Use nint for native-sized integers in Marshal

[xtqqczze]

• Fix CA2020: Prevent behavioral change

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[AaronRobinsonMSFT]

Should we also update the ref assembly definitions?

[jkotas]

Should we also update the ref assembly definitions?

Ref assembly sources are auto-formatted. I would do any reformatting of ref assemblies in dedicated PRs.

[xtqqczze]

Related: dotnet/dotnet-api-docs#11652

[agocke]

I’m out of the loop a little here: why is this change necessary? Just noting that this looks strange:

public static nint ReadIntPtr(object ptr, int ofs)

[tannergooding]

It is no more strange than static int ReadInt32(object ptr, int ofs)

APIs use the framework type name such as Int32 or IntPtr. Code style is then to prefer the language keyword such as int or nint.

There is no semantic difference (on modern .NET) between IntPtr vs nint and the IDE, IntelliSense, docs, and most other places default to using the language keyword. There is only the historical difference in that some people used IntPtr to represent handles or pointers, rather than using a more correct type (like safe handle or void*).

[jkotas]

It is both about code style and clarify about unsafe code boundaries.

Historically, IntPtr has been used to represent both integers and unmanaged pointers. We want to change the places where it is used as an integer to nint, and the places where it is as used as a pointer to use unmanaged pointer. The later one is much more common under libraries in this repo. We have approved API overloads to help with this transition: #75630.

There are situations where the meaning is ambiguous. It can be either number or pointer. I think it makes sense to go with nint in ambiguous cases like ReadIntPtr.

And there are situations where IntPtr represents pointer, but we cannot change it to be actual pointer since it is part of public API. We can keep them as IntPtr in the source to make it clear that it is legacy baggage, or we can change them to nint for more consistent (but also somewhat more confusing) style. I do not have a strong opinion. It is relatively few places in the grand scheme of things.