I'm using that, sometimes

src/preserves.nim

@@ -890,7 +890,7 @@ proc fromPreserve*[T, E](v: var T; pr: Preserve[E]): bool =
     of pkRecord, pkSequence:
       if pr.len <= tupleLen(T):
         result = true
-        var i: int
+        var i {.used.}: int
         for f in fields(v):
           if result and i < pr.len:
             result = result and fromPreserve(f, pr[i])