From 01029165ccb32c90a3079947d76a1ff0d49febff Mon Sep 17 00:00:00 2001
From: Javier de Jesus <javier.dejesusj9@gmail.com>
Date: Mon, 22 Jun 2026 00:02:50 +0000
Subject: [PATCH] fix: avoid ENAMETOOLONG when chat_template is an inline jinja
 string

A long literal chat_template made the .jinja resource lookup build a
path whose final component exceeds NAME_MAX, so .is_file() raised
OSError(ENAMETOOLONG) instead of returning False. Only attempt the
template-name lookup when chat_template looks like a bare name, falling
through to treat the value as an inline template otherwise.
---
 mergekit/merge.py           | 13 +++++++++----
 tests/test_chat_template.py | 24 ++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/mergekit/merge.py b/mergekit/merge.py
index 5c3a7ea4..4f24caff 100644
--- a/mergekit/merge.py
+++ b/mergekit/merge.py
@@ -186,10 +186,15 @@ def _set_chat_template(
         LOG.info(f"Auto-selected chat template: {chat_template}")
 
     elif (
-        t := importlib.resources.files(chat_templates).joinpath(
-            chat_template + ".jinja"
-        )
-    ).is_file():
+        len(chat_template) < 256
+        and "\n" not in chat_template
+        and "{" not in chat_template
+        and (
+            t := importlib.resources.files(chat_templates).joinpath(
+                chat_template + ".jinja"
+            )
+        ).is_file()
+    ):
         chat_template = t.read_text()
 
     elif len(chat_template) < 20 or "{" not in chat_template:
diff --git a/tests/test_chat_template.py b/tests/test_chat_template.py
index a5e98d14..bdc1e083 100644
--- a/tests/test_chat_template.py
+++ b/tests/test_chat_template.py
@@ -62,3 +62,27 @@ def test_template_literal_jinja(self, model_base, model_b):
             config,
             validate=lambda p: check_chat_template(p, "{{messages[0]['content']}}"),
         )
+
+    def test_template_long_literal_jinja(self, model_base, model_b):
+        template = (
+            "{% for message in messages %}"
+            + "{{ message['role'] }}: {{ message['content'] }}\n"
+            + "{% endfor %}"
+            + "{# "
+            + "x" * 300
+            + " #}"
+        )
+        config = MergeConfiguration(
+            merge_method="linear",
+            models=[
+                InputModelDefinition(model=model_base, parameters={"weight": 0.5}),
+                InputModelDefinition(model=model_b, parameters={"weight": 0.5}),
+            ],
+            base_model=model_base,
+            dtype="bfloat16",
+            chat_template=template,
+        )
+        run_and_check_merge(
+            config,
+            validate=lambda p: check_chat_template(p, "x" * 300),
+        )