From 4d235ad2bd2a2741290ba6aa57de17409ffd3383 Mon Sep 17 00:00:00 2001
From: som-snytt <som.snytt@gmail.com>
Date: Mon, 14 Jul 2025 14:49:04 -0700
Subject: [PATCH] Check path of module prefix for tailrec (#23491)

Fixes #23444
[Cherry-picked 9396bbe267b844a8cf4262ad375e1e4e96d0cf38]
---
 .../dotty/tools/dotc/transform/TailRec.scala  |  5 ++++-
 tests/run/i23444.scala                        | 22 +++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 tests/run/i23444.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/TailRec.scala b/compiler/src/dotty/tools/dotc/transform/TailRec.scala
index e1bd3136f895..a9cfd40967e2 100644
--- a/compiler/src/dotty/tools/dotc/transform/TailRec.scala
+++ b/compiler/src/dotty/tools/dotc/transform/TailRec.scala
@@ -344,7 +344,10 @@ class TailRec extends MiniPhase {
               case prefix: This if prefix.symbol == enclosingClass =>
                 // Avoid assigning `this = this`
                 assignParamPairs
-              case prefix if prefix.symbol.is(Module) && prefix.symbol.moduleClass == enclosingClass =>
+              case prefix
+              if prefix.symbol.is(Module)
+              && prefix.symbol.moduleClass == enclosingClass
+              && isPurePath(prefix) =>
                 // Avoid assigning `this = MyObject`
                 assignParamPairs
               case _ =>
diff --git a/tests/run/i23444.scala b/tests/run/i23444.scala
new file mode 100644
index 000000000000..ada7545e077f
--- /dev/null
+++ b/tests/run/i23444.scala
@@ -0,0 +1,22 @@
+
+import annotation.*
+
+class Path(action: () => Unit, parent: Option[Path]):
+  object O:
+    @tailrec
+    def apply(): Unit =
+      action()
+
+      parent match
+        case Some(p) =>
+          p.O.apply()
+        case None =>
+
+@main def Test: Unit =
+  var counter = 0
+  val fun = () => {
+    counter += 1
+    if counter > 2 then throw AssertionError("bad loop")
+  }
+  val path = Path(fun, Some(Path(fun, None)))
+  path.O()