Regression: Compiler crashes when overriding method returning context function

[abosshard]

Compiler version

3.1.2

Minimized code

trait Foo:
   def foo: String ?=> Int =
      0

trait Bar extends Foo:
   override def foo =
      super.foo

class Baz extends Bar

Any of the following changes will avoid the crash:

• use normal function instead of context function
• do not override foo
• return 0 instead of calling super.foo
• remove class Baz
• make Baz a trait

Output (click arrow to expand)

exception while typing def Bar$$super$foo: (String) ?=> Int = super[Foo].foo of class class dotty.tools.dotc.ast.Trees$DefDef # -1
exception while typing @SourceFile("Foo.scala") class Baz() extends Object(), Bar {
  def Bar$$super$foo: (String) ?=> Int = super[Foo].foo
} of class class dotty.tools.dotc.ast.Trees$TypeDef # -1
exception while typing package <empty> {
  @SourceFile("Foo.scala") trait Foo() extends Object {
    @ContextResultCount(1) def foo: (String) ?=> Int = 
      {
        def $anonfun(using evidence$1: String): Int = 0
        closure($anonfun)
      }
  }
  @SourceFile("Foo.scala") trait Bar() extends Object, Foo {
    def Bar$$super$foo: (String) ?=> Int
    @ContextResultCount(1) override def foo: (String) ?=> Int = 
      {
        def $anonfun(using evidence$2: String): Int = 
          this.Bar$$super$foo.apply(evidence$2)
        closure($anonfun)
      }
  }
  @SourceFile("Foo.scala") class Baz() extends Object(), Bar {
    def Bar$$super$foo: (String) ?=> Int = super[Foo].foo
  }
} of class class dotty.tools.dotc.ast.Trees$PackageDef # -1
exception occurred while compiling Foo.scala
java.lang.AssertionError: assertion failed while compiling Foo.scala
Exception in thread "main" java.lang.AssertionError: assertion failed
        at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:11)
        at dotty.tools.dotc.transform.Erasure$Boxing$.adaptToType(Erasure.scala:387)
        at dotty.tools.dotc.transform.Erasure$Typer.adapt(Erasure.scala:1042)
        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.$anonfun$47(Typer.scala:2256)
        at dotty.tools.dotc.typer.PrepareInlineable$.dropInlineIfError(PrepareInlineable.scala:238)
        at dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:2256)
        at dotty.tools.dotc.transform.Erasure$Typer.typedDefDef(Erasure.scala:932)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2786)
        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.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)

[Kordyjan]

After bisecting the nightlies I determined that the change was introduced between 3.1.2-RC1-bin-20211102-82172ed-NIGHTLY and 3.1.2-RC1-bin-20211112-4025951-NIGHTLY (weird that we did not publish nightlies for 10 days).

It may be the fault of #13736.

If that's not it, here is the output of git log 82172ed..4025951 --merges --oneline:

4025951220 Merge pull request #13909 from dotty-staging/scaladoc/too-implicit-classes
9794737c76 Merge pull request #13908 from dotty-staging/scaladoc/root-content-pos
e23f815704 Merge pull request #13911 from dwijnand/fix-leaky-tryImplicits
f836589707 Merge pull request #13736 from dotty-staging/fix-13691-v2
aa25df2523 Merge pull request #13886 from dotty-staging/fix-13838
5ce25fe758 Merge pull request #13782 from etorreborre/master
4ad416fc31 Merge pull request #13872 from dotty-staging/fix-#13871
045c8bddaf Merge pull request #13866 from dotty-staging/fix-13846
ae0f8281b0 Merge pull request #13729 from dotty-staging/wip-expnull-library
7da659ba38 Merge pull request #13898 from danicheg/dead-links
add58e9230 Merge pull request #13894 from dotty-staging/fix-13893
673698d25e Merge pull request #13881 from dotty-staging/fix-13820
e7cbbd6ad9 Merge pull request #13883 from dotty-staging/set-untyped-to-nothing
483bf2cecd Merge pull request #13879 from dotty-staging/fix-13873
83effc3601 Merge pull request #13792 from dwijnand/lint-too-big-constants-pr
fa56a4e068 Merge pull request #13779 from dotty-staging/constrain-finalResultType-2
9153fe5f29 Merge pull request #13742 from dotty-staging/less-constrainResult
8ee672c919 Merge pull request #13791 from michelou/dotty-test-ioexception
0a8520717a Merge pull request #13709 from SethTisue/issue-9880

[griggt]

Further bisection confirms it regressed in #13736