only make order summary sticky when it's not longer than view

plugins/woocommerce-blocks/assets/js/base/components/sidebar-layout/sidebar.tsx

@@ -9,7 +9,7 @@ import classNames from 'classnames';
  */
 import { ForwardRefProps } from './types';
 
-const Sidebar = forwardRef< HTMLInputElement, ForwardRefProps >(
+const Sidebar = forwardRef< HTMLDivElement, ForwardRefProps >(
 	( { children, className = '' }, ref ): JSX.Element => {
 		return (
 			<div

plugins/woocommerce-blocks/assets/js/base/hooks/index.js

@@ -8,3 +8,4 @@ export * from './use-typography-props';
 export * from './use-is-mounted';
 export * from './use-spoken-message';
 export * from './use-style-props';
+export * from './use-observed-viewport';

plugins/woocommerce-blocks/assets/js/base/hooks/use-observed-viewport.ts

@@ -0,0 +1,93 @@
+/**
+ * External dependencies
+ */
+import { useState, useRef, useEffect } from '@wordpress/element';
+
+/**
+ * Returns a ref, its dimensions, and its visible viewport dimensions. Useful to know if an element should be sticky or not. This hook only runs when an element changes its intersection or dimensions.
+ *
+ * @example
+ *
+ * ```js
+ * const App = () => {
+ * 	const [ observedRef, observedElement, viewWindow ] = useObservedViewport();
+ *
+ * 	return (
+ * 		<MyElement ref={ observedRef } className={ observedElement.height < viewWindow.height ? 'is-sticky': '' } />
+ * 	);
+ * };
+ * ```
+ */
+export function useObservedViewport< T extends HTMLElement >(): [
+	React.Ref< T >,
+	{ height: number; width: number },
+	{ height: number; width: number }
+] {
+	const [ observedElement, setObservedElement ] = useState( {
+		height: 0,
+		width: 0,
+	} );
+
+	const [ viewWindow, setViewWindow ] = useState( {
+		height: 0,
+		width: 0,
+	} );
+
+	const observedRef = useRef< T >( null );
+
+	useEffect( () => {
+		if ( ! observedRef.current ) {
+			return;
+		}
+		const element = observedRef.current;
+		const resizeObserver = new ResizeObserver( ( entries ) => {
+			entries.forEach( ( entry ) => {
+				if ( entry.target === element ) {
+					const { height, width } = entry.contentRect;
+					const elementTop =
+						element.computedStyleMap().get( 'top' )?.toString() ||
+						'0';
+					setObservedElement( {
+						height: height + parseInt( elementTop, 10 ),
+						width,
+					} );
+				}
+			} );
+		} );
+
+		const intersectionObserver = new IntersectionObserver(
+			( entries ) => {
+				entries.forEach( ( entry ) => {
+					const { height, width } = entry.boundingClientRect;
+					setObservedElement( { height, width } );
+					if ( entry.target.ownerDocument.defaultView ) {
+						setViewWindow( {
+							height: entry.target.ownerDocument.defaultView
+								?.innerHeight,
+							width: entry.target.ownerDocument.defaultView
+								?.innerWidth,
+						} );
+					}
+				} );
+			},
+			{
+				root: null,
+				rootMargin: '0px',
+				threshold: 1,
+			}
+		);
+
+		resizeObserver.observe( element );
+		intersectionObserver.observe( element );
+
+		return () => {
+			if ( ! element ) {
+				return;
+			}
+
+			resizeObserver.unobserve( element );
+			intersectionObserver.unobserve( element );
+		};
+	}, [] );
+	return [ observedRef, observedElement, viewWindow ];
+}

plugins/woocommerce-blocks/assets/js/blocks/checkout/inner-blocks/checkout-totals-block/frontend.tsx

@@ -4,17 +4,23 @@
 import classnames from 'classnames';
 import { Sidebar } from '@woocommerce/base-components/sidebar-layout';
 import { StoreNoticesContainer } from '@woocommerce/blocks-components';
-
+import { useObservedViewport } from '@woocommerce/base-hooks';
 const FrontendBlock = ( {
 	children,
 	className,
 }: {
 	children: JSX.Element;
 	className?: string;
 } ): JSX.Element => {
+	const [ observedRef, observedElement, viewWindow ] =
+		useObservedViewport< HTMLDivElement >();
+	const isSticky = observedElement.height < viewWindow.height;
 	return (
 		<Sidebar
-			className={ classnames( 'wc-block-checkout__sidebar', className ) }
+			ref={ observedRef }
+			className={ classnames( 'wc-block-checkout__sidebar', className, {
+				'is-sticky': isSticky,
+			} ) }
 		>
 			<StoreNoticesContainer
 				context={ 'woocommerce/checkout-totals-block' }

plugins/woocommerce-blocks/assets/js/blocks/checkout/inner-blocks/checkout-totals-block/style.scss

@@ -23,8 +23,10 @@
 
 .is-large {
 	.wc-block-checkout__sidebar {
-		position: sticky;
-		top: $gap-largest;
 		align-self: flex-start;
+		top: $gap-large;
+		&.is-sticky {
+			position: sticky;
+		}
 	}
 }

plugins/woocommerce-blocks/assets/js/blocks/checkout/styles/editor.scss

@@ -31,6 +31,12 @@
 			position: relative;
 		}
 	}
+
+	.is-large {
+		.wc-block-checkout__sidebar {
+			top: 0;
+		}
+	}
 }
 
 body.wc-lock-selected-block--move {

plugins/woocommerce-blocks/assets/js/blocks/checkout/test/block.js

@@ -42,6 +42,18 @@ jest.mock( '@wordpress/compose', () => ( {
 	useResizeObserver: jest.fn().mockReturnValue( [ null, { width: 0 } ] ),
 } ) );
 
+global.ResizeObserver = jest.fn().mockImplementation( () => ( {
+	observe: jest.fn(),
+	unobserve: jest.fn(),
+	disconnect: jest.fn(),
+} ) );
+
+global.IntersectionObserver = jest.fn().mockImplementation( () => ( {
+	observe: jest.fn(),
+	unobserve: jest.fn(),
+	disconnect: jest.fn(),
+} ) );
+
 jest.mock( '@wordpress/element', () => {
 	return {
 		...jest.requireActual( '@wordpress/element' ),

plugins/woocommerce/changelog/47680-fix-only-sticky-summary-if-smaller-than-screen

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fix
+Comment: This is a follow up to another PR not yet shipped.
+