Make instance defs final

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -685,7 +685,7 @@ object desugar {
         // implicit wrapper is typechecked in same scope as constructor, so
         // we can reuse the constructor parameters; no derived params are needed.
         DefDef(className.toTermName, constrTparams, defParamss, classTypeRef, creatorExpr)
-          .withMods(companionMods | Synthetic | Implicit)
+          .withMods(companionMods | Synthetic | Implicit | Final)
           .withSpan(cdef.span) :: Nil
       }
 

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2582,7 +2582,7 @@ object Parsers {
           if (tparams.isEmpty && vparamss.isEmpty) ModuleDef(name, templ)
           else TypeDef(name.toTypeName, templ)
         }
-      finalizeDef(instDef, addMod(mods, instanceMod), start)
+      finalizeDef(instDef, addMod(mods, instanceMod) | Final, start)
     }
 
 /* -------- TEMPLATES ------------------------------------------- */