fix(rust): microsecond noise on date >> time cast (add 00:00:00…

… fast-path) (#5149)

polars/polars-core/src/chunked_array/logical/date.rs

@@ -1,6 +1,5 @@
 use super::*;
 use crate::prelude::*;
-
 pub type DateChunked = Logical<DateType, Int32Type>;
 
 impl From<Int32Chunked> for DateChunked {
@@ -40,6 +39,9 @@ impl LogicalType for DateChunked {
                     .into_datetime(*tu, tz.clone())
                     .into_series())
             }
+            (Date, Time) => Ok(Int64Chunked::full(self.name(), 0i64, self.len())
+                .into_time()
+                .into_series()),
             _ => self.0.cast(dtype),
         }
     }

py-polars/tests/unit/test_datelike.py

@@ -1371,6 +1371,22 @@ def test_time_microseconds_3843() -> None:
     assert s.to_list() == in_val
 
 
+def test_date_to_time_cast_5111() -> None:
+    # check date -> time casts (fast-path: always 00:00:00)
+    df = pl.DataFrame(
+        {
+            "xyz": [
+                date(1969, 1, 1),
+                date(1990, 3, 8),
+                date(2000, 6, 16),
+                date(2010, 9, 24),
+                date(2022, 12, 31),
+            ]
+        }
+    ).with_column(pl.col("xyz").cast(pl.Time))
+    assert df["xyz"].to_list() == [time(0), time(0), time(0), time(0), time(0)]
+
+
 def test_year_empty_df() -> None:
     df = pl.DataFrame(pl.Series(name="date", dtype=pl.Date))
     assert df.select(pl.col("date").dt.year()).dtypes == [pl.Int32]