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Fix ArgumentOutOfRangeException when Concat called after Skip that skips more elements than exist #123295

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Merged
stephentoub merged 6 commits into from
Jan 20, 2026
Merged

Fix ArgumentOutOfRangeException when Concat called after Skip that skips more elements than exist #123295

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6799463
Initial plan
Copilot Jan 16, 2026
d87b1ef
Fix ArgumentOutOfRangeException when Concat called after Skip that sk…
Copilot Jan 17, 2026
290913b
Move bounds check inside span path and check sourceIndex against sour…
Copilot Jan 17, 2026
8157525
Move regression test to SkipTests.cs with multiple source types and o…
Copilot Jan 17, 2026
a907161
Add tests for Skip followed by Select, Where, Take, Distinct, OrderBy…
Copilot Jan 17, 2026
5d85ed8
Add Contains tests for Skip that skips more elements than exist
Copilot Jan 19, 2026
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6 changes: 5 additions & 1 deletion src/libraries/System.Linq/src/System/Linq/SkipTake.SpeedOpt.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -148,7 +148,11 @@ private static void Fill(IList<TSource> source, Span<TSource> destination, int s
{
if (source.TryGetSpan(out ReadOnlySpan<TSource> sourceSpan))
{
sourceSpan.Slice(sourceIndex, destination.Length).CopyTo(destination);
if (sourceIndex < sourceSpan.Length)
{
sourceSpan.Slice(sourceIndex, destination.Length).CopyTo(destination);
}

return;
}

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30 changes: 30 additions & 0 deletions src/libraries/System.Linq/tests/SkipTests.cs
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Expand Up @@ -388,5 +388,35 @@ public void DisposeSource(int sourceCount, int count)
Assert.False(iterator.MoveNext());
Assert.Equal(-1, state);
}

[Fact]
public void SkipMoreThanCountFollowedByOperators()
{
int[] items = [2, 3];

foreach (IEnumerable<int> source in CreateSources([1]))
{
Assert.Equal(items, source.Skip(2).Concat(items).ToArray());
Assert.Equal(items, source.Skip(2).Concat(items).ToList());
Assert.Equal(items, source.Skip(2).Append(2).Append(3).ToArray());
Assert.Equal(items, source.Skip(2).Append(2).Append(3).ToList());
Assert.Equal(items, items.Concat(source.Skip(2)).ToArray());
Assert.Equal(items, items.Concat(source.Skip(2)).ToList());
Assert.Empty(source.Skip(2).Select(x => x * 2).ToArray());
Assert.Empty(source.Skip(2).Select(x => x * 2).ToList());
Assert.Empty(source.Skip(2).Where(x => x > 0).ToArray());
Assert.Empty(source.Skip(2).Where(x => x > 0).ToList());
Assert.Empty(source.Skip(2).Take(10).ToArray());
Assert.Empty(source.Skip(2).Take(10).ToList());
Assert.Empty(source.Skip(2).Skip(1).ToArray());
Assert.Empty(source.Skip(2).Skip(1).ToList());
Assert.Empty(source.Skip(2).Distinct().ToArray());
Assert.Empty(source.Skip(2).Distinct().ToList());
Assert.Empty(source.Skip(2).OrderBy(x => x).ToArray());
Assert.Empty(source.Skip(2).OrderBy(x => x).ToList());
Assert.False(source.Skip(2).Contains(1));
Assert.False(source.Skip(2).Contains(2));
}
}
}
}