List<T>.AddRange with erroneous input has inconsistent behavior #76116
Description
Description
Out of curiosity I experimented with the List<T>.AddRange method, by passing as argument a custom ICollection<T> implementation with maximum Count and no-op CopyTo. The behavior changes depending on the existing size of the list, and may result in a negative List<T>.Count value.
Reproduction Steps
Here is my custom ICollection<T>:
class MyCollection<T> : ICollection<T>
{
public int Count => Int32.MaxValue;
public void CopyTo(T[] array, int arrayIndex) { } // Do nothing
public bool IsReadOnly => throw new NotImplementedException();
public void Add(T item) => throw new NotImplementedException();
public bool Remove(T item) => throw new NotImplementedException();
public void Clear() => throw new NotImplementedException();
public bool Contains(T item) => throw new NotImplementedException();
public IEnumerator<T> GetEnumerator() => throw new NotImplementedException();
IEnumerator IEnumerable.GetEnumerator() => throw new NotImplementedException();
}Passing an instance to List<T>.AddRange I expected to get an exception of some kind, which is indeed what happens:
new List<int>().AddRange(new MyCollection<int>());Output:
System.OutOfMemoryException: Array dimensions exceeded supported range.
at System.Collections.Generic.List`1.set_Capacity(Int32 value)
at System.Collections.Generic.List`1.Grow(Int32 capacity)
at System.Collections.Generic.List`1.InsertRange(Int32 index, IEnumerable`1 collection)
at System.Collections.Generic.List`1.AddRange(IEnumerable`1 collection)
at Program.Main(String[] args) in C:\Projects\Console1\Program.cs:line 9
But if the list is not empty before the AddRange, then there is no exception:
List<int> list = new();
list.Add(1);
list.AddRange(new MyCollection<int>());
Console.WriteLine($"list.Count: {list.Count}, list.Capacity: {list.Capacity}");Output:
list.Count: -2147483648, list.Capacity: 8
Configuration
- .NET 6.0
- Console application
- 64-bit operating system, x64-based processor
This is not a realistic scenario, since the MyCollection<T> is not correctly implemented, but nevertheless I thought I should report it.