Report the role of ComposeSceneAccessible on macOS as PANEL

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/awt/ComposeWindowPanel.desktop.kt

@@ -55,7 +55,7 @@ internal class ComposeWindowPanel(
         window = window,
         useSwingGraphics = false,
         layerType = ComposeFeatureFlags.layerType.let {
-            // LayerType.OnComponent might be used only with rendering to Swing graphics,
+            // LayerType.OnComponent may can only be used with rendering via Swing graphics,
             // but it's always disabled here. Using fallback instead of [check] to support
             // opening separate windows from [ComposePanel] with such layer type.
             if (it == LayerType.OnComponent) LayerType.OnSameCanvas else it

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/platform/a11y/ComposeSceneAccessible.kt

@@ -21,6 +21,8 @@ import java.awt.*
 import java.awt.event.FocusListener
 import java.util.*
 import javax.accessibility.*
+import org.jetbrains.skiko.OS
+import org.jetbrains.skiko.hostOs
 
 /**
  * This is a root [Accessible] for a [androidx.compose.ui.ComposeScene]
@@ -153,7 +155,16 @@ internal class ComposeSceneAccessible(
         }
 
         override fun getAccessibleRole(): AccessibleRole {
-            return AccessibleRole.UNKNOWN
+            // We want to return a role that makes the ComposeScene container "transparent" to
+            // accessibility, as if its contents are inside the parent directly.
+            // On macOS, PANEL is ignored by Java's a11y (see CAccessibility.ignoredRoles), but on
+            // Windows, it makes NVDA read it as "panel".
+            // On Windows, NVDA ignores UNKNOWN, but on macOS UNKNOWN causes VoiceOver to highlight
+            // the entire component when traversing via VoiceOver shortcuts.
+            return when (hostOs) {
+                OS.MacOS -> AccessibleRole.PANEL
+                else -> AccessibleRole.UNKNOWN
+            }
         }
 
         override fun getAccessibleStateSet(): AccessibleStateSet {

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/scene/ComposeContainer.desktop.kt

@@ -183,7 +183,7 @@ internal class ComposeContainer(
         this.windowContainer = windowContainer
 
         if (layerType == LayerType.OnComponent && !useSwingGraphics) {
-            error("Unsupported LayerType.OnComponent might be used only with rendering to Swing graphics")
+            error("LayerType.OnComponent can only be used with rendering via Swing graphics")
         }
     }
 

compose/ui/ui/src/skikoMain/kotlin/androidx/compose/ui/node/RootNodeOwner.skiko.kt

@@ -66,6 +66,8 @@ import androidx.compose.ui.scene.ComposeSceneInputHandler
 import androidx.compose.ui.scene.ComposeScenePointer
 import androidx.compose.ui.semantics.EmptySemanticsElement
 import androidx.compose.ui.semantics.SemanticsOwner
+import androidx.compose.ui.semantics.isTraversalGroup
+import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.text.font.createFontFamilyResolver
 import androidx.compose.ui.text.input.TextInputService
 import androidx.compose.ui.unit.Constraints
@@ -118,6 +120,11 @@ internal class RootNodeOwner(
             // Consume the key event if we moved focus.
             focusOwner.moveFocus(focusDirection)
         }
+        .semantics {
+            // This makes the reported role of the root node "PANEL", which is ignored by VoiceOver
+            // (which is what we want).
+            isTraversalGroup = true
+        }
     val owner: Owner = OwnerImpl(layoutDirection, coroutineContext)
     val semanticsOwner = SemanticsOwner(owner.root)
     var size by mutableStateOf(size)