Add accessibilityHint for iOS (#18093)

Summary:
This adds the accessibilityHint for View, Text and Touchable* on iOS.
The accessibilityHint provides some more information about an element
when the accessibilityLabel is not enough.

The accessibilityHint is a core accessibility property on iOS.

From https://developer.apple.com/documentation/objectivec/nsobject/1615093-accessibilityhint:
> An accessibility hint helps users understand what will happen when they perform an action on the accessibility element when that result is not obvious from the accessibility label.

Related issue: https://github.com/facebook/react-native/issues/14706

The npm scripts `test`, `flow`, `lint` and `prettier` are satisfied.

I added a couple of examples to the RNTester app. The Accessibility Inspector on Mac helps debugging accessibility stuff on a simulator, but it does not show the accessibilityHint. Therefore I tested the RNTester app on an iPhone 8 device using VoiceOver to verify the hint functionality. It works fine, and I've tested disabling and enabling "read hints" in the VoiceOver settings on the phone.

https://github.com/facebook/react-native-website/pull/222

[IOS][FEATURE][Accessibility] - Add accessibilityHint for View, Text, Touchable* on iOS
Closes https://github.com/facebook/react-native/pull/18093

Reviewed By: hramos

Differential Revision: D7230780

Pulled By: ziqichen6

fbshipit-source-id: 172ad28dc9ae2b67ea256100f6acb939f2466d0b

Libraries/Components/Touchable/TouchableBounce.js

@@ -160,6 +160,7 @@ const TouchableBounce = ((createReactClass({
         style={[{transform: [{scale: this.state.scale}]}, this.props.style]}
         accessible={this.props.accessible !== false}
         accessibilityLabel={this.props.accessibilityLabel}
+        accessibilityHint={this.props.accessibilityHint}
         accessibilityComponentType={this.props.accessibilityComponentType}
         accessibilityTraits={this.props.accessibilityTraits}
         nativeID={this.props.nativeID}

Libraries/Components/Touchable/TouchableHighlight.js

@@ -348,6 +348,7 @@ const TouchableHighlight = ((createReactClass({
       <View
         accessible={this.props.accessible !== false}
         accessibilityLabel={this.props.accessibilityLabel}
+        accessibilityHint={this.props.accessibilityHint}
         accessibilityComponentType={this.props.accessibilityComponentType}
         accessibilityTraits={this.props.accessibilityTraits}
         style={StyleSheet.compose(

Libraries/Components/Touchable/TouchableOpacity.js

@@ -256,6 +256,7 @@ const TouchableOpacity = ((createReactClass({
       <Animated.View
         accessible={this.props.accessible !== false}
         accessibilityLabel={this.props.accessibilityLabel}
+        accessibilityHint={this.props.accessibilityHint}
         accessibilityComponentType={this.props.accessibilityComponentType}
         accessibilityTraits={this.props.accessibilityTraits}
         style={[this.props.style, {opacity: this.state.anim}]}

Libraries/Components/Touchable/TouchableWithoutFeedback.js

@@ -43,6 +43,7 @@ export type Props = $ReadOnly<{|
     | string
     | Array<any>
     | any,
+  accessibilityHint?: string,
   accessibilityTraits?: ?AccessibilityTraitsFlow,
   children?: ?React.Node,
   delayLongPress?: ?number,
@@ -75,6 +76,7 @@ const TouchableWithoutFeedback = ((createReactClass({
   propTypes: {
     accessible: PropTypes.bool,
     accessibilityLabel: PropTypes.node,
+    accessibilityHint: PropTypes.string,
     accessibilityComponentType: PropTypes.oneOf(AccessibilityComponentTypes),
     accessibilityTraits: PropTypes.oneOfType([
       PropTypes.oneOf(AccessibilityTraits),
@@ -238,6 +240,7 @@ const TouchableWithoutFeedback = ((createReactClass({
     return (React: any).cloneElement(child, {
       accessible: this.props.accessible !== false,
       accessibilityLabel: this.props.accessibilityLabel,
+      accessibilityHint: this.props.accessibilityHint,
       accessibilityComponentType: this.props.accessibilityComponentType,
       accessibilityTraits: this.props.accessibilityTraits,
       nativeID: this.props.nativeID,

Libraries/Components/View/ReactNativeViewAttributes.js

@@ -24,6 +24,7 @@ ReactNativeViewAttributes.UIView = {
   accessibilityRole: true,
   accessibilityStates: true,
   accessibilityTraits: true,
+  accessibilityHint: true,
   importantForAccessibility: true,
   nativeID: true,
   testID: true,

Libraries/Components/View/ViewPropTypes.js

@@ -87,6 +87,7 @@ export type ViewProps = $ReadOnly<{|
     | string
     | Array<any>
     | any,
+  accessibilityHint?: string,
   accessibilityActions?: Array<string>,
   accessibilityComponentType?: AccessibilityComponentType,
   accessibilityLiveRegion?: 'none' | 'polite' | 'assertive',
@@ -128,6 +129,17 @@ module.exports = {
    */
   accessibilityLabel: PropTypes.node,
 
+  /**
+   * An accessibility hint helps users understand what will happen when they perform
+   * an action on the accessibility element when that result is not obvious from the
+   * accessibility label.
+   *
+   * @platform ios
+   *
+   * See http://facebook.github.io/react-native/docs/view.html#accessibilityHint
+   */
+  accessibilityHint: PropTypes.string,
+
   /**
    * Provides an array of custom actions available for accessibility.
    *

RNTester/js/AccessibilityIOSExample.js

@@ -12,7 +12,7 @@
 
 var React = require('react');
 var ReactNative = require('react-native');
-var {AccessibilityInfo, Text, View} = ReactNative;
+var {AccessibilityInfo, Text, View, TouchableOpacity} = ReactNative;
 
 class AccessibilityIOSExample extends React.Component<{}> {
   render() {
@@ -39,6 +39,31 @@ class AccessibilityIOSExample extends React.Component<{}> {
         <Text accessibilityLabel="Test of accessibilityLabel" accessible={true}>
           This text component's accessibilityLabel is set explicitly.
         </Text>
+        <View
+          accessibilityLabel="Test of accessibilityHint"
+          accessibilityHint="The hint provides more info than the label does"
+          accessible={true}>
+          <Text>
+            This view component has both an accessibilityLabel and an
+            accessibilityHint explicitly set.
+          </Text>
+        </View>
+        <Text
+          accessibilityLabel="Test of accessibilityHint"
+          accessibilityHint="The hint provides more info than the label does">
+          This text component has both an accessibilityLabel and an
+          accessibilityHint explicitly set.
+        </Text>
+        <TouchableOpacity
+          accessibilityLabel="Test of accessibilityHint"
+          accessibilityHint="The hint provides more info than the label does">
+          <View>
+            <Text>
+              This button has both an accessibilityLabel and an
+              accessibilityHint explicitly set.
+            </Text>
+          </View>
+        </TouchableOpacity>
         <View accessibilityElementsHidden={true}>
           <Text>
             This view's children are hidden from the accessibility tree

React/Views/RCTViewManager.m

@@ -111,6 +111,7 @@ RCT_EXPORT_VIEW_PROPERTY(nativeID, NSString)
 RCT_REMAP_VIEW_PROPERTY(accessible, reactAccessibilityElement.isAccessibilityElement, BOOL)
 RCT_REMAP_VIEW_PROPERTY(accessibilityActions, reactAccessibilityElement.accessibilityActions, NSString)
 RCT_REMAP_VIEW_PROPERTY(accessibilityLabel, reactAccessibilityElement.accessibilityLabel, NSString)
+RCT_REMAP_VIEW_PROPERTY(accessibilityHint, reactAccessibilityElement.accessibilityHint, NSString)
 RCT_REMAP_VIEW_PROPERTY(accessibilityTraits, reactAccessibilityElement.accessibilityTraits, UIAccessibilityTraits)
 RCT_REMAP_VIEW_PROPERTY(accessibilityViewIsModal, reactAccessibilityElement.accessibilityViewIsModal, BOOL)
 RCT_REMAP_VIEW_PROPERTY(accessibilityElementsHidden, reactAccessibilityElement.accessibilityElementsHidden, BOOL)