SI-8894 dealias when looking at tuple components

Classic bait-and-switch: `isTupleType` dealiases, but `typeArgs` does not.
When deciding with `isTupleType`, process using `tupleComponents`.
Similar for other combos. We should really enforce this using extractors,
and only decouple when performance is actually impacted.

1 files changed, 12 insertions, 0 deletions

diff --git a/test/files/pos/t8894.scala b/test/files/pos/t8894.scala
new file mode 100644
index 0000000000..3b26f1ae7e
--- /dev/null
+++ b/test/files/pos/t8894.scala
@@ -0,0 +1,12 @@
+class CC(val i: Int, val s: String)
+object CC extends {
+  type P = (Int, String)
+
+  //def unapply(c: CC): Option[(Int, String)] = Some((c.i, c.s)) // OK
+  def unapply(c: CC): Option[P] = Some((c.i, c.s)) // fails (because of the type alias)
+}
+
+class Test {
+  val cc = new CC(23, "foo")
+  val CC(i, s) = cc
+}
\ No newline at end of file