[v10] fix(ui-modal): voiceOver in Chrome treats scrollable modal body as single interactive object preventing line-by-line navigation

packages/ui-modal/src/Modal/ModalBody/index.tsx

@@ -36,6 +36,7 @@ import generateComponentTheme from './theme'
 import { propTypes, allowedProps } from './props'
 import type { ModalBodyProps } from './props'
 import { UIElement } from '@instructure/shared-types'
+import ModalContext from '../ModalContext'
 
 /**
 ---
@@ -120,29 +121,36 @@ class ModalBody extends Component<ModalBodyProps> {
     // TODO rethink, the 'as' prop, likely its not a good idea to allow React
     // components. See INSTUI-4674
     const finalRef = this.getFinalRef(this.ref)
-
+    const hasScrollbar =
+      finalRef &&
+      Math.abs(
+        (finalRef.scrollHeight ?? 0) -
+          (finalRef.getBoundingClientRect()?.height ?? 0)
+      ) > 1
     return (
-      <View
-        {...passthroughProps}
-        display="block"
-        width={isFit ? '100%' : undefined}
-        height={isFit ? '100%' : undefined}
-        elementRef={this.handleRef}
-        as={as}
-        css={this.props.styles?.modalBody}
-        padding={padding}
-        // check if there is a scrollbar, if so, the element has to be tabbable to be able to scroll with keyboard only
-        // epsilon tolerance is used to avoid false positives, this is generally safer than Math rounding techniques
-        {...(finalRef &&
-        Math.abs(
-          (finalRef.scrollHeight ?? 0) -
-            (finalRef.getBoundingClientRect()?.height ?? 0)
-        ) > 0.05
-          ? { tabIndex: 0 }
-          : {})}
-      >
-        {children}
-      </View>
+      <ModalContext.Consumer>
+        {(value) => (
+          <View
+            {...passthroughProps}
+            display="block"
+            width={isFit ? '100%' : undefined}
+            height={isFit ? '100%' : undefined}
+            elementRef={this.handleRef}
+            as={as}
+            css={this.props.styles?.modalBody}
+            padding={padding}
+            // check if there is a scrollbar, if so, the element has to be tabbable
+            {...(hasScrollbar
+              ? {
+                  tabIndex: 0,
+                  'aria-label': value.bodyScrollAriaLabel
+                }
+              : {})}
+          >
+            {children}
+          </View>
+        )}
+      </ModalContext.Consumer>
     )
   }
 }

packages/ui-modal/src/Modal/ModalContext.ts

@@ -0,0 +1,46 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 - present Instructure, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+import { createContext } from 'react'
+
+type ModalContextType = {
+  /**
+   * Needed for setting the correct aria-label in the modal body when its scrollable.
+   * This is a value read from the Modal's Header.
+   */
+  bodyScrollAriaLabel?: string
+  setBodyScrollAriaLabel?: (txt: string) => void
+}
+
+/**
+ * React context created by the `Modal` component
+ * @private
+ */
+const ModalContext = createContext<ModalContextType>({
+  bodyScrollAriaLabel: undefined
+})
+
+export default ModalContext
+export { ModalContext }
+export type { ModalContextType }

packages/ui-modal/src/Modal/ModalHeader/index.tsx

@@ -40,6 +40,7 @@ import generateComponentTheme from './theme'
 
 import { propTypes, allowedProps } from './props'
 import type { ModalHeaderProps, ModalHeaderStyleProps } from './props'
+import ModalContext from '../ModalContext'
 
 type CloseButtonChild = ComponentElement<CloseButtonProps, CloseButton>
 
@@ -62,9 +63,34 @@ class ModalHeader extends Component<ModalHeaderProps> {
   }
 
   ref: HTMLDivElement | null = null
+  declare context: React.ContextType<typeof ModalContext>
+  static contextType = ModalContext
+
+  /**
+   * Gets all text in a DOM subtree, text under <button> nodes is excluded
+   */
+  getTextExcludingButtons = (root: Node) => {
+    const walker = document.createTreeWalker(root, NodeFilter.SHOW_TEXT, {
+      acceptNode(node) {
+        return node.parentElement?.closest('button')
+          ? NodeFilter.FILTER_REJECT
+          : NodeFilter.FILTER_ACCEPT
+      }
+    })
+    let text = ''
+    let current
+    while ((current = walker.nextNode())) {
+      text += current.nodeValue
+    }
+    return text
+  }
 
   handleRef = (el: HTMLDivElement | null) => {
     this.ref = el
+    if (el) {
+      const txt = this.getTextExcludingButtons(el)
+      this.context.setBodyScrollAriaLabel?.(txt)
+    }
   }
 
   componentDidMount() {

packages/ui-modal/src/Modal/index.tsx

@@ -50,6 +50,7 @@ import type {
   ModalPropsForPortal,
   ModalPropsForTransition
 } from './props'
+import ModalContext from './ModalContext'
 
 /**
 ---
@@ -86,7 +87,8 @@ class Modal extends Component<ModalProps, ModalState> {
     this.state = {
       transitioning: false,
       open: props.open ?? false,
-      windowHeight: 99999
+      windowHeight: 99999,
+      bodyScrollAriaLabel: undefined
     }
   }
 
@@ -302,13 +304,21 @@ class Modal extends Component<ModalProps, ModalState> {
             onClose
           )}
         >
-          {constrain === 'parent' ? (
-            <span css={this.props.styles?.constrainContext}>
-              {this.renderDialog(passthroughProps)}
-            </span>
-          ) : (
-            this.renderDialog(passthroughProps)
-          )}
+          <ModalContext.Provider
+            value={{
+              bodyScrollAriaLabel: this.state.bodyScrollAriaLabel,
+              setBodyScrollAriaLabel: (txt: string) =>
+                this.setState({ bodyScrollAriaLabel: txt })
+            }}
+          >
+            {constrain === 'parent' ? (
+              <span css={this.props.styles?.constrainContext}>
+                {this.renderDialog(passthroughProps)}
+              </span>
+            ) : (
+              this.renderDialog(passthroughProps)
+            )}
+          </ModalContext.Provider>
         </Transition>
       </Portal>
     )

packages/ui-modal/src/Modal/props.ts

@@ -197,6 +197,10 @@ type ModalState = {
   transitioning: boolean
   open: boolean
   windowHeight: number
+  /**
+   * The `aria-label` on the Modal's body if it's scrollable.
+   */
+  bodyScrollAriaLabel?: string
 }
 
 const propTypes: PropValidators<PropKeys> = {