#20145 - bugfix when a return tail recurse is called inside a val definition, previously this would neither optimise nor fail.

Author: Lucy Martin

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)

tests/run/i20145.check

@@ -0,0 +1 @@
+10000001

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))