From 06116df2289fcd611a9e3191c4c0534ec01debc1 Mon Sep 17 00:00:00 2001
From: Marco Edward Gorelli <marcogorelli@protonmail.com>
Date: Sun, 10 Mar 2024 15:07:28 +0000
Subject: [PATCH] fix: raise proper error instead of panicking when result of
 truncation is non-existent datetime (#14958)

---
 crates/polars-time/src/windows/duration.rs     | 18 +++++++++---------
 .../tests/unit/datatypes/test_temporal.py      |  7 +++++++
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/crates/polars-time/src/windows/duration.rs b/crates/polars-time/src/windows/duration.rs
index 9f9640af4d6b..28a409a0391a 100644
--- a/crates/polars-time/src/windows/duration.rs
+++ b/crates/polars-time/src/windows/duration.rs
@@ -458,18 +458,18 @@ impl Duration {
         original_dt_utc: NaiveDateTime,
         result_dt_local: NaiveDateTime,
         tz: &Tz,
-    ) -> NaiveDateTime {
+    ) -> PolarsResult<NaiveDateTime> {
         match localize_datetime_opt(result_dt_local, tz, Ambiguous::Raise) {
-            Some(dt) => dt,
+            Some(dt) => Ok(dt),
             None => {
-                if try_localize_datetime(original_dt_local, tz, Ambiguous::Earliest).unwrap()
+                if try_localize_datetime(original_dt_local, tz, Ambiguous::Earliest)?
                     == original_dt_utc
                 {
-                    try_localize_datetime(result_dt_local, tz, Ambiguous::Earliest).unwrap()
-                } else if try_localize_datetime(original_dt_local, tz, Ambiguous::Latest).unwrap()
+                    try_localize_datetime(result_dt_local, tz, Ambiguous::Earliest)
+                } else if try_localize_datetime(original_dt_local, tz, Ambiguous::Latest)?
                     == original_dt_utc
                 {
-                    try_localize_datetime(result_dt_local, tz, Ambiguous::Latest).unwrap()
+                    try_localize_datetime(result_dt_local, tz, Ambiguous::Latest)
                 } else {
                     unreachable!()
                 }
@@ -503,7 +503,7 @@ impl Duration {
                 let result_timestamp = t - remainder;
                 let result_dt_local = _timestamp_to_datetime(result_timestamp);
                 let result_dt_utc =
-                    self.localize_result(original_dt_local, original_dt_utc, result_dt_local, tz);
+                    self.localize_result(original_dt_local, original_dt_utc, result_dt_local, tz)?;
                 Ok(_datetime_to_timestamp(result_dt_utc))
             },
             _ => {
@@ -564,7 +564,7 @@ impl Duration {
                     _original_dt_utc.unwrap(),
                     result_dt_local,
                     tz,
-                );
+                )?;
                 Ok(_datetime_to_timestamp(result_dt_utc))
             },
             _ => Ok(result_t_local),
@@ -647,7 +647,7 @@ impl Duration {
             Some(tz) if tz != &chrono_tz::UTC => {
                 let result_dt_local = timestamp_to_datetime(t - remainder_days * daily_duration);
                 let result_dt_utc =
-                    self.localize_result(original_dt_local, original_dt_utc, result_dt_local, tz);
+                    self.localize_result(original_dt_local, original_dt_utc, result_dt_local, tz)?;
                 Ok(datetime_to_timestamp(result_dt_utc))
             },
             _ => Ok(t - remainder_days * daily_duration),
diff --git a/py-polars/tests/unit/datatypes/test_temporal.py b/py-polars/tests/unit/datatypes/test_temporal.py
index 7f78dec6fb6e..7e6dc4a0c7f5 100644
--- a/py-polars/tests/unit/datatypes/test_temporal.py
+++ b/py-polars/tests/unit/datatypes/test_temporal.py
@@ -2296,6 +2296,13 @@ def test_truncate_ambiguous() -> None:
     assert_series_equal(result, expected)
 
 
+def test_truncate_non_existent_14957() -> None:
+    with pytest.raises(ComputeError, match="non-existent"):
+        pl.Series([datetime(2020, 3, 29, 2, 1)]).dt.replace_time_zone(
+            "Europe/London"
+        ).dt.truncate("46m")
+
+
 def test_round_ambiguous() -> None:
     t = (
         pl.datetime_range(