SI-6881 Detect reference equality when comparing streams

`==` already covers this case. We override `equals` in `Stream` to do
the same when `equals` is called directly. This takes care of identical
streams.

To support short-circuiting equality checks on elements prepended to
identical streams we also override `sameElements` in `Cons` to treat
the case where both sides are `Cons` separately.

Tests in StreamTest.test_reference_equality.

1 files changed, 10 insertions, 0 deletions

diff --git a/test/junit/scala/collection/immutable/StreamTest.scala b/test/junit/scala/collection/immutable/StreamTest.scala
index fad4e502eb..7046525f37 100644
--- a/test/junit/scala/collection/immutable/StreamTest.scala
+++ b/test/junit/scala/collection/immutable/StreamTest.scala
@@ -107,4 +107,14 @@ class StreamTest {
   def withFilter_map_properly_lazy_in_tail: Unit = {
     assertStreamOpLazyInTail(_.withFilter(_ % 2 == 0).map(identity), List(1, 2))
   }
+
+  @Test // SI-6881
+  def test_reference_equality: Unit = {
+    // Make sure we're tested with reference equality
+    val s = Stream.from(0)
+    assert(s == s, "Referentially identical streams should be equal (==)")
+    assert(s equals s, "Referentially identical streams should be equal (equals)")
+    assert((0 #:: 1 #:: s) == (0 #:: 1 #:: s), "Cons of referentially identical streams should be equal (==)")
+    assert((0 #:: 1 #:: s) equals (0 #:: 1 #:: s), "Cons of referentially identical streams should be equal (equals)")
+  }
 }