Disallow unsound &-type modifications

Author: KacperFKorban

quicklens/src/main/scala-3/com/softwaremill/quicklens/QuicklensMacros.scala

@@ -157,6 +157,8 @@ object QuicklensMacros {
       def poorMansLUB: TypeRepr = tpe match {
         case AndType(l, r) if l <:< r => l
         case AndType(l, r) if r <:< l => r
+        case AndType(_, _) =>
+          report.errorAndAbort(s"Implementation limitation: Cannot modify an & type with unrelated types.")
         case _                        => tpe
       }
 

quicklens/src/test/scala-3/com/softwaremill/quicklens/test/ModifyAndTypeTest.scala

@@ -9,6 +9,7 @@ object ModifyAndTypeTest {
   case class A(a: Int) extends B
   trait B {
     def a: Int
+    def b: Int = 0
   }
 
   case class A1(a: Int)
@@ -26,6 +27,7 @@ class ModifyAndTypeTest extends AnyFlatSpec with Matchers {
 
     val modified = ab.modify(_.a).setTo(1)
 
+    modified.b shouldBe 0
     modified.a shouldBe 1
   }
 
@@ -34,22 +36,7 @@ class ModifyAndTypeTest extends AnyFlatSpec with Matchers {
 
     val modified = ab.modify(_.a).setTo(1)
 
-    modified.a shouldBe 1
-  }
-
-  it should "modify an & type object 2" in {
-    val ab: B & A1 = new A1(0) with B
-
-    val modified = ab.modify(_.a).setTo(1)
-
-    modified.a shouldBe 1
-  }
-
-  it should "modify an & type object 3" in {
-    val ab: A1 & B = new A1(0) with B
-
-    val modified = ab.modify(_.a).setTo(1)
-
+    modified.b shouldBe 0
     modified.a shouldBe 1
   }