Unable to invoke a varargs method with non-one number of arguments in reflect api

[rayrobdod]

Compiler version

3.3.1, 3.4.0-RC1-bin-20231027-c0eae68-NIGHTLY

Minimized code

import scala.quoted.*

object Macro {
  def template(args:List[Expr[Int]])(using Quotes):Expr[List[Int]] = {
    import quotes.reflect.*
    val listObjectTerm = '{ List }.asTerm
    Apply(
      TypeApply(
        Select.unique(listObjectTerm, "apply"),
        List(TypeTree.of[Int])
      ),
      args.map(_.asTerm)
    ).asExprOf[List[Int]]
  }

  inline def apply_0 = ${Macro.impl_0}
  def impl_0(using quotes:Quotes):Expr[List[Int]] =
    Macro.template(List.empty)

  inline def apply_1 = ${Macro.impl_1}
  def impl_1(using quotes:Quotes):Expr[List[Int]] =
    Macro.template(List(Expr(1)))

  inline def apply_2 = ${Macro.impl_2}
  def impl_2(using quotes:Quotes):Expr[List[Int]] =
    Macro.template(List(Expr(1), Expr(2)))

  inline def repeated = ${Macro.repeatedImpl}
  def repeatedImpl(using Quotes):Expr[List[Int]] = {
    import quotes.reflect.*
    val args = List(Expr(1), Expr(2))
    val listObjectTerm = '{ List }.asTerm
    Apply(
      TypeApply(
        Select.unique(listObjectTerm, "apply"),
        List(TypeTree.of[Int])
      ),
      List(Repeated(args.map(_.asTerm), TypeTree.of[Int]))
    ).asExprOf[List[Int]]
  }
}

Macro.apply_0
Macro.apply_1
Macro.apply_2
Macro.repeated

Output

scala> Macro.apply_0
-- Error: ----------------------------------------------------------------------
1 |Macro.apply_0
  |^^^^^^^^^^^^^
  |wrong number of arguments at pickler for (elems: Int*): List[Int]: (elems: Int*): List[Int], expected: 1, found: 0
1 error found

scala> Macro.apply_1
val res0: List[Int] = List(1)

scala> Macro.apply_2
-- Error: ----------------------------------------------------------------------
1 |Macro.apply_2
  |^^^^^^^^^^^^^
  |wrong number of arguments at pickler for (elems: Int*): List[Int]: (elems: Int*): List[Int], expected: 1, found: 2
1 error found

scala> Macro.repeated
-- [E007] Type Mismatch Error: -------------------------------------------------
1 |Macro.repeated
  |^^^^^^^^^^^^^^
  |Found:    Seq[Int]
  |Required: Int
  |
  | longer explanation available when compiling with `-explain`
1 error found

Expectation

The three apply_x calls should all succeed, producing List(), List(1) and List(1, 2) respectively

Alternatively, the three apply_x call should all be compile errors, and the repeated call should succeed, producing List(1, 2)

[nicolasstucki]

This is a bug in the user code. It is not an obvious one. We will need to add documentation to the Repeated explaining this.

The Repeated needs to have a type ascription <repeated>[T] which can be written as follows.

-  Repeated(args.map(_.asTerm), TypeTree.of[Int])
+ Typed(
+   Repeated(args.map(_.asTerm), TypeTree.of[Int]),
+   Inferred(defn.RepeatedParamClass.typeRef.appliedTo(TypeRepr.of[Int]))