Sligthly better anonymous givens names

[Lasering]

The following:

object Connector:
  enum Type:
    case CHAdeMO, Mennekes

object Parking:
  enum Type:
    case AlongMotorway, OnStreet

trait Decoder[T]

given Decoder[Connector.Type] = new Decoder[Connector.Type] {}
given Decoder[Parking.Type] = new Decoder[Parking.Type] {}

Fails with:

Double definition:
final lazy given val given_Decoder_Type:
  Playground.Decoder[Playground.Connector.Type] in object Playground at line 13 and
final lazy given val given_Decoder_Type:
  Playground.Decoder[Playground.Parking.Type] in object Playground at line 14

Scastie link

Which is as expected reading the documentation Anonymous Given Instances. Namely the point 2:

2. the simple name(s) of the implemented type(s), leaving out any prefixes

However this could be improved. If the user declared the given with a prefix, then use that prefix to generate the anonymous given name. So in this case the generated names would be: given_Decoder_Connector_Type and given_Decoder_Parking_Type

[sjrd]

We cannot change the generated names in a compatible way. So I'm afraid we're stuck with the current spec.

[Lasering]

It was worth a shot.

[som-snytt]

#18034

#15316

where it's recommended to just name them. I proposed auto-suggesting a unique name, as when registering for a web site with a user name or generating a password.

Alternatively, disambiguate during incremental compilation only, with the expectation that the final edit will be unambiguous. It would warn until then.