Could not find proxy in macro #13571

cquiroz · 2021-09-21T12:29:10Z

cquiroz
Sep 21, 2021

This is a minimization of a larger macro that I'm constructing for spire. My macro looks like:

  inline def checked2[A](inline n: A): A =
    ${ checkedImpl2[A]('{n}) }

  private def checkedImpl2[A](n: Expr[A])(using Quotes, Type[A]): Expr[A] =
    import quotes.reflect.*
    val tree: Term = n.asTerm
    val acc = new TreeMap:
      override def transformTerm(tree: Term)(owner: Symbol): Term =
        tree match
          case Apply(Select(x, "*"), List(y)) =>
            '{
              val xt = ${x.asExprOf[Long]}
              xt
            }.asTerm
          case _ =>
            super.transformTerm(tree)(owner)
    acc.transformTerm(tree)(tree.symbol).asExprOf[A]

On test code this compiles just fine:

  test("border case") {
    val u = 3L
    checked2(u * 2L)
  }

But this fails

  test("border case") {
    val u = 3L
    checked2(List(1L, 2L).map { k =>
       u * 2L
     })
  }

And the latest code gives this error:

[error] java.lang.IllegalArgumentException: Could not find proxy for val u: Long in List(val u, method $anonfun, method <init>, class CheckedScalaCheckSuite, module class macros, module class spire, module class <root>), encl = class CheckedScalaCheckSuite, owners = class CheckedScalaCheckSuite, package spire.macros, package spire, package <root>; enclosures = class CheckedScalaCheckSuite, package spire.macros, package spire, package <root>
[error] dotty.tools.dotc.transform.LambdaLift$Lifter.searchIn$1(LambdaLift.scala:148)
[error] dotty.tools.dotc.transform.LambdaLift$Lifter.proxy(LambdaLift.scala:161)
[error] dotty.tools.dotc.transform.LambdaLift$Lifter.proxyRef(LambdaLift.scala:179)
[error] dotty.tools.dotc.transform.LambdaLift.transformIdent(LambdaLift.scala:297)
[error] dotty.tools.dotc.transform.MegaPhase.goIdent(MegaPhase.scala:584)
[error] dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:224)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
[error] dotty.tools.dotc.transform.MegaPhase.mapValDef$1(MegaPhase.scala:235)

I'm not really sure where this comes from or how to fix it. any ideas?

Answered by nicolasstucki

Oct 1, 2021

Using the -Xcheck-macros compiler flag we get

-- Error: tests/pos-macros/i13571/Test_2.scala:3:12 ----------------------------
3 |    checked2(List(1L, 2L).map { k =>
  |    ^
  |Exception occurred while executing macro expansion.
  |java.lang.AssertionError: assertion failed: Tree had an unexpected owner for val xt
  |Expected: method $anonfun (Test_2$package$._$_$$anonfun)
  |But was: val macro (Test_2$package$._$macro)
  |
  |
  |The code of the definition of val xt is
  |val xt: scala.Long = u
  |
  |which was found in the code
  |{
  |  val xt: scala.Long = u
  |
  |  (xt: scala.Long)
  |}
  |
  |which has the AST representation
  |Block(Nil, Inlined(Some(TypeIdent("Macro_1$package$")…

View full answer

nicolasstucki · 2021-10-01T15:14:58Z

nicolasstucki
Oct 1, 2021

Using the -Xcheck-macros compiler flag we get

-- Error: tests/pos-macros/i13571/Test_2.scala:3:12 ----------------------------
3 |    checked2(List(1L, 2L).map { k =>
  |    ^
  |Exception occurred while executing macro expansion.
  |java.lang.AssertionError: assertion failed: Tree had an unexpected owner for val xt
  |Expected: method $anonfun (Test_2$package$._$_$$anonfun)
  |But was: val macro (Test_2$package$._$macro)
  |
  |
  |The code of the definition of val xt is
  |val xt: scala.Long = u
  |
  |which was found in the code
  |{
  |  val xt: scala.Long = u
  |
  |  (xt: scala.Long)
  |}
  |
  |which has the AST representation
  |Block(Nil, Inlined(Some(TypeIdent("Macro_1$package$")), Nil, Block(List(ValDef("xt", Inferred(), Some(Inlined(None, Nil, Ident("u"))))), Typed(Ident("xt"), Inferred()))))
  |
  |
  |     at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
  |     at scala.quoted.runtime.impl.QuotesImpl$$anon$9.traverse(QuotesImpl.scala:2906)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1656)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1656)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.fold$1(Trees.scala:1531)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.apply(Trees.scala:1533)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1564)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1657)
  |     at scala.quoted.runtime.impl.QuotesImpl$$anon$9.traverse(QuotesImpl.scala:2909)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1656)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1656)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1584)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1537)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1657)
  |     at scala.quoted.runtime.impl.QuotesImpl$$anon$9.traverse(QuotesImpl.scala:2909)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1656)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1656)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1564)
  |     at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1657)
  |     at scala.quoted.runtime.impl.QuotesImpl$$anon$9.traverse(QuotesImpl.scala:2909)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$.xCheckMacroOwners(QuotesImpl.scala:2910)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$.scala$quoted$runtime$impl$QuotesImpl$reflect$$$xCheckMacroedOwners(QuotesImpl.scala:2872)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$DefDef$.copy(QuotesImpl.scala:266)
  |     at scala.quoted.runtime.impl.QuotesImpl$reflect$DefDef$.copy(QuotesImpl.scala:265)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformStatement(Quotes.scala:4479)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformStatement$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformStatement(Macro_1.scala:9)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformStats$$anonfun$1(Quotes.scala:4573)
  |     at scala.collection.immutable.List.mapConserve(List.scala:472)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformStats(Quotes.scala:4573)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformStats$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformStats(Macro_1.scala:9)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm(Quotes.scala:4517)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformTerm(Macro_1.scala:18)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm(Quotes.scala:4517)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformTerm(Macro_1.scala:18)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerms$$anonfun$1(Quotes.scala:4579)
  |     at scala.collection.immutable.List.mapConserve(List.scala:472)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerms(Quotes.scala:4579)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerms$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformTerms(Macro_1.scala:9)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm(Quotes.scala:4503)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformTerm(Macro_1.scala:18)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm(Quotes.scala:4533)
  |     at scala.quoted.Quotes$reflectModule$TreeMap.transformTerm$(Quotes.scala:4433)
  |     at Macro_1$package$$anon$1.transformTerm(Macro_1.scala:18)
  |     at Macro_1$package$.checkedImpl2(Macro_1.scala:19)
  |     at Macro_1$package$.inline$checkedImpl2(Macro_1.scala:6)

The issue is that the quote is constructed using the owner of the Quotes instance (Symbol.spliceOwner).

The code can be fixed by changing the owner to the correct one

          '{
            val xt = ${x.asExprOf[Long]}
            xt
-          }.asTerm
+          }.asTerm.changeOwner(owner)

1 reply

nicolasstucki Oct 1, 2021

Also see #13652

cquiroz · 2021-10-01T18:29:31Z

cquiroz
Oct 1, 2021
Author

Thanks, this helped me to get this solved:
typelevel/spire@ac301a4

0 replies

tpolecat · 2021-10-01T18:48:04Z

tpolecat
Oct 1, 2021

Is this a bug, or is it something one would be expected to know? If so, how?

3 replies

cquiroz Oct 1, 2021
Author

That's a good point. I was a bit confused on what to use as an argument and the only references I found were in other discussions and bug reports. I don't seem to recall a discussion on the docs. It would be nice if it were more documentation around it

nicolasstucki Oct 2, 2021

It is a bug in the code. What users should know is to use the -Xcheck-macros which checks that owners are correct.

On the other hand, the current API forces you to change the owner explicitly. In #13652 I experimenting with an addition that will make it easier to get the correct owner directly.

kubukoz Nov 17, 2022

If -Xcheck-macros tells me nothing (literally - no extra output), what else can I do to understand what I'm doing wrong? (edit: created a separate discussion in #16366)

-Xcheck:all also doesn't show any errors or warnings.

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Could not find proxy in macro #13571

cquiroz Sep 21, 2021

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