From 351b2e445fe288652251b16ee1f69077dd5e77c7 Mon Sep 17 00:00:00 2001
From: Jah-yee <166608075+Jah-yee@users.noreply.github.com>
Date: Sat, 3 Oct 2026 22:29:55 +0800
Subject: [PATCH] fix: preserve dict subclass types in
 _deepcopy_with_exceptions

When copying dict subclasses (defaultdict, OrderedDict, Counter),
the function was returning a plain dict instead of preserving the type.
A defaultdict would lose its default_factory, and an OrderedDict
would become a regular dict.

The fix checks if the dict is a plain dict (type is dict) and uses
the fast path. For subclasses, it creates a shallow copy, clears it,
and repopulates with deep-copied values, preserving the subclass type.
---
 haystack/core/pipeline/utils.py | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/haystack/core/pipeline/utils.py b/haystack/core/pipeline/utils.py
index d1263dec973..efed945d749 100644
--- a/haystack/core/pipeline/utils.py
+++ b/haystack/core/pipeline/utils.py
@@ -4,7 +4,7 @@
 
 import heapq
 from collections.abc import Callable
-from copy import deepcopy
+import copy
 from functools import wraps
 from itertools import count
 from typing import Any
@@ -42,7 +42,16 @@ def _deepcopy_with_exceptions(obj: Any) -> Any:
         return type(obj)(_deepcopy_with_exceptions(v) for v in obj)
 
     if isinstance(obj, dict):
-        return {k: _deepcopy_with_exceptions(v) for k, v in obj.items()}
+        if type(obj) is dict:
+            return {k: _deepcopy_with_exceptions(v) for k, v in obj.items()}
+        try:
+            new = copy.copy(obj)
+            new.clear()
+            for k, v in obj.items():
+                new[k] = _deepcopy_with_exceptions(v)
+            return new
+        except Exception:
+            return {k: _deepcopy_with_exceptions(v) for k, v in obj.items()}
 
     # Components and Tools often contain objects that we do not want to deepcopy or are not deepcopyable
     # (e.g. models, clients, etc.). In this case we return the object as-is.