Give a constructorless type a private/internal constructor

[dsyme]

Transferring dotnet/fsharp#8093

Shouldn't a constructorless type have a private/internal constructor in IL?

Looking at these two types in sharplab https://sharplab.io/#v2:DYLgZgzgNAJiDUAfALgTwA4FMAEAxA9vgIzYC8AsAFDY3YTICGyAlgMbYC2mHARpgE7ZmMbAA8yYqlTRY8hAEzZ0/ZgDcmOABQBKMlVp1GLdl14ChI8aTFA=

type Foo1 =
    static member id x = x

type Foo2 private () =
    static member id x = x

Foo1 can't be constructed in F# similar to Foo2 but only Foo2 has an internal constructor in IL, leaving Foo1 to be constructed from C# without issue, is this by design?

[abelbraaksma]

is this by design?

Since it'll be relevant to this discussion, let me answer that last question (copied from dotnet/fsharp#8093 (comment)):

Do note that the F# Spec specifically says that if the default constructors are omitted that default constructors are not created. So technically this seems to me to be a change to the spec.

If I understand the issue at hand correctly, the absence of a default ctor allows C# to create an instance. But adding a default (private) ctor, while fixing the C# issue, will allow creating instances in F#, wouldn't it (though only in private scope)?

It seems perhaps more reasonable that if there's no constructor at all that we mark it AbstractClass? We might even warn and/or disallow creating instance methods, as there's no way to call them, not even through inheritance.