Merge pull request #9017 from dotty-staging/fix-#9011

Fix #9016: Fix stackoverflows in provablyDisjoint

Author: OlivierBlanvillain

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

@@ -2413,13 +2413,12 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
         provablyDisjoint(tp1.tp1, tp2) && provablyDisjoint(tp1.tp2, tp2)
       case (_, tp2: OrType)  =>
         provablyDisjoint(tp1, tp2.tp1) && provablyDisjoint(tp1, tp2.tp2)
-      case (tp1: AndType, tp2: AndType) =>
-        (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/patmat/andtype-opentype-interaction.check

@@ -2,6 +2,5 @@
 27: Pattern Match Exhaustivity: _: Trait & OpenTrait & OpenTrait2, _: Clazz & OpenTrait & OpenTrait2, _: AbstractClass & OpenTrait & OpenTrait2, _: SealedClass & OpenTrait & OpenTrait2
 31: Pattern Match Exhaustivity: _: Trait & OpenClass
 35: Pattern Match Exhaustivity: _: Trait & OpenTrait & OpenClass
-39: Pattern Match Exhaustivity: _: Trait & OpenClass & (OpenTrait & OpenClass2)
 43: Pattern Match Exhaustivity: _: Trait & OpenAbstractClass
 47: Pattern Match Exhaustivity: _: Trait & OpenClass & (OpenTrait & OpenClassSubclass)

tests/patmat/andtype-opentype-interaction.scala

@@ -37,7 +37,7 @@ object Test {
   }
 
   def m2c(s: (T & OpenClass) & (OpenTrait & OpenClass2)) = s match {
-    case _: Unrelated => ;
+    case _: Unrelated => ;  // OK since scrutinee is the empty type
   }
 
   def m3(s: T & OpenAbstractClass) = s match {

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 {