Enumeration should derive `CanEqual`

When using an enumeration, we expect pattern matching on the objects to work by default even under strictEquality.

Compiler version

v3.1.0-RC1

Minimized code

import scala.language.strictEquality
enum FooBar:
  case Foo, Bar

def check(fb : FooBar): Unit =
  fb match
    case FooBar.Foo =>
    case FooBar.Bar =>

Output

Values of types FooBar and FooBar cannot be compared with == or !=
Values of types FooBar and FooBar cannot be compared with == or !=

Expectation

No error.

[soronpo]

Paraphrasing @smarter It would potentially be problematic if you define custom equals for your enum, and then that case should probably not derive CanEqual

IMO, if you define an enum you want to do basic patten matching. If not, then you don’t want an enum.

[Lasering]

Somewhat related enums whose cases are singletons should also derive Ordering with this implementation:

given Ordering[T] = Ordering.by(_.ordinal)

Alternatively add the above code to the SingletonEnumCompanion in the https://github.com/lampepfl/dotty/pull/14136 PR