Fix missing members reporting for var setters

Suppress reporting a missing setter only if the corresponding getter was also reported as missing. Fixes #23474

Author: odersky

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

@@ -703,10 +703,16 @@ object RefChecks {
  // to consolidate getters and setters.
  val grouped = missing.groupBy(_.underlyingSymbol.name)
 
+ def isDuplicateSetter(sym: Symbol): Boolean =
+ sym.isSetter && {
+ val field = sym.accessedFieldOrGetter
+ grouped.getOrElse(field.name, Nil).contains(field)
+ }
+
  val missingMethods = grouped.toList flatMap {
  case (name, syms) =>
  lastOverrides(syms)
- .filterConserve(!_.isSetter)
+ .filterConserve(!isDuplicateSetter(_)) // Avoid reporting override error for both `x` and setter `x_=`
  .distinctBy(_.signature) // Avoid duplication for similar definitions (#19731)
  }
 

tests/neg/i23474.check

@@ -0,0 +1,25 @@
+-- Error: tests/neg/i23474.scala:5:11 ----------------------------------------------------------------------------------
+5 |case class Y(val comment: String) extends Comment // error
+ | ^
+ | class Y needs to be abstract, since var comment_=(x$1: String): Unit in trait Comment is not defined 
+ | (Note that an abstract var requires a setter in addition to the getter)
+-- Error: tests/neg/i23474.scala:7:6 -----------------------------------------------------------------------------------
+7 |class Z extends Comment: // error
+ | ^
+ | class Z needs to be abstract, since var comment_=(x$1: String): Unit in trait Comment is not defined 
+ | (Note that an abstract var requires a setter in addition to the getter)
+-- [E164] Declaration Error: tests/neg/i23474.scala:11:15 --------------------------------------------------------------
+11 | override def comment: String = "" // error
+ | ^
+ | error overriding variable comment in trait Comment of type String;
+ | method comment of type => String cannot override a mutable variable
+-- Error: tests/neg/i23474.scala:10:6 ----------------------------------------------------------------------------------
+10 |class X extends Comment: // error
+ | ^
+ | class X needs to be abstract, since var comment_=(x$1: String): Unit in trait Comment is not defined 
+ | (Note that an abstract var requires a setter in addition to the getter)
+-- Error: tests/neg/i23474.scala:13:6 ----------------------------------------------------------------------------------
+13 |class W extends Comment // error
+ | ^
+ | class W needs to be abstract, since var comment: String in trait Comment is not defined 
+ | (Note that variables need to be initialized to be defined)

tests/neg/i23474.scala

@@ -0,0 +1,19 @@
+trait Comment {
+ var comment: String
+}
+
+case class Y(val comment: String) extends Comment // error
+
+class Z extends Comment: // error
+ val comment: String = ""
+
+class X extends Comment: // error
+ override def comment: String = "" // error
+
+class W extends Comment // error
+
+
+class OK:
+ val comment: String = ""
+ def comment_=(x: String): Unit = ()
+