Error message not helpful when val definition contains extra '()'

[scabug]

If a val definition contains an extra set of parenthesis, like if not correctly transforming a def into a val, the error reported by the compiler is not really helpful.

$ scalac test.scala 
test.scala:5: error: not found: value a
  val a(): String = ""
      ^
one error found

It would be better if the error was something like: expected ':' or '=', found '('

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6564?orig=1
Reporter: @skyluc
Affected Versions: 2.9.2, 2.10.0-RC1

[scabug]

@retronym said:
Problem is that is is valid syntactically.

scala> object a { def unapply(a: Any): Boolean = true }
defined module a

scala> { val a(): String = ""; 0 }
res3: Int = 0

scala> cm.universe.reify { val a(): String = "" }
res18: cm.universe.Expr[Unit] =
Expr[Unit]({
  <synthetic> private[this] val x$1 = ("": @unchecked: String) match {
    case a() => ()
  };
  ()
})

scala> val cm = reflect.runtime.currentMirror
cm: reflect.runtime.universe.Mirror = JavaMirror with ...

scala> cm.universe.showRaw(res18)
res19: String =
Expr[Unit]({
  <synthetic> private[this] val x$1 = ("": @unchecked: String) match {
    case a() => ()
  };
  ()
})

scala> cm.universe.showRaw(res18.tree)
res20: String = Block(List(ValDef(Modifiers(PRIVATE | LOCAL | SYNTHETIC), newTermName("x$1"), TypeTree(), Match(Typed(Annotated(Apply(Select(New(Ident(scala.unchecked)), nme.CONSTRUCTOR), List()), Literal(Constant(""))), Ident(newTypeName("String"))), List(CaseDef(Apply(Select(Select(Select(Select(Ident($line34), newTermName("$read")), newTermName("$iw")), newTermName("$iw")), newTermName("a")), List()), EmptyTree, Literal(Constant(()))))))), Literal(Constant(())))

[scabug]

@adriaanm said:
Unassigning as milestone deadline was reached.

[som-snytt]

Punting this in favor of actual correctness bugs in this area. Possible umbrella issue: #11800

The use case is switching def to val.

This case is probably a scalafix lint.