Possible Compiler Bug RE constraints

[TonyValenti]

The code below seems to me that it should compile but it does not.
Here's what seems wonky:
MyBase specifies a constraint on Parse
MyClass implements the Parse function
You get a compiler error saying you can't specify constraints (other than class or struct) if you uncomment where T : DisplayRecord
You get a compiler errors if no constraints are specified on MyClass's Parse.
The code only compiles if you specify where T : class on MyClass but this seems as though it shouldn't be necessary because T : DisplayRecord and DisplayRecord : record and record : class.

Thoughts?

#nullable enable

using System;

namespace ConsoleApp1
{
    
    public class MyClass : MyBase
    {
        public override T? Parse<T>(string Text)
            //where T : DisplayRecord
            //where T: class

        {
            return base.Parse<T>(Text);
        }
    }

    public abstract class MyBase
    {
        public virtual T? Parse<T>(string Text) 
            where T : DisplayRecord
        {
            throw new NotImplementedException();
        }
    }

    public record DisplayRecord
    {

    }

}

[HaloFour]

Are you suggesting that this is a bug in the specification, or a bug in the compiler? If it's the latter it should probably be reported to the Roslyn repo.

[TonyValenti]

@HaloFour - I'm not sure but it seems to me the above should compile without needing to specify ````T : class```.
I'll reopen in Roslyn.

[jnm2]

I believe you're missing where T : default. Overrides require it when T? is used in the signature of the base method and T is not constrained to a class or struct. https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters#default-constraint

[svick]

@jnm2 This code doesn't compile with where T : default. It requires where T : class, because the base method is already constrained to a class.