CyclicReference exception when working with `toExprOfList` in context of `Reflection`

[anatoliykmetyuk]

minimized code

Macro:

import scala.quoted._
import delegate scala.quoted._
import scala.tasty._

delegate for Toolbox = Toolbox.make(getClass.getClassLoader)

inline def crash = ${crashImpl}
def crashImpl given (refl: Reflection) = {
  import refl._  // Works if commented out
  val res = List('{"One"}).toExprOfList  // Works if replaced with '{"One" :: Nil}
  println(res.show)  // Works if commented out
  res
}

Usage:

object Main {
  def main(args: Array[String]): Unit = {
    val res = crash  // Works if these two lines are commented out at the same time
    println(res)     // Works if these two lines are commented out at the same time
    
    println(crash)
  }
}

If as much as one of the four pointed out comments is applied, the code works.

Stack trace

[error] -- Error: /Users/anatolii/Projects/dotty/playground/core/src/main/scala/playground/Main.scala:35:14
[error] 35 |    val res = crash
[error]    |              ^^^^^
[error]    |An exception occurred while executing macro expansion
[error]    |
[error]    |dotty.tools.dotc.core.CyclicReference:
[error]    |	at dotty.tools.dotc.core.CyclicReference$.apply(TypeErrors.scala:157)
[error]    |	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:237)
[error]    |	at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:180)
[error]    |	at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:182)
[error]    |	at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:345)
[error]    |	at dotty.tools.dotc.core.SymDenotations$SymDenotation.flags(SymDenotations.scala:150)
[error]    |	at dotty.tools.dotc.tastyreflect.KernelImpl.Symbol_flags(KernelImpl.scala:1476)
[error]    |	at dotty.tools.dotc.tastyreflect.KernelImpl.Symbol_flags(KernelImpl.scala:1476)
[error]    |	at scala.tasty.reflect.SymbolOps$SymbolAPI.flags(SymbolOps.scala:15)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printType(Printers.scala:1506)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printTypeAndAnnots$1(Printers.scala:1412)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printTypeTree(Printers.scala:1414)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printTree(Printers.scala:703)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printSeparated$2(Printers.scala:1045)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printStats(Printers.scala:1051)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printFlatBlock$$anonfun$1(Printers.scala:1014)
[error]    |	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.indented(Printers.scala:502)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printFlatBlock(Printers.scala:1015)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter$Buffer.printTree(Printers.scala:893)
[error]    |	at scala.tasty.reflect.Printers$SourceCodePrinter.showTree(Printers.scala:443)
[error]    |	at scala.tasty.reflect.Printers$TreeShowDeco.show(Printers.scala:30)
[error]    |	at scala.tasty.reflect.QuotedOps$QuotedExprAPI.show(QuotedOps.scala:17)
[error]    |	at playground.macros$.crashImpl(macros.scala:41)
[error]    |	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error]    |	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[error]    |	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error]    |	at java.lang.reflect.Method.invoke(Method.java:498)
[error]    |	at dotty.tools.dotc.transform.Splicer$Interpreter.interpretStaticMethodCall$$anonfun$1(Splicer.scala:135)
[error]    |	at dotty.tools.dotc.transform.Splicer$Interpreter.stopIfRuntimeException(Splicer.scala:188)
[error]    |	at dotty.tools.dotc.transform.Splicer$Interpreter.interpretStaticMethodCall(Splicer.scala:135)
[error]    |	at dotty.tools.dotc.transform.Splicer$AbstractInterpreter.interpretTree(Splicer.scala:343)
[error]    |	at dotty.tools.dotc.transform.Splicer$Interpreter.interpret(Splicer.scala:90)
[error]    |	at dotty.tools.dotc.transform.Splicer$.splice(Splicer.scala:44)
[error]    |	at dotty.tools.dotc.typer.Inliner.dotty$tools$dotc$typer$Inliner$$expandMacro(Inliner.scala:1160)
[error]    |	at dotty.tools.dotc.typer.Inliner$InlineTyper.typedApply(Inliner.scala:1000)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2151)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2205)
[error]    |	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:124)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2237)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Inliner.inlined(Inliner.scala:512)
[error]    |	at dotty.tools.dotc.typer.Inliner$.inlineCall(Inliner.scala:109)
[error]    |	at dotty.tools.dotc.typer.Typer.adaptNoArgsOther$6(Typer.scala:2821)
[error]    |	at dotty.tools.dotc.typer.Typer.adaptNoArgs$1(Typer.scala:2918)
[error]    |	at dotty.tools.dotc.typer.Typer.adapt1(Typer.scala:3127)
[error]    |	at dotty.tools.dotc.typer.Typer.adapt(Typer.scala:2539)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Namer.typedAheadExpr$$anonfun$1(Namer.scala:1173)
[error]    |	at dotty.tools.dotc.typer.Namer.typedAhead(Namer.scala:1163)
[error]    |	at dotty.tools.dotc.typer.Namer.typedAheadExpr(Namer.scala:1173)
[error]    |	at dotty.tools.dotc.typer.Namer.rhsType$2(Namer.scala:1308)
[error]    |	at dotty.tools.dotc.typer.Namer.cookedRhsType$1(Namer.scala:1320)
[error]    |	at dotty.tools.dotc.typer.Namer.lhsType$1(Namer.scala:1321)
[error]    |	at dotty.tools.dotc.typer.Namer.inferredType$1(Namer.scala:1339)
[error]    |	at dotty.tools.dotc.typer.Namer.valOrDefDefSig(Namer.scala:1347)
[error]    |	at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:756)
[error]    |	at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:873)
[error]    |	at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:786)
[error]    |	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:239)
[error]    |	at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:180)
[error]    |	at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:182)
[error]    |	at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:345)
[error]    |	at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:2103)
[error]    |	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2128)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2204)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2270)
[error]    |	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2316)
[error]    |	at dotty.tools.dotc.typer.Typer.typedBlockStats(Typer.scala:711)
[error]    |	at dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:714)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2158)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2205)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2329)
[error]    |	at dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:1549)
[error]    |	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2138)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2204)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2270)
[error]    |	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2316)
[error]    |	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:1678)
[error]    |	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2141)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2204)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2270)
[error]    |	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2316)
[error]    |	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:1802)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2181)
[error]    |	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2205)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2239)
[error]    |	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2251)
[error]    |	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2329)
[error]    |	at dotty.tools.dotc.typer.FrontEnd.typeCheck$$anonfun$1(FrontEnd.scala:75)
[error]    |	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error]    |	at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:41)
[error]    |	at dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:79)
[error]    |	at dotty.tools.dotc.typer.FrontEnd.runOn$$anonfun$3(FrontEnd.scala:109)
[error]    |	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error]    |	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error]    |	at scala.collection.immutable.List.foreach(List.scala:392)
[error]    |	at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:109)
[error]    |	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:158)
[error]    |	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error]    |	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error]    |	at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:36)
[error]    |	at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:33)
[error]    |	at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:198)
[error]    |	at dotty.tools.dotc.Run.runPhases$5(Run.scala:170)
[error]    |	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:178)
[error]    |	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error]    |	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:102)
[error]    |	at dotty.tools.dotc.Run.compileUnits(Run.scala:185)
[error]    |	at dotty.tools.dotc.Run.compileSources(Run.scala:120)
[error]    |	at dotty.tools.dotc.Run.compile(Run.scala:104)
[error]    |	at dotty.tools.dotc.Driver.doCompile(Driver.scala:34)
[error]    |	at dotty.tools.dotc.Driver.process(Driver.scala:172)
[error]    |	at dotty.tools.dotc.Main.process(Main.scala)
[error]    |	at xsbt.CachedCompilerImpl.run(CachedCompilerImpl.java:69)
[error]    |	at xsbt.CompilerInterface.run(CompilerInterface.java:41)
[error]    |	at sun.reflect.GeneratedMethodAccessor14.invoke(Unknown Source)
[error]    |	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error]    |	at java.lang.reflect.Method.invoke(Method.java:498)
[error]    |	at sbt.internal.inc.AnalyzingCompiler.call(AnalyzingCompiler.scala:237)
[error]    |	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:111)
[error]    |	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:90)
[error]    |	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$3(MixedAnalyzingCompiler.scala:82)
[error]    |	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error]    |	at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:133)
[error]    |	at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:73)
[error]    |	at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:116)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:307)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:307)
[error]    |	at sbt.internal.inc.Incremental$.doCompile(Incremental.scala:106)
[error]    |	at sbt.internal.inc.Incremental$.$anonfun$compile$4(Incremental.scala:87)
[error]    |	at sbt.internal.inc.IncrementalCommon.recompileClasses(IncrementalCommon.scala:116)
[error]    |	at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:63)
[error]    |	at sbt.internal.inc.Incremental$.$anonfun$compile$3(Incremental.scala:89)
[error]    |	at sbt.internal.inc.Incremental$.manageClassfiles(Incremental.scala:134)
[error]    |	at sbt.internal.inc.Incremental$.compile(Incremental.scala:80)
[error]    |	at sbt.internal.inc.IncrementalCompile$.apply(Compile.scala:67)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:311)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:269)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:159)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:238)
[error]    |	at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:69)
[error]    |	at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:1549)
[error]    |	at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:1523)
[error]    |	at scala.Function1.$anonfun$compose$1(Function1.scala:44)
[error]    |	at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:40)
[error]    |	at sbt.std.Transform$$anon$4.work(System.scala:67)
[error]    |	at sbt.Execute.$anonfun$submit$2(Execute.scala:269)
[error]    |	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:16)
[error]    |	at sbt.Execute.work(Execute.scala:278)
[error]    |	at sbt.Execute.$anonfun$submit$1(Execute.scala:269)
[error]    |	at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:178)
[error]    |	at sbt.CompletionService$$anon$2.call(CompletionService.scala:37)
[error]    |	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
[error]    |	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
[error]    |	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
[error]    |	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
[error]    |	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
[error]    |	at java.lang.Thread.run(Thread.java:745)
[error]    |
[error]    | This location is in code that was inlined at Main.scala:35

[anatoliykmetyuk]

Worth noting that List('{"One"}, '{"Two"}).toExprOfList desugars to:

{
  type x$1$_$1
  val x$2: x$1$_$1 = "One"
  {
    type x$1$_$1
    val x$2: x$1$_$1 = "Two"
    scala.Nil.::[x$1$_$1](x$2)
  }.::[x$1$_$1](x$2)
}

Which is not a Scala code that would typecheck. If you try to execute it as is:

[error] -- [E007] Type Mismatch Error: /Users/anatolii/Projects/dotty/playground/core/src/main/scala/playground/Main.scala:42:27
[error] 42 |        val x$2: x$1$_$1 = "Two"
[error]    |                           ^^^^^
[error]    |                           Found:    String("Two")
[error]    |                           Required: x$1$_$1
[error] -- [E007] Type Mismatch Error: /Users/anatolii/Projects/dotty/playground/core/src/main/scala/playground/Main.scala:43:29
[error] 43 |        scala.Nil.::[x$1$_$1](x$2)
[error]    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^
[error]    |        Found:    List[x$1$_$1]
[error]    |        Required: Int

As to toExprOfList, it is currently defined as:

def (list: List[Expr[T]]) toExprOfList[T] given Type[T]: Expr[List[T]] = list match {
  case x :: xs  => '{ $x :: ${xs.toExprOfList} }
  case Nil => '{ Nil }
}

I believe given Type[T] is an issue here: before encountering this standard function, I tried to implement a similar function on my own:

def flattenExpr[T](exs: List[Expr[T]]) given (tt: Type[T]): Expr[List[T]] =
  exs.foldRight('{Nil: List[$tt]}) { (next, accum) => '{$next :: $accum} }

Bug-wise, it behaves the same way as toExprOfList. However, if you make a non-generic version of it:

def flattenExprStr(exs: List[Expr[String]]): Expr[List[String]] =
  exs.foldRight('{Nil: List[String]}) { (next, accum) => '{$next :: $accum} }

And call it as:

inline def crash = ${crashImpl}
def crashImpl given (refl: Reflection) = {
  import refl._
  // val res = List('{"One"}).toExprOfList
  val res = flattenExprStr(List('{"One"}))
  println(res.show)
  res
}

All works well. This one also works:

def flattenExprStr2(exs: List[Expr[String]]): Expr[List[String]] = {
  val tpe = the[Type[String]]
  exs.foldRight('{Nil: List[${tpe}]}) { (next, accum) => '{$next :: $accum} }
}

However, this one:

def flattenExprStr3(exs: List[Expr[String]]): Expr[List[String]] =
  exs.foldRight('{Nil: List[${the[Type[String]]}]}) { (next, accum) => '{$next :: $accum} }

Says:

[error] -- Error: /Users/anatolii/Projects/dotty/playground/macros/src/main/scala/playground/macros.scala:49:32
[error] 49 |    exs.foldRight('{Nil: List[${the[Type[String]]}]}) { (next, accum) => '{$next :: $accum} }
[error]    |                                ^^^^^^^^^^^^^^^^^
[error]    |                                quoted.Type[String] is not stable

[nicolasstucki]

This was fixed in #6700