Promote enum error to Checking

Author: som-snytt

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

@@ -1486,6 +1486,9 @@ trait Checking {
         report.error(ClassCannotExtendEnum(cls, firstParent), cdef.srcPos)
     if cls.isEnumClass && !isJavaEnum then
       checkExistingOrdinal
+    if cls.isEnum  && cls.is(Abstract) then
+      if cls.children.exists(!_.isClass) && cls.info.decls.exists(_.is(Deferred)) then
+        report.error(em"enum $cls has an abstract member and an unparameterized case", cdef.srcPos)
   }
 
   /** Check that the firstParent for an enum case derives from the declaring enum class, if not, adds it as a parent

tests/neg/i22734.check

@@ -1,8 +1,9 @@
--- Error: tests/neg/i22734.scala:3:7 -----------------------------------------------------------------------------------
-3 |object X extends T // error status quo
-  |       ^
-  |       object creation impossible, since def item: String in trait T is not defined
--- Error: tests/neg/i22734.scala:6:7 -----------------------------------------------------------------------------------
-6 |  case Empty // error
-  |       ^
-  |       object creation impossible, since def item: String in class Foo is not defined
+-- Error: tests/neg/i22734.scala:5:5 -----------------------------------------------------------------------------------
+ 5 |enum Foo { // error
+   |^
+   |enum class Foo has an abstract member and an unparameterized case
+ 6 |  case Empty // refchecks error
+ 7 |  case NonEmpty(item: String)
+ 8 |  case Decoy // hopefully not here
+ 9 |  def item: String
+10 |}

tests/neg/i22734.scala

@@ -1,9 +1,9 @@
 trait T:
   def item: String
-object X extends T // error status quo
+object X extends T // refchecks error status quo
 
-enum Foo {
-  case Empty // error
+enum Foo { // error
+  case Empty // refchecks error
   case NonEmpty(item: String)
   case Decoy // hopefully not here