From 4368847a98916c1c675f856b86ab337b16b64a24 Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Wed, 29 Dec 2021 16:27:00 +0100
Subject: [PATCH] Visit all trees

---
 .../dotty/tools/dotc/transform/TailRec.scala  | 16 +-----
 tests/run/tailrec-return.check                |  5 ++
 tests/run/tailrec-return.scala                | 50 +++++++++++++++++++
 3 files changed, 57 insertions(+), 14 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/TailRec.scala b/compiler/src/dotty/tools/dotc/transform/TailRec.scala
index eb239f00bcce..ba6f1599def6 100644
--- a/compiler/src/dotty/tools/dotc/transform/TailRec.scala
+++ b/compiler/src/dotty/tools/dotc/transform/TailRec.scala
@@ -277,23 +277,11 @@ class TailRec extends MiniPhase {
     def yesTailTransform(tree: Tree)(using Context): Tree =
       transform(tree, tailPosition = true)
 
-    /** If not in tail position a tree traversal may not be needed.
-     *
-     *  A recursive  call may still be in tail position if within the return
-     *  expression of a labeled block.
-     *  A tree traversal may also be needed to report a failure to transform
-     *  a recursive call of a @tailrec annotated method (i.e. `isMandatory`).
-     */
-    private def isTraversalNeeded =
-      isMandatory || tailPositionLabeledSyms.size > 0
-
     def noTailTransform(tree: Tree)(using Context): Tree =
-      if (isTraversalNeeded) transform(tree, tailPosition = false)
-      else tree
+      transform(tree, tailPosition = false)
 
     def noTailTransforms[Tr <: Tree](trees: List[Tr])(using Context): List[Tr] =
-      if (isTraversalNeeded) trees.mapConserve(noTailTransform).asInstanceOf[List[Tr]]
-      else trees
+      trees.mapConserve(noTailTransform).asInstanceOf[List[Tr]]
 
     override def transform(tree: Tree)(using Context): Tree = {
       /* Rewrite an Apply to be considered for tail call transformation. */
diff --git a/tests/run/tailrec-return.check b/tests/run/tailrec-return.check
index 6b81a566d1a7..361e76d8a285 100644
--- a/tests/run/tailrec-return.check
+++ b/tests/run/tailrec-return.check
@@ -1,2 +1,7 @@
 6
 false
+true
+false
+true
+Ada Lovelace, Alan Turing
+List(9, 10)
diff --git a/tests/run/tailrec-return.scala b/tests/run/tailrec-return.scala
index 53b5ae73b82d..aa760960403d 100644
--- a/tests/run/tailrec-return.scala
+++ b/tests/run/tailrec-return.scala
@@ -11,6 +11,56 @@ object Test:
     if n == 1 then return false
     true
 
+  @annotation.tailrec
+  def isEvenApply(n: Int): Boolean =
+    // Return inside an `Apply.fun`
+    (
+      if n != 0 && n != 1 then return isEvenApply(n - 2)
+      else if n == 1 then return false
+      else (x: Boolean) => x
+    )(true)
+
+  @annotation.tailrec
+  def isEvenWhile(n: Int): Boolean =
+    // Return inside a `WhileDo.cond`
+    while(
+      if n != 0 && n != 1 then return isEvenWhile(n - 2)
+      else if n == 1 then return false
+      else true
+    ) {}
+    true
+
+  @annotation.tailrec
+  def isEvenReturn(n: Int): Boolean =
+    // Return inside a `Return`
+    return
+      if n != 0 && n != 1 then return isEvenReturn(n - 2)
+      else if n == 1 then return false
+      else true
+
+  @annotation.tailrec
+  def names(l: List[(String, String) | Null], acc: List[String] = Nil): List[String] =
+    l match
+      case Nil => acc.reverse
+      case x :: xs =>
+        if x == null then return names(xs, acc)
+
+        val displayName = x._1 + " " + x._2
+        names(xs, displayName :: acc)
+
+  def nonTail(l: List[Int]): List[Int] =
+    l match
+      case Nil => Nil
+      case x :: xs =>
+        // The call to nonTail should *not* be eliminated
+        (x + 1) :: nonTail(xs)
+
+
   def main(args: Array[String]): Unit =
     println(sum(3))
     println(isEven(5))
+    println(isEvenApply(6))
+    println(isEvenWhile(7))
+    println(isEvenReturn(8))
+    println(names(List(("Ada",  "Lovelace"), null, ("Alan", "Turing"))).mkString(", "))
+    println(nonTail(List(8, 9)))