Consider the following annotation:
// ok to have more meta
@field
@param
@compileTimeOnly("Only for code generation")
case class Annot(value: String) extends ConstantAnnotation
Now three uses:
case class A(x: Int, @Annot("z") y: String)
object A:
def f1(x: Int, y: String @Annot("z")): A = ???
def f2(x: Int, @Annot("z") y: String): A = ???
I would like to use Scala 3 macros to find each of these annotations.
Symbol.caseFields
gives me the list of parameters, and on each of those parameters (of type Symbol
), method annotations
gives me what I am looking for.ValDef
. If param.tpt.tpe
matches AnnotatedType(tpe, t)
then t
is the annotation that I am looking for.Any idea how I can get the annotations that are given to an argument in a method? When I print terms/symbols/trees/... I cannot even see "z" in this case.
You can write in a macro
import scala.annotation.experimental
import scala.quoted.*
inline def printAnnotations[A]: Unit = ${printAnnotationsImpl[A]}
@experimental // because .typeRef is @experimental
def printAnnotationsImpl[A](using Quotes, Type[A]): Expr[Unit] = {
import quotes.reflect.*
val symbol = TypeTree.of[A].symbol
println(symbol.caseFields.map(_.annotations)) // Case Class
val companion = symbol.companionModule
val methods = companion.declaredMethods
// Annotated method argument
println(methods.map(_.paramSymss.map(_.map(_.annotations))))
// Annotated Type
println(methods.collect(method => companion.typeRef.memberType(method) match {
case lt: LambdaType => lt.paramTypes.collect {
case at: AnnotatedType => at.annotation
}
}))
'{()}
}
Then for
case class A(x: Int, @Annot("z1") y: String)
object A:
def f1(x: Int, y: String @Annot("z2")): A = ???
def f2(x: Int, @Annot("z3") y: String): A = ???
printAnnotations[A]
will print
List(List(), List(Apply(Select(New(Ident(Annot)),<init>),List(Literal(Constant(z1))))))
List(List(List(List(), List())), List(List(List())), List(), List(List(List(), List())), List(List(List(), List(Apply(Select(New(Ident(Annot)),<init>),List(Literal(Constant(z3))))))), List(List()), List(List(List())))
List(List(), List(), List(Apply(Select(New(Ident(Annot)),<init>),List(Literal(Constant(z2))))), List(), List(), List())
Scala 3.1.3