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Lists.transform: Preserve spliterator characteristics from backing list #8170

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Lists.transform: Preserve spliterator characteristics from backing list #8170

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19 changes: 19 additions & 0 deletions guava-tests/test/com/google/common/collect/ListsTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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));
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13 changes: 13 additions & 0 deletions guava/src/com/google/common/collect/Lists.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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;
}

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