SI-6675 -Xlint arity enforcement for extractors

Extractor Patterns changed in 2.10.0 to implement
the letter of the spec, which allows a single binding
to capture an entire TupleN. But this can hide arity
mismatches, especially if the case body uses the
bound value as an `Any`.

This change warns when this happens under -Xlint.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/files/neg/t6675.scala b/test/files/neg/t6675.scala
new file mode 100644
index 0000000000..4d500b77ba
--- /dev/null
+++ b/test/files/neg/t6675.scala
@@ -0,0 +1,13 @@
+object X {
+  def unapply(s: String): Option[(Int,Int,Int)] = Some((1,2,3))
+}
+
+object Y {
+  def unapplySeq(s: String): Option[Seq[(Int,Int,Int)]] = Some(Seq((1,2,3)))
+}
+
+object Test {
+  "" match { case X(b) => b } // should warn under -Xlint. Not an error because of SI-6111
+
+  "" match { case Y(b) => b } // no warning
+}