MethodHandle invoke does not play well with macros

[markehammons]

Compiler version

Scala 3.3.0-RC3

Minimized code

File1:

import java.lang.invoke.MethodHandle
import scala.quoted.*
import java.lang.invoke.MethodHandles
import java.lang.invoke.MethodType

class FnTest:
  def target(i: Int, j: Int): Int = i + j

object FnTest:
  val x = 4
  inline def fn() = ${
    fnImpl('mh, 'x)
  }

  val methodType =
    MethodType.methodType(classOf[Int], classOf[Int], classOf[Int])
  def target(i: Int): Int = i
  val mh = MethodHandles
    .publicLookup()
    .nn
    .findVirtual(classOf[FnTest], "target", methodType)
    .nn
    .bindTo(FnTest())
    .nn

  def fnImpl(mh: Expr[MethodHandle], num: Expr[Int])(using Quotes) =
    import quotes.reflect.*

    val invoke = Symbol
      .classSymbol("java.lang.invoke.MethodHandle")
      .declaredMethod("invoke")
      .head

    val mhInvocation = Apply(
      Select(
        Inlined(
          None,
          Nil,
          Inlined(None, Nil, mh.asTerm)
        ),
        invoke
      ),
      List(
        Typed(
          Inlined(
            None,
            Nil,
            Repeated(
              List(
                Inlined(None, Nil, Inlined(None, Nil, num.asTerm)),
                Inlined(None, Nil, Inlined(None, Nil, num.asTerm))
              ),
              Inferred(TypeRepr.of[Int])
            )
          ),
          Inferred(TypeRepr.of[Seq[Int]])
        )
      )
    )
    val invocation = Inlined(
      Some(TypeTree.of[FnTest.type]),
      Nil,
      TypeApply(
        Select(
          mhInvocation,
          TypeRepr.of[Any].classSymbol.get.declaredMethod("asInstanceOf").head
        ),
        List(TypeTree.of[Int])
      )
    ).asExprOf[Int]

    invocation

  inline def fn2() = ${
    fn2Impl('mh, 'x)
  }

  def fn2Impl(mh: Expr[MethodHandle], num: Expr[Int])(using Quotes) =
    import quotes.reflect.*
    val code = '{
      $mh.invoke(${ Varargs(List(num, num)) }*).asInstanceOf[Int]
    }

    report.info(code.asTerm.show(using Printer.TreeStructure))

    code

  inline def fn3() = ${
    fn3Impl('mh, 'x)
  }

  def fn3Impl(mh: Expr[MethodHandle], num: Expr[Int])(using Quotes) =
    import quotes.reflect.*
    val code = '{
      $mh.invoke($num, $num).asInstanceOf[Int]
    }

    report.info(code.asTerm.show(using Printer.TreeStructure))
    code

File2:

import scala.util.Try

@main def run() =
  Try(FnTest.fn3()).recover(t => println(t.getMessage()))
  Try(FnTest.fn2()).recover(t => println(t.getMessage()))
  Try(FnTest.fn()).recover(t => println(t.getMessage()))

Output

expected (int,int)int but found (int[])int
expected (int,int)int but found (Seq)Object

Expectation

All three of these macros should work, while only fn3 works in practice. What this means is that to deal with n-arity invocations of invoke on MethodHandles I have to manually write out the inputs for each arity by hand.

[markehammons]

This example is a bit long, mainly to show my attempts using compile-time reflection. In theory though, this should work with fn2 at least, and that is a much simpler example of the problem.

[prolativ]

@markehammons how exactly do you run these snippets? File2 seems to be incorrect, as import scala.util.Try is missing and you cannot put expressions top-level. I changed this to

import scala.util.Try

object Test:
  Try(FnTest.fn3()).recover(t => println(t.getMessage()))
  Try(FnTest.fn2()).recover(t => println(t.getMessage()))
  Try(FnTest.fn()).recover(t => println(t.getMessage()))

But then everything compiles without errors (I'm using scala-cli to compile the files).
Interestingly, when I try to test this in REPL (copy-pasting the snippets one after another) I get errors like

-- Error: ----------------------------------------------------------------------
 3 |Try(FnTest.fn3()).recover(t => println(t.getMessage()))
   |    ^^^^^^^^^^^^
   |    Could not find class rs$line$1$FnTest$ in classpath

[markehammons]

@markehammons how exactly do you run these snippets? File2 seems to be incorrect, as import scala.util.Try is missing and you cannot put expressions top-level. I changed this to

import scala.util.Try

object Test:
  Try(FnTest.fn3()).recover(t => println(t.getMessage()))
  Try(FnTest.fn2()).recover(t => println(t.getMessage()))
  Try(FnTest.fn()).recover(t => println(t.getMessage()))

But then everything compiles without errors (I'm using scala-cli to compile the files).
Interestingly, when I try to test this in REPL (copy-pasting the snippets one after another) I get errors like

-- Error: ----------------------------------------------------------------------
 3 |Try(FnTest.fn3()).recover(t => println(t.getMessage()))
   |    ^^^^^^^^^^^^
   |    Could not find class rs$line$1$FnTest$ in classpath

The errors are runtime errors, not compiletime.

[prolativ]

Ok, I can now reproduce it when I run it with

import scala.util.Try

@main def run() =
  Try(FnTest.fn3()).recover(t => println(t.getMessage()))
  Try(FnTest.fn2()).recover(t => println(t.getMessage()))
  Try(FnTest.fn()).recover(t => println(t.getMessage()))

as File2