Change default time_zone to None (was "+00:00") (#18359)

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- Closes 
- #18204
- #18081
- fixes #18219 as a side effect

## Rationale for this change

Default timezone was previously zulu however with the recent change to
support default tz in now(), current_date(), etc which used to have no
default tz the choice was made to unset the system wide timezone.

## What changes are included in this PR?

Code, tests, upgrading doc.

## Are these changes tested?

Yes, with existing tests.

## Are there any user-facing changes?

Yes. Any query that used to use the default timezone would return a
timestamp with a timezone of 'Z' will now return a timestamp without a
timezone. This can be changed back to the previous behaviour with the
sql

```sql
SET TIMEZONE = '+00:00';
```

---------

Co-authored-by: Andrew Lamb <[email protected]>

Author: Omega359

datafusion/common/src/config.rs

@@ -467,9 +467,8 @@ config_namespace! {
 
         /// The default time zone
         ///
-        /// Some functions, e.g. `EXTRACT(HOUR from SOME_TIME)`, shift the underlying datetime
-        /// according to this time zone, and then extract the hour
-        pub time_zone: String, default = "+00:00".into()
+        /// Some functions, e.g. `now` return timestamps in this time zone
+        pub time_zone: Option<String>, default = None
 
         /// Parquet options
         pub parquet: ParquetOptions, default = Default::default()

datafusion/core/tests/expr_api/simplification.rs

@@ -514,7 +514,7 @@ fn multiple_now() -> Result<()> {
     // expect the same timestamp appears in both exprs
     let actual = get_optimized_plan_formatted(plan, &time);
     let expected = format!(
-        "Projection: TimestampNanosecond({}, Some(\"+00:00\")) AS now(), TimestampNanosecond({}, Some(\"+00:00\")) AS t2\n  TableScan: test",
+        "Projection: TimestampNanosecond({}, None) AS now(), TimestampNanosecond({}, None) AS t2\n  TableScan: test",
         time.timestamp_nanos_opt().unwrap(),
         time.timestamp_nanos_opt().unwrap()
     );

datafusion/core/tests/user_defined/user_defined_scalar_functions.rs

@@ -1812,7 +1812,7 @@ async fn test_config_options_work_for_scalar_func() -> Result<()> {
     });
 
     let mut config = SessionConfig::new();
-    config.options_mut().execution.time_zone = "AEST".into();
+    config.options_mut().execution.time_zone = Some("AEST".into());
 
     let ctx = SessionContext::new_with_config(config);
 

datafusion/functions/src/datetime/current_date.rs

@@ -108,7 +108,14 @@ impl ScalarUDFImpl for CurrentDateFunc {
         let days = info
             .execution_props()
             .config_options()
-            .and_then(|config| config.execution.time_zone.parse::<Tz>().ok())
+            .and_then(|config| {
+                config
+                    .execution
+                    .time_zone
+                    .as_ref()
+                    .map(|tz| tz.parse::<Tz>().ok())
+            })
+            .flatten()
             .map_or_else(
                 || datetime_to_days(&now_ts),
                 |tz| {

datafusion/functions/src/datetime/current_time.rs

@@ -104,7 +104,14 @@ impl ScalarUDFImpl for CurrentTimeFunc {
         let nano = info
             .execution_props()
             .config_options()
-            .and_then(|config| config.execution.time_zone.parse::<Tz>().ok())
+            .and_then(|config| {
+                config
+                    .execution
+                    .time_zone
+                    .as_ref()
+                    .map(|tz| tz.parse::<Tz>().ok())
+            })
+            .flatten()
             .map_or_else(
                 || datetime_to_time_nanos(&now_ts),
                 |tz| {
@@ -167,7 +174,11 @@ mod tests {
 
     fn set_session_timezone_env(tz: &str, start_time: DateTime<Utc>) -> MockSimplifyInfo {
         let mut config = datafusion_common::config::ConfigOptions::default();
-        config.execution.time_zone = tz.to_string();
+        config.execution.time_zone = if tz.is_empty() {
+            None
+        } else {
+            Some(tz.to_string())
+        };
         let mut execution_props =
             ExecutionProps::new().with_query_execution_start_time(start_time);
         execution_props.config_options = Some(Arc::new(config));

datafusion/functions/src/datetime/now.rs

@@ -33,7 +33,7 @@ use datafusion_macros::user_doc;
 #[user_doc(
     doc_section(label = "Time and Date Functions"),
     description = r#"
-Returns the current UTC timestamp.
+Returns the current timestamp in the system configured timezone (None by default).
 
 The `now()` return value is determined at query time and will return the same timestamp, no matter when in the query plan the function executes.
 "#,
@@ -58,8 +58,7 @@ impl NowFunc {
     ///
     /// 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()`.
+    /// canonical default offset (None) provided by `ConfigOptions::default()`.
     pub fn new() -> Self {
         Self::new_with_config(&ConfigOptions::default())
     }
@@ -68,7 +67,11 @@ impl NowFunc {
         Self {
             signature: Signature::nullary(Volatility::Stable),
             aliases: vec!["current_timestamp".to_string()],
-            timezone: Some(Arc::from(config.execution.time_zone.as_str())),
+            timezone: config
+                .execution
+                .time_zone
+                .as_ref()
+                .map(|tz| Arc::from(tz.as_str())),
         }
     }
 }
@@ -178,6 +181,6 @@ mod tests {
             ScalarValue::TimestampNanosecond(None, configured_now.timezone.clone());
 
         assert_eq!(legacy_scalar, configured_scalar);
-        assert_eq!(Some("+00:00"), legacy_now.timezone.as_deref());
+        assert_eq!(None, legacy_now.timezone.as_deref());
     }
 }

datafusion/sql/src/planner.rs

@@ -693,7 +693,7 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
                     // Timestamp With Time Zone
                     // INPUT : [SQLDataType]   TimestampTz + [Config] Time Zone
                     // OUTPUT: [ArrowDataType] Timestamp<TimeUnit, Some(Time Zone)>
-                    Some(self.context_provider.options().execution.time_zone.clone())
+                    self.context_provider.options().execution.time_zone.clone()
                 } else {
                     // Timestamp Without Time zone
                     None

datafusion/sqllogictest/test_files/arrow_typeof.slt

@@ -67,7 +67,7 @@ Timestamp(ns)
 query T
 SELECT arrow_typeof(now())
 ----
-Timestamp(ns, "+00:00")
+Timestamp(ns)
 
 # arrow_typeof_timestamp_date32(
 query T

datafusion/sqllogictest/test_files/dates.slt

@@ -91,7 +91,7 @@ where d3_date > now() + '5 days';
 ----
 DataFusion error: type_coercion
 caused by
-Error during planning: Cannot coerce arithmetic expression Timestamp(ns, "+00:00") + Utf8 to valid types
+Error during planning: Cannot coerce arithmetic expression Timestamp(ns) + Utf8 to valid types
 
 
 # DATE minus DATE

datafusion/sqllogictest/test_files/ddl.slt

@@ -867,7 +867,7 @@ query TTTTTT
 show columns FROM table_with_pk;
 ----
 datafusion public table_with_pk sn Int32 NO
-datafusion public table_with_pk ts Timestamp(ns, "+00:00") NO
+datafusion public table_with_pk ts Timestamp(ns) NO
 datafusion public table_with_pk currency Utf8View NO
 datafusion public table_with_pk amount Float32 YES