Merge pull request #10560 from dotty-staging/fix-9871

Fix #9871: use toNestedPairs in provablyDisjoint

Author: bishabosha

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

@@ -2449,8 +2449,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
             decompose(cls2, tp2).forall(x => provablyDisjoint(x, tp1))
           else
             false
-      case (AppliedType(tycon1, args1), AppliedType(tycon2, args2))
-      if tycon1.typeSymbol == tycon2.typeSymbol && tycon1 =:= tycon2 =>
+      case (AppliedType(tycon1, args1), AppliedType(tycon2, args2)) if isSame(tycon1, tycon2) =>
         // It is possible to conclude that two types applies are disjoint by
         // looking at covariant type parameters if the said type parameters
         // are disjoin and correspond to fields.
@@ -2520,6 +2519,10 @@ 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: Type, tp2: Type) if defn.isTupleType(tp1) =>
+        provablyDisjoint(tp1.toNestedPairs, tp2)
+      case (tp1: Type, tp2: Type) if defn.isTupleType(tp2) =>
+        provablyDisjoint(tp1, tp2.toNestedPairs)
       case (tp1: TypeProxy, tp2: TypeProxy) =>
         provablyDisjoint(tp1.superType, tp2) || provablyDisjoint(tp1, tp2.superType)
       case (tp1: TypeProxy, _) =>

tests/pos/9871.scala

@@ -0,0 +1,10 @@
+object Test {
+  type IsTypeInTuple[T, Tup <: Tuple] = Tup match {
+    case EmptyTuple => false
+    case T *: ts => true
+    case _ *: ts => IsTypeInTuple[T, ts]
+  }
+  summon[(Int *: String *: EmptyTuple) =:= (Int, String)] //they are the same
+  summon[IsTypeInTuple[String, Int *: String *: EmptyTuple] =:= true] //compiles
+  summon[IsTypeInTuple[String, (Int, String)] =:= true] //doesn't compile
+}