From 036b86bea26c1cd082b0a9dca31fcdf2b7b7dd87 Mon Sep 17 00:00:00 2001
From: Lucy Martin <lucy.martin@nttdata.com>
Date: Wed, 19 Jun 2024 16:56:34 +0100
Subject: [PATCH] #20145 - bugfix when a return tail recurse is called inside a
 val definition, previously this would neither optimise nor fail.

---
 .../src/dotty/tools/dotc/transform/TailRec.scala  |  4 ++--
 tests/run/i20145.check                            |  1 +
 tests/run/i20145.scala                            | 15 +++++++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)
 create mode 100644 tests/run/i20145.check
 create mode 100644 tests/run/i20145.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/TailRec.scala b/compiler/src/dotty/tools/dotc/transform/TailRec.scala
index d054c5aa6232..b8052721ff27 100644
--- a/compiler/src/dotty/tools/dotc/transform/TailRec.scala
+++ b/compiler/src/dotty/tools/dotc/transform/TailRec.scala
@@ -430,8 +430,8 @@ class TailRec extends MiniPhase {
           tree
 
         case tree: ValDef =>
-          if (isMandatory) noTailTransform(tree.rhs)
-          tree
+          // This could contain a return statement in a code block, so we do have to go into it.
+          cpy.ValDef(tree)(rhs = noTailTransform(tree.rhs))
 
         case tree: DefDef =>
           if (isMandatory)
diff --git a/tests/run/i20145.check b/tests/run/i20145.check
new file mode 100644
index 000000000000..f6af6debe594
--- /dev/null
+++ b/tests/run/i20145.check
@@ -0,0 +1 @@
+10000001
diff --git a/tests/run/i20145.scala b/tests/run/i20145.scala
new file mode 100644
index 000000000000..ea26f00e2c89
--- /dev/null
+++ b/tests/run/i20145.scala
@@ -0,0 +1,15 @@
+import scala.annotation.tailrec
+@tailrec
+def foo(i: Int): Int = {
+  if (i > 10000000) {
+    i
+  } else {
+    val bar: String = {
+      return foo(i + 1)
+      "foo"
+    }
+    -1
+  }
+}
+@main def Test =
+  println(foo(0))
\ No newline at end of file