From 4ccf3fc02f6a1b1bcadda2cf251bf1645d6a9135 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Fri, 5 Jun 2026 17:51:18 +0800
Subject: [PATCH] progress

---
 compiler/transf.nim | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/compiler/transf.nim b/compiler/transf.nim
index 3fae44b391..47be5b9c61 100644
--- a/compiler/transf.nim
+++ b/compiler/transf.nim
@@ -725,7 +725,9 @@ proc putArgInto(arg: PNode, formal: PType; borrowedFirstArg = false): TPutArgInt
   else:
     if skipTypes(formal, abstractInst).kind in {tyVar, tyLent}: result = paVarAsgn
     else: result = paFastAsgn
-  if borrowedFirstArg and result == paDirectMapping and parampatterns.exprRoot(arg) == nil:
+
+  if borrowedFirstArg and result == paDirectMapping and parampatterns.exprRoot(arg) == nil and
+           parampatterns.isAssignable(nil, arg) == arNone:
     # Inline iterators like `items(array)` borrow from the first argument.
     # If that argument is just a transient expression, materialize it so the
     # lifted closure keeps the backing storage alive across yields.