From d260855f35dee424b86e19c8d264266a7dadce62 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Wed, 15 Oct 2025 13:24:48 +0800
Subject: [PATCH] fixes  #25048; Closure environment wrongly marked as cyclic
 (#25220)

fixes  #25048

```nim
proc canFormAcycleAux =
  of tyObject:
    # Inheritance can introduce cyclic types, however this is not relevant
    # as the type that is passed to 'new' is statically known!
    # er but we use it also for the write barrier ...
    if tfFinal notin t.flags:
      # damn inheritance may introduce cycles:
      result = true
```

It seems that all objects without `tfFinal` in their flags are
registering cycles. It doesn't seem that `Env` can be a cyclic type
because of inheritance since it is not going to be inherited after all
by another `Env` object type

(cherry picked from commit f191ba8dddb3e61fb013a4fa9771bd95272faaa7)
---
 compiler/lambdalifting.nim | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/lambdalifting.nim b/compiler/lambdalifting.nim
index c8c5acf974..048b286aae 100644
--- a/compiler/lambdalifting.nim
+++ b/compiler/lambdalifting.nim
@@ -150,6 +150,7 @@ template isIterator*(owner: PSym): bool =
 
 proc createEnvObj(g: ModuleGraph; idgen: IdGenerator; owner: PSym; info: TLineInfo): PType =
   result = createObj(g, idgen, owner, info, final=false)
+  result.flags.incl tfFinal
   if owner.isIterator:
     rawAddField(result, createStateField(g, owner, idgen))