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Incorrect loop bound in SizeOptIListSelectIterator.ToList #137126
Description
Description
SizeOptIListSelectIterator<TSource, TResult>.ToList() checks the destination list’s Count immediately after constructing it with a capacity. Since Count is zero, the loop never executes and the override returns an empty list for a nonempty source.
Admittedly, this path is non-public and functionally dead, but it hides a ticking time bomb, so would be nice to fix for good hygiene (or remove altogether)
Reproduction Steps
With true
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
IEnumerable<int> query = new[] { 1, 2, 3 }.Select(x => x * 10);
MethodInfo method = query.GetType().GetMethod(
"ToList",
BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)
?? throw new InvalidOperationException("ToList override not found");
List<int> result = (List<int>)(method.Invoke(query, null)
?? throw new InvalidOperationException("ToList returned null"));
Console.WriteLine(query.GetType().Name);
Console.WriteLine($"Reflection: [{string.Join(", ", result)}]");
Console.WriteLine($"Public API: [{string.Join(", ", query.ToList())}]");Expected behavior
printing [10, 20, 30], matching enumeration of the query
Actual behavior
prints []
Regression?
The erroneous loop was included when this iterator was introduced in #118156
Known Workarounds
No workaround is needed
Configuration
Windows 10, x64
Reproduced on .NET 10, 11 rc3 and main
Other information
List<TResult> list = new List<TResult>(_source.Count);
for (int i = 0; i < list.Count; i++)
{
list.Add(_selector(_source[i]));
}
return list;The constructor initializes Capacity, not Count
Activity
dotnet-policy-service commentedon Nov 7, 2026
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