Disable distribution of intersection types over applied types

Fixes #23435

Author: EugeneFlesselle

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

@@ -2771,7 +2771,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
    *  @pre !(tp1 <: tp2) && !(tp2 <:< tp1) -- these cases were handled before
    */
   private def distributeAnd(tp1: Type, tp2: Type): Type = tp1 match {
-    case tp1 @ AppliedType(tycon1, args1) =>
+    case tp1 @ AppliedType(tycon1, args1) if false =>
       tp2 match {
         case AppliedType(tycon2, args2)
         if tycon1.typeSymbol == tycon2.typeSymbol && tycon1 =:= tycon2 =>

tests/neg/i23435-min.scala

@@ -0,0 +1,14 @@
+
+type Or[+A, +B] = A | B
+
+object Test1:
+  val x: Or[Int, String] & Or[String, Int] = 3
+  val y: Or[Int & String, String & Int] = x // error
+  val z: String = y
+
+// shows the distributeAnd logic should not be applied even when
+// the targs are pairwise TypeComparer#singletonInterval
+object Test2:
+  val x: Or["3", Singleton] & Or[Singleton, "3"] = 3
+  val y: Or["3", "3"] = x // error
+  val z: String = y

tests/neg/i23435.scala

@@ -0,0 +1,16 @@
+
+trait L[+A]{val a:A}
+trait R[+B]{val b: B}
+
+class LR(val a: Int, val b: String) extends L[Int] with R[String]
+
+type E[+A] = L[A] | R[A]
+
+val x: E[Int] & E[String] = LR(4, "hi")
+val y: E[Int&String] = x // error
+
+val z = y match
+  case l : L[Int&String] => l.a
+  case r : R[Int&String] => r.b
+
+val _ = z:String // was: java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.String