The interop marshaller should recognize the 'IsReadOnly' attribute

[tannergooding]

The C# language is gaining support for ref readonly parameters (dotnet/roslyn#19713 and dotnet/csharplang#38).

Today the marshaller will treat ref as [In, Out] unless explicitly marked as just [In]. That is, by default, it will both initialize with the managed state and then copy back any changes to the instance on return. While, when explicitly marked with just the [In] attribute, it will only initialize with the managed state and will not copy back any changes on return.

Without modification, the marshaller will also treat ref readonly in the same way ([In, Out]). As such, the marshaller should be updated to handle and recognize ref readonly parameters as [In].

[tannergooding]

FYI. @VSadov, @jaredpar

[yizhang82]

@tannergooding Thanks for logging the issue. Let's take the discussion there on the csharplang issue (which I've commented).

[tannergooding]

Closing this. C# 7.3 is going to ensure the attribute is added.

FYI. @OmarTawfik