Compiler crashes when illegal signature of `applyDynamic` is used

[road21]

Compiler version

3.7.3
3.7.2

Minimized code

val s = new Selectable:
  type Fields = (f: Int)

  def selectDynamic(f: String): Any = 1
  def applyDynamic(f: String): Any = 1

s.f

Output (click arrow to expand)

Error: Encountered a StackOverflowError coming from the compiler. You might need to restart your Bloop build server:
dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:145)
dotty.tools.dotc.core.TypeOps$.simplify(TypeOps.scala:138)
dotty.tools.dotc.core.Types$Type.simplified(Types.scala:2122)
dotty.tools.dotc.typer.Typer.simplify(Typer.scala:3778)
dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3762)
dotty.tools.dotc.typer.Typer.typed(Typer.scala:3836)
dotty.tools.dotc.typer.Typer.typed(Typer.scala:3841)
dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3952)
dotty.tools.dotc.typer.Typer.typeSelectOnTerm$1(Typer.scala:1058)
dotty.tools.dotc.typer.Typer.typedSelect(Typer.scala:1112)
dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3646)
dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3758)
dotty.tools.dotc.typer.Typer.typed(Typer.scala:3836)
dotty.tools.dotc.typer.Typer.typed(Typer.scala:3841)
dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3952)
dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:1109)
dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:1336)
dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:470)
dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:155)
dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3671)
dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3759)
dotty.tools.dotc.typer.Typer.typed(Typer.scala:3836)
dotty.tools.dotc.typer.Typer.typed(Typer.scala:3841)
dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3952)

[Gedochao]

Only started crashing in 3.7.0, returns a valid error in 3.6.4.

Last good release: 3.7.0-RC1-bin-20250211-37206cc-NIGHTLY
First bad release: 3.7.0-RC1-bin-20250212-4518ce5-NIGHTLY
075f5e6 is the first bad commit (#22520)
cc @hamzaremmal

[Gedochao]

Some richer output for the crash:

-- Error: ~/compiler-repro/repro.scala:8:4 
8 |  s.f
  |  ^^^
  |Cannot use selectDynamic here since it needs another selectDynamic to be invoked

  Exception while compiling /Users/pchabelski/IdeaProjects/scala-cli-tests-3/scala-cli-tests-3/compiler-repro/repro.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: <no file>
        during phase: parser
                mode: Mode()
     library version: version 2.13.16
    compiler version: version 3.7.3
            settings: -classpath /Users/pchabelski/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.7.3/scala3-library_3-3.7.3.jar:/Users/pchabelski/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.16/scala-library-2.13.16.jar -d /Users/pchabelski/IdeaProjects/scala-cli-tests-3/scala-cli-tests-3/compiler-repro/.scala-build/compiler-repro_7c09b8b29b-9acd81c9bc/classes/main -sourceroot /Users/pchabelski/IdeaProjects/scala-cli-tests-3/scala-cli-tests-3/compiler-repro

Exception in thread "main" java.lang.StackOverflowError
        at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:227)
        at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:235)
        at dotty.tools.dotc.core.TypeComparer.topLevelSubType(TypeComparer.scala:143)
        at dotty.tools.dotc.core.TypeComparer.testSubType(TypeComparer.scala:160)
        at dotty.tools.dotc.core.TypeComparer$.testSubType(TypeComparer.scala:3440)
        at dotty.tools.dotc.typer.Typer.adaptNoArgsOther$1(Typer.scala:4648)
        at dotty.tools.dotc.typer.Typer.adaptNoArgs$1(Typer.scala:4735)
        at dotty.tools.dotc.typer.Typer.adapt1(Typer.scala:4998)
        at dotty.tools.dotc.typer.Typer.adapt(Typer.scala:4216)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3836)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3841)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3952)
        at dotty.tools.dotc.typer.Typer.typeSelectOnTerm$1(Typer.scala:1058)
        at dotty.tools.dotc.typer.Typer.typedSelect(Typer.scala:1112)
        at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3646)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3758)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3836)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3841)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3952)
        at dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:1109)
        at dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:1336)
        at dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:470)
        at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:155)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3671)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3759)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3836)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3841)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3952)
       (...)

[Gedochao]

Good catch, thanks for raising @road21!