */
			$important_pages   = array();
			$suppress_page_ids = array();
			if ( 0 === $page && 'page' === $object ) {
				// Insert Front Page or custom "Home" link.
				$front_page = 'page' === get_option( 'show_on_front' ) ? (int) get_option( 'page_on_front' ) : 0;
				if ( ! empty( $front_page ) ) {
					$front_page_obj      = get_post( $front_page );
					$important_pages[]   = $front_page_obj;
					$suppress_page_ids[] = $front_page_obj->ID;
				} else {
					// Add "Home" link. Treat as a page, but switch to custom on add.
					$items[] = array(
						'id'         => 'home',
						'title'      => _x( 'Home', 'nav menu home label' ),
						'type'       => 'custom',
						'type_label' => __( 'Custom Link' ),
						'object'     => '',
						'url'        => home_url(),
					);
				}

				// Insert Posts Page.
				$posts_page = 'page' === get_option( 'show_on_front' ) ? (int) get_option( 'page_for_posts' ) : 0;
				if ( ! empty( $posts_page ) ) {
					$posts_page_obj      = get_post( $posts_page );
					$important_pages[]   = $posts_page_obj;
					$suppress_page_ids[] = $posts_page_obj->ID;
				}

				// Insert Privacy Policy Page.
				$privacy_policy_page_id = (int) get_option( 'wp_page_for_privacy_policy' );
				if ( ! empty( $privacy_policy_page_id ) ) {
					$privacy_policy_page = get_post( $privacy_policy_page_id );
					if ( $privacy_policy_page instanceof WP_Post && 'publish' === $privacy_policy_page->post_status ) {
						$important_pages[]   = $privacy_policy_page;
						$suppress_page_ids[] = $privacy_policy_page->ID;
					}
				}
			} elseif ( 'post' !== $object && 0 === $page && $post_type->has_archive ) {
				// Add a post type archive link.
				$items[] = array(
					'id'         => $object . '-archive',
					'title'      => $post_type->labels->archives,
					'type'       => 'post_type_archive',
					'type_label' => __( 'Post Type Archive' ),
					'object'     => $object,
					'url'        => get_post_type_archive_link( $object ),
				);
			}

			// Prepend posts with nav_menus_created_posts on first page.
			$posts = array();
			if ( 0 === $page && $this->manager->get_setting( 'nav_menus_created_posts' ) ) {
				foreach ( $this->manager->get_setting( 'nav_menus_created_posts' )->value() as $post_id ) {
					$auto_draft_post = get_post( $post_id );
					if ( $post_type->name === $auto_draft_post->post_type ) {
						$posts[] = $auto_draft_post;
					}
				}
			}

			$args = array(
				'numberposts' => 10,
				'offset'      => 10 * $page,
				'orderby'     => 'date',
				'order'       => 'DESC',
				'post_type'   => $object,
			);

			// Add suppression array to arguments for get_posts.
			if ( ! empty( $suppress_page_ids ) ) {
				$args['post__not_in'] = $suppress_page_ids;
			}

			$posts = array_merge(
				$posts,
				$important_pages,
				get_posts( $args )
			);

			foreach ( $posts as $post ) {
				$post_title = $post->post_title;
				if ( '' === $post_title ) {
					/* translators: %d: ID of a post. */
					$post_title = sprintf( __( '#%d (no title)' ), $post->ID );
				}

				$post_type_label = get_post_type_object( $post->post_type )->labels->singular_name;
				$post_states     = get_post_states( $post );
				if ( ! empty( $post_states ) ) {
					$post_type_label = implode( ',', $post_states );
				}

				$items[] = array(
					'id'         => "post-{$post->ID}",
					'title'      => html_entity_decode( $post_title, ENT_QUOTES, get_bloginfo( 'charset' ) ),
					'type'       => 'post_type',
					'type_label' => $post_type_label,
					'object'     => $post->post_type,
					'object_id'  => intval( $post->ID ),
					'url'        => get_permalink( intval( $post->ID ) ),
				);
			}
		} elseif ( 'taxonomy' === $type ) {
			$terms = get_terms(
				array(
					'taxonomy'     => $object,
					'child_of'     => 0,
					'exclude'      => '',
					'hide_empty'   => false,
					'hierarchical' => 1,
					'include'      => '',
					'number'       => 10,
					'offset'       => 10 * $page,
					'order'        => 'DESC',
					'orderby'      => 'count',
					'pad_counts'   => false,
				)
			);

			if ( is_wp_error( $terms ) ) {
				return $terms;
			}

			foreach ( $terms as $term ) {
				$items[] = array(
					'id'         => "term-{$term->term_id}",
					'title'      => html_entity_decode( $term->name, ENT_QUOTES, get_bloginfo( 'charset' ) ),
					'type'       => 'taxonomy',
					'type_label' => get_taxonomy( $term->taxonomy )->labels->singular_name,
					'object'     => $term->taxonomy,
					'object_id'  => intval( $term->term_id ),
					'url'        => get_term_link( intval( $term->term_id ), $term->taxonomy ),
				);
			}
		}

		/**
		 * Filters the available menu items.
		 *
		 * @since 4.3.0
		 *
		 * @param array  $items  The array of menu items.
		 * @param string $type   The object type.
		 * @param string $object The object name.
		 * @param int    $page   The current page number.
		 */
		$items = apply_filters( 'customize_nav_menu_available_items', $items, $type, $object, $page );

		return $items;
	}