re-add shadow DOM styles when reparented

.changeset/shy-mangos-arrive.md

@@ -0,0 +1,5 @@
+---
+'@itwin/itwinui-react': patch
+---
+
+Fixed an issue where some components (e.g. `VisuallyHidden` inside `ProgressRadial`) were losing their styles when reparented into a different window.

packages/itwinui-react/src/utils/components/ShadowRoot.tsx

@@ -81,6 +81,29 @@ function useShadowRoot(
   const latestCss = useLatestRef(css);
   const latestShadowRoot = useLatestRef(shadowRoot);
 
+  const createStyleSheet = React.useCallback(
+    (shadow: ShadowRoot | null) => {
+      if (shadow && supportsAdoptedStylesheets) {
+        const currentWindow = shadow.ownerDocument.defaultView || globalThis;
+
+        // bail if stylesheet already exists in the current window
+        if (styleSheet.current instanceof currentWindow.CSSStyleSheet) {
+          return;
+        }
+
+        // create an empty stylesheet and add it to the shadowRoot
+        styleSheet.current = new currentWindow.CSSStyleSheet();
+        shadow.adoptedStyleSheets.push(styleSheet.current);
+
+        // add the CSS immediately to avoid FOUC (one-time)
+        if (latestCss.current) {
+          styleSheet.current.replaceSync(latestCss.current);
+        }
+      }
+    },
+    [latestCss],
+  );
+
   useLayoutEffect(() => {
     const parent = templateRef.current?.parentElement;
     if (!parent) {
@@ -93,18 +116,7 @@ function useShadowRoot(
       }
 
       const shadow = parent.shadowRoot || parent.attachShadow({ mode: 'open' });
-
-      if (supportsAdoptedStylesheets) {
-        // create an empty stylesheet and add it to the shadowRoot
-        const currentWindow = shadow.ownerDocument.defaultView || globalThis;
-        styleSheet.current = new currentWindow.CSSStyleSheet();
-        shadow.adoptedStyleSheets = [styleSheet.current];
-
-        // add the CSS immediately to avoid FOUC (one-time)
-        if (latestCss.current) {
-          styleSheet.current.replaceSync(latestCss.current);
-        }
-      }
+      createStyleSheet(shadow);
 
       // Flush the state immediately after shadow-root is attached, to ensure that layout
       // measurements in parent component are correct.
@@ -118,7 +130,7 @@ function useShadowRoot(
     });
 
     return () => void setShadowRoot(null);
-  }, [templateRef, latestCss, latestShadowRoot]);
+  }, [templateRef, createStyleSheet, latestShadowRoot]);
 
   // Synchronize `css` with contents of the existing stylesheet
   useLayoutEffect(() => {
@@ -127,5 +139,16 @@ function useShadowRoot(
     }
   }, [css]);
 
+  // Re-create stylesheet if the element is moved to a different window (by AppUI)
+  React.useEffect(() => {
+    const listener = () => createStyleSheet(latestShadowRoot.current);
+
+    // See https://github.com/iTwin/appui/blob/0a4cc7d127b50146e003071320d06064a09a06ae/ui/appui-react/src/appui-react/layout/widget/ContentRenderer.tsx#L74-L80
+    window.addEventListener('appui:reparent', listener);
+    return () => {
+      window.removeEventListener('appui:reparent', listener);
+    };
+  }, [createStyleSheet, latestShadowRoot]);
+
   return shadowRoot;
 }

testing/e2e/app/routes/VisuallyHidden/route.tsx

@@ -0,0 +1,45 @@
+import * as React from 'react';
+import * as ReactDOM from 'react-dom';
+import { VisuallyHidden, ThemeProvider } from '@itwin/itwinui-react';
+import { useSearchParams } from '@remix-run/react';
+
+export default function Page() {
+  const [searchParams] = useSearchParams();
+
+  if (searchParams.get('popout') === 'true') {
+    return <PopoutTest />;
+  }
+
+  return null;
+}
+
+/** https://github.com/iTwin/iTwinUI/pull/2252#discussion_r1766676900 */
+function PopoutTest() {
+  const popout = usePopout();
+
+  return (
+    <>
+      <button onClick={popout.open}>Open popout</button>
+      {popout.popout &&
+        ReactDOM.render(
+          <ThemeProvider>
+            <VisuallyHidden>Hello</VisuallyHidden>
+          </ThemeProvider>,
+          popout.popout.document.body,
+        )}
+    </>
+  );
+}
+
+// ----------------------------------------------------------------------------
+
+function usePopout() {
+  const [popout, setPopout] = React.useState<Window | null>(null);
+
+  const open = React.useCallback(() => {
+    const popout = window.open('', 'popout', 'width=400,height=400');
+    setPopout(popout);
+  }, []);
+
+  return React.useMemo(() => ({ open, popout }), [open, popout]);
+}

testing/e2e/app/routes/VisuallyHidden/spec.ts

@@ -0,0 +1,11 @@
+import { test, expect } from '@playwright/test';
+
+test('styles should exist in popout window', async ({ page }) => {
+  const popoutPromise = page.waitForEvent('popup');
+  await page.goto('/VisuallyHidden?popout=true');
+  await page.click('button');
+  const popout = await popoutPromise;
+
+  const visuallyHidden = popout.getByText('Hello');
+  await expect(visuallyHidden).toHaveCSS('position', 'absolute');
+});