Just to be clear, the warning itself has nothing to do with doesNotUnderstand. It is what happens in general when you call a method and the argument name is not found.

But it seems like a very good idea, and very useful to have.

Perhaps it is possible to have a special case in the case no selector is found, and call another method, doesNotUnderstandWithKeys. By default, doesNotUnderstandWithKeys would then call doesNotUnderstand, with the arguments – this is important, because a lot of code depends on it.

Object {

    doesNotUnderstandWithKeys { |selector, argNamePairs|
          ^this.doesNotUnderstand(selector, argNamePairs[1,3..])
    }
}

That method doesNotUnderstandWithKeys then can be re-routed, e.g. in the case of IdentityDictionary to do something reasonable, just like doesNotUnderstand.

I've thought about this some more and the conversation over on scsynth was useful to, although the recommendation there was that this was a bad idea!

I think the interface would have to be...

Object{
   doesNotUnderstandWithKeys {|selector, argsArray, namedArgsArray|
      ^this.doesNotUnderstand(selector, *argsArray) // as a default
   }
}

This way, on the stack you can push the receiver and selector, followed by two new arrays containing all the args.
I've read some of the documentation on writing primitives and could probably give this ago at some point... but I'm a little busy right now, so might have to wait.

As I understand it...

This line in cpp doesNotUnderstandWithKeys needs to be updated to call the new sc method, along with registering it in the global.

https://github.com/supercollider/supercollider/blob/ef627ce2c564fe323125234e4374c9c4b0fc7f1d/lang/LangSource/PyrMessage.cpp#L724C1-L725C1

Then the new stuff needs to be pushed on the stack. I don't know if this should overwrite the old stuff?

In that function there is a large number of nested ifs ... I don't know what they do, but at the end it calls blockValueWithKeys. I think this is like exectueWithKeys, but on primitives?

The final line of this function would then just call cpp executeMethod.

This line in cpp doesNotUnderstandWithKeys needs to be updated to call the new sc method, along with registering it in the global.

https://github.com/supercollider/supercollider/blob/ef627ce2c564fe323125234e4374c9c4b0fc7f1d/lang/LangSource/PyrMessage.cpp#L724C1-L725C1

This is the optimisation for the uniqueMethod interface (i.e. when you have used addUniqueMethod(...), this is how it gets called.

You really should just need doesNotUnderstandWithKeys, but I am not sure how to get sclang to actually call it. For introspection, I have tried to add this to Object:

doesNotUnderstandWithKeys { arg selector ... args;
		^args
	}

But it isn't called by, e.g. nil.pinguin(x: 8).

So maybe someone who has a bit more knowledge about this part of the engine could chime in?

Fixed by #6227