Fix #9016: Fix stackoverflows in provablyDisjoint

Author: odersky

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

@@ -2417,9 +2417,11 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
         (provablyDisjoint(tp1.tp1, tp2.tp1) || provablyDisjoint(tp1.tp2, tp2.tp2)) &&
         (provablyDisjoint(tp1.tp1, tp2.tp2) || provablyDisjoint(tp1.tp2, tp2.tp1))
       case (tp1: AndType, _) =>
-        provablyDisjoint(tp1.tp2, tp2) || provablyDisjoint(tp1.tp1, tp2)
+        !(tp1 <:< tp2)
+        && (provablyDisjoint(tp1.tp2, tp2) || provablyDisjoint(tp1.tp1, tp2))
       case (_, tp2: AndType) =>
-        provablyDisjoint(tp1, tp2.tp2) || provablyDisjoint(tp1, tp2.tp1)
+        !(tp2 <:< tp1)
+        && (provablyDisjoint(tp1, tp2.tp2) || provablyDisjoint(tp1, tp2.tp1))
       case (tp1: TypeProxy, tp2: TypeProxy) =>
         provablyDisjoint(tp1.underlying, tp2) || provablyDisjoint(tp1, tp2.underlying)
       case (tp1: TypeProxy, _) =>

tests/run/enum-Tree.scala

@@ -1,12 +1,13 @@
+trait P
 enum Tree[T] {
-  case True                 extends Tree[Boolean]
-  case False                extends Tree[Boolean]
-  case Zero                 extends Tree[Int]
-  case Succ(n: Tree[Int])   extends Tree[Int]
-  case Pred(n: Tree[Int])   extends Tree[Int]
-  case IsZero(n: Tree[Int]) extends Tree[Boolean]
+  case True                 extends Tree[Boolean], P
+  case False                extends Tree[Boolean], P
+  case Zero                 extends Tree[Int], P
+  case Succ(n: Tree[Int])   extends Tree[Int], P
+  case Pred(n: Tree[Int])   extends Tree[Int], P
+  case IsZero(n: Tree[Int]) extends Tree[Boolean], P
   case If(cond: Tree[Boolean], thenp: Tree[T], elsep: Tree[T])
-                            extends Tree[T]
+                            extends Tree[T], P
 }
 
 object Test {