CS0809 should mention that the ObsoleteAttribute will not work if applied to an overidden member only

[rhys-vdw]

Type of issue

Missing information

Description

Seems that the following will not trigger an obsolete warning.

class A {
  public virtual void Foo() {}
}

class B : A {
  [Obsolete("doesn't work")]
  public override void Foo() {}
}

static class C {
  public static void Test() {
    B b = new();
    b.Foo(); // <-- no warning raised
  }
}

The current docs say:

Typically, a member that is marked as obsolete should not override a member that is not marked as obsolete.

Which suggests this is a code smell or unidiomatic. More relevant (imo) is that the attribute will be ignored by compiler.

In this case I visited the info page to find out whether it would actually be a problem to ignore the warning. I don't fully understand the reasons why it's ignored, but I feel an explanation here would be helpful.

Thanks!

Page URL

https://learn.microsoft.com/en-us/dotnet/csharp/misc/cs0809

Content source URL

https://github.com/dotnet/docs/blob/main/docs/csharp/misc/cs0809.md

Document Version Independent Id

d83911ea-0426-fc82-622a-3c607d7b787a

Article author

@BillWagner

Metadata

• ID: 315af9fc-a5f1-9a51-a154-a7c703975a91
• Service: dotnet-csharp
• Sub-service: errors-warnings

[BillWagner]

I've added this to our backlog, and I've added the "help wanted" label. We should mention this. It's because the declaration is in the base class, not the derived class.

[BartoszKlonowski]

@BillWagner I will work on this!

[BillWagner]

Hi @BartoszKlonowski

I've assigned it to you.