From b13bdbff35c775e20ea16c3d01128b8b17ea3f03 Mon Sep 17 00:00:00 2001
From: Nickita Khylkouski
 <90287684+nickita-khylkouski@users.noreply.github.com>
Date: Mon, 26 Jan 2026 08:08:57 -0800
Subject: [PATCH] Lists.transform: Preserve spliterator characteristics from
 backing list.

---
 .../com/google/common/collect/ListsTest.java  | 19 +++++++++++++++++++
 .../src/com/google/common/collect/Lists.java  | 13 +++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/guava-tests/test/com/google/common/collect/ListsTest.java b/guava-tests/test/com/google/common/collect/ListsTest.java
index bd46674a18d2..542ab8301db2 100644
--- a/guava-tests/test/com/google/common/collect/ListsTest.java
+++ b/guava-tests/test/com/google/common/collect/ListsTest.java
@@ -57,6 +57,7 @@
 import java.util.ListIterator;
 import java.util.NoSuchElementException;
 import java.util.RandomAccess;
+import java.util.Spliterator;
 import java.util.concurrent.CopyOnWriteArrayList;
 import junit.framework.Test;
 import junit.framework.TestCase;
@@ -892,6 +893,24 @@ private static void assertTransformIterator(List<String> list) {
     assertFalse(iterator.hasNext());
   }
 
+  @J2ktIncompatible // CopyOnWriteArrayList
+  @GwtIncompatible // CopyOnWriteArrayList
+  public void testTransformSpliteratorPreservesCharacteristics() {
+    // Test for Issue #8165: Lists.transform should preserve spliterator characteristics
+    CopyOnWriteArrayList<Integer> cow = new CopyOnWriteArrayList<>(asList(1, 2, 3));
+
+    // CopyOnWriteArrayList's spliterator has IMMUTABLE characteristic
+    int cowCharacteristics = cow.spliterator().characteristics();
+    assertTrue((cowCharacteristics & Spliterator.IMMUTABLE) != 0);
+
+    // Lists.transform should preserve the IMMUTABLE characteristic
+    List<Integer> transformed = transform(cow, x -> x);
+    int transformedCharacteristics = transformed.spliterator().characteristics();
+    assertTrue(
+        "Lists.transform should preserve IMMUTABLE characteristic from CopyOnWriteArrayList",
+        (transformedCharacteristics & Spliterator.IMMUTABLE) != 0);
+  }
+
   public void testPartition_badSize() {
     List<Integer> source = singletonList(1);
     assertThrows(IllegalArgumentException.class, () -> partition(source, 0));
diff --git a/guava/src/com/google/common/collect/Lists.java b/guava/src/com/google/common/collect/Lists.java
index 32e032edd1bf..32b0ede09e4d 100644
--- a/guava/src/com/google/common/collect/Lists.java
+++ b/guava/src/com/google/common/collect/Lists.java
@@ -50,6 +50,7 @@
 import java.util.NoSuchElementException;
 import java.util.Objects;
 import java.util.RandomAccess;
+import java.util.Spliterator;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.function.Predicate;
 import org.jspecify.annotations.Nullable;
@@ -605,6 +606,12 @@ public boolean removeIf(Predicate<? super T> filter) {
       return fromList.removeIf(element -> filter.test(function.apply(element)));
     }
 
+    @Override
+    @GwtIncompatible("Spliterator")
+    public Spliterator<T> spliterator() {
+      return CollectSpliterators.map(fromList.spliterator(), 0, function);
+    }
+
     @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
   }
 
@@ -678,6 +685,12 @@ public int size() {
       return fromList.size();
     }
 
+    @Override
+    @GwtIncompatible("Spliterator")
+    public Spliterator<T> spliterator() {
+      return CollectSpliterators.map(fromList.spliterator(), 0, function);
+    }
+
     @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
   }