From e7e8ea4752505f6c90a1fc747782b164c65be76b Mon Sep 17 00:00:00 2001
From: Arie Bovenberg <a.c.bovenberg@gmail.com>
Date: Mon, 5 Oct 2026 20:34:58 +0200
Subject: [PATCH] Remove call-stack inspection from DateTime.__add__

---
 src/pendulum/datetime.py        | 20 ++++++++++++++------
 tests/datetime/test_add.py      |  9 +++++++++
 tests/datetime/test_timezone.py | 25 +++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/src/pendulum/datetime.py b/src/pendulum/datetime.py
index 0d7e4f9a0..4a363a500 100644
--- a/src/pendulum/datetime.py
+++ b/src/pendulum/datetime.py
@@ -2,7 +2,6 @@
 
 import calendar
 import datetime
-import traceback
 
 from typing import TYPE_CHECKING
 from typing import Any
@@ -1238,10 +1237,6 @@ def __add__(self, other: datetime.timedelta) -> Self:
         if not isinstance(other, datetime.timedelta):
             return NotImplemented
 
-        caller = traceback.extract_stack(limit=2)[0].name
-        if caller == "astimezone":
-            return super().__add__(other)
-
         return self._add_timedelta_(other)
 
     def __radd__(self, other: datetime.timedelta) -> Self:
@@ -1278,7 +1273,20 @@ def combine(
         return cls.instance(datetime.datetime.combine(date, time), tz=tzinfo)
 
     def astimezone(self, tz: datetime.tzinfo | None = None) -> Self:
-        dt = super().astimezone(tz)
+        # Convert a plain datetime: tzinfo.fromutc() implementations add
+        # timedeltas to the value they're given and expect the standard
+        # library's arithmetic, not the overridden __add__.
+        dt = datetime.datetime(
+            self.year,
+            self.month,
+            self.day,
+            self.hour,
+            self.minute,
+            self.second,
+            self.microsecond,
+            tzinfo=self.tzinfo,
+            fold=self.fold,
+        ).astimezone(tz)
 
         return self.__class__(
             dt.year,
diff --git a/tests/datetime/test_add.py b/tests/datetime/test_add.py
index 409f5bd40..94ac26df4 100644
--- a/tests/datetime/test_add.py
+++ b/tests/datetime/test_add.py
@@ -108,6 +108,15 @@ def test_add_timedelta():
     assert d.microsecond == 777777
 
 
+def test_add_timedelta_does_not_depend_on_caller_name():
+    def astimezone(d):
+        return d + timedelta(hours=24)
+
+    d = pendulum.datetime(2013, 3, 30, 12, tz="Europe/Paris")
+
+    assert_datetime(astimezone(d), 2013, 3, 31, 13)
+
+
 def test_add_duration():
     duration = pendulum.duration(
         years=2, months=3, days=6, seconds=45, microseconds=123456
diff --git a/tests/datetime/test_timezone.py b/tests/datetime/test_timezone.py
index 343435d86..af757ef62 100644
--- a/tests/datetime/test_timezone.py
+++ b/tests/datetime/test_timezone.py
@@ -1,5 +1,11 @@
 from __future__ import annotations
 
+from datetime import datetime
+
+import pytest
+
+from dateutil import tz
+
 import pendulum
 
 from tests.conftest import assert_datetime
@@ -36,3 +42,22 @@ def test_astimezone():
     d = d.astimezone(pendulum.timezone("Europe/Paris"))
     assert d.timezone_name == "Europe/Paris"
     assert_datetime(d, now.year, now.month, now.day, now.hour + 1, now.minute)
+
+
+def test_astimezone_with_tzinfo_doing_arithmetic_in_fromutc():
+    # dateutil's tzoffset.fromutc() adds its offset to the datetime it's given
+    cest = tz.tzoffset("CEST", 7200)
+    d = pendulum.datetime(2024, 7, 1, 12)
+
+    d = d.astimezone(cest)
+    assert isinstance(d, pendulum.DateTime)
+    assert d.tzinfo is cest
+    assert_datetime(d, 2024, 7, 1, 14)
+
+
+@pytest.mark.parametrize("fold, hour", [(0, 0), (1, 1)])
+def test_astimezone_respects_fold(fold, hour):
+    d = pendulum.datetime(2024, 10, 27, 2, 30, tz="Europe/Paris", fold=fold)
+
+    d = d.astimezone(pendulum.UTC)
+    assert d == datetime(2024, 10, 27, hour, 30, tzinfo=pendulum.UTC)