Dotty: Wrong overload resolution when expanding macro call

[biboudis]

minimized code

Macro definition:

import scala.quoted._

object Macros {

  inline def m[R](sym: Symantics[R]) : R = ${  mImpl[R]('{sym}) }

  def mImpl[R: Type](sym: Expr[Symantics[R]]) given (qctx: QuoteContext): Expr[R] =  '{
    $sym.Meth(42)
  }
}

trait Symantics[R]  {
  def Meth(exp: Int): R
  def Meth(): R
}

Use:

import scala.quoted._
import Macros._

object Test {
  def main(args: Array[String]): Unit = {

    val sym = new Symantics[Int] {
      def Meth(exp: Int): Int = exp
      def Meth(): Int = 42
    }

    val test = m[Int](sym)
  }
}

expectation

Overloading should work. Instead it reports:

8 |    $sym.Meth(42)
  |    ^^^^^^^^^^^^
  |    wrong number of arguments at <no phase> for (): Int: ((): Int)(sym.Meth), expected: 0, found: 1
  | This location is in code that was inlined at Test_2.scala:13

If I remove the macro call it works (TASTy problem), if the Symantics is not parametric it also works. I don't think that it directly related to #7022 but it is definitely in the same area (@smarter WDYT?). BTW, the <no phase> in the error is also a bug I assume.

[nicolasstucki]

It looks like the issue is starts at this line.

        val d = qualType.findMember(name, pre).atSignature(sig)

where qualType and pre are TermRef(NoPrefix,val sym) which is a Symantics[Int].

findMember returns

<SingleDenotation of type MethodType(List(), List(), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),module scala),class Int))> 
<and> 
<SingleDenotation of type MethodType(List(exp), List(TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),module scala),Int)), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),module scala),class Int))>

Which kind of looks correct except that the return type in the signature that we are looking for is Object and not Int.

[nicolasstucki]

The issue is that when we pickle, we see the signature from Symantics[R] with a generic R and then when we unpickle and will in the prefix hole, the prefix becomes Symantics[Int] changing the signatures.

[anatoliykmetyuk]

Do we need it before we can release RC18?

[biboudis]

I moved it on the next one! It is not a blocker.