The second foreach in each case should not produce a warning since the collection cannot be null after the first dereference.
[module: System.Runtime.CompilerServices.NonNullTypes]
class Enumerable
{
public System.Collections.IEnumerator GetEnumerator() => throw null;
}
class Program
{
static void F1(object[]? x)
{
foreach (var i in x) { } // warning: possibly null
foreach (var i in x) { } // ok
}
static void F2(Enumerable? y)
{
foreach (var i in y) { } // warning: possibly null
foreach (var i in y) { } // ok
}
}
The second
foreachin each case should not produce a warning since the collection cannot be null after the first dereference.