Emit nullable ref annotated code

[AArnott]

When the project langversion is >= 8, could you also put #nullable enable or at least #nullable annotations in the file or around the parameter declaration and use SafeHandle? as the parameter type so that IntelliSense shows me that nulls are anticipated?

Originally posted by @jnm2 in #129 (comment)

If we annotate at all, we need to be consistent so users can trust that a parameter is required when we don't annotate it. The metadata has many [Optional] annotations on its inputs to help with this, but I don't know how consistently it is applied.

[jnm2]

The metadata has many [Optional] annotations on its inputs to help with this, but I don't know how consistently it is applied.

One place where [Optional] is currently missing is on SafeHandle parameters.

[JeremyKuhne]

This would be nice to have as a consuming library that has nullable enabled.

[AArnott]

@JeremyKuhne, as nullable refs only apply for reference types, how often do you expect to be passing reference types into interop? Can you give a few examples of APIs that you use where a null ref is allowed and you'd like to see that expressed?

[JeremyKuhne]

@AArnott Not looking for this for the [DllImport]s themselves, looking for the wrappers you generate. Most notably for us this comes up with string. CreateWindowEx is an example where there are optional LPCWSTR parameters.

[AArnott]

We ought to be able to do that. CreateWindowEx's parameter is annotated as optional in the metadata.

[rampaa]

Can you give a few examples of APIs that you use where a null ref is allowed and you'd like to see that expressed?

FindWindowW

Considering migrating my app from LibraryImport to CsWin32 but not having the nullability annotations feels like a step down.