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Compiler crashs at path-dependent function containing TypeParamRef during implicit searching #22827

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Compiler crashs at path-dependent function containing TypeParamRef during implicit searching#22827
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area:implicitsrelated to implicitsitype:bugitype:crash
@noti0na1

Description

@noti0na1
noti0na1
opened on Mar 18, 2025

Found a crash while investigating #22210

Compiler version

3.7.1-RC1-bin-SNAPSHOT-nonbootstrapped-git-744ba92

Minimized code

trait Module:
  trait Reader[T]

class Builder[M <: Module](val m: M):
  def json[Receive](reader: m.Reader[Receive]): Unit = {}

object Main:

  val mod = new Module {}

  def builder[M <: Module](m: M): Builder[M] = new Builder[M](m)

  def test =
    val f: String = builder(mod).json

Output (click arrow to expand)

Exception in thread "main" java.lang.AssertionError: assertion failed: `wildApprox` failed to remove uninstantiated M

  exception occurred while typechecking function_assign_crash.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/scala/scala3/issues/new/choose
  For non-enriched exceptions, compile with -Xno-enrich-error-messages.


     while compiling: function_assign_crash.scala
        during phase: typer
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.16
    compiler version: version 3.7.1-RC1-bin-SNAPSHOT-nonbootstrapped-git-744ba92
            settings: -classpath /Users/yaoyuzhao/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.16/scala-library-2.13.16.jar:/Users/yaoyuzhao/Work/dotty/library/../out/bootstrap/scala3-library-bootstrapped/scala-3.7.1-RC1-bin-SNAPSHOT-nonbootstrapped/scala3-library_3-3.7.1-RC1-bin-SNAPSHOT.jar -d /Users/yaoyuzhao/Work/dotty/compiler/../out/default-last-scalac-out.jar     at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)

        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:674)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeAccumulator.foldOver(Types.scala:6738)
        at dotty.tools.dotc.core.Types$TypeTraverser.traverseChildren(Types.scala:6811)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:682)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:665)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:660)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeAccumulator.foldOver(Types.scala:6725)
        at dotty.tools.dotc.core.Types$TypeTraverser.traverseChildren(Types.scala:6811)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:682)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeAccumulator.op$proxy27$1(Types.scala:6721)
        at dotty.tools.dotc.core.Types$TypeAccumulator.foldArgs$3(Types.scala:6721)
        at dotty.tools.dotc.core.Types$TypeAccumulator.foldOver(Types.scala:6725)
        at dotty.tools.dotc.core.Types$TypeTraverser.traverseChildren(Types.scala:6811)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:682)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.core.Types$TypeTraverser.apply(Types.scala:6810)
        at dotty.tools.dotc.typer.ProtoTypes$ViewProto.fold(ProtoTypes.scala:664)
        at dotty.tools.dotc.core.Types$TypeAccumulator.foldOver(Types.scala:6773)
        at dotty.tools.dotc.core.Types$TypeTraverser.traverseChildren(Types.scala:6811)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.traverse(Implicits.scala:682)
        at dotty.tools.dotc.typer.ImplicitRunInfo$collectParts$2$.apply(Implicits.scala:688)
        at dotty.tools.dotc.typer.ImplicitRunInfo.recur$1(Implicits.scala:764)
        at dotty.tools.dotc.typer.ImplicitRunInfo.computeIScope(Implicits.scala:775)
        at dotty.tools.dotc.typer.ImplicitRunInfo.$anonfun$1(Implicits.scala:855)
        at dotty.tools.dotc.util.ReadOnlyMap.getOrElse(ReadOnlyMap.scala:23)
        at dotty.tools.dotc.typer.ImplicitRunInfo.implicitScope(Implicits.scala:855)
        at dotty.tools.dotc.typer.ImplicitRunInfo.implicitScope$(Implicits.scala:626)
        at dotty.tools.dotc.Run.implicitScope(Run.scala:45)
        at dotty.tools.dotc.typer.Implicits$ImplicitSearch.implicitScope(Implicits.scala:1801)
        at dotty.tools.dotc.typer.Implicits$ImplicitSearch.searchImplicit(Implicits.scala:1683)
        at dotty.tools.dotc.typer.Implicits$ImplicitSearch.searchImplicit$$anonfun$3(Implicits.scala:1770)
        at dotty.tools.dotc.typer.Implicits$SearchResult.recoverWith(Implicits.scala:430)
        at dotty.tools.dotc.typer.Implicits$ImplicitSearch.searchImplicit(Implicits.scala:1756)
        at dotty.tools.dotc.typer.Implicits$ImplicitSearch.bestImplicit(Implicits.scala:1797)
        at dotty.tools.dotc.typer.Implicits.inferImplicit(Implicits.scala:1115)
        at dotty.tools.dotc.typer.Implicits.inferImplicit$(Implicits.scala:866)
        at dotty.tools.dotc.typer.Typer.inferImplicit(Typer.scala:154)
        at dotty.tools.dotc.typer.Implicits.inferView(Implicits.scala:906)
        at dotty.tools.dotc.typer.Implicits.inferView$(Implicits.scala:866)
        at dotty.tools.dotc.typer.Typer.inferView(Typer.scala:154)
        at dotty.tools.dotc.typer.Typer.adaptToSubType$1(Typer.scala:4722)
        at dotty.tools.dotc.typer.Typer.adaptNoArgsOther$1(Typer.scala:4533)
        at dotty.tools.dotc.typer.Typer.adaptNoArgs$1(Typer.scala:4613)
        at dotty.tools.dotc.typer.Typer.adapt1(Typer.scala:4875)
        at dotty.tools.dotc.typer.Typer.adapt(Typer.scala:4105)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.typedFunctionValue(Typer.scala:1968)
        at dotty.tools.dotc.typer.Typer.typedFunction(Typer.scala:1705)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3570)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3648)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3841)
        at dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:1493)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3568)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3648)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.adaptNoArgsUnappliedMethod$1(Typer.scala:4458)
        at dotty.tools.dotc.typer.Typer.adaptNoArgs$1(Typer.scala:4611)
        at dotty.tools.dotc.typer.Typer.adapt1(Typer.scala:4875)
        at dotty.tools.dotc.typer.Typer.adapt(Typer.scala:4105)
        at dotty.tools.dotc.typer.Typer.readapt$1(Typer.scala:4115)
        at dotty.tools.dotc.typer.Typer.adapt1(Typer.scala:4863)
        at dotty.tools.dotc.typer.Typer.adapt(Typer.scala:4105)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3841)
        at dotty.tools.dotc.typer.Typer.typedValDef(Typer.scala:2888)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3539)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3647)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3752)
        at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3798)
        at dotty.tools.dotc.typer.Typer.typedBlockStats(Typer.scala:1486)
        at dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:1490)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3568)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3648)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3841)
        at dotty.tools.dotc.typer.Namer.typedAheadExpr$$anonfun$1(Namer.scala:1794)
        at dotty.tools.dotc.typer.Namer.typedAhead(Namer.scala:1784)
        at dotty.tools.dotc.typer.Namer.typedAheadExpr(Namer.scala:1794)
        at dotty.tools.dotc.typer.Namer.typedAheadRhs$1$$anonfun$1(Namer.scala:2210)
        at dotty.tools.dotc.inlines.PrepareInlineable$.dropInlineIfError(PrepareInlineable.scala:256)
        at dotty.tools.dotc.typer.Namer.typedAheadRhs$1(Namer.scala:2210)
        at dotty.tools.dotc.typer.Namer.rhsType$1(Namer.scala:2218)
        at dotty.tools.dotc.typer.Namer.cookedRhsType$1(Namer.scala:2243)
        at dotty.tools.dotc.typer.Namer.lhsType$1(Namer.scala:2244)
        at dotty.tools.dotc.typer.Namer.inferredResultType(Namer.scala:2255)
        at dotty.tools.dotc.typer.Namer.inferredType$1(Namer.scala:1837)
        at dotty.tools.dotc.typer.Namer.valOrDefDefSig(Namer.scala:1843)
        at dotty.tools.dotc.typer.Namer.defDefSig(Namer.scala:1969)
        at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:843)
        at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:1003)
        at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:872)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:175)
        at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:190)
        at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:192)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:393)
        at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:3507)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3532)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3647)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3752)
        at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3798)
        at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:3220)
        at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:3548)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3552)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3647)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3752)
        at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3798)
        at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:3353)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3594)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3648)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3725)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3730)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3841)
        at dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:47)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:510)
        at dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:53)
        at dotty.tools.dotc.typer.TyperPhase.$anonfun$4(TyperPhase.scala:99)
        at scala.collection.Iterator$$anon$6.hasNext(Iterator.scala:479)
        at scala.collection.Iterator$$anon$9.hasNext(Iterator.scala:583)
        at scala.collection.immutable.List.prependedAll(List.scala:152)
        at scala.collection.immutable.List$.from(List.scala:685)
        at scala.collection.immutable.List$.from(List.scala:682)
        at scala.collection.IterableOps$WithFilter.map(Iterable.scala:900)
        at dotty.tools.dotc.typer.TyperPhase.runOn(TyperPhase.scala:98)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:367)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:360)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$2(Run.scala:407)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$adapted$1(Run.scala:407)
        at scala.Function0.apply$mcV$sp(Function0.scala:42)
        at dotty.tools.dotc.Run.showProgress(Run.scala:469)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:407)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:419)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:419)
        at dotty.tools.dotc.Run.compileSources(Run.scala:306)
        at dotty.tools.dotc.Run.compile(Run.scala:291)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
        at dotty.tools.dotc.Driver.process(Driver.scala:201)
        at dotty.tools.dotc.Driver.process(Driver.scala:169)
        at dotty.tools.dotc.Driver.process(Driver.scala:181)
        at dotty.tools.dotc.Driver.main(Driver.scala:211)
        at dotty.tools.dotc.Main.main(Main.scala)

The error is at def computeIScope(rootTp: Type): OfTypeImplicits of ImplicitRunInfo:

case t: TypeParamRef =>
  assert(!ctx.typerState.constraint.contains(t), i"`wildApprox` failed to remove uninstantiated $t")
  traverse(t.underlying)

builder(mod) in the code is necessary to trigger the crash. If we assign it to a variable and call json, there will be no error, so I guess the type variable M from builder is related to this.

In addition, if f is not annotated with a type, there is also no error.

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