From 7ca8466a8828a62ddc48e44952b69b6206da866e Mon Sep 17 00:00:00 2001
From: KBS <youdie006@naver.com>
Date: Sun, 27 Sep 2026 23:56:46 +0900
Subject: [PATCH] Normalize offset strings to UTC when casting to naive types

#4775 normalized a non-UTC %DateTime{} to UTC for :date, :naive_datetime and
:naive_datetime_usec, but an ISO 8601 string with the same offset still went
through NaiveDateTime.from_iso8601, which drops the offset. The same instant
cast two ways gave two values:

    cast(:naive_datetime, "2020-06-01T00:30:07+02:00")  ~N[2020-06-01 00:30:07]
    cast(:naive_datetime, <the same instant as %DateTime{}>)  ~N[2020-05-31 22:30:07]

Parse with DateTime.from_iso8601 first and fall back to
NaiveDateTime.from_iso8601, so strings without an offset are unchanged.
---
 CHANGELOG.md            |  1 +
 lib/ecto/type.ex        | 26 ++++++++++++++++++--------
 test/ecto/type_test.exs |  8 ++++++++
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c3b0e76bff..395b67a0b3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@
   * [Ecto.Query] Fix subqueries in interpolated join filters (this changes the representation of `JoinExpr.on` fields to a `BooleanExpr`)
   * [Ecto.Query] Fix selecting lists of fields and using `map/2` from subqueries
   * [Ecto.Type] Normalize `DateTime` casts to UTC for `:time` and `:time_usec`
+  * [Ecto.Type] Normalize ISO 8601 strings with a UTC offset to UTC when casting to `:date`, `:naive_datetime` and `:naive_datetime_usec`
 
 ## v3.14.2 (2026-08-14)
 
diff --git a/lib/ecto/type.ex b/lib/ecto/type.ex
index 107cafce71..adadc92eb3 100644
--- a/lib/ecto/type.ex
+++ b/lib/ecto/type.ex
@@ -1062,9 +1062,9 @@ defmodule Ecto.Type do
         ok
 
       {:error, _} ->
-        case NaiveDateTime.from_iso8601(binary) do
+        case parse_naive_datetime(binary) do
           {:ok, naive_datetime} -> {:ok, NaiveDateTime.to_date(naive_datetime)}
-          {:error, _} -> :error
+          :error -> :error
         end
     end
   end
@@ -1199,12 +1199,8 @@ defmodule Ecto.Type do
     end
   end
 
-  defp cast_naive_datetime(binary) when is_binary(binary) do
-    case NaiveDateTime.from_iso8601(binary) do
-      {:ok, _} = ok -> ok
-      {:error, _} -> :error
-    end
-  end
+  defp cast_naive_datetime(binary) when is_binary(binary),
+    do: parse_naive_datetime(binary)
 
   defp cast_naive_datetime(%DateTime{} = datetime) do
     case cast_utc_datetime(datetime) do
@@ -1240,6 +1236,20 @@ defmodule Ecto.Type do
     :error
   end
 
+  # A string with a UTC offset is normalized to UTC, like a %DateTime{}.
+  defp parse_naive_datetime(binary) do
+    case DateTime.from_iso8601(binary) do
+      {:ok, datetime, _offset} ->
+        {:ok, DateTime.to_naive(datetime)}
+
+      {:error, _} ->
+        case NaiveDateTime.from_iso8601(binary) do
+          {:ok, _} = ok -> ok
+          {:error, _} -> :error
+        end
+    end
+  end
+
   ## UTC datetime
 
   defp cast_utc_datetime("-" <> rest) do
diff --git a/test/ecto/type_test.exs b/test/ecto/type_test.exs
index b84aa03961..74b50dff84 100644
--- a/test/ecto/type_test.exs
+++ b/test/ecto/type_test.exs
@@ -450,6 +450,7 @@ defmodule Ecto.TypeTest do
 
       assert Ecto.Type.cast(:date, "2015-12-31T00:00:00") == {:ok, @date}
       assert Ecto.Type.cast(:date, "2015-12-31 00:00:00") == {:ok, @date}
+      assert Ecto.Type.cast(:date, "2016-01-01T01:00:00+02:00") == {:ok, @date}
     end
 
     test "dump" do
@@ -653,6 +654,10 @@ defmodule Ecto.TypeTest do
 
       assert Ecto.Type.cast(:naive_datetime, "2015-01-23T23:50:07.008000") == {:ok, @datetime}
       assert Ecto.Type.cast(:naive_datetime, "2015-01-23T23:50:07.008000Z") == {:ok, @datetime}
+      assert Ecto.Type.cast(:naive_datetime, "2015-01-24T09:50:07+10:00") == {:ok, @datetime}
+
+      assert Ecto.Type.cast(:naive_datetime, "2015-01-23T17:50:07.008000-06:00") ==
+               {:ok, @datetime}
 
       assert Ecto.Type.cast(:naive_datetime, "2015-01-23P23:50:07") == :error
       assert Ecto.Type.cast(:naive_datetime, "2015-01-23 23:50.123") == :error
@@ -869,6 +874,9 @@ defmodule Ecto.TypeTest do
       assert Ecto.Type.cast(:naive_datetime_usec, "2015-01-23T23:50:07.008000Z") ==
                {:ok, @datetime_usec}
 
+      assert Ecto.Type.cast(:naive_datetime_usec, "2015-01-23T17:50:07.008000-06:00") ==
+               {:ok, @datetime_usec}
+
       assert Ecto.Type.cast(:naive_datetime_usec, "2015-01-23P23:50:07") == :error
     end