autoGiven.scala

autoGiven.scala

import scala.annotation.MacroAnnotation
import scala.quoted.*

class autoGiven extends MacroAnnotation {
  final def transform(using Quotes)(tree: quotes.reflect.Definition): List[quotes.reflect.Definition] = {
    import quotes.reflect.*

    tree match {
      case ValDef(name, tpt, Some(rhs)) => rhs.asExpr match {
        case '{ $rhsExpr: t } =>
          val treeSym = tree.symbol
          val givenSym = Symbol.newVal(treeSym.owner, name ++ "Given", TypeRepr.of[t], Flags.Given | treeSym.flags, Symbol.noSymbol)
          val givenVal = ValDef(givenSym, Some(Ref(treeSym)))

          List(tree, givenVal)

        case _ =>
          report.error("Annotation only supported on `val`")
          List(tree)
      }

      case _ =>
        report.error("Annotation only supported on `val`")
        List(tree)
    }
  }
}