Avoid inf recursion in provablyDisjointClasses

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -3211,17 +3211,18 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
       cls.is(Sealed) && !cls.hasAnonymousChild
 
     def decompose(cls: Symbol): List[Symbol] =
-      cls.children.flatMap { child =>
+      cls.children.map: child =>
         if child.isTerm then
-          child.info.classSymbols // allow enum vals to be decomposed to their enum class (then filtered out) and any mixins
-        else child :: Nil
-      }.filter(child => child.exists && child != cls)
+          child.info.classSymbol.orElse(child)
+        else child
+      .filter(child => child.exists && child != cls)
 
     def eitherDerivesFromOther(cls1: Symbol, cls2: Symbol): Boolean =
       cls1.derivesFrom(cls2) || cls2.derivesFrom(cls1)
 
     def smallestNonTraitBase(cls: Symbol): Symbol =
-      cls.asClass.baseClasses.find(!_.is(Trait)).get
+      val classes = if cls.isClass then cls.asClass.baseClasses else cls.info.classSymbols
+      classes.find(!_.is(Trait)).get
 
     if (eitherDerivesFromOther(cls1, cls2))
       false

tests/pos/i22266.scala

@@ -0,0 +1,22 @@
+sealed trait NonPolygon
+sealed trait Polygon
+
+sealed trait SymmetryAspect
+sealed trait RotationalSymmetry      extends SymmetryAspect
+sealed trait MaybeRotationalSymmetry extends SymmetryAspect
+
+enum Shape:
+  case Circle   extends Shape with NonPolygon with RotationalSymmetry
+  case Triangle extends Shape with Polygon with MaybeRotationalSymmetry
+  case Square   extends Shape with Polygon with RotationalSymmetry
+
+object Shape:
+
+  def hasPolygon(
+    rotationalSyms: Vector[Shape & RotationalSymmetry],
+    maybeSyms: Vector[Shape & MaybeRotationalSymmetry]
+  ): Boolean =
+    val all = rotationalSyms.concat(maybeSyms)
+    all.exists:
+      case _: Polygon => true
+      case _          => false

tests/pos/i22266.unenum.scala

@@ -0,0 +1,22 @@
+sealed trait NonPolygon
+sealed trait Polygon
+
+sealed trait SymmetryAspect
+sealed trait RotationalSymmetry      extends SymmetryAspect
+sealed trait MaybeRotationalSymmetry extends SymmetryAspect
+
+sealed abstract class Shape
+
+object Shape:
+  case object Circle   extends Shape with NonPolygon with RotationalSymmetry
+  case object Triangle extends Shape with Polygon with MaybeRotationalSymmetry
+  case object Square   extends Shape with Polygon with RotationalSymmetry
+
+  def hasPolygon(
+    rotationalSyms: Vector[Shape & RotationalSymmetry],
+    maybeSyms: Vector[Shape & MaybeRotationalSymmetry]
+  ): Boolean =
+    val all = rotationalSyms.concat(maybeSyms)
+    all.exists:
+      case _: Polygon => true
+      case _          => false

tests/warn/i21860.unenum.scala

@@ -3,7 +3,7 @@ sealed trait Corners { self: Figure => }
 
 sealed abstract class Shape extends Figure
 object Shape:
-  case object Triange  extends Shape with Corners
+  case object Triangle extends Shape with Corners
   case object Square   extends Shape with Corners
   case object Circle   extends Shape
   case object Ellipsis extends Shape