Merge pull request #14724 from dotty-staging/fix-14722

Extend "cannot override mutable variable" restriction to deferred var…

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -474,7 +474,7 @@ object RefChecks {
           overrideError("needs `override` modifier")
       else if (other.is(AbsOverride) && other.isIncompleteIn(clazz) && !member.is(AbsOverride))
         overrideError("needs `abstract override` modifiers")
-      else if member.is(Override) && other.is(Accessor, butNot = Deferred) && other.accessedFieldOrGetter.is(Mutable, butNot = Lazy) then
+      else if member.is(Override) && other.is(Mutable) then
         overrideError("cannot override a mutable variable")
       else if (member.isAnyOverride &&
         !(member.owner.thisType.baseClasses exists (_ isSubClass other.owner)) &&

tests/pos/i13019.scala → tests/neg/i13019.scala

@@ -10,4 +10,4 @@ class Ok2C extends Ok2 { override var i: Int = 1 }
 
 // was: variable i of type Int cannot override a mutable variable
 trait NotOk {var i: Int}
-class NotOkC extends NotOk { override var i: Int = 1 }
+class NotOkC extends NotOk { override var i: Int = 1 } // error

tests/neg/i14722.scala

@@ -0,0 +1,20 @@
+abstract class HasId(var id: String)
+
+case class Entity(override val id: String) extends HasId(id) // error
+
+object Test extends App {
+  val entity = Entity("0001")
+  entity.id = "0002"
+  println(entity.id)
+}
+
+trait HasId2:
+  var id: String = ""
+
+case class Entity2(override val id: String) extends HasId2 // error
+
+trait HasId3:
+  def id: String
+  def id_=(x: String): Unit
+
+case class Entity3(override var id: String) extends HasId3 // ok