SI-9943 final/sealed class does not yield SAM type

Cannot subclass such a class. (Well, we could subclass a sealed
class in the same compilation unit. We ignore this for simplicity.)

This is a bit of a sneaky fix for this bug, but our hand
is pretty much forced by other constraints, in this intersection
of overload resolution involving built-in function types and SAMs,
and type inference for higher-order function literals (#5307).

Luckily, in this particular issue, the overloading clash seems
accidental. The `sealed` `<:<` class is not a SAM type as it
cannot be subclassed outside of `Predef`. For simplicity,
we don't consider where the SAM conversion occurs and exclude
all sealed classes from yielding SAM types.

Thanks to Miles for pointing out that `final` was missing in my
first iteration of this fix.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/files/pos/t9943.scala b/test/files/pos/t9943.scala
new file mode 100644
index 0000000000..0d4717ccbb
--- /dev/null
+++ b/test/files/pos/t9943.scala
@@ -0,0 +1,9 @@
+class Foo[T] {
+  def toMap[K, V](implicit ev: Foo[T] <:< Foo[(K, V)]): Foo[Map[K, V]] = null
+  def toMap[K](keySelector:    T      =>  K): Foo[Map[K, T]] = null
+}
+
+object Foo {
+  (??? : Foo[Int])           toMap (_ % 2)
+  (??? : Foo[(Int, String)]).toMap
+}