test(android): pin that a child vanishing mid-read reads as gone

android/snapshot-helper/src/main/java/com/callstack/agentdevice/snapshothelper/AccessibilityNodeReads.java

@@ -30,17 +30,30 @@ static AccessibilityNodeInfo root(AccessibilityWindowInfo window) {
     return window.getRoot();
   }
 
+  interface Read<T> {
+    T read();
+  }
+
   /**
    * The child, or null when it is gone. When the child's window closes during the read, the
    * framework can throw a NullPointerException from its result integrity check instead of answering
    * null (seen on API 35 while an alert dialog closed), so that throw means the same as null.
+   *
+   * <p>A null {@code node} is a programmer error, but the same catch hides its NullPointerException
+   * as a gone child.
    */
   static AccessibilityNodeInfo child(AccessibilityNodeInfo node, int index) {
+    return nullIfGone(
+        () ->
+            Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU
+                ? node.getChild(index, PREFETCH_STRATEGY)
+                : node.getChild(index));
+  }
+
+  /** Runs a framework read that answers null for a vanished node and can throw instead. */
+  static <T> T nullIfGone(Read<T> read) {
     try {
-      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
-        return node.getChild(index, PREFETCH_STRATEGY);
-      }
-      return node.getChild(index);
+      return read.read();
     } catch (NullPointerException vanished) {
       return null;
     }

android/snapshot-helper/src/test/java/com/callstack/agentdevice/snapshothelper/AccessibilityReadBatchTest.java

@@ -14,6 +14,7 @@ static void run() throws Exception {
     releasesUnreadResultsAfterFailure();
     waitsForReadersBeforeReleasingTheParent();
     preservesInterruptionDuringCleanup();
+    readsAChildThatVanishedMidReadAsGone();
   }
 
   private static void queuesConcurrentReadsAndPreservesOrder() throws Exception {
@@ -134,6 +135,41 @@ private static void preservesInterruptionDuringCleanup() {
     }
   }
 
+  private static void readsAChildThatVanishedMidReadAsGone() {
+    List<Integer> recycled = new ArrayList<>();
+    try (AccessibilityReadBatch<Integer> batch =
+        new AccessibilityReadBatch<>(
+            0, 3,
+            index ->
+                AccessibilityNodeReads.nullIfGone(
+                    () -> {
+                      if (index == 1) {
+                        throw new NullPointerException("window closed");
+                      }
+                      if (index == 2) {
+                        throw new IllegalStateException("not a vanished child");
+                      }
+                      return index;
+                    }),
+            recycled::add)) {
+      if (batch.get(0) != 0) {
+        throw new AssertionError("Expected the first child");
+      }
+      if (batch.get(1) != null) {
+        throw new AssertionError("A child that vanished mid-read must read as gone");
+      }
+      try {
+        batch.get(2);
+        throw new AssertionError("Other read failures must propagate");
+      } catch (IllegalStateException expected) {
+        // Only the vanished-window throw means a gone child.
+      }
+    }
+    if (!recycled.equals(Arrays.asList(0))) {
+      throw new AssertionError("Only the present child must be released: " + recycled);
+    }
+  }
+
   private static void await(CountDownLatch latch) {
     try {
       if (!latch.await(2, TimeUnit.SECONDS)) {