Add note on recursive lazy vals

Author: allanrenucci

docs/docs/reference/changed/lazy-vals-spec.md

@@ -69,6 +69,12 @@ initialized by some thread. The state 2 denotes that there are concurrent reader
 The state 3 represents a lazy val that has been initialized. `<field-id>` is the id of the lazy
 val. This id grows with the number of volatile lazy vals defined in the class.
 
+## Note on recursive lazy vals
+
+Ideally recursive lazy vals should be flagged as an error. The current behavior for `@volatile`
+recursive lazy vals is undefined (initialization may result in a deadlock). Non `@volatile` lazy
+vals behave as in Scala 2.
+
 ## Reference
 
 * [SIP-20]

tests/run/i1856.check

@@ -0,0 +1,22 @@
+Iteration 0
+Iteration 1
+Iteration 2
+Iteration 3
+Iteration 4
+Iteration 5
+Iteration 6
+Iteration 7
+Iteration 8
+Iteration 9
+42
+Iteration 0
+Iteration 1
+Iteration 2
+Iteration 3
+Iteration 4
+Iteration 5
+Iteration 6
+Iteration 7
+Iteration 8
+Iteration 9
+42

tests/run/i1856.scala

@@ -0,0 +1,27 @@
+object Test {
+  var count = 0
+  lazy val lzy: Int = {
+    if (count < 10) {
+      println(s"Iteration $count")
+      count += 1
+      lzy
+    } else 42
+  }
+
+  def lzy2 = {
+    var countLocal = 0
+    lazy val lzyLocal: Int = {
+      if (countLocal < 10) {
+        println(s"Iteration $countLocal")
+        countLocal += 1
+        lzyLocal
+      } else 42
+    }
+    lzyLocal
+  }
+
+  def main(args: Array[String]): Unit = {
+    println(lzy)
+    println(lzy2)
+  }
+}