fixes #11523

(cherry picked from commit 135fdde6a9)

compiler/lambdalifting.nim

@@ -758,7 +758,8 @@ proc liftCapturedVars(n: PNode; owner: PSym; d: DetectionPass;
       # transform, let's not touch the LHS in order to make the lifting pass
       # correct when `result` is lifted
       n[0].sons[1] = liftCapturedVars(n[0].sons[1], owner, d, c)
-    else: assert n[0].kind == nkEmpty
+    else:
+      n.sons[0] = liftCapturedVars(n[0], owner, d, c)
   else:
     if owner.isIterator:
       if nfLL in n.flags:

tests/closure/tclosure_issues.nim

@@ -1,5 +1,6 @@
 discard """
-  output: '''true'''
+  output: '''true
+(999, 0)'''
 """
 
 
@@ -52,3 +53,11 @@ block tissue1911:
     proc baz() : int = helper()
 
     return (bar, baz)
+
+# bug #11523
+proc foo(): proc =
+  let a = 999
+  return proc(): (int, int) =
+    return (a, 0)
+
+echo foo()()