feat: Add support for disclosure animation

packages/@react-aria/disclosure/src/useDisclosure.ts

@@ -41,14 +41,13 @@ export interface DisclosureAria {
  * @param state - State for the disclosure, as returned by `useDisclosureState`.
  * @param ref - A ref for the disclosure panel.
  */
-export function useDisclosure(props: AriaDisclosureProps, state: DisclosureState, ref: RefObject<Element | null>): DisclosureAria {
+export function useDisclosure(props: AriaDisclosureProps, state: DisclosureState, ref: RefObject<HTMLElement | null>): DisclosureAria {
   let {
     isDisabled
   } = props;
   let triggerId = useId();
   let panelId = useId();
   let isSSR = useIsSSR();
-  let supportsBeforeMatch = !isSSR && 'onbeforematch' in document.body;
 
   let raf = useRef<number | null>(null);
 
@@ -66,22 +65,64 @@ export function useDisclosure(props: AriaDisclosureProps, state: DisclosureState
   }, [ref, state]);
 
   // @ts-ignore https://github.com/facebook/react/pull/24741
-  useEvent(ref, 'beforematch', supportsBeforeMatch ? handleBeforeMatch : null);
+  useEvent(ref, 'beforematch', handleBeforeMatch);
 
+  let isExpandedRef = useRef<boolean | null>(null);
   useLayoutEffect(() => {
     // Cancel any pending RAF to prevent stale updates
     if (raf.current) {
       cancelAnimationFrame(raf.current);
     }
-    // Until React supports hidden="until-found": https://github.com/facebook/react/pull/24741
-    if (supportsBeforeMatch && ref.current && !isDisabled) {
-      if (state.isExpanded) {
-        ref.current.removeAttribute('hidden');
-      } else {
-        ref.current.setAttribute('hidden', 'until-found');
+    if (ref.current && !isDisabled && !isSSR) {
+      let panel = ref.current;
+
+      if (isExpandedRef.current == null || typeof panel.getAnimations !== 'function') {
+        // On initial render (and in tests), set attributes without animation.
+        if (state.isExpanded) {
+          panel.removeAttribute('hidden');
+          panel.style.setProperty('--disclosure-panel-width', 'auto');
+          panel.style.setProperty('--disclosure-panel-height', 'auto');
+        } else {
+          panel.setAttribute('hidden', 'until-found');
+          panel.style.setProperty('--disclosure-panel-width', '0px');
+          panel.style.setProperty('--disclosure-panel-height', '0px');
+        }
+      } else if (state.isExpanded !== isExpandedRef.current) {
+        if (state.isExpanded) {
+          panel.removeAttribute('hidden');
+
+          // Set the width and height as pixels so they can be animated.
+          panel.style.setProperty('--disclosure-panel-width', panel.scrollWidth + 'px');
+          panel.style.setProperty('--disclosure-panel-height', panel.scrollHeight + 'px');
+
+          Promise.all(panel.getAnimations().map(a => a.finished))
+            .then(() => {
+              // After the animations complete, switch back to auto so the content can resize.
+              panel.style.setProperty('--disclosure-panel-width', 'auto');
+              panel.style.setProperty('--disclosure-panel-height', 'auto');
+            })
+            .catch(() => {});
+        } else {
+          panel.style.setProperty('--disclosure-panel-width', panel.scrollWidth + 'px');
+          panel.style.setProperty('--disclosure-panel-height', panel.scrollHeight + 'px');
+
+          // Force style re-calculation to trigger animations.
+          window.getComputedStyle(panel).height;
+
+          // Animate to zero size.
+          panel.style.setProperty('--disclosure-panel-width', '0px');
+          panel.style.setProperty('--disclosure-panel-height', '0px');
+
+          // Wait for animations to apply the hidden attribute.
+          Promise.all(panel.getAnimations().map(a => a.finished))
+            .then(() => panel.setAttribute('hidden', 'until-found'))
+            .catch(() => {});
+        }
       }
+
+      isExpandedRef.current = state.isExpanded;
     }
-  }, [isDisabled, ref, state.isExpanded, supportsBeforeMatch]);
+  }, [isDisabled, ref, state.isExpanded, isSSR]);
 
   useEffect(() => {
     return () => {
@@ -114,7 +155,7 @@ export function useDisclosure(props: AriaDisclosureProps, state: DisclosureState
       role: 'group',
       'aria-labelledby': triggerId,
       'aria-hidden': !state.isExpanded,
-      hidden: supportsBeforeMatch ? true : !state.isExpanded
+      hidden: isSSR ? !state.isExpanded : undefined
     }
   };
 }

packages/@react-aria/disclosure/test/useDisclosure.test.ts

@@ -31,7 +31,6 @@ describe('useDisclosure', () => {
     let {buttonProps, panelProps} = result.current;
 
     expect(buttonProps['aria-expanded']).toBe(false);
-    expect(panelProps.hidden).toBe(true);
     expect(panelProps['aria-hidden']).toBe(true);
   });
 
@@ -44,7 +43,7 @@ describe('useDisclosure', () => {
     let {buttonProps, panelProps} = result.current;
 
     expect(buttonProps['aria-expanded']).toBe(true);
-    expect(panelProps.hidden).toBe(false);
+    expect(panelProps['aria-hidden']).toBe(false);
   });
 
   it('should handle expanding on press event (with mouse)', () => {

packages/@react-spectrum/s2/src/Disclosure.tsx

@@ -297,20 +297,20 @@ export interface DisclosurePanelProps extends Omit<RACDisclosurePanelProps, 'cla
 
 const panelStyles = style({
   font: 'body',
-  paddingTop: {
-    isExpanded: 8
-  },
-  paddingBottom: {
-    isExpanded: 16
-  },
+  height: '--disclosure-panel-height',
+  overflow: 'clip',
+  transition: '[height]'
+});
+
+const panelInner = style({
+  paddingTop: 8,
+  paddingBottom: 16,
   paddingX: {
-    isExpanded: {
-      size: {
-        S: 8,
-        M: space(9),
-        L: 12,
-        XL: space(15)
-      }
+    size: {
+      S: 8,
+      M: space(9),
+      L: 12,
+      XL: space(15)
     }
   }
 });
@@ -326,15 +326,16 @@ export const DisclosurePanel = forwardRef(function DisclosurePanel(props: Disclo
   } = props;
   const domProps = filterDOMProps(otherProps);
   let {size} = useSlottedContext(DisclosureContext)!;
-  let {isExpanded} = useContext(DisclosureStateContext)!;
   let panelRef = useDOMRef(ref);
   return (
     <RACDisclosurePanel
       {...domProps}
       ref={panelRef}
       style={UNSAFE_style}
-      className={(UNSAFE_className ?? '') + panelStyles({size, isExpanded})}>
-      {props.children}
+      className={(UNSAFE_className ?? '') + panelStyles}>
+      <div className={panelInner({size})}>
+        {props.children}
+      </div>
     </RACDisclosurePanel>
   );
 });

packages/react-aria-components/docs/Disclosure.mdx

@@ -50,7 +50,7 @@ import {ChevronRight} from 'lucide-react';
     </Button>
   </Heading>
   <DisclosurePanel>
-    <p>Details about system requirements here.</p>
+    Details about system requirements here.
   </DisclosurePanel>
 </Disclosure>
 ```
@@ -74,6 +74,7 @@ import {ChevronRight} from 'lucide-react';
     display: flex;
     align-items: center;
     gap: 8px;
+    padding: 8px 0;
 
     svg {
       rotate: 0deg;
@@ -84,13 +85,20 @@ import {ChevronRight} from 'lucide-react';
     }
   }
 
+  .react-aria-Heading {
+    margin-bottom: 0;
+  }
+
   &[data-expanded] .react-aria-Button[slot=trigger] svg {
     rotate: 90deg;
   }
 }
 
 .react-aria-DisclosurePanel {
-  margin-left: 32px;
+  margin-left: 26px;
+  height: var(--disclosure-panel-height);
+  transition: height 250ms;
+  overflow: clip;
 }
 ```
 
@@ -149,7 +157,7 @@ function MyDisclosure({title, children, ...props}: MyDisclosureProps) {
         </Button>
       </Heading>
       <DisclosurePanel>
-        <p>{children}</p>
+        {children}
       </DisclosurePanel>
     </Disclosure>
   )
@@ -213,7 +221,7 @@ In some use cases, you may want to add an interactive element, like a button, ad
     <Button>Click me</Button>
   </div>
   <DisclosurePanel>
-    <p>Details about system requirements here.</p>
+    Details about system requirements here.
   </DisclosurePanel>
 </Disclosure>
 ```
@@ -282,6 +290,8 @@ A `Disclosure` can be targeted with the `.react-aria-Disclosure` CSS selector, o
 
 <StateTable properties={docs.exports.DisclosureRenderProps.properties} />
 
+Use the `--disclosure-panel-width` and `--disclosure-panel-height` CSS variables to implement animations.
+
 ### Button
 
 A `Button` can be targeted with the `.react-aria-Button` CSS selector, or by overriding with a custom `className`. It supports the following states:

packages/react-aria-components/docs/DisclosureGroup.mdx

@@ -53,7 +53,7 @@ import {ChevronRight} from 'lucide-react';
       </Button>
     </Heading>
     <DisclosurePanel>
-      <p>Personal information form here.</p>
+      Personal information form here.
     </DisclosurePanel>
   </Disclosure>
   <Disclosure id="billing">
@@ -64,7 +64,7 @@ import {ChevronRight} from 'lucide-react';
       </Button>
     </Heading>
     <DisclosurePanel>
-      <p>Billing address form here.</p>
+      Billing address form here.
     </DisclosurePanel>
   </Disclosure>
 </DisclosureGroup>
@@ -139,7 +139,7 @@ function MyDisclosure({title, children, ...props}: MyDisclosureProps) {
         </Button>
       </Heading>
       <DisclosurePanel>
-        <p>{children}</p>
+        {children}
       </DisclosurePanel>
     </Disclosure>
   )
@@ -228,7 +228,7 @@ In some use cases, you may want to add an interactive element, like a button, ad
       <Button>Click me</Button>
     </div>
     <DisclosurePanel>
-      <p>Details about system requirements here.</p>
+      Details about system requirements here.
     </DisclosurePanel>
   </Disclosure>
   <Disclosure id="personal">
@@ -242,7 +242,7 @@ In some use cases, you may want to add an interactive element, like a button, ad
       <Button>Click me</Button>
     </div>
     <DisclosurePanel>
-      <p>Details about personal information here.</p>
+      Details about personal information here.
     </DisclosurePanel>
   </Disclosure>
 </DisclosureGroup>
@@ -329,6 +329,8 @@ A `Disclosure` can be targeted with the `.react-aria-Disclosure` CSS selector, o
 
 <StateTable properties={docs.exports.DisclosureRenderProps.properties} />
 
+Use the `--disclosure-panel-width` and `--disclosure-panel-height` CSS variables to implement animations.
+
 ### Button
 
 A `Button` can be targeted with the `.react-aria-Button` CSS selector, or by overriding with a custom `className`. It supports the following states:

starters/docs/src/Disclosure.css

@@ -33,6 +33,9 @@
 }
 
 .react-aria-DisclosurePanel {
-  margin-left: 32px;
+  margin-left: 26px;
   color: var(--text-color);
+  height: var(--disclosure-panel-height);
+  transition: height 250ms;
+  overflow: clip;
 }

starters/tailwind/src/Disclosure.tsx

@@ -97,8 +97,8 @@ export interface DisclosurePanelProps extends AriaDisclosurePanelProps {
 
 export function DisclosurePanel({ children, ...props }: DisclosurePanelProps) {
   return (
-    <AriaDisclosurePanel {...props} className={composeTailwindRenderProps(props.className, 'group-data-[expanded]:px-4 group-data-[expanded]:py-2')}>
-      {children}
+    <AriaDisclosurePanel {...props} className={composeTailwindRenderProps(props.className, 'h-(--disclosure-panel-height) transition-[height] overflow-clip')}>
+      <div className="px-4 py-2">{children}</div>
     </AriaDisclosurePanel>
   );
 }