IllegalArgumentException: Could not find proxy for Lambda/ValDef combination in quotes

[cchantep]

Compiler version

3.1.2-RC1-bin-20211022-f7abd32-NIGHTLY-git-f7abd32

Minimized code

import scala.quoted.*

  inline def optPrettyPrinter[T]: Option[T] => Option[T] =
    ${ optPrettyPrinterImpl[T] }

  private def optPrettyPrinterImpl[T: Type](
      using
      q: Quotes
    ): Expr[Option[T] => Option[T]] = {
    import q.reflect.*

    val tpe = TypeRepr.of[T]

    val fn = Lambda(
      Symbol.spliceOwner,
      MethodType(List("macroVal"))(
        _ => List(tpe),
        _ => tpe
      ),
      {
        case (_, List(arg: Term)) =>
          ValDef.let(Symbol.spliceOwner, "v", arg) { v =>
            '{
              val vv = ${ v.asExprOf[T] }
              println("v=" + vv.toString())
              vv
            }.asTerm
          }

        case _ =>
          report.errorAndAbort("Fails compile")
      }
    ).asExprOf[T => T]

    '{ (_: Option[T]).map(${ fn }) }
  }

optPrettyPrinter(Some("foo"))

Output

(run-main-2) java.lang.IllegalArgumentException: Could not find proxy for val vv: String in List(val vv, method res0, module class rs$line$1$, module class repl$, module class ), encl = package repl, owners = package repl, package ; enclosures = package repl, package java.lang.IllegalArgumentException: Could not find proxy for val vv: String in List(val vv, method res0, module class rs$line$1$, module class repl$, module class ), encl = package repl, owners = package repl, package ; enclosures = package repl, package

	at dotty.tools.dotc.transform.LambdaLift$Lifter.searchIn$1(LambdaLift.scala:148)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.proxy(LambdaLift.scala:161)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.proxyRef(LambdaLift.scala:179)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.addFreeArgs$$anonfun$1(LambdaLift.scala:185)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.addFreeArgs(LambdaLift.scala:185)
	at dotty.tools.dotc.transform.LambdaLift.transformApply(LambdaLift.scala:322)
	at dotty.tools.dotc.transform.LambdaLift.transformApply(LambdaLift.scala:321)
	at dotty.tools.dotc.transform.MegaPhase.goApply(MegaPhase.scala:644)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:281)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.mapValDef$1(MegaPhase.scala:235)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:240)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
	at dotty.tools.dotc.transform.MegaPhase.transformStat$1(MegaPhase.scala:437)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:382)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:385)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:448)
	at dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:460)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:308)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:309)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:261)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:272)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:280)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:289)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:228)
	at dotty.tools.repl.ReplCompiler.runCompilationUnit(ReplCompiler.scala:167)
	at dotty.tools.repl.ReplCompiler.compile(ReplCompiler.scala:178)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:251)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:219)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:153)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:156)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:175)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:156)
	at xsbt.ConsoleInterface.run(ConsoleInterface.java:52)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at sbt.internal.inc.AnalyzingCompiler.invoke(AnalyzingCompiler.scala:329)
	at sbt.internal.inc.AnalyzingCompiler.console(AnalyzingCompiler.scala:233)
	at sbt.Console.console0$1(Console.scala:64)
	at sbt.Console.$anonfun$apply$5(Console.scala:74)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.util.InterfaceUtil$$anon$1.get(InterfaceUtil.scala:17)
	at sbt.TrapExit$App.run(TrapExit.scala:258)
	at java.base/java.lang.Thread.run(Thread.java:844)

Expectation

val res0: Option[String] = Some(foo)

Details

The following is working fine, not mixing '{ ... } with tree constructed using Lambda/ValDef.

  inline def prettyPrinter[T]: T => T = ${ prettyPrinterImpl[T] }

  private def prettyPrinterImpl[T: Type](using q: Quotes): Expr[T => T] = {
    import q.reflect.*

    val tpe = TypeRepr.of[T]

    Lambda(
      Symbol.spliceOwner,
      MethodType(List("macroVal"))(
        _ => List(tpe),
        _ => tpe
      ),
      {
        case (_, List(arg: Term)) =>
          ValDef.let(Symbol.spliceOwner, "v", arg) { v =>
            '{
              val vv = ${ v.asExprOf[T] }
              println("v=" + vv.toString())
              vv
            }.asTerm
          }

        case _ =>
          report.errorAndAbort("Fails compile")
      }
    ).asExprOf[T => T]
  }

Also coming back to macro optPrettyPrinter it can be fixed using changeOwner.

  inline def optPrettyPrinter[T]: Option[T] => Option[T] =
    ${ optPrettyPrinterImpl[T] }

  private def optPrettyPrinterImpl[T: Type](
      using
      q: Quotes
    ): Expr[Option[T] => Option[T]] = {
    import q.reflect.*

    val tpe = TypeRepr.of[T]

    val fn = Lambda(
      Symbol.spliceOwner,
      MethodType(List("macroVal"))(
        _ => List(tpe),
        _ => tpe
      ),
      {
        case (m, List(arg: Term)) =>
          ValDef
            .let(Symbol.spliceOwner, "v", arg) { v =>
              '{
                val vv = ${ v.asExprOf[T] }
                println("v=" + vv.toString())
                vv
              }.asTerm
            }
            .changeOwner(m) // <---- HERE

        case _ =>
          report.errorAndAbort("Fails compile")
      }
    ).asExprOf[T => T]

    '{ (_: Option[T]).map(${ fn }) }
  }

The importance of changeOwner should at least be documented on the Lambda factories, maybe always enforced.

[nicolasstucki]

In the original example it seems fishy to ignore the lambda symbol in

        case (_, List(arg: Term)) =>

This is supposed to be the owner of any definition within the lambda.

The code should probably be

        case (meth, List(arg: Term)) =>
          ValDef.let(meth, "v", arg) { v =>

[nicolasstucki]

Running the code with -Xcheck-macros shows the place where this bug in the implementation of the macro tries to add the val with the wrong owner to the lambda.

-- Error: tests/pos-macros/i13922/Test_2.scala:1:11 ----------------------------
1 |def test = optPrettyPrinter(Some("foo"))
  |           ^^^^^^^^^^^^^^^^
  |Exception occurred while executing macro expansion.
  |java.lang.AssertionError: assertion failed: Tree had an unexpected owner for val v
  |Expected: method $anonfun (Test_2$package$._$_$$anonfun)
  |But was: val macro (Test_2$package$._$macro)
  |
  |
  |The code of the definition of val v is
  |val v: java.lang.String = macroVal
  |
  |which was found in the code
  |{
  |  val v: java.lang.String = macroVal
  |  val vv: java.lang.String = v
  |  scala.Predef.println("v=".+(vv.toString()))
  |
  |  (vv: java.lang.String)
  |}
  |
  |which has the AST representation
  |Block(List(ValDef("v", Inferred(), Some(Ident("macroVal")))), Inlined(Some(TypeIdent("Macro_1$package$")), Nil, Block(List(ValDef("vv", Inferred(), Some(Inlined(None, Nil, Ident("v")))), Apply(Ident("println"), List(Apply(Select(Literal(StringConstant("v=")), "+"), List(Apply(Select(Ident("vv"), "toString"), Nil)))))), Typed(Ident("vv"), Inferred()))))
  |
  |
  |     at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
  |     at scala.quoted.runtime.impl.QuotesImpl$$anon$9.traverse(QuotesImpl.scala:2910)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1640)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1640)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.fold$1(Trees.scala:1515)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.apply(Trees.scala:1517)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1548)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1641)
  |     at scala.quoted.runtime.impl.QuotesImpl$$anon$9.traverse(QuotesImpl.scala:2913)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$.xCheckMacroOwners(QuotesImpl.scala:2914)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$.scala$quoted$runtime$impl$QuotesImpl$reflect$$$xCheckMacroedOwners(QuotesImpl.scala:2885)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$Lambda$.apply$$anonfun$22$$anonfun$1(QuotesImpl.scala:797)
  |     at dotty.tools.dotc.ast.tpd$.DefDef(tpd.scala:285)
  |     at dotty.tools.dotc.ast.tpd$.Closure(tpd.scala:120)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$Lambda$.apply$$anonfun$22(QuotesImpl.scala:797)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$.scala$quoted$runtime$impl$QuotesImpl$reflect$$$withDefaultPos(QuotesImpl.scala:2867)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$Lambda$.apply(QuotesImpl.scala:797)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$Lambda$.apply(QuotesImpl.scala:795)
  |     at Macro_1$package$.optPrettyPrinterImpl(Macro_1.scala:32)
  |     at Macro_1$package$.inline$optPrettyPrinterImpl(Macro_1.scala:6)
  |
  | This location contains code that was inlined from Test_2.scala:1

[nicolasstucki]

The following is the correct fix

        case (meth, List(arg: Term)) =>
          ValDef.let(meth, "v", arg) { v =>

but then we hit another issue with the owner of the quote in the ValDef.let as we also need to change its owner

        '{
            val vv = ${ v.asExprOf[T] }
            println("v=" + vv.toString())
            vv
-          }.asTerm
+          }.asTerm.changeOwner(owner)

To set the owner of the quote correctly from the start we need #13652 and would need to do

        given Quotes = owner.asQuotes
        ValDef.let(m, "v", arg) { v =>
          '{
            val vv = ${ v.asExprOf[T] }
            println("v=" + vv.toString())
            vv
          }.asTerm
        }

#13652 should add an example of this usecase added examples in documentation of Lambda and let in #13652.

[cchantep]

For now .changeOwner at top-level is the soundest workaround.