line 3 and 5 seem to work just fine; line 4 yields that unfriendly error message

compile output

[error] package.scala:4: macros cannot be partially applied
[error]     def mf(args: Any*): String = sc.f(args:_*).stripMargin
[error]                                      ^

package.scala

package object app {
  implicit class MultilineInterpolation(val sc: StringContext) extends AnyVal {
    def ms(args: Any*): String = sc.s(args:_*).stripMargin
    def mf(args: Any*): String = sc.f(args:_*).stripMargin
    def mraw(args: Any*): String = sc.raw(args:_*).stripMargin
  }
}