$ scala
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_60).
Type in expressions for evaluation. Or try :help.

scala> val x = "hi" ; "$x"
x: String = hi
res0: String = $x

scala> :se -Xlint:missing-interpolator

scala> val x = "hi" ; "$x"
<console>:13: warning: possible missing interpolator: detected interpolated identifier `$x`
        "$x"
        ^
x: String = hi
res1: String = $x

scala> :se -Xlint:-missing-interpolator

scala> val x = "hi" ; "$x"
<console>:13: warning: possible missing interpolator: detected interpolated identifier `$x`
        "$x"
        ^
x: String = hi
res2: String = $x