Crash when extending class with some indirections because it “does not have an outer accessor”

[rmgk]

Compiler version

3.1.2 & 3.1.1 throw the exception below
Something that scala-cli describes as 3.2.0-RC1-bin-20220412-1503044-NIGHTLY also has the same issue
2.13.8 OK

Minimized code

trait Core {
  class Base[T]()
}

class Module(val core: Core) {
  object Indirection {
    class Extension[T]() extends core.Base[T]()
  }
}

Note, this works if any of the following changes is applied
• Base is a trait
• Base has no type parameters
• Indirection is removed
• Module becomes a function

Output (click arrow to expand)

The gist of the crash seems to be:
object Indirection in class Module does not have an outer accessor

exception while typing new Module.this.core.Base[T]() of class class dotty.tools.dotc.ast.Trees$Apply # -1
exception while typing class Extension[T]() extends Module.this.core.Base[T]() {
  private type T
  private val $outer: Module.this.Indirection
  final def Module$Indirection$Extension$$$outer: Module.this.Indirection = 
    Extension.this.$outer
} of class class dotty.tools.dotc.ast.Trees$TypeDef # -1
exception while typing final module class Indirection() extends Object() {
  class Extension[T]() extends Module.this.core.Base[T]() {
    private type T
    private val $outer: Module.this.Indirection
    final def Module$Indirection$Extension$$$outer: Module.this.Indirection = 
      Extension.this.$outer
  }
} of class class dotty.tools.dotc.ast.Trees$TypeDef # -1
exception while typing @SourceFile("test2.scala") class Module(core: Core) extends Object() {
  def core: Core
  final lazy module def Indirection: Module.this.Indirection = 
    new Module.this.Indirection()
  final module class Indirection() extends Object() {
    class Extension[T]() extends Module.this.core.Base[T]() {
      private type T
      private val $outer: Module.this.Indirection
      final def Module$Indirection$Extension$$$outer: Module.this.Indirection = 
        Extension.this.$outer
    }
  }
} of class class dotty.tools.dotc.ast.Trees$TypeDef # -1
exception while typing package <empty> {
  @SourceFile("test2.scala") trait Core() extends Object {
    class Base[T]() extends Object() {
      private type T
      private val $outer: Core
      final def Core$Base$$$outer: Core = Base.this.$outer
    }
  }
  @SourceFile("test2.scala") class Module(core: Core) extends Object() {
    def core: Core
    final lazy module def Indirection: Module.this.Indirection = 
      new Module.this.Indirection()
    final module class Indirection() extends Object() {
      class Extension[T]() extends Module.this.core.Base[T]() {
        private type T
        private val $outer: Module.this.Indirection
        final def Module$Indirection$Extension$$$outer: Module.this.Indirection
           = 
        Extension.this.$outer
      }
    }
  }
} of class class dotty.tools.dotc.ast.Trees$PackageDef # -1
exception occurred while compiling $HOME/test2.scala
java.lang.AssertionError: assertion failed: failure to construct path from constructor Extension/class Extension/object Indirection/class Module/package <empty>/package <root> to `this` of class Module;
object Indirection in class Module does not have an outer accessor while compiling $HOME/test2.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: failure to construct path from constructor Extension/class Extension/object Indirection/class Module/package <empty>/package <root> to `this` of class Module;
object Indirection in class Module does not have an outer accessor
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.loop$1(ExplicitOuter.scala:419)
	at dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.path$extension(ExplicitOuter.scala:438)
	at dotty.tools.dotc.ast.tpd$.followOuterLinks(tpd.scala:423)
	at dotty.tools.dotc.ast.tpd$.ref(tpd.scala:413)
	at dotty.tools.dotc.ast.tpd$.singleton(tpd.scala:429)
	at dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.outerArg$1(ExplicitOuter.scala:380)
	at dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.args$extension(ExplicitOuter.scala:392)
	at dotty.tools.dotc.transform.Erasure$Typer.typedApply(Erasure.scala:824)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2809)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2872)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:121)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2937)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2941)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3057)
	at dotty.tools.dotc.typer.Typer.typedParent$1(Typer.scala:2366)
	at dotty.tools.dotc.typer.Typer.$anonfun$48(Typer.scala:2441)
	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.typer.Typer.typedClassDef(Typer.scala:2441)
	at dotty.tools.dotc.transform.Erasure$Typer.typedClassDef(Erasure.scala:1020)
	at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2797)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2801)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2871)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:121)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2937)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2941)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2963)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3013)
	at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1030)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2454)
	at dotty.tools.dotc.transform.Erasure$Typer.typedClassDef(Erasure.scala:1020)
	at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2797)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2801)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2871)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:121)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2937)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2941)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2963)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3013)
	at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1030)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2454)
	at dotty.tools.dotc.transform.Erasure$Typer.typedClassDef(Erasure.scala:1020)
	at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2797)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2801)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2871)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:121)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2937)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2941)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2963)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3013)
	at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1030)
	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2581)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2842)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2872)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:121)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2937)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2941)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3057)
	at dotty.tools.dotc.transform.Erasure.run(Erasure.scala:144)
	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$$anonfun$1(Run.scala:259)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1328)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:270)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:278)
	at scala.runtime.java8.JFunction0$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:287)
	at dotty.tools.dotc.Run.compileSources(Run.scala:220)
	at dotty.tools.dotc.Run.compile(Run.scala:204)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
	at dotty.tools.scripting.ScriptingDriver.compileAndRun(ScriptingDriver.scala:21)
	at dotty.tools.scripting.Main$.main(Main.scala:43)
	at dotty.tools.MainGenericRunner$.run$1(MainGenericRunner.scala:248)
	at dotty.tools.MainGenericRunner$.main(MainGenericRunner.scala:267)
	at dotty.tools.MainGenericRunner.main(MainGenericRunner.scala)

[romanowski]

It fails in a similar way in 3.0.0