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Merged
ViveliDuCh merged 5 commits into from
Feb 24, 2026
Merged

Use Requires.Range in LastIndexOf #124560

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b1ee226
Use Requires.Range in LastIndexOf
prozolic Feb 18, 2026
35b481e
Fix test case in FindLastIndexTest
prozolic Feb 18, 2026
8cd336b
Fix test case to also validate the parameter name
prozolic Feb 19, 2026
9d6ef8f
Use nameof(count) in FindLastIndex range check
prozolic Feb 21, 2026
901ee2d
Rename LastIndexOf index param to startIndex
prozolic Feb 21, 2026
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20 changes: 10 additions & 10 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 @@ -791,36 +791,36 @@ internal int IndexOf(T item, int index, int count, IEqualityComparer<T>? equalit
/// The object to locate in the <see cref="ImmutableList{T}"/>. The value
/// can be null for reference types.
/// </param>
/// <param name="index">The zero-based starting index of the backward search.</param>
/// <param name="startIndex">The zero-based starting index of the backward search.</param>
/// <param name="count">The number of elements in the section to search.</param>
/// <param name="equalityComparer">The equality comparer to use for testing the match of two elements.</param>
/// <returns>
/// The zero-based index of the last occurrence of <paramref name="item"/> within the range of elements
/// in the <see cref="ImmutableList{T}"/> that contains <paramref name="count"/> number of elements
/// and ends at <paramref name="index"/>, if found; otherwise, -1.
/// and ends at <paramref name="startIndex"/>, if found; otherwise, -1.
/// </returns>
internal int LastIndexOf(T item, int index, int count, IEqualityComparer<T>? equalityComparer)
internal int LastIndexOf(T item, int startIndex, int count, IEqualityComparer<T>? equalityComparer)
{
if (index == 0 && count == 0)
if (startIndex == 0 && count == 0)
{
return -1;
}

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

equalityComparer ??= EqualityComparer<T>.Default;
using (var enumerator = new Enumerator(this, startIndex: index, count: count, reversed: true))
using (var enumerator = new Enumerator(this, startIndex: startIndex, count: count, reversed: true))
{
while (enumerator.MoveNext())
{
if (equalityComparer.Equals(item, enumerator.Current))
{
return index;
return startIndex;
}

index--;
startIndex--;
}
}

Expand Down Expand Up @@ -1246,7 +1246,7 @@ internal int FindLastIndex(int startIndex, int count, Predicate<T> match)

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

using (var enumerator = new Enumerator(this, startIndex: startIndex, count: count, reversed: true))
{
Expand Down
13 changes: 8 additions & 5 deletions src/libraries/System.Collections.Immutable/tests/ImmutableListTestBase.cs
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Expand Up @@ -177,14 +177,17 @@ public void FindLastIndexTest()
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));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(singleElementList).FindLastIndex(1, n => n == 10));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(singleElementList).FindLastIndex(1, 1, n => n == 10));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => this.GetListQuery(singleElementList).FindLastIndex(0, 2, 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));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(4, n => n == 1));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => this.GetListQuery(multipleElementList).FindLastIndex(2, 4, n => n == 1));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(4, 1, n => n == 1));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(4, 4, n => n == 1));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => this.GetListQuery(multipleElementList).FindLastIndex(3, 5, 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)));
Expand Down
29 changes: 15 additions & 14 deletions src/libraries/System.Collections.Immutable/tests/IndexOfTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,20 +91,21 @@ public static void LastIndexOfTest<TCollection>(
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));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, new CustomComparer(50)));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, new CustomComparer(50)));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, new CustomComparer(50)));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, new CustomComparer(50)));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, new CustomComparer(1)));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, new CustomComparer(1)));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndex(collection1256, 2, 5));
AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => lastIndexOfItemIndexCountEQ(collection1256, 6, 2, 4, EqualityComparer<int>.Default));
AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => lastIndexOfItemIndexCountEQ(collection1256, 6, 4, 4, EqualityComparer<int>.Default));

Assert.Equal(-1, lastIndexOfItem(emptyCollection, 5));
Assert.Equal(-1, lastIndexOfItemEQ(emptyCollection, 5, EqualityComparer<int>.Default));
Expand Down
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