Add support for Scala 3 enum derivation

[nb-ceffa]

Would it be possible to support derivation of Scala 3 enums, please?

I would love to use something like this:

enum MyTestEnum derives Read {
  case MyFirstCase extends MyTestEnum
  case MySecondCase extends MyTestEnum
}

Version 1.0.0-RC7 returns the following error:

-- [E172] Type Error: ----------------------------------------------------------
1 |enum MyTestEnum derives Read {
  |                        ^
  |Cannot derive Read instance. Please check that each field in the case class has a Read instance or can derive one.
  |I found:
  |
  |    doobie.implicits.derived[MyTestEnum, A](
  |      /* missing */summon[scala.deriving.Mirror.ProductOf[MyTestEnum]], ???, ???,
  |      ???)
  |
  |But Failed to synthesize an instance of type scala.deriving.Mirror.ProductOf[MyTestEnum]: class MyTestEnum is not a generic product because it is not a case class.

[jatcwang]

I don't think it's possible to provide a derivation strategy that's generally correct. Even in the simple example you provided, how will we know what's the target column type suppose to be?

For "enum" use cases, I recommend creating the Put/Get instance by hand.

Perhaps something like this:

given Put[MyTestEnum] = Put.deriveEnumString

I think it'll need to be macro based though - need to make sure all cases are case objects. Design / PRs welcome!

[drewfeelsblue]

hi, @jatcwang

I made an attempt - PR for addressing the issue was created. Could you pls take a look?