extractor error message is not clear

[He-Pin]

Minimized code

val (a,b) = (1,2,3)

Output

1 |val (a,b) = (1,2,3)
  |    ^
  |this case is unreachable since type (Int, Int, Int) is not a subclass of class Tuple2

and Scala2 gives:

constructor cannot be instantiated to expected type;
 found   : (T1, T2)
 required: (Int, Int, Int)

Expectation