Add missing datetime functions (#1467)

* Add missing datetime functions: make_time, current_timestamp, date_format

Closes #1451. Adds make_time Rust binding and Python wrapper, and adds
current_timestamp (alias for now) and date_format (alias for to_char)
Python functions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Add unit tests for make_time, current_timestamp, and date_format

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timsaucer

crates/core/src/functions.rs

@@ -616,6 +616,7 @@ expr_fn!(date_part, part date);
 expr_fn!(date_trunc, part date);
 expr_fn!(date_bin, stride source origin);
 expr_fn!(make_date, year month day);
+expr_fn!(make_time, hour minute second);
 expr_fn!(to_char, datetime format);
 
 expr_fn!(translate, string from to, "Replaces each character in string that matches a character in the from set with the corresponding character in the to set. If from is longer than to, occurrences of the extra characters in from are deleted.");
@@ -974,6 +975,7 @@ pub(crate) fn init_module(m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_wrapped(wrap_pyfunction!(date_part))?;
     m.add_wrapped(wrap_pyfunction!(date_trunc))?;
     m.add_wrapped(wrap_pyfunction!(make_date))?;
+    m.add_wrapped(wrap_pyfunction!(make_time))?;
     m.add_wrapped(wrap_pyfunction!(digest))?;
     m.add_wrapped(wrap_pyfunction!(ends_with))?;
     m.add_wrapped(wrap_pyfunction!(exp))?;

python/datafusion/functions.py

@@ -128,7 +128,9 @@
     "cume_dist",
     "current_date",
     "current_time",
+    "current_timestamp",
     "date_bin",
+    "date_format",
     "date_part",
     "date_trunc",
     "datepart",
@@ -200,6 +202,7 @@
     "make_array",
     "make_date",
     "make_list",
+    "make_time",
     "max",
     "md5",
     "mean",
@@ -1948,6 +1951,15 @@ def now() -> Expr:
     return Expr(f.now())
 
 
+def current_timestamp() -> Expr:
+    """Returns the current timestamp in nanoseconds.
+
+    See Also:
+        This is an alias for :py:func:`now`.
+    """
+    return now()
+
+
 def to_char(arg: Expr, formatter: Expr) -> Expr:
     """Returns a string representation of a date, time, timestamp or duration.
 
@@ -1970,6 +1982,15 @@ def to_char(arg: Expr, formatter: Expr) -> Expr:
     return Expr(f.to_char(arg.expr, formatter.expr))
 
 
+def date_format(arg: Expr, formatter: Expr) -> Expr:
+    """Returns a string representation of a date, time, timestamp or duration.
+
+    See Also:
+        This is an alias for :py:func:`to_char`.
+    """
+    return to_char(arg, formatter)
+
+
 def _unwrap_exprs(args: tuple[Expr, ...]) -> list:
     return [arg.expr for arg in args]
 
@@ -2270,6 +2291,21 @@ def make_date(year: Expr, month: Expr, day: Expr) -> Expr:
     return Expr(f.make_date(year.expr, month.expr, day.expr))
 
 
+def make_time(hour: Expr, minute: Expr, second: Expr) -> Expr:
+    """Make a time from hour, minute and second component parts.
+
+    Examples:
+        >>> ctx = dfn.SessionContext()
+        >>> df = ctx.from_pydict({"h": [12], "m": [30], "s": [0]})
+        >>> result = df.select(
+        ...     dfn.functions.make_time(dfn.col("h"), dfn.col("m"),
+        ...     dfn.col("s")).alias("t"))
+        >>> result.collect_column("t")[0].as_py()
+        datetime.time(12, 30)
+    """
+    return Expr(f.make_time(hour.expr, minute.expr, second.expr))
+
+
 def translate(string: Expr, from_val: Expr, to_val: Expr) -> Expr:
     """Replaces the characters in ``from_val`` with the counterpart in ``to_val``.
 

python/tests/test_functions.py

@@ -1107,6 +1107,39 @@ def test_today_alias_matches_current_date(df):
     assert result.column(0) == result.column(1)
 
 
+def test_current_timestamp_alias_matches_now(df):
+    result = df.select(
+        f.now().alias("now"),
+        f.current_timestamp().alias("current_timestamp"),
+    ).collect()[0]
+
+    assert result.column(0) == result.column(1)
+
+
+def test_date_format_alias_matches_to_char(df):
+    result = df.select(
+        f.to_char(
+            f.to_timestamp(literal("2021-01-01T00:00:00")), literal("%Y/%m/%d")
+        ).alias("to_char"),
+        f.date_format(
+            f.to_timestamp(literal("2021-01-01T00:00:00")), literal("%Y/%m/%d")
+        ).alias("date_format"),
+    ).collect()[0]
+
+    assert result.column(0) == result.column(1)
+    assert result.column(0)[0].as_py() == "2021/01/01"
+
+
+def test_make_time(df):
+    ctx = SessionContext()
+    df_time = ctx.from_pydict({"h": [12], "m": [30], "s": [0]})
+    result = df_time.select(
+        f.make_time(column("h"), column("m"), column("s")).alias("t")
+    ).collect()[0]
+
+    assert result.column(0)[0].as_py() == time(12, 30)
+
+
 def test_arrow_cast(df):
     df = df.select(
         # we use `string_literal` to return utf8 instead of `literal` which returns