Align NowFunc::new() with canonical ConfigOptions timezone and enhance documentation

datafusion/functions/src/datetime/now.rs

@@ -54,12 +54,14 @@ impl Default for NowFunc {
 
 impl NowFunc {
     #[deprecated(since = "50.2.0", note = "use `new_with_config` instead")]
+    /// Deprecated constructor retained for backwards compatibility.
+    ///
+    /// Prefer [`NowFunc::new_with_config`] which allows specifying the
+    /// timezone via [`ConfigOptions`]. This helper now mirrors the
+    /// canonical default offset (`"+00:00"`) provided by
+    /// `ConfigOptions::default()`.
     pub fn new() -> Self {
-        Self {
-            signature: Signature::nullary(Volatility::Stable),
-            aliases: vec!["current_timestamp".to_string()],
-            timezone: Some(Arc::from("+00")),
-        }
+        Self::new_with_config(&ConfigOptions::default())
     }
 
     pub fn new_with_config(config: &ConfigOptions) -> Self {
@@ -138,3 +140,44 @@ impl ScalarUDFImpl for NowFunc {
         self.doc()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[allow(deprecated)]
+    #[test]
+    fn now_func_default_matches_config() {
+        let default_config = ConfigOptions::default();
+
+        let legacy_now = NowFunc::new();
+        let configured_now = NowFunc::new_with_config(&default_config);
+
+        let empty_fields: [FieldRef; 0] = [];
+        let empty_scalars: [Option<&ScalarValue>; 0] = [];
+
+        let legacy_field = legacy_now
+            .return_field_from_args(ReturnFieldArgs {
+                arg_fields: &empty_fields,
+                scalar_arguments: &empty_scalars,
+            })
+            .expect("legacy now() return field");
+
+        let configured_field = configured_now
+            .return_field_from_args(ReturnFieldArgs {
+                arg_fields: &empty_fields,
+                scalar_arguments: &empty_scalars,
+            })
+            .expect("configured now() return field");
+
+        assert_eq!(legacy_field.as_ref(), configured_field.as_ref());
+
+        let legacy_scalar =
+            ScalarValue::TimestampNanosecond(None, legacy_now.timezone.clone());
+        let configured_scalar =
+            ScalarValue::TimestampNanosecond(None, configured_now.timezone.clone());
+
+        assert_eq!(legacy_scalar, configured_scalar);
+        assert_eq!(Some("+00:00"), legacy_now.timezone.as_deref());
+    }
+}