CPS: enable return expressions in CPS code if they are in tail position

Adds a stack of context trees to AnnotationChecker(s). Here, it is used to
enforce that adaptAnnotations will only adapt the annotation of a return
expression if the expected type is a CPS type.

The remove-tail-return transform is reasonably general, covering cases such as
try-catch-finally. Moreover, an error is thrown if, in a CPS method, a return
is encountered which is not in a tail position such that it will be removed
subsequently.

6 files changed, 103 insertions, 0 deletions

diff --git a/test/files/continuations-neg/ts-1681-nontail-return.check b/test/files/continuations-neg/ts-1681-nontail-return.check
new file mode 100644
index 0000000000..8fe15f154b
--- /dev/null
+++ b/test/files/continuations-neg/ts-1681-nontail-return.check
@@ -0,0 +1,4 @@
+ts-1681-nontail-return.scala:10: error: return expressions in CPS code must be in tail position
+      return v
+      ^
+one error found
diff --git a/test/files/continuations-neg/ts-1681-nontail-return.scala b/test/files/continuations-neg/ts-1681-nontail-return.scala
new file mode 100644
index 0000000000..af86ad304f
--- /dev/null
+++ b/test/files/continuations-neg/ts-1681-nontail-return.scala
@@ -0,0 +1,18 @@
+import scala.util.continuations._
+
+class ReturnRepro { 
+  def s1: Int @cpsParam[Any, Unit] = shift { k => k(5) } 
+  def caller = reset { println(p(3)) }
+
+  def p(i: Int): Int @cpsParam[Unit, Any] = { 
+    val v= s1 + 3 
+    if (v == 8)
+      return v
+    v + 1
+  } 
+}
+
+object Test extends App {
+  val repro = new ReturnRepro
+  repro.caller
+}
diff --git a/test/files/continuations-run/ts-1681-2.check b/test/files/continuations-run/ts-1681-2.check
new file mode 100644
index 0000000000..35b3c93780
--- /dev/null
+++ b/test/files/continuations-run/ts-1681-2.check
@@ -0,0 +1,5 @@
+8
+hi
+8
+from try
+8
diff --git a/test/files/continuations-run/ts-1681-2.scala b/test/files/continuations-run/ts-1681-2.scala
new file mode 100644
index 0000000000..8a896dec2c
--- /dev/null
+++ b/test/files/continuations-run/ts-1681-2.scala
@@ -0,0 +1,44 @@
+import scala.util.continuations._
+
+class ReturnRepro { 
+  def s1: Int @cps[Any] = shift { k => k(5) } 
+  def caller = reset { println(p(3)) }
+  def caller2 = reset { println(p2(3)) }
+  def caller3 = reset { println(p3(3)) }
+
+  def p(i: Int): Int @cps[Any] = { 
+    val v= s1 + 3 
+    return v 
+  } 
+
+  def p2(i: Int): Int @cps[Any] = {
+    val v = s1 + 3
+    if (v > 0) {
+      println("hi")
+      return v
+    } else {
+      println("hi")
+      return 8
+    }
+  }
+
+  def p3(i: Int): Int @cps[Any] = {
+    val v = s1 + 3
+    try {
+      println("from try")
+      return v
+    } catch {
+      case e: Exception =>
+        println("from catch")
+        return 7
+    }
+  }
+
+}
+
+object Test extends App {
+  val repro = new ReturnRepro
+  repro.caller
+  repro.caller2
+  repro.caller3
+}
diff --git a/test/files/continuations-run/ts-1681.check b/test/files/continuations-run/ts-1681.check
new file mode 100644
index 0000000000..85176d8e66
--- /dev/null
+++ b/test/files/continuations-run/ts-1681.check
@@ -0,0 +1,3 @@
+8
+hi
+8
diff --git a/test/files/continuations-run/ts-1681.scala b/test/files/continuations-run/ts-1681.scala
new file mode 100644
index 0000000000..efb1abae15
--- /dev/null
+++ b/test/files/continuations-run/ts-1681.scala
@@ -0,0 +1,29 @@
+import scala.util.continuations._
+
+class ReturnRepro { 
+  def s1: Int @cpsParam[Any, Unit] = shift { k => k(5) } 
+  def caller = reset { println(p(3)) }
+  def caller2 = reset { println(p2(3)) }
+
+  def p(i: Int): Int @cpsParam[Unit, Any] = { 
+    val v= s1 + 3 
+    return v 
+  } 
+
+  def p2(i: Int): Int @cpsParam[Unit, Any] = {
+    val v = s1 + 3
+    if (v > 0) {
+      println("hi")
+      return v
+    } else {
+      println("hi")
+      return 8
+    }
+  }
+}
+
+object Test extends App {
+  val repro = new ReturnRepro
+  repro.caller
+  repro.caller2
+}