Improve behavior of usePreventScroll on iOS

packages/@react-aria/overlays/src/usePopover.ts

@@ -93,7 +93,7 @@ export function usePopover(props: AriaPopoverProps, state: OverlayTriggerState):
   });
 
   usePreventScroll({
-    isDisabled: isNonModal
+    isDisabled: isNonModal || !state.isOpen
   });
 
   useLayoutEffect(() => {

packages/@react-aria/overlays/src/usePreventScroll.ts

@@ -92,8 +92,9 @@ function preventScrollStandard() {
 //
 // 1. Prevent default on `touchmove` events that are not in a scrollable element. This prevents touch scrolling
 //    on the window.
-// 2. Prevent default on `touchmove` events inside a scrollable element when the scroll position is at the
-//    top or bottom. This avoids the whole page scrolling instead, but does prevent overscrolling.
+// 2. Set `overscroll-behavior: contain` on nested scrollable regions so they do not scroll the page when at
+//    the top or bottom. Work around a bug where this does not work when the element does not actually overflow
+//    by preventing default in a `touchmove` event.
 // 3. Prevent default on `touchend` events on input elements and handle focusing the element ourselves.
 // 4. When focusing an input, apply a transform to trick Safari into thinking the input is at the top
 //    of the page, which prevents it from scrolling the page. After the input is focused, scroll the element
@@ -105,15 +106,20 @@ function preventScrollStandard() {
 //    to navigate to an input with the next/previous buttons that's outside a modal.
 function preventScrollMobileSafari() {
   let scrollable: Element;
-  let lastY = 0;
+  let restoreScrollableStyles;
   let onTouchStart = (e: TouchEvent) => {
     // Store the nearest scrollable parent element from the element that the user touched.
     scrollable = getScrollParent(e.target as Element);
     if (scrollable === document.documentElement && scrollable === document.body) {
       return;
     }
 
-    lastY = e.changedTouches[0].pageY;
+    // Prevent scrolling up when at the top and scrolling down when at the bottom
+    // of a nested scrollable area, otherwise mobile Safari will start scrolling
+    // the window instead.
+    if (scrollable instanceof HTMLElement && window.getComputedStyle(scrollable).overscrollBehavior === 'auto') {
+      restoreScrollableStyles = setStyle(scrollable, 'overscrollBehavior', 'contain');
+    }
   };
 
   let onTouchMove = (e: TouchEvent) => {
@@ -123,23 +129,15 @@ function preventScrollMobileSafari() {
       return;
     }
 
-    // Prevent scrolling up when at the top and scrolling down when at the bottom
-    // of a nested scrollable area, otherwise mobile Safari will start scrolling
-    // the window instead. Unfortunately, this disables bounce scrolling when at
-    // the top but it's the best we can do.
-    let y = e.changedTouches[0].pageY;
-    let scrollTop = scrollable.scrollTop;
-    let bottom = scrollable.scrollHeight - scrollable.clientHeight;
-
-    if (bottom === 0) {
-      return;
-    }
-
-    if ((scrollTop <= 0 && y > lastY) || (scrollTop >= bottom && y < lastY)) {
+    // overscroll-behavior should prevent scroll chaining, but currently does not
+    // if the element doesn't actually overflow. https://bugs.webkit.org/show_bug.cgi?id=243452
+    // This checks that both the width and height do not overflow, otherwise we might
+    // block horizontal scrolling too. In that case, adding `touch-action: pan-x` to
+    // the element will prevent vertical page scrolling. We can't add that automatically
+    // because it must be set before the touchstart event.
+    if (scrollable.scrollHeight === scrollable.clientHeight && scrollable.scrollWidth === scrollable.clientWidth) {
       e.preventDefault();
     }
-
-    lastY = y;
   };
 
   let onTouchEnd = (e: TouchEvent) => {
@@ -148,6 +146,7 @@ function preventScrollMobileSafari() {
     // Apply this change if we're not already focused on the target element
     if (willOpenKeyboard(target) && target !== document.activeElement) {
       e.preventDefault();
+      setupStyles();
 
       // Apply a transform to trick Safari into thinking the input is at the top of the page
       // so it doesn't try to scroll it into view. When tapping on an input, this needs to
@@ -158,11 +157,17 @@ function preventScrollMobileSafari() {
         target.style.transform = '';
       });
     }
+
+    if (restoreScrollableStyles) {
+      restoreScrollableStyles();
+    }
   };
 
   let onFocus = (e: FocusEvent) => {
     let target = e.target as HTMLElement;
     if (willOpenKeyboard(target)) {
+      setupStyles();
+
       // Transform also needs to be applied in the focus event in cases where focus moves
       // other than tapping on an input directly, e.g. the next/previous buttons in the
       // software keyboard. In these cases, it seems applying the transform in the focus event
@@ -190,40 +195,50 @@ function preventScrollMobileSafari() {
     }
   };
 
-  let onWindowScroll = () => {
-    // Last resort. If the window scrolled, scroll it back to the top.
-    // It should always be at the top because the body will have a negative margin (see below).
-    window.scrollTo(0, 0);
-  };
+  let restoreStyles = null;
+  let setupStyles = () => {
+    if (restoreStyles) {
+      return;
+    }
 
-  // Record the original scroll position so we can restore it.
-  // Then apply a negative margin to the body to offset it by the scroll position. This will
-  // enable us to scroll the window to the top, which is required for the rest of this to work.
-  let scrollX = window.pageXOffset;
-  let scrollY = window.pageYOffset;
+    let onWindowScroll = () => {
+      // Last resort. If the window scrolled, scroll it back to the top.
+      // It should always be at the top because the body will have a negative margin (see below).
+      window.scrollTo(0, 0);
+    };
 
-  let restoreStyles = chain(
-    setStyle(document.documentElement, 'paddingRight', `${window.innerWidth - document.documentElement.clientWidth}px`),
-    setStyle(document.documentElement, 'overflow', 'hidden'),
-    setStyle(document.body, 'marginTop', `-${scrollY}px`)
-  );
+    // Record the original scroll position so we can restore it.
+    // Then apply a negative margin to the body to offset it by the scroll position. This will
+    // enable us to scroll the window to the top, which is required for the rest of this to work.
+    let scrollX = window.pageXOffset;
+    let scrollY = window.pageYOffset;
+
+    restoreStyles = chain(
+      addEvent(window, 'scroll', onWindowScroll),
+      setStyle(document.documentElement, 'paddingRight', `${window.innerWidth - document.documentElement.clientWidth}px`),
+      setStyle(document.documentElement, 'overflow', 'hidden'),
+      setStyle(document.body, 'marginTop', `-${scrollY}px`),
+      () => {
+        window.scrollTo(scrollX, scrollY);
+      }
+    );
 
-  // Scroll to the top. The negative margin on the body will make this appear the same.
-  window.scrollTo(0, 0);
+    // Scroll to the top. The negative margin on the body will make this appear the same.
+    window.scrollTo(0, 0);
+  };
 
   let removeEvents = chain(
     addEvent(document, 'touchstart', onTouchStart, {passive: false, capture: true}),
     addEvent(document, 'touchmove', onTouchMove, {passive: false, capture: true}),
     addEvent(document, 'touchend', onTouchEnd, {passive: false, capture: true}),
-    addEvent(document, 'focus', onFocus, true),
-    addEvent(window, 'scroll', onWindowScroll)
+    addEvent(document, 'focus', onFocus, true)
   );
 
   return () => {
     // Restore styles and scroll the page back to where it was.
-    restoreStyles();
+    restoreScrollableStyles?.();
+    restoreStyles?.();
     removeEvents();
-    window.scrollTo(scrollX, scrollY);
   };
 }
 

packages/@react-spectrum/dialog/stories/Dialog.stories.tsx

@@ -435,15 +435,16 @@ function renderWithDividerInContent({width = 'auto', ...props}) {
 
 function renderHorizontalScrolling({width = 'auto', ...props}) {
   return (
-    <div style={{display: 'flex', width, margin: '100px 0'}}>
+    <div style={{display: 'flex', flexDirection: 'column', alignItems: 'start', width}}>
+      {fiveParagraphs()}
       <DialogTrigger defaultOpen>
         <ActionButton>Trigger</ActionButton>
         {(close) => (
           <Dialog {...props}>
             <Heading>The Heading</Heading>
             <Header>The Header</Header>
             <Divider />
-            <Content UNSAFE_style={{overflow: 'auto'}}>
+            <Content UNSAFE_style={{overflow: 'auto', touchAction: 'pan-x'}}>
               <TextField label="Top textfield" minWidth="100vw" />
               <p>scroll this content horizontally</p>
             </Content>
@@ -454,6 +455,7 @@ function renderHorizontalScrolling({width = 'auto', ...props}) {
           </Dialog>
         )}
       </DialogTrigger>
+      {fiveParagraphs()}
     </div>
   );
 }