fix(rust): Fix datetime cast behavior for pre-epoch times (#19949)

pola-rs · Nov 29, 2024 · 09f2a31 · 09f2a31
1 parent 44ddbc2
commit 09f2a31
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Showing 2 changed files with 23 additions and 3 deletions.
diff --git a/crates/polars-core/src/chunked_array/temporal/datetime.rs b/crates/polars-core/src/chunked_array/temporal/datetime.rs
@@ -123,12 +123,12 @@ impl DatetimeChunked {
         use TimeUnit::*;
         match (current_unit, tu) {
             (Nanoseconds, Microseconds) => {
-                let ca = (&self.0).wrapping_trunc_div_scalar(1_000);
+                let ca = (&self.0).wrapping_floor_div_scalar(1_000);
                 out.0 = ca;
                 out
             },
             (Nanoseconds, Milliseconds) => {
-                let ca = (&self.0).wrapping_trunc_div_scalar(1_000_000);
+                let ca = (&self.0).wrapping_floor_div_scalar(1_000_000);
                 out.0 = ca;
                 out
             },
@@ -138,7 +138,7 @@ impl DatetimeChunked {
                 out
             },
             (Microseconds, Milliseconds) => {
-                let ca = (&self.0).wrapping_trunc_div_scalar(1_000);
+                let ca = (&self.0).wrapping_floor_div_scalar(1_000);
                 out.0 = ca;
                 out
             },

diff --git a/py-polars/tests/unit/datatypes/test_temporal.py b/py-polars/tests/unit/datatypes/test_temporal.py
@@ -2402,3 +2402,23 @@ def test_weekday_vs_stdlib_date(value: date) -> None:
     result = pl.Series([value]).dt.weekday().item()
     expected = value.isoweekday()
     assert result == expected
+
+
+def test_temporal_downcast_construction_19309() -> None:
+    # implicit cast from us to ms upon construction
+    s = pl.Series(
+        [
+            datetime(1969, 1, 1, 0, 0, 0, 1),
+            datetime(1969, 12, 31, 23, 59, 59, 999999),
+            datetime(1970, 1, 1, 0, 0, 0, 0),
+            datetime(1970, 1, 1, 0, 0, 0, 1),
+        ],
+        dtype=pl.Datetime("ms"),
+    )
+
+    assert s.to_list() == [
+        datetime(1969, 1, 1),
+        datetime(1969, 12, 31, 23, 59, 59, 999000),
+        datetime(1970, 1, 1),
+        datetime(1970, 1, 1),
+    ]