Admin: Automatically enqueue postbox scripts for custom meta boxes

src/js/_enqueues/admin/postbox.js

@@ -657,4 +657,14 @@
 		pbhide : false
 	};
 
+	/*
+	 * @since 7.0.0
+	 * @see https://core.trac.wordpress.org/ticket/17704
+	 */
+	$( function() {
+		if ( typeof window.pagenow !== 'undefined' && ! postboxes.page && $( '.postbox' ).length ) {
+			postboxes.add_postbox_toggles( window.pagenow );
+		}
+	} );
+
 }(jQuery));

src/wp-admin/includes/class-wp-screen.php

@@ -1001,6 +1001,14 @@ public function show_screen_options() {
 
 		$show_screen = ! empty( $wp_meta_boxes[ $this->id ] ) || $columns || $this->get_option( 'per_page' );
 
+		/*
+		 * @since 7.0.0
+		 * @see https://core.trac.wordpress.org/ticket/17704
+		 */
+		if ( ! empty( $wp_meta_boxes[ $this->id ] ) ) {
+			wp_enqueue_script( 'postbox' );
+		}
+
 		$this->_screen_settings = '';
 
 		if ( 'post' === $this->base ) {

tests/phpunit/tests/admin/includesScreen.php

@@ -630,4 +630,45 @@ public function test_is_block_editor( $hook, $filter, $expected ) {
 
 		$this->assertSame( $expected, $screen->is_block_editor );
 	}
+
+	/**
+	 * @ticket 17704
+	 */
+	public function test_show_screen_options_enqueues_postbox_script_when_meta_boxes_exist() {
+		global $wp_meta_boxes;
+
+		set_current_screen( 'tools.php' );
+		$screen = get_current_screen();
+
+		add_meta_box( 'testbox-17704', 'Test Meta Box', '__return_false', $screen );
+
+		$screen->show_screen_options();
+
+		$this->assertTrue(
+			wp_script_is( 'postbox', 'enqueued' ),
+			'The postbox script should be enqueued when meta boxes are registered for the screen.'
+		);
+
+		remove_meta_box( 'testbox-17704', $screen, 'advanced' );
+		wp_dequeue_script( 'postbox' );
+	}
+
+	/**
+	 * @ticket 17704
+	 */
+	public function test_show_screen_options_does_not_enqueue_postbox_script_when_no_meta_boxes() {
+		global $wp_meta_boxes;
+
+		set_current_screen( 'options-general.php' );
+		$screen = get_current_screen();
+
+		unset( $wp_meta_boxes[ $screen->id ] );
+
+		$screen->show_screen_options();
+
+		$this->assertFalse(
+			wp_script_is( 'postbox', 'enqueued' ),
+			'The postbox script should not be enqueued when no meta boxes are registered for the screen.'
+		);
+	}
 }