Unsafe.NullRef<T> and IsNullRef<T> are missing from the public APIs

[Sergio0694]

Summary

There are two new Unsafe APIs that have been added to CoreCLR recently: Unsafe.NullRef<T> and Unsafe.IsNullRef<T>, but they're not publicly available (tested this both on just .NET 5 Preview 6, and from the System.Runtime.CompilerServices.Unsafe packages, latest version as well). The comments say this file should be kept in sync with the public Unsafe.il file with the APIs that are available outside of CoreCLR, but these two are currently missing. Is this just an oversight or was it on purpose?

These are the two APIs in question:

runtime/src/libraries/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/Unsafe.cs

Lines 377 to 390 in 4fb2a68

	/// <summary>
	/// Returns a by-ref to type <typeparamref name="T"/> that is a null reference.
	/// </summary>
	[Intrinsic]
	[NonVersionable]
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public static ref T NullRef<T>()
	{
	return ref Unsafe.AsRef<T>(null);
	// ldc.i4.0
	// conv.u
	// ret
	}

runtime/src/libraries/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/Unsafe.cs

Lines 392 to 410 in 4fb2a68

	/// <summary>
	/// Returns if a given by-ref to type <typeparamref name="T"/> is a null reference.
	/// </summary>
	/// <remarks>
	/// This check is conceptually similar to "(void*)(&amp;source) == nullptr".
	/// </remarks>
	[Intrinsic]
	[NonVersionable]
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public static bool IsNullRef<T>(ref T source)
	{
	return Unsafe.AsPointer(ref source) == null;
	// ldarg.0
	// ldc.i4.0
	// conv.u
	// ceq
	// ret
	}

They'd extremely useful to have, especially because working around them is quite verbose (in particular IsNullRef), and most importantly because it forces you to have an unsafe block, since you have to go through a pointer to implement these two.

Having these two publicly available would be super handy! 😄

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[stephentoub]

The implementation in corelib is for internal use only in corelib. It's often augmented first, as it doesn't have the same bar as for public API. Exposing these publicly is tracked by #31170. Thanks.

[Sergio0694]

Oof, my bad, completely missed that duplicate issue. Thanks! 😊

[stephentoub]

No worries :)

[jkotas]

API proposal #31170 was approved. @Sergio0694 Are you interested in submitting PR with the implementation?

[Sergio0694]

@jkotas Absolutely, I'd be happy to! 😊

EDIT: see #40008.