Fix #12546: Handle enum or object in provablyDisjoint

A enum or object is provably disjoint with a class A if the module
class does not derive from A.

Author: liufengyun

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

@@ -2586,6 +2586,10 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         provablyDisjoint(tp1, gadtBounds(tp2.symbol).hi) || provablyDisjoint(tp1, tp2.superType)
       case (tp1: TermRef, tp2: TermRef) if isEnumValueOrModule(tp1) && isEnumValueOrModule(tp2) =>
         tp1.termSymbol != tp2.termSymbol
+      case (tp1: TermRef, tp2: TypeRef) if isEnumValueOrModule(tp1) && !tp1.symbol.moduleClass.derivesFrom(tp2.classSymbol) =>
+        true
+      case (tp1: TypeRef, tp2: TermRef) if isEnumValueOrModule(tp2) && !tp2.symbol.moduleClass.derivesFrom(tp1.classSymbol) =>
+        true
       case (tp1: Type, tp2: Type) if defn.isTupleType(tp1) =>
         provablyDisjoint(tp1.toNestedPairs, tp2)
       case (tp1: Type, tp2: Type) if defn.isTupleType(tp2) =>

tests/patmat/i12546.scala

@@ -0,0 +1,14 @@
+trait SomeRestriction
+
+enum ADT {
+  case A extends ADT
+  case B extends ADT with SomeRestriction
+}
+
+object MinimalExample {
+  val b: ADT & SomeRestriction = ADT.B
+
+  b match {
+    case ADT.B => ???
+  }
+}