$ scala -J -Xss512k
scala>val tup = <paste>
scala>summon[Tuple.Last[tup.type] =:= Int]
-- Error: ----------------------------------------------------------------------
1 |summon[Tuple.Last[tup.type] =:= Int]
 | ^
 |Recursion limit exceeded.
 |Maybe there is an illegal cyclic reference?
 |If that's not the case, you could also try to increase the stacksize using the -Xss JVM option.
 |For the unprocessed stack trace, compile with -Xno-enrich-error-messages.
 |A recurring operation is (inner to outer):
 |
 | reduce type (Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int,
 | Int, Int, Int, Int, Int, Int) match ...

object Tuple {
 ...
 /** Type of the last element of a tuple */
 type Last[X <: Tuple] = X match {
 case x *: EmptyTuple => x
 case _ *: xs => Last[xs]
 }