Merge pull request #8614 from dotty-staging/fix-#8598

Fix #8598: Refinements cannot have default arguments

Author: bishabosha

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

@@ -3771,6 +3771,8 @@ object Parsers {
         val problem = tree match
           case tree: MemberDef if !(tree.mods.flags & ModifierFlags).isEmpty =>
             i"refinement cannot be ${(tree.mods.flags & ModifierFlags).flagStrings().mkString("`", "`, `", "`")}"
+          case tree: DefDef if tree.vparamss.exists(_.exists(!_.rhs.isEmpty)) =>
+            i"refinement cannot have default arguments"
           case tree: ValOrDefDef =>
             if tree.rhs.isEmpty then ""
             else "refinement in cannot have a right-hand side"

tests/neg/default-arg-in-refinement.scala

@@ -0,0 +1 @@
+def foo[T <: AnyRef { def bar(a: Int = 0): Unit }](t: T): Unit = t.bar // error // error