1 files changed, 45 insertions, 0 deletions
diff --git a/test/files/neg/t0764.scala b/test/files/neg/t0764.scala
new file mode 100644
index 0000000000..9f77a59414
--- /dev/null
+++ b/test/files/neg/t0764.scala
@@ -0,0 +1,45 @@
+class Top[A] {
+        type AType = A
+}
+
+trait Node { outer =>
+        type T <: Node
+        def prepend = new Node { type T = outer.type }
+}
+
+class Main[NextType <: Node](value: Node { type T = NextType })
+        extends Top[Node { type T = NextType }] {
+
+        new Main[AType]( (value: AType).prepend )
+}
+
+/* we've been back-and-forth on this one -- see PRs on SI-8177 for the reasoning
+I think it should compile and that the following error is due to broken =:= on existentials
+ found   : Node{type T = _1.type} where val _1: Node{type T = NextType}
+ required: Node{type T = Main.this.AType}
+    (which expands to)  Node{type T = Node{type T = NextType}}
+
+I claim (omitting the forSome for brevity, even though the premature skolemization is probably the issue)
+_1.type =:= Main.this.AType
+because
+(1) _1.type <:< Main.this.AType and (2) Main.this.AType  <:< _1.type
+(1), because:
+_1.type <:< Node{type T = NextType} (because skolemization and _1's upper bound)
+(2), because:
+Node{type T = NextType} <:< _1.type forSome val _1: Node{type T = NextType}
+because:
+Node{type T = NextType} <:< T forSome {type T <: Node{type T = NextType} with Singleton}
+because 
+Node{type T = NextType} <:< Node{type T = NextType} with Singleton
+
+hmmm.. might the with Singleton be throwing a wrench in our existential house?
+
+Behold the equivalent program which type checks without the fix for SI-8177.
+(Expand type alias, convert type member to type param;
+note the covariance to encode subtyping on type members.)
+
+class Node[+T <: Node[_]] { def prepend = new Node[this.type] }
+class Main[NextType <: Node[_]](value: Node[NextType]) {
+  new Main(value.prepend)
+}
+*/
+\ No newline at end of file