Version Used: 15.6 Preview 2

Steps to Reproduce:

1. Add a reference to System.Collections.Immutable

2. Add the following code:

   var array = ImmutableArray.CreateRange(Enumerable.Range(0, 1), x => x);

3. Navigate to ImmutableArray.CreateRange

Expected Behavior:

1. The signature of CreateRange is the following:

   public static ImmutableArray<TResult> CreateRange<TSource, TResult>(ImmutableArray<TSource> items, Func<TSource, TResult> selector)

2. The decompiled method body does not have comments regarding invalid IL

3. The use of selector is proper C# code

Actual Behavior:

1. The signature of CreateRange is incorrect. Specifically, the generic arguments for the type of selector are omitted:

   public static ImmutableArray<TResult> CreateRange<TSource, TResult>(ImmutableArray<TSource> items, Func selector)

2. The decompiled method body has comments regarding invalid IL:

   //IL_0000: Unknown result type (might be due to invalid IL)
   //IL_0029: Unknown result type (might be due to invalid IL)
   //IL_0032: Expected Ref, but got Unknown

3. When selector is used to assign values to array[i], the types and syntax are incorrect (both (?) and (!0) are incorrect):

   array[i] = (TResult)((Func)(?)selector).Invoke((!0)items[i]);

📝 For reference, here is the complete decompiled method:

public static ImmutableArray<TResult> CreateRange<TSource, TResult>(ImmutableArray<TSource> items, Func selector)
{
	//IL_0000: Unknown result type (might be due to invalid IL)
	//IL_0029: Unknown result type (might be due to invalid IL)
	//IL_0032: Expected Ref, but got Unknown
	Requires.NotNull<Func>(selector, "selector");
	int length = items.Length;
	if (length == 0)
	{
		return ImmutableArray.Create<TResult>();
	}
	TResult[] array = new TResult[length];
	for (int i = 0; i < array.Length; i++)
	{
		array[i] = (TResult)((Func)(?)selector).Invoke((!0)items[i]);
	}
	return new ImmutableArray<TResult>(array);
}