From ba4ab5272cab6b9e1e2e020795f4bd348da5a71e Mon Sep 17 00:00:00 2001
From: Eddie A Tejeda <669988+eddietejeda@users.noreply.github.com>
Date: Mon, 27 Jul 2026 14:05:37 -0700
Subject: [PATCH 1/2] fix: convert_timezone must use to_local_time(), not the
 Postgres pattern

The double-AT TIME ZONE + cast-to-naive-timestamp pattern silently loses
the shift on DataFusion: the final cast re-renders the UTC instant rather
than the target zone's wall clock. to_local_time() yields the local wall
clock and is DST-aware. Verified live: 2024-01-01 12:00 UTC -> 04:00
(PST) and 2024-07-01 12:00 UTC -> 05:00 (PDT).

Found by review on hotdata-dev/jaffle-shop#7.
---
 dbt/include/hotdata/macros/utils.sql | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/dbt/include/hotdata/macros/utils.sql b/dbt/include/hotdata/macros/utils.sql
index 5ccd413..6bd4a7c 100644
--- a/dbt/include/hotdata/macros/utils.sql
+++ b/dbt/include/hotdata/macros/utils.sql
@@ -13,12 +13,16 @@
 {%- endmacro %}
 
 {% macro hotdata__convert_timezone(column, target_tz, source_tz) -%}
-  {#- dbt_date dispatch hook: DataFusion supports the Postgres double
-      AT TIME ZONE pattern, so delegate to it. -#}
-  cast(
-    cast({{ column }} as timestamp)
-    at time zone '{{ source_tz }}' at time zone '{{ target_tz }}'
-    as timestamp
+  {#-
+    dbt_date dispatch hook (packages need a root-project shim or dispatch
+    config to reach it). NOT the Postgres double-AT TIME ZONE pattern: on
+    DataFusion the final cast back to a naive timestamp re-renders the UTC
+    instant, silently losing the shift. to_local_time() yields the target
+    zone's wall clock (DST-aware).
+  -#}
+  to_local_time(
+    (cast({{ column }} as timestamp) at time zone '{{ source_tz }}')
+    at time zone '{{ target_tz }}'
   )
 {%- endmacro %}
 

From 5951bb6dae30bc32b3813aad6537740de93a54ce Mon Sep 17 00:00:00 2001
From: Eddie A Tejeda <669988+eddietejeda@users.noreply.github.com>
Date: Mon, 27 Jul 2026 14:11:31 -0700
Subject: [PATCH 2/2] Address review: default falsy source_tz to UTC; changelog
 entry
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

source_tz itself works — verified live that AT TIME ZONE on a naive
timestamp localizes it as the source zone's wall clock (12:00
America/New_York -> 17:00 UTC, -> 09:00 LA). The earlier round-trip
loss was in the cast-to-naive rendering step, not AT TIME ZONE.
---
 CHANGELOG.md                         |  6 ++++++
 dbt/include/hotdata/macros/utils.sql | 11 +++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 12c0788..9240801 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- `convert_timezone` returned the UTC instant unshifted; it now converts via
+  `to_local_time()` (DST-aware, non-UTC sources verified) and defaults a
+  falsy `source_tz` to UTC.
+
 ## [0.1.0] - 2026-07-27
 
 ### Added
diff --git a/dbt/include/hotdata/macros/utils.sql b/dbt/include/hotdata/macros/utils.sql
index 6bd4a7c..35688e6 100644
--- a/dbt/include/hotdata/macros/utils.sql
+++ b/dbt/include/hotdata/macros/utils.sql
@@ -15,11 +15,14 @@
 {% macro hotdata__convert_timezone(column, target_tz, source_tz) -%}
   {#-
     dbt_date dispatch hook (packages need a root-project shim or dispatch
-    config to reach it). NOT the Postgres double-AT TIME ZONE pattern: on
-    DataFusion the final cast back to a naive timestamp re-renders the UTC
-    instant, silently losing the shift. to_local_time() yields the target
-    zone's wall clock (DST-aware).
+    config to reach it). NOT the Postgres double-AT TIME ZONE + cast-to-naive
+    pattern: on DataFusion that final cast re-renders the UTC instant,
+    silently losing the shift. Here AT TIME ZONE on a naive timestamp
+    localizes it as the source zone's wall clock (12:00 @ America/New_York
+    -> 12:00-05:00, verified — non-UTC sources convert correctly), and
+    to_local_time() renders the target zone's wall clock (DST-aware).
   -#}
+  {%- set source_tz = source_tz or 'UTC' -%}
   to_local_time(
     (cast({{ column }} as timestamp) at time zone '{{ source_tz }}')
     at time zone '{{ target_tz }}'