polars_time::date_range produces incorrect results when time unit is Milliseconds

[mt-caret]

Polars version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Issue description

When trying to reproduce https://pola-rs.github.io/polars-book/user-guide/expressions/casting/#dates in a library that uses Polars, I ran across surprising behavior where date_range will return surprising results.

Reproducible example

https://github.com/mt-caret/polars-ocaml/blob/9fa0eb6c59034413ce679b63068d7f9db2bbc0f9/rust/src/lib.rs:

#[cfg(test)]
mod tests {
    use chrono::naive::NaiveDate;
    use expect_test::{expect, Expect};
    use polars::prelude::prelude::*;
    use polars::prelude::*;
    use std::fmt::Debug;

    fn check<T: Debug>(actual: T, expect: Expect) {
        let actual = format!("{:?}", actual);
        expect.assert_eq(&actual);
    }

    #[test]
    fn check_date_range() {
        let start = NaiveDate::from_ymd_opt(2022, 1, 1)
            .unwrap()
            .and_hms_opt(0, 0, 0)
            .unwrap();
        let stop = NaiveDate::from_ymd_opt(2022, 1, 5)
            .unwrap()
            .and_hms_opt(0, 0, 0)
            .unwrap();
        check(
            date_range(
                "date",
                start,
                stop,
                Duration::parse("1d"),
                ClosedWindow::Both,
                TimeUnit::Nanoseconds,
                None,
            )
            .map(|date_range| date_range.into_series()),
            expect![[r#"
                Ok(shape: (5,)
                Series: 'date' [datetime[ns]]
                [
                	2022-01-01 00:00:00
                	2022-01-02 00:00:00
                	2022-01-03 00:00:00
                	2022-01-04 00:00:00
                	2022-01-05 00:00:00
                ])"#]],
        );
        check(
            date_range(
                "date",
                start,
                stop,
                Duration::parse("1d"),
                ClosedWindow::Both,
                TimeUnit::Microseconds, // TODO: BUG!
                None,
            )
            .map(|date_range| date_range.into_series()),
            expect![[r#"
                Ok(shape: (1,)
                Series: 'date' [datetime[μs]]
                [
                	1970-01-01 00:27:20.995200
                ])"#]],
        );
        check(
            date_range(
                "date",
                start,
                stop,
                Duration::parse("1d"),
                ClosedWindow::Both,
                TimeUnit::Milliseconds,
                None,
            )
            .map(|date_range| date_range.into_series()),
            expect![[r#"
                Ok(shape: (5,)
                Series: 'date' [datetime[ms]]
                [
                	2022-01-01 00:00:00
                	2022-01-02 00:00:00
                	2022-01-03 00:00:00
                	2022-01-04 00:00:00
                	2022-01-05 00:00:00
                ])"#]],
        )
    }
}

Expected behavior

date_range to produce the same result regardless of the time unit specified for this particular case.

Installed versions

[ "lazy", "dot_diagram", "parquet", "approx_unique", "dtype-date", "dtype-datetime", "dtype-i8", "dtype-i16", "dtype-u8", "dtype-u16", "random", "describe", "streaming" ]

[MarcoGorelli]

thanks @mt-caret for the report! fix incoming