C# 7.2 in ValueType parameters are not supported with .NET Standard / Core

[stakx]

See this discussion over at DynamicProxy's repo: castleproject/Core#339 (comment).

What needs to be done to add C# 7.2 reference semantics support in Moq for value types is this:

• Upgrade Castle.Core package dependency to vNext once it's available (see Release 4.3.0 castleproject/Core#354).
• Add .NET Standard 2.0 as a target framework. Not required, see below.
• Possibly update delegate generator logic, as per C# 7.2 in ValueType parameters are not supported with .NET Standard / Core #605 (comment). Not required, see below.
• Check whether DynamicInvoke e.g. for Callback and Returns is already lenient enough given differences in delegate signatures (presence of in parameter modifier), as per C# 7.2 in ValueType parameters are not supported with .NET Standard / Core #605 (comment)

[zvirja]

BTW, just noticed that probably you and NSubstitute should also update our delegate generators. We don't copy the required modifiers as well, so in theory if you have delegate with in ValueType, it will fail.

[stakx]

@zvirja - Thanks a lot for that hint! True, this needs to be tested as well.

Another thing that comes to mind (which may or may not be relevant to NSubstitute) is that Moq does a lot of DynamicInvoke-ing on delegates, e.g. when you configure a Callback or Returns callback for a method call setup. Not sure at this point whether DynamicInvoke is flexible enough to glance over small differences in the delegate signatures, i.e. when the method being set up has an in parameter but the configured callback doesn't have the in modifier on the parameter. Will need to be tested, too.

Adding these two points to the list above.

[stakx]

Add .NET Standard 2.0 as a target framework. As it turns out, it appears that Moq doesn't need to add an additional TFM. The upgrade of Castle.Core to version 4.3.0 should be enough. If user code targets a platform that supports .NET Standard 1.5 (or newer), then the .NET Standard 1.5 version of Castle.Core will be selected even though Moq (which sits between Castle.Core and the targeted platform) only has a .NET Standard 1.3 assembly.

Possibly update delegate generator logic. Added some tests to verify delegate mocking works in the presence of in parameters. It seems for once, System.Reflection.Emit just does what it's supposed to.

Check whether DynamicInvoke e.g. for Callback and Returns is already lenient enough given differences in delegate signatures. Ran some quick successful tests; given that DynamicInvoke already worked with differences in ref / no-ref, perhaps it's not too surprising that in appears to be supported just fine, too.