Opt-in a11y argument for iOS interop (#1350)

It's non-trivial to figure out if the UIKit content has any
accessibility element in its subtree in a general case. In the same time
interop UIViews can _taint_ the tree of SemanticsModifierNode merging
its children and redirecting all accessibility input to interop UIView,
missing all other data. This lead to unexpected situations, where
Compose controls were inaccessible because they contained a native UIKit
element inside.

Add `accesibilityEnabled` argument to `UIKitView`/`UIKitViewController`
APIs
Don't set `interopView` semantics property unless `accesibilityEnabled`
is true.
Document the interaction thoroughly.

## Testing
- InteropViewAndSemanticsConfigMerge: first button is not _tainted_ by
UIKitView content and is possible to interact via a11y input.

## Release Notes

### Features - iOS
- Added source-compatible `accessibilityEnabled: Boolean = true`
argument to `UIKitView` and `UIKitViewController`.

## Note
Additive API changes consequences are unclear for Kotlin/Native source
sets. Should we do overloads with extra parameters as well? cc @igordmn

compose/mpp/demo/src/uikitMain/kotlin/androidx/compose/mpp/demo/InteropViewAndSemanticsConfigMerge.kt

@@ -38,7 +38,8 @@ val InteropViewAndSemanticsConfigMerge = Screen.Example("InteropViewAndSemantics
                     view.text = "UILabel"
                     view
                 },
-                modifier = Modifier.size(80.dp, 40.dp)
+                modifier = Modifier.size(80.dp, 40.dp),
+                accessibilityEnabled = false
             )
         }
 

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/interop/UIKitView.uikit.kt

@@ -25,6 +25,7 @@ import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.runtime.snapshots.SnapshotStateObserver
+import androidx.compose.ui.Modifier
 import androidx.compose.ui.*
 import androidx.compose.ui.draw.drawBehind
 import androidx.compose.ui.graphics.BlendMode
@@ -91,6 +92,19 @@ internal val InteropViewSemanticsKey = AccessibilityKey<InteropWrappingView>(
 
 private var SemanticsPropertyReceiver.interopView by InteropViewSemanticsKey
 
+/**
+ * Chain [this] with [Modifier.semantics] that sets the [interopView] of the node if [enabled] is true.
+ * If [enabled] is false, [this] is returned as is.
+ */
+private fun Modifier.interopSemantics(enabled: Boolean, wrappingView: InteropWrappingView): Modifier =
+    if (enabled) {
+        this then semantics {
+            interopView = wrappingView
+        }
+    } else {
+        this
+    }
+
 /**
  * @param factory The block creating the [UIView] to be composed.
  * @param modifier The modifier to be applied to the layout. Size should be specified in modifier.
@@ -102,6 +116,22 @@ private var SemanticsPropertyReceiver.interopView by InteropViewSemanticsKey
  * View should be freed at this time.
  * @param onResize May be used to custom resize logic.
  * @param interactive If true, then user touches will be passed to this UIView
+ * @param accessibilityEnabled If `true`, then the view will be visible to accessibility services.
+ *
+ * If this Composable is within a modifier chain that merges
+ * the semantics of its children (such as `Modifier.clickable`), the merged subtree data will be ignored in favor of
+ * the native UIAccessibility resolution for the view constructed by [factory]. For example, `Button` containing [UIKitView]
+ * will be invisible for accessibility services, only the [UIView] created by [factory] will be accessible.
+ * To avoid this behavior, set [accessibilityEnabled] to `false` and use custom [Modifier.semantics] for `Button` to
+ * make the information associated with this view accessible.
+ *
+ * If there are multiple [UIKitView] or [UIKitViewController] with [accessibilityEnabled] set to `true` in the merged tree, only the first one will be accessible.
+ * Consider using a single [UIKitView] or [UIKitViewController] with multiple views inside it if you need multiple accessible views.
+ *
+ * In general, [accessibilityEnabled] set to `true` is not recommended to use in such cases.
+ * Consider using [Modifier.semantics] on Composable that merges its semantics instead.
+ *
+ * @see Modifier.semantics
  */
 @Composable
 fun <T : UIView> UIKitView(
@@ -112,6 +142,7 @@ fun <T : UIView> UIKitView(
     onRelease: (T) -> Unit = STUB_CALLBACK_WITH_RECEIVER,
     onResize: (view: T, rect: CValue<CGRect>) -> Unit = DefaultViewResize,
     interactive: Boolean = true,
+    accessibilityEnabled: Boolean = true,
 ) {
     // TODO: adapt UIKitView to reuse inside LazyColumn like in AndroidView:
     //  https://developer.android.com/reference/kotlin/androidx/compose/ui/viewinterop/package-summary#AndroidView(kotlin.Function1,kotlin.Function1,androidx.compose.ui.Modifier,kotlin.Function1,kotlin.Function1)
@@ -157,9 +188,7 @@ fun <T : UIView> UIKitView(
             } else {
                 it
             }
-        }.semantics {
-            interopView = embeddedInteropComponent.wrappingView
-        }
+        }.interopSemantics(accessibilityEnabled, embeddedInteropComponent.wrappingView)
     )
 
     DisposableEffect(Unit) {
@@ -201,6 +230,24 @@ fun <T : UIView> UIKitView(
  * view controller should be freed at this time.
  * @param onResize May be used to custom resize logic.
  * @param interactive If true, then user touches will be passed to this UIViewController
+ * @param accessibilityEnabled If `true`, then the [UIViewController.view] will be visible to accessibility services.
+ *
+ * If this Composable is within a modifier chain that merges the semantics of its children (such as `Modifier.clickable`),
+ * the merged subtree data will be ignored in favor of
+ * the native UIAccessibility resolution for the [UIViewController.view] of [UIViewController] constructed by [factory].
+ * For example, `Button` containing [UIKitViewController] will be invisible for accessibility services,
+ * only the [UIViewController.view] of [UIViewController] created by [factory] will be accessible.
+ * To avoid this behavior, set [accessibilityEnabled] to `false` and use custom [Modifier.semantics] for `Button` to
+ * make the information associated with the [UIViewController] accessible.
+ *
+ * If there are multiple [UIKitView] or [UIKitViewController] with [accessibilityEnabled] set to `true` in the merged tree,
+ * only the first one will be accessible.
+ * Consider using a single [UIKitView] or [UIKitViewController] with multiple views inside it if you need multiple accessible views.
+ *
+ * In general, [accessibilityEnabled] set to `true` is not recommended to use in such cases.
+ * Consider using [Modifier.semantics] on Composable that merges its semantics instead.
+ *
+ * @see Modifier.semantics
  */
 @Composable
 fun <T : UIViewController> UIKitViewController(
@@ -211,6 +258,7 @@ fun <T : UIViewController> UIKitViewController(
     onRelease: (T) -> Unit = STUB_CALLBACK_WITH_RECEIVER,
     onResize: (viewController: T, rect: CValue<CGRect>) -> Unit = DefaultViewControllerResize,
     interactive: Boolean = true,
+    accessibilityEnabled: Boolean = true,
 ) {
     // TODO: adapt UIKitViewController to reuse inside LazyColumn like in AndroidView:
     //  https://developer.android.com/reference/kotlin/androidx/compose/ui/viewinterop/package-summary#AndroidView(kotlin.Function1,kotlin.Function1,androidx.compose.ui.Modifier,kotlin.Function1,kotlin.Function1)
@@ -259,9 +307,7 @@ fun <T : UIViewController> UIKitViewController(
             } else {
                 it
             }
-        }.semantics {
-            interopView = embeddedInteropComponent.wrappingView
-        }
+        }.interopSemantics(accessibilityEnabled, embeddedInteropComponent.wrappingView)
     )
 
     DisposableEffect(Unit) {