✨ Skip nullable parameters when doing GuardClauseAssertion

[zvirja]

Description

With the most recent Reflection API it's possible to retrieve nullability info about code. So we can use that nullability info in GuardClauseAssertion to not assert that nullable parameters must be null.

Example

#nullable enable

public class Sut
{
    public void Method(string arg1, string? arg2) { }
}

We can be smart about arg2 and skip null verification for it, as we know it can be null.

[Kralizek]

Would it also make sense/be possible for optional parameters?

[zvirja]

Wouldn't it be covered automatically? If optional parameter is nullable - we would skip it because it's nullable. If it's not nullable - well, then it should be guarded even if you supply the default value.

All of it makes sense ofc only if you have null guards at all and do not rely purely on compiler nullability checks 😉

[rvazqueziglesias]

I have just come across this topic right now as I was indeed trying to check the code and verify if there was some way of skipping null verification for these parameters.

The problem I saw is that Constructor.GetParameters(); in https://github.com/AutoFixture/AutoFixture/blob/master/Src/AutoFixture/Kernel/ConstructorMethod.cs doesn't return a type of Nullable < T> for reference types.
That works if you're dealing with value types (for example Guid) but doesn't work when dealing with reference types.
That being said, optional parameters can be potentially excluded by reading the properties HasDefaultValue and DefaultValue (and compare against null) that are returned for each parameter with the GetParameters() method

[aivascu]

I think the optional parameters change can go into the next version, however the nullable reference type change will have to go into v6 since only after .NET 6 the reflection API makes it possible to reliably detect these types.