From 0c02ecf45448775913238533f60eed7c14146cdb Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 7 Feb 2019 21:49:54 +0100
Subject: [PATCH] Tests to clarify projection and erased paths

---
 tests/neg/erased-path.scala            | 10 +++++++++
 tests/neg/erased-singleton.scala       |  7 +++++++
 tests/pos-scala2/type-projection.scala | 28 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+)
 create mode 100644 tests/neg/erased-path.scala
 create mode 100644 tests/neg/erased-singleton.scala
 create mode 100644 tests/pos-scala2/type-projection.scala

diff --git a/tests/neg/erased-path.scala b/tests/neg/erased-path.scala
new file mode 100644
index 000000000000..f7fbda262e8e
--- /dev/null
+++ b/tests/neg/erased-path.scala
@@ -0,0 +1,10 @@
+
+trait Sys { type X }
+
+trait Obj {
+  erased val s: Sys
+  lazy val t: Sys
+
+  type S = s.X  // error: not a legal path, since nonfinal
+  type T = t.X  // error: not a legal path, since nonfinal
+}
\ No newline at end of file
diff --git a/tests/neg/erased-singleton.scala b/tests/neg/erased-singleton.scala
new file mode 100644
index 000000000000..d1aad7093e4c
--- /dev/null
+++ b/tests/neg/erased-singleton.scala
@@ -0,0 +1,7 @@
+trait Sys
+
+trait Obj {
+  erased val s: Sys
+
+  type S = s.type  // error: non final
+}
diff --git a/tests/pos-scala2/type-projection.scala b/tests/pos-scala2/type-projection.scala
new file mode 100644
index 000000000000..e7d932fe83cf
--- /dev/null
+++ b/tests/pos-scala2/type-projection.scala
@@ -0,0 +1,28 @@
+trait Txn[S <: Sys[S]] {
+  def system: S
+
+  def newId(): S#Id
+
+  def newVar[A](id: S#Id, init: A): S#Vr[A]
+}
+
+trait Var[Tx, A] {
+  def apply()(implicit tx: Tx): A
+
+  def update(x: A)(implicit tx: Tx): Unit
+}
+
+trait Sys[S <: Sys[S]] {
+  type Tx <: Txn[S]
+  type Id
+  type Vr[A] <: Var[S#Tx, A]
+}
+
+abstract class UseCase[S <: Sys[S]](id: S#Id) {
+  def mk(x: Int)(implicit tx: S#Tx): S#Vr[Int] = {
+    val vr = tx.newVar[Int](id, x)
+    vr
+  }
+
+  def rd(vr: S#Vr[Int])(implicit tx: S#Tx): Int = vr()
+}