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Cyclic reference involving variable with match type #13495

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ndido98 opened this issue Sep 9, 2021 · 2 comments
Closed

Cyclic reference involving variable with match type #13495

ndido98 opened this issue Sep 9, 2021 · 2 comments
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@OlivierBlanvillain
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area:match-types itype:bug

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@ndido98
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ndido98 commented Sep 9, 2021

Compiler version

Scala 3.0.2 (Scastie)

Minimized code

import scala.annotation.showAsInfix

trait Component
sealed trait Deleted extends Component

type Deletable[L <: CList] <: CList = L match {
  case h &: t => (h | Deleted) &: Deletable[t]
  case CNil => CNil
}

sealed trait CList
sealed trait CNil extends CList
@showAsInfix case class &:[+C <: Component, +L <: CList](h: C, t: L) extends CList

case class A(x: Int, y: Int) extends Component
case class B(x: Int, y: Int) extends Component

val x: Deletable[A &: B &: CNil] = ???

Output

Compiler error:

Cyclic reference involving val x

Expectation

No compiler error. I expect the type of x to be (A | Deleted) &: (B | Deleted) &: CNil.
@smarter
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smarter commented Sep 9, 2021

The code snippet as is doesn't emit any error when pasted in a file, but it does emit the cyclic reference error if I wrap it in an object Test (and scastie automatically wraps the code in an object in worksheet mode).
The error goes away if I move the definition of CList and CNil out of the object.

The stack trace we get for the cyclic error is:

java.lang.Exception: Stack trace
        at java.lang.Thread.dumpStack(Thread.java:1336)
        at dotty.tools.dotc.core.CyclicReference.<init>(TypeErrors.scala:113)
        at dotty.tools.dotc.core.CyclicReference$.apply(TypeErrors.scala:157)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:149)
        at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:188)
        at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:190)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:369)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeChildrenIn$3$$anonfun$2(SymDenotations.scala:1615)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:563)
        at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:561)
        at scala.collection.AbstractIterable.foreach(Iterable.scala:919)
        at scala.collection.IterableOps$WithFilter.foreach(Iterable.scala:889)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeChildrenIn$1(SymDenotations.scala:1615)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.children(SymDenotations.scala:1623)
        at dotty.tools.dotc.transform.SymUtils$.hasAnonymousChild(SymUtils.scala:247)
        at dotty.tools.dotc.core.TypeComparer.isClosedSum$1(TypeComparer.scala:2531)
        at dotty.tools.dotc.core.TypeComparer.provablyDisjoint$$anonfun$2(TypeComparer.scala:2573)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.TypeComparer.provablyDisjoint(TypeComparer.scala:2516)
        at dotty.tools.dotc.core.TypeComparer.provablyDisjoint$$anonfun$2(TypeComparer.scala:2647)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.TypeComparer.provablyDisjoint(TypeComparer.scala:2516)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCase$2$$anonfun$2(TypeComparer.scala:2913)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCase$3(TypeComparer.scala:2891)
        at dotty.tools.dotc.core.TrackingTypeComparer.recur$1(TypeComparer.scala:2923)
        at dotty.tools.dotc.core.TrackingTypeComparer.op$proxy68$1(TypeComparer.scala:2954)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCases(TypeComparer.scala:2955)
        at dotty.tools.dotc.core.Types$MatchType.liftedTree1$2(Types.scala:4709)
        at dotty.tools.dotc.core.Types$MatchType.matchCases$1(Types.scala:4714)
        at dotty.tools.dotc.core.Types$MatchType.reduced$$anonfun$4$$anonfun$1(Types.scala:4718)
        at dotty.tools.dotc.core.TypeComparer.inSubComparer(TypeComparer.scala:2663)
        at dotty.tools.dotc.core.TypeComparer.tracked(TypeComparer.scala:2673)
        at dotty.tools.dotc.core.TypeComparer$.tracked(TypeComparer.scala:2826)
        at dotty.tools.dotc.core.Types$MatchType.reduced$$anonfun$3(Types.scala:4718)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.Types$MatchType.reduced(Types.scala:4719)
        at dotty.tools.dotc.core.Types$MatchType.tryNormalize(Types.scala:4667)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$4$$anonfun$3$$anonfun$1(Types.scala:4143)
        at dotty.tools.dotc.core.MatchTypeTrace$.recurseWith(MatchTypeTrace.scala:83)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$5$$anonfun$4(Types.scala:4144)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$1(Types.scala:4145)
        at dotty.tools.dotc.core.Types$AppliedType.tryNormalize(Types.scala:4149)
        at dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:145)
        at dotty.tools.dotc.core.TypeOps$.mapArgs$1(TypeOps.scala:146)
        at dotty.tools.dotc.core.TypeOps$.mapArgs$1(TypeOps.scala:146)
        at dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:146)
        at dotty.tools.dotc.core.Types$Type.simplified(Types.scala:1863)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCase$2$$anonfun$2(TypeComparer.scala:2908)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCase$3(TypeComparer.scala:2891)
        at dotty.tools.dotc.core.TrackingTypeComparer.recur$1(TypeComparer.scala:2923)
        at dotty.tools.dotc.core.TrackingTypeComparer.op$proxy68$1(TypeComparer.scala:2954)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCases(TypeComparer.scala:2955)
        at dotty.tools.dotc.core.Types$MatchType.liftedTree1$2(Types.scala:4709)
        at dotty.tools.dotc.core.Types$MatchType.matchCases$1(Types.scala:4714)
        at dotty.tools.dotc.core.Types$MatchType.reduced$$anonfun$4$$anonfun$1(Types.scala:4718)
        at dotty.tools.dotc.core.TypeComparer.inSubComparer(TypeComparer.scala:2663)
        at dotty.tools.dotc.core.TypeComparer.tracked(TypeComparer.scala:2673)
        at dotty.tools.dotc.core.TypeComparer$.tracked(TypeComparer.scala:2826)
        at dotty.tools.dotc.core.Types$MatchType.reduced$$anonfun$3(Types.scala:4718)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.Types$MatchType.reduced(Types.scala:4719)
        at dotty.tools.dotc.core.Types$MatchType.tryNormalize(Types.scala:4667)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$4$$anonfun$3$$anonfun$1(Types.scala:4143)
        at dotty.tools.dotc.core.MatchTypeTrace$.recurseWith(MatchTypeTrace.scala:83)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$5$$anonfun$4(Types.scala:4144)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$1(Types.scala:4145)
        at dotty.tools.dotc.core.Types$AppliedType.tryNormalize(Types.scala:4149)
        at dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:145)
        at dotty.tools.dotc.core.TypeOps$.mapArgs$1(TypeOps.scala:146)
        at dotty.tools.dotc.core.TypeOps$.mapArgs$1(TypeOps.scala:146)
        at dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:146)
        at dotty.tools.dotc.core.Types$Type.simplified(Types.scala:1863)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCase$2$$anonfun$2(TypeComparer.scala:2908)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCase$3(TypeComparer.scala:2891)
        at dotty.tools.dotc.core.TrackingTypeComparer.recur$1(TypeComparer.scala:2923)
        at dotty.tools.dotc.core.TrackingTypeComparer.op$proxy68$1(TypeComparer.scala:2954)
        at dotty.tools.dotc.core.TrackingTypeComparer.matchCases(TypeComparer.scala:2955)
        at dotty.tools.dotc.core.Types$MatchType.liftedTree1$2(Types.scala:4709)
        at dotty.tools.dotc.core.Types$MatchType.matchCases$1(Types.scala:4714)
        at dotty.tools.dotc.core.Types$MatchType.reduced$$anonfun$4$$anonfun$1(Types.scala:4718)
        at dotty.tools.dotc.core.TypeComparer.inSubComparer(TypeComparer.scala:2663)
        at dotty.tools.dotc.core.TypeComparer.tracked(TypeComparer.scala:2673)
        at dotty.tools.dotc.core.TypeComparer$.tracked(TypeComparer.scala:2826)
        at dotty.tools.dotc.core.Types$MatchType.reduced$$anonfun$3(Types.scala:4718)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.Types$MatchType.reduced(Types.scala:4719)
        at dotty.tools.dotc.core.Types$MatchType.tryNormalize(Types.scala:4667)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$4$$anonfun$3$$anonfun$1(Types.scala:4143)
        at dotty.tools.dotc.core.MatchTypeTrace$.recurseWith(MatchTypeTrace.scala:83)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$5$$anonfun$4(Types.scala:4144)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.core.Types$AppliedType.tryMatchAlias$1(Types.scala:4145)
        at dotty.tools.dotc.core.Types$AppliedType.tryNormalize(Types.scala:4149)
        at dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:145)
        at dotty.tools.dotc.core.Types$Type.simplified(Types.scala:1863)
        at dotty.tools.dotc.typer.Typer.simplify(Typer.scala:2835)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2820)
        at dotty.tools.dotc.typer.Typer.typed$$anonfun$3(Typer.scala:2883)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2884)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2887)
        at dotty.tools.dotc.typer.Typer.typedType(Typer.scala:3005)
        at dotty.tools.dotc.typer.Namer.typedAheadType$$anonfun$1(Namer.scala:1426)
        at dotty.tools.dotc.typer.Namer.typedAhead(Namer.scala:1419)
        at dotty.tools.dotc.typer.Namer.typedAheadType(Namer.scala:1426)
        at dotty.tools.dotc.typer.Namer.valOrDefDefSig(Namer.scala:1508)
        at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:751)
        at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:887)
        at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:779)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:153)
        at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:188)
        at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:190)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:369)
        at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:2697)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2722)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2817)
        at dotty.tools.dotc.typer.Typer.typed$$anonfun$3(Typer.scala:2883)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2884)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2887)
        at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2909)
        at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2959)
        at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2409)
        at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$2(Typer.scala:2743)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2747)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2817)
        at dotty.tools.dotc.typer.Typer.typed$$anonfun$3(Typer.scala:2883)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2884)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2887)
        at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2909)
        at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2959)
        at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2532)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2788)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2818)
        at dotty.tools.dotc.typer.Typer.typed$$anonfun$3(Typer.scala:2883)
        at dotty.tools.dotc.reporting.TraceSyntax.doTrace(trace.scala:65)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:61)
        at dotty.tools.dotc.reporting.TraceSyntax.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace$(trace.scala:23)
        at dotty.tools.dotc.reporting.trace$.dotty$tools$dotc$reporting$TraceSyntax$$inline$doTrace(trace.scala:10)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2884)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2887)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3003)
        at dotty.tools.dotc.typer.TyperPhase.liftedTree1$1(TyperPhase.scala:56)
        at dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:62)
        at dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:411)
        at dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:63)
        at dotty.tools.dotc.typer.TyperPhase.runOn$$anonfun$1(TyperPhase.scala:105)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.typer.TyperPhase.runOn(TyperPhase.scala:105)
        at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:261)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
        at dotty.tools.dotc.Run.runPhases$5(Run.scala:272)
        at dotty.tools.dotc.Run.compileUnits$$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.compileSources(Run.scala:222)
        at dotty.tools.dotc.Run.compile(Run.scala:206)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
        at dotty.tools.dotc.Driver.process(Driver.scala:199)
        at dotty.tools.dotc.Driver.process(Driver.scala:167)
        at dotty.tools.dotc.Driver.process(Driver.scala:179)
        at dotty.tools.dotc.Driver.main(Driver.scala:209)
        at dotty.tools.dotc.Main.main(Main.scala)
-- [E046] Cyclic Error: try/i13495.scala:21:9 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

So basically while completing x we try to normalize its type and because it's a match type on CList, we need to find the children of CNil which involves completing some members of the owner of CNil, and at that point we end up completing x again, hence the cycle. I tried simply not forcing the completion of symbols currently being completed:

diff --git compiler/src/dotty/tools/dotc/core/SymDenotations.scala compiler/src/dotty/tools/dotc/core/SymDenotations.scala
index fcfbba208eb..067faa09689 100644
--- compiler/src/dotty/tools/dotc/core/SymDenotations.scala
+++ compiler/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -1611,7 +1611,7 @@ object SymDenotations {
                   case _ => false

         if owner.isClass then
-          for c <- owner.info.decls.toList if maybeChild(c) do
+          for c <- owner.info.decls.toList if !c.isCompleting && maybeChild(c) do
             c.ensureCompleted()
       end completeChildrenIn

which seemingly fixed the issue but lead to a crash in PostTyper:

```scala java.lang.AssertionError: assertion failed: no member this.h . ==, members = Scope{ def (): Test.Component } while compiling try/i13495.scala Exception in thread "main" java.lang.AssertionError: assertion failed: no member this.h . ==, members = Scope{ def (): Test.Component } at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8) at dotty.tools.dotc.ast.Trees$Instance.applyOverloaded(Trees.scala:1738) at dotty.tools.dotc.ast.tpd$TreeOps$.equal$extension(tpd.scala:962) at dotty.tools.dotc.transform.SyntheticMembers.$anonfun$12(SyntheticMembers.scala:253) at scala.collection.immutable.List.map(List.scala:246) at dotty.tools.dotc.transform.SyntheticMembers.equalsBody$1(SyntheticMembers.scala:253) at dotty.tools.dotc.transform.SyntheticMembers.syntheticRHS$1(SyntheticMembers.scala:144) at dotty.tools.dotc.transform.SyntheticMembers.syntheticDef$3$$anonfun$2$$anonfun$1(SyntheticMembers.scala:153) at dotty.tools.dotc.transform.SyntheticMembers.synthesizeDef$$anonfun$1(SyntheticMembers.scala:83) at dotty.tools.dotc.ast.tpd$.DefDef(tpd.scala:285) at dotty.tools.dotc.transform.SyntheticMembers.synthesizeDef(SyntheticMembers.scala:83) at dotty.tools.dotc.transform.SyntheticMembers.syntheticDef$1(SyntheticMembers.scala:153) at dotty.tools.dotc.transform.SyntheticMembers.syntheticDefIfMissing$1(SyntheticMembers.scala:108) at dotty.tools.dotc.transform.SyntheticMembers.caseAndValueMethods$$anonfun$1(SyntheticMembers.scala:381) at scala.collection.immutable.List.flatMap(List.scala:293) at dotty.tools.dotc.transform.SyntheticMembers.caseAndValueMethods(SyntheticMembers.scala:381) at dotty.tools.dotc.transform.SyntheticMembers.addSyntheticMembers(SyntheticMembers.scala:602) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform$$anonfun$4(PostTyper.scala:348) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.withNoCheckNews(PostTyper.scala:98) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:349) at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1473) at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:51) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:378) at dotty.tools.dotc.transform.MacroTransform$Transformer.transformStat$1(MacroTransform.scala:39) at dotty.tools.dotc.transform.MacroTransform$Transformer.transformStats$$anonfun$1(MacroTransform.scala:42) at dotty.tools.dotc.core.Decorators$ListDecorator$.loop$1(Decorators.scala:92) at dotty.tools.dotc.core.Decorators$ListDecorator$.mapconserve$extension(Decorators.scala:108) at dotty.tools.dotc.transform.MacroTransform$Transformer.transformStats(MacroTransform.scala:42) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transformStats(PostTyper.scala:452) at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:58) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform$$anonfun$8$$anonfun$1(PostTyper.scala:347) at dotty.tools.dotc.transform.SuperAccessors.wrapTemplate(SuperAccessors.scala:210) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform$$anonfun$4(PostTyper.scala:347) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.withNoCheckNews(PostTyper.scala:98) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:349) at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1473) at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:51) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:378) at dotty.tools.dotc.transform.MacroTransform$Transformer.transformStat$1(MacroTransform.scala:39) at dotty.tools.dotc.transform.MacroTransform$Transformer.transformStats$$anonfun$1(MacroTransform.scala:42) at dotty.tools.dotc.core.Decorators$ListDecorator$.loop$1(Decorators.scala:92) at dotty.tools.dotc.core.Decorators$ListDecorator$.mapconserve$extension(Decorators.scala:108) at dotty.tools.dotc.transform.MacroTransform$Transformer.transformStats(MacroTransform.scala:42) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transformStats(PostTyper.scala:452) at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1484) at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:51) at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:443) at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:21) at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:308) at scala.collection.immutable.List.map(List.scala:246) at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:309) at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:261) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323) at dotty.tools.dotc.Run.runPhases$5(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.compileSources(Run.scala:222) at dotty.tools.dotc.Run.compile(Run.scala:206) at dotty.tools.dotc.Driver.doCompile(Driver.scala:39) at dotty.tools.dotc.Driver.process(Driver.scala:199) at dotty.tools.dotc.Driver.process(Driver.scala:167) at dotty.tools.dotc.Driver.process(Driver.scala:179) at dotty.tools.dotc.Driver.main(Driver.scala:209) at dotty.tools.dotc.Main.main(Main.scala) ```

I don't know if this is the right approach or if we should try to not normalize on completions to avoid this sort of issue instead.

@smarter
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smarter commented Sep 9, 2021

Something like this seems to work:

diff --git compiler/src/dotty/tools/dotc/core/SymDenotations.scala compiler/src/dotty/tools/dotc/core/SymDenotations.scala
index fcfbba208eb..5bf766d6c9b 100644
--- compiler/src/dotty/tools/dotc/core/SymDenotations.scala
+++ compiler/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -1611,7 +1611,7 @@ object SymDenotations {
                   case _ => false

         if owner.isClass then
-          for c <- owner.info.decls.toList if maybeChild(c) do
+          for c <- owner.info.decls.toList if maybeChild(c) && (c.isClass || c.is(EnumVal)) do
             c.ensureCompleted()
       end completeChildrenIn

OlivierBlanvillain added a commit to dotty-staging/dotty that referenced this issue Sep 23, 2021
@OlivierBlanvillain
Fix scala#13495: break Bmpletion cycle by onl
d2db4b2
OlivierBlanvillain added a commit to dotty-staging/dotty that referenced this issue Sep 23, 2021
@OlivierBlanvillain
Fix scala#13495: break completion cycles
4936fee
smarter added a commit that referenced this issue Sep 28, 2021
@smarter
Merge pull request #13596 from dotty-staging/fix-13495
8246a7b 
Fix #13495: Break completion cycles
olsdavis pushed a commit to olsdavis/dotty that referenced this issue Apr 4, 2022
@OlivierBlanvillain @olsdavis
Fix scala#13495: break completion cycles
8d9410d
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