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Fix missing upper-bound guard in LastIndexOf and FindLastIndex #124161

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Merged
ViveliDuCh merged 2 commits into from
Feb 17, 2026
+80 −3
Merged

Fix missing upper-bound guard in LastIndexOf and FindLastIndex #124161

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f5d7963
Fix missing upper-bound guard in LastIndexOf and FindLastIndex
prozolic Feb 9, 2026
39f5430
Merge branch 'main' into immutablelistlastindexof
prozolic Feb 12, 2026
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17 changes: 14 additions & 3 deletions ...ies/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -801,7 +801,12 @@ internal int IndexOf(T item, int index, int count, IEqualityComparer<T>? equalit
/// </returns>
internal int LastIndexOf(T item, int index, int count, IEqualityComparer<T>? equalityComparer)
{
Requires.Range(index >= 0, nameof(index));
if (index == 0 && count == 0)
{
return -1;
}

Requires.Range(index >= 0 && index < this.Count, nameof(index));
Requires.Range(count >= 0 && count <= this.Count, nameof(count));
Requires.Argument(index - count + 1 >= 0);

Expand Down Expand Up @@ -1233,8 +1238,14 @@ internal int FindLastIndex(int startIndex, Predicate<T> match)
internal int FindLastIndex(int startIndex, int count, Predicate<T> match)
{
Requires.NotNull(match, nameof(match));
Requires.Range(startIndex >= 0, nameof(startIndex));
Requires.Range(count <= this.Count, nameof(count));

if (startIndex == 0 && count == 0)
{
return -1;
}

Requires.Range(startIndex >= 0 && startIndex < this.Count, nameof(startIndex));
Requires.Range(count >= 0 && count <= this.Count, nameof(count));
Requires.Range(startIndex - count + 1 >= 0, nameof(startIndex));

using (var enumerator = new Enumerator(this, startIndex: startIndex, count: count, reversed: true))
Expand Down
25 changes: 25 additions & 0 deletions src/libraries/System.Collections.Immutable/tests/ImmutableListTest.cs
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Expand Up @@ -522,6 +522,31 @@ public void LastIndexOf()
(b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq));
}

[Fact]
public void LastIndexOfMultipleMatches()
{
ImmutableList<string> list = ImmutableList.Create("NonMatch", "Match", "Match", "NonMatch");
Assert.Equal(2, list.LastIndexOf("Match", index: 3, count: 4, equalityComparer: null));
Assert.Throws<ArgumentOutOfRangeException>(() => list.LastIndexOf("Match", index: 4, count: 4, equalityComparer: null));
}

[Fact]
public void LastIndexOfConsistentWithImmutableArray()
{
ImmutableList<int> list = ImmutableList.Create(1, 2, 3);
ImmutableArray<int> array = ImmutableArray.Create(1, 2, 3);

Assert.Throws<ArgumentOutOfRangeException>(() => list.LastIndexOf(1, list.Count, 1, equalityComparer: null));
Assert.Throws<ArgumentOutOfRangeException>(() => array.LastIndexOf(1, array.Length, 1, equalityComparer: null));

for (int i = 0; i < list.Count; i++)
{
int listResult = list.LastIndexOf(list[i], list.Count - 1, list.Count, equalityComparer: null);
int arrayResult = array.LastIndexOf(array[i], array.Length - 1, array.Length, equalityComparer: null);
Assert.Equal(arrayResult, listResult);
}
}

[Fact]
public void ReplaceTest()
{
Expand Down
20 changes: 20 additions & 0 deletions src/libraries/System.Collections.Immutable/tests/ImmutableListTestBase.cs
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Expand Up @@ -174,6 +174,18 @@ public void FindLastIndexTest()
Assert.Equal(-1, this.GetListQuery(ImmutableList<int>.Empty).FindLastIndex(0, n => true));
Assert.Equal(-1, this.GetListQuery(ImmutableList<int>.Empty).FindLastIndex(0, 0, n => true));

ImmutableList<int> singleElementList = ImmutableList.Create(10);
Assert.Equal(0, this.GetListQuery(singleElementList).FindLastIndex(0, 1, n => n == 10));
Assert.Equal(-1, this.GetListQuery(singleElementList).FindLastIndex(0, 1, n => n == 99));
Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(singleElementList).FindLastIndex(1, n => n == 10));
Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(singleElementList).FindLastIndex(1, 1, n => n == 10));

ImmutableList<int> multipleElementList = ImmutableList.Create(1, 2, 3, 4);
Assert.Equal(2, this.GetListQuery(multipleElementList).FindLastIndex(3, 4, n => n == 3));
Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(multipleElementList).FindLastIndex(4, n => n == 1));
Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(multipleElementList).FindLastIndex(4, 1, n => n == 1));
Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(multipleElementList).FindLastIndex(4, 4, n => n == 1));

// Create a list with contents: 100,101,102,103,104,100,101,102,103,104
ImmutableList<int> list = ImmutableList<int>.Empty.AddRange(Enumerable.Range(100, 5).Concat(Enumerable.Range(100, 5)));
List<int> bclList = list.ToList();
Expand Down Expand Up @@ -221,6 +233,14 @@ public void FindLastIndexTest()
}
}

[Fact]
public void FindLastIndexTestMultipleMatches()
{
ImmutableList<string> list = ImmutableList.Create("NonMatch", "Match", "Match", "NonMatch");
Assert.Equal(2, this.GetListQuery(list).FindLastIndex(3, 4, n => n == "Match"));
Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(list).FindLastIndex(4, 4, n => n == "Match"));
}

[Fact]
public void IList_IndexOf_NullArgument()
{
Expand Down
21 changes: 21 additions & 0 deletions src/libraries/System.Collections.Immutable/tests/IndexOfTests.cs
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Expand Up @@ -88,23 +88,44 @@ public static void LastIndexOfTest<TCollection>(
Func<TCollection, int, int, int, IEqualityComparer<int>, int> lastIndexOfItemIndexCountEQ)
{
TCollection emptyCollection = factory(new int[0]);
TCollection singleCollection = factory(new[] { 10 });
TCollection collection1256 = factory(new[] { 1, 2, 5, 6 });

Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, EqualityComparer<int>.Default));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, EqualityComparer<int>.Default));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, EqualityComparer<int>.Default));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, EqualityComparer<int>.Default));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, EqualityComparer<int>.Default));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, EqualityComparer<int>.Default));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, new CustomComparer(50)));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, new CustomComparer(50)));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, new CustomComparer(50)));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, new CustomComparer(50)));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, new CustomComparer(1)));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, new CustomComparer(1)));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndex(collection1256, 2, 5));
Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 6, 4, 4, EqualityComparer<int>.Default));

Assert.Equal(-1, lastIndexOfItem(emptyCollection, 5));
Assert.Equal(-1, lastIndexOfItemEQ(emptyCollection, 5, EqualityComparer<int>.Default));
Assert.Equal(-1, lastIndexOfItemIndex(emptyCollection, 5, 0));
Assert.Equal(-1, lastIndexOfItemIndexCount(emptyCollection, 5, 0, 0));

Assert.Equal(0, lastIndexOfItem(singleCollection, 10));
Assert.Equal(0, lastIndexOfItemEQ(singleCollection, 10, EqualityComparer<int>.Default));
Assert.Equal(0, lastIndexOfItemIndex(singleCollection, 10, 0));
Assert.Equal(0, lastIndexOfItemIndexCount(singleCollection, 10, 0, 1));
Assert.Equal(0, lastIndexOfItemIndexCountEQ(singleCollection, 10, 0, 1, EqualityComparer<int>.Default));
Assert.Equal(-1, lastIndexOfItemIndexCountEQ(singleCollection, 100, 0, 1, EqualityComparer<int>.Default));

Assert.Equal(1, lastIndexOfItem(collection1256, 2));
Assert.Equal(1, lastIndexOfItemEQ(collection1256, 2, EqualityComparer<int>.Default));
Assert.Equal(1, lastIndexOfItemIndex(collection1256, 2, 3));
Assert.Equal(1, lastIndexOfItemIndexCount(collection1256, 2, 3, 4));
Assert.Equal(2, lastIndexOfItemIndexCountEQ(collection1256, 5, 3, 4, EqualityComparer<int>.Default));
Assert.Equal(3, lastIndexOfItemIndexCountEQ(collection1256, 6, 3, 4, EqualityComparer<int>.Default));
Assert.Equal(-1, lastIndexOfItemIndexCountEQ(collection1256, 100, 3, 4, EqualityComparer<int>.Default));

// Create a list with contents: 100,101,102,103,104,100,101,102,103,104
ImmutableList<int> list = ImmutableList<int>.Empty.AddRange(Enumerable.Range(100, 5).Concat(Enumerable.Range(100, 5)));
List<int> bclList = list.ToList();
Expand Down
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