codegen: support enum query params

[hughsimpson]

Support for enum query params in codegen. I've gone for case-insensitive decoding here, but arguably case-sensitive would be the better option; it should be very easy to change or make configurable later on.

[hughsimpson]

I think the failure was due to an unrelated flaky test rather than an issue with the code. Would someone mind kicking the test?

[kciesielski]

Sure, tests kicked and now all pass. I'll do a review soon.

[kciesielski]

I managed to hack a working solution for Scala 3:

package sttp.tapir.generated

object TapirGeneratedEndpoints {

  import sttp.tapir._
  import sttp.tapir.model._
  import sttp.tapir.json.circe._
  import sttp.tapir.generic.auto._
  import io.circe.generic.auto._
  import scala.compiletime.{erasedValue, summonInline}
  import scala.deriving.Mirror
  import enumextensions.EnumMirror

  def enumMap[E: EnumMirror]: Map[String, E] =
    Map.from(                   
      for e <- EnumMirror[E].values yield e.name.toUpperCase -> e
    )

  def makeQueryCodecForEnum3[T: EnumMirror]: sttp.tapir.Codec[List[String], T, sttp.tapir.CodecFormat.TextPlain] =
    sttp.tapir.Codec
      .listHead[String, String, sttp.tapir.CodecFormat.TextPlain]
      .mapDecode(s =>
        // Case-insensitive mapping
        scala.util
          .Try(enumMap[T](using EnumMirror[T])(s.toUpperCase)) // TODO a nicer error on the stack trace instead of java.util.NoSuchElementException: key not found
          .fold(sttp.tapir.DecodeResult.Error(s, _), sttp.tapir.DecodeResult.Value(_))
      )(_.name)

  enum MyEnumKc derives org.latestbit.circe.adt.codec.JsonTaggedAdt.PureCodec, EnumMirror {
    case paperback, hardback
  }

  object MyEnumKc {
    given codecTapir: sttp.tapir.Codec[List[String], MyEnumKc, sttp.tapir.CodecFormat.TextPlain] =
      makeQueryCodecForEnum3[MyEnumKc]
  }

  import cats.effect.IO
  lazy val postQueryTest =
    endpoint.post
      .in(("queryTest"))
      .in(query[MyEnumKc]("test"))
      .out(statusCode(sttp.model.StatusCode.NoContent))
      .serverLogic[IO] { (test: MyEnumKc) =>
        // Some server logic
        IO.println(s"Received: $test").map(Right(_))

      }
        

  lazy val generatedEndpoints = List(postQueryTest)

}

It requires an additional dependency on "io.github.bishabosha" %% "enum-extensions" % "0.1.1", but I think it's a safe and stable library without risky transitive deps. Note that the enum needs a derives EnumMirror for this to work.

What do you think @hughsimpson?

[hughsimpson]

Nice! I was a bit uncomfortable about not having scala 3 support. Let's include that in this pr

[hughsimpson]

Pushed up. Shame we can't directly check the scala 3 support in the test 😪 but it looks right to me...

[kciesielski]

Thanks! I checked Scala 3 in my side project and it works, I also added a small improvement to the error message. Could you update the description to reflect Scala 3 support? Feel free to merge after that (if you have permissions, I'm not sure about that :)

[hughsimpson]

I don't have permissions to merge, sadly, and the test makes some rather bold assertions about the precise code generated for scala 3, so I think that will need updating anyway. End of my day now but I'll push up a fix first thing tomorrow morning

[hughsimpson]

Pushed a fix for the test; also updated the scala 2 decoding to provide the same nicer error message as for scala 3

[hughsimpson]

Thanks for your help with this, @kciesielski! I'm hoping to be able to open a pr with support for jsoniter later on today once I've tidied up a bit, and it builds off this branch (because it turns out that tracking which positions the models are used in is very useful for that 😄)

[kciesielski]

Thank you for these great contributions! Keep'em coming 😅