test: add date_trunc DST regression test

docs/source/user-guide/latest/compatibility.md

@@ -88,6 +88,22 @@ the [Comet Supported Expressions Guide](expressions.md) for more information on
 - **StructsToJson (to_json)**: Does not support `+Infinity` and `-Infinity` for numeric types (float, double).
   [#3016](https://github.com/apache/datafusion-comet/issues/3016)
 
+## Date and Time Functions
+
+Comet's native implementation of date and time functions may produce different results than Spark for dates
+far in the future (approximately beyond year 2100). This is because Comet uses the chrono-tz library for
+timezone calculations, which has limited support for Daylight Saving Time (DST) rules beyond the IANA
+time zone database's explicit transitions.
+
+For dates within a reasonable range (approximately 1970-2100), Comet's date and time functions are compatible
+with Spark. For dates beyond this range, functions that involve timezone-aware calculations (such as
+`date_trunc` with timezone-aware timestamps) may produce results with incorrect DST offsets.
+
+If you need to process dates far in the future with accurate timezone handling, consider:
+
+- Using timezone-naive types (`timestamp_ntz`) when timezone conversion is not required
+- Falling back to Spark for these specific operations
+
 ## Regular Expressions
 
 Comet uses the Rust regexp crate for evaluating regular expressions, and this has different behavior from Java's

native/spark-expr/src/datetime_funcs/timestamp_trunc.rs

@@ -113,20 +113,33 @@ impl PhysicalExpr for TimestampTruncExpr {
         let tz = self.timezone.clone();
         match (timestamp, format) {
             (ColumnarValue::Array(ts), ColumnarValue::Scalar(Utf8(Some(format)))) => {
-                let ts = array_with_timezone(
-                    ts,
-                    tz.clone(),
-                    Some(&DataType::Timestamp(Microsecond, Some(tz.into()))),
-                )?;
+                // For TimestampNTZ (Timestamp(Microsecond, None)), skip timezone conversion.
+                // NTZ values are timezone-independent and truncation should operate directly
+                // on the naive microsecond values without any timezone resolution.
+                let is_ntz = matches!(ts.data_type(), DataType::Timestamp(Microsecond, None));
+                let ts = if is_ntz {
+                    ts
+                } else {
+                    array_with_timezone(
+                        ts,
+                        tz.clone(),
+                        Some(&DataType::Timestamp(Microsecond, Some(tz.into()))),
+                    )?
+                };
                 let result = timestamp_trunc_dyn(&ts, format)?;
                 Ok(ColumnarValue::Array(result))
             }
             (ColumnarValue::Array(ts), ColumnarValue::Array(formats)) => {
-                let ts = array_with_timezone(
-                    ts,
-                    tz.clone(),
-                    Some(&DataType::Timestamp(Microsecond, Some(tz.into()))),
-                )?;
+                let is_ntz = matches!(ts.data_type(), DataType::Timestamp(Microsecond, None));
+                let ts = if is_ntz {
+                    ts
+                } else {
+                    array_with_timezone(
+                        ts,
+                        tz.clone(),
+                        Some(&DataType::Timestamp(Microsecond, Some(tz.into()))),
+                    )?
+                };
                 let result = timestamp_trunc_array_fmt_dyn(&ts, &formats)?;
                 Ok(ColumnarValue::Array(result))
             }

native/spark-expr/src/datetime_funcs/unix_timestamp.rs

@@ -78,6 +78,27 @@ impl ScalarUDFImpl for SparkUnixTimestamp {
 
         match args {
             [ColumnarValue::Array(array)] => match array.data_type() {
+                DataType::Timestamp(Microsecond, None) => {
+                    // TimestampNTZ: No timezone conversion needed - simply divide microseconds
+                    // by MICROS_PER_SECOND. TimestampNTZ stores local time without timezone.
+                    let timestamp_array =
+                        array.as_primitive::<arrow::datatypes::TimestampMicrosecondType>();
+
+                    let result: PrimitiveArray<Int64Type> = if timestamp_array.null_count() == 0 {
+                        timestamp_array
+                            .values()
+                            .iter()
+                            .map(|&micros| micros / MICROS_PER_SECOND)
+                            .collect()
+                    } else {
+                        timestamp_array
+                            .iter()
+                            .map(|v| v.map(|micros| div_floor(micros, MICROS_PER_SECOND)))
+                            .collect()
+                    };
+
+                    Ok(ColumnarValue::Array(Arc::new(result)))
+                }
                 DataType::Timestamp(_, _) => {
                     let is_utc = self.timezone == "UTC";
                     let array = if is_utc

native/spark-expr/src/kernels/temporal.rs

@@ -17,7 +17,10 @@
 
 //! temporal kernels
 
-use chrono::{DateTime, Datelike, Duration, NaiveDate, Timelike, Utc};
+use chrono::{
+    DateTime, Datelike, Duration, LocalResult, NaiveDate, NaiveDateTime, Offset, TimeZone,
+    Timelike, Utc,
+};
 
 use std::sync::Arc;
 
@@ -153,10 +156,30 @@ where
     Ok(())
 }
 
-// Apply the Tz to the Naive Date Time,,convert to UTC, and return as microseconds in Unix epoch
+// Apply the Tz to the Naive Date Time, convert to UTC, and return as microseconds in Unix epoch.
+// This function re-interprets the local datetime in the timezone to ensure the correct DST offset
+// is used for the target date (not the original date's offset). This is important when truncation
+// changes the date to a different DST period (e.g., from December/PST to October/PDT).
+//
+// Note: For far-future dates (approximately beyond year 2100), chrono-tz may not accurately
+// calculate DST transitions, which can result in incorrect offsets. See the compatibility
+// guide for more information.
 #[inline]
 fn as_micros_from_unix_epoch_utc(dt: Option<DateTime<Tz>>) -> i64 {
-    dt.unwrap().with_timezone(&Utc).timestamp_micros()
+    let dt = dt.unwrap();
+    let naive = dt.naive_local();
+    let tz = dt.timezone();
+
+    // Re-interpret the local time in the timezone to get the correct DST offset
+    // for the truncated date. Use noon to avoid DST gaps that occur around midnight.
+    let noon = naive.date().and_hms_opt(12, 0, 0).unwrap_or(naive);
+
+    let offset = match tz.offset_from_local_datetime(&noon) {
+        LocalResult::Single(off) | LocalResult::Ambiguous(off, _) => off.fix(),
+        LocalResult::None => return dt.with_timezone(&Utc).timestamp_micros(),
+    };
+
+    (naive - offset).and_utc().timestamp_micros()
 }
 
 #[inline]
@@ -529,6 +552,85 @@ pub(crate) fn timestamp_trunc_dyn(
     }
 }
 
+/// Convert microseconds since epoch to NaiveDateTime
+#[inline]
+fn micros_to_naive(micros: i64) -> Option<NaiveDateTime> {
+    DateTime::from_timestamp_micros(micros).map(|dt| dt.naive_utc())
+}
+
+/// Convert NaiveDateTime back to microseconds since epoch
+#[inline]
+fn naive_to_micros(dt: NaiveDateTime) -> i64 {
+    dt.and_utc().timestamp_micros()
+}
+
+/// Truncate a TimestampNTZ array without any timezone conversion.
+/// NTZ values are timezone-independent; we treat the raw microseconds as a naive datetime.
+fn timestamp_trunc_ntz<T>(
+    array: &PrimitiveArray<T>,
+    format: String,
+) -> Result<TimestampMicrosecondArray, SparkError>
+where
+    T: ArrowTemporalType + ArrowNumericType,
+    i64: From<T::Native>,
+{
+    let trunc_fn: fn(NaiveDateTime) -> Option<NaiveDateTime> = match format.to_uppercase().as_str()
+    {
+        "YEAR" | "YYYY" | "YY" => trunc_date_to_year,
+        "QUARTER" => trunc_date_to_quarter,
+        "MONTH" | "MON" | "MM" => trunc_date_to_month,
+        "WEEK" => trunc_date_to_week,
+        "DAY" | "DD" => trunc_date_to_day,
+        "HOUR" => trunc_date_to_hour,
+        "MINUTE" => trunc_date_to_minute,
+        "SECOND" => trunc_date_to_second,
+        "MILLISECOND" => trunc_date_to_ms,
+        "MICROSECOND" => trunc_date_to_microsec,
+        _ => {
+            return Err(SparkError::Internal(format!(
+                "Unsupported format: {format:?} for function 'timestamp_trunc'"
+            )))
+        }
+    };
+
+    let result: TimestampMicrosecondArray = array
+        .iter()
+        .map(|opt_val| {
+            opt_val.and_then(|v| {
+                let micros: i64 = v.into();
+                micros_to_naive(micros)
+                    .and_then(trunc_fn)
+                    .map(naive_to_micros)
+            })
+        })
+        .collect();
+
+    Ok(result)
+}
+
+/// Truncate a single NTZ value and append to builder
+fn timestamp_trunc_ntz_single<F>(
+    value: Option<i64>,
+    builder: &mut PrimitiveBuilder<TimestampMicrosecondType>,
+    op: F,
+) -> Result<(), SparkError>
+where
+    F: Fn(NaiveDateTime) -> Option<NaiveDateTime>,
+{
+    match value {
+        Some(micros) => match micros_to_naive(micros).and_then(op) {
+            Some(truncated) => builder.append_value(naive_to_micros(truncated)),
+            None => {
+                return Err(SparkError::Internal(
+                    "Unable to truncate NTZ timestamp".to_string(),
+                ))
+            }
+        },
+        None => builder.append_null(),
+    }
+    Ok(())
+}
+
 pub(crate) fn timestamp_trunc<T>(
     array: &PrimitiveArray<T>,
     format: String,
@@ -540,6 +642,10 @@ where
     let builder = TimestampMicrosecondBuilder::with_capacity(array.len());
     let iter = ArrayIter::new(array);
     match array.data_type() {
+        DataType::Timestamp(TimeUnit::Microsecond, None) => {
+            // TimestampNTZ: operate directly on naive microsecond values without timezone
+            timestamp_trunc_ntz(array, format)
+        }
         DataType::Timestamp(TimeUnit::Microsecond, Some(tz)) => {
             match format.to_uppercase().as_str() {
                 "YEAR" | "YYYY" | "YY" => {
@@ -687,6 +793,60 @@ macro_rules! timestamp_trunc_array_fmt_helper {
             "lengths of values array and format array must be the same"
         );
         match $datatype {
+            DataType::Timestamp(TimeUnit::Microsecond, None) => {
+                // TimestampNTZ: operate directly on naive microsecond values
+                for (index, val) in iter.enumerate() {
+                    let micros_val = val.map(|v| i64::from(v));
+                    let op_result = match $formats.value(index).to_uppercase().as_str() {
+                        "YEAR" | "YYYY" | "YY" => {
+                            timestamp_trunc_ntz_single(micros_val, &mut builder, trunc_date_to_year)
+                        }
+                        "QUARTER" => timestamp_trunc_ntz_single(
+                            micros_val,
+                            &mut builder,
+                            trunc_date_to_quarter,
+                        ),
+                        "MONTH" | "MON" | "MM" => timestamp_trunc_ntz_single(
+                            micros_val,
+                            &mut builder,
+                            trunc_date_to_month,
+                        ),
+                        "WEEK" => {
+                            timestamp_trunc_ntz_single(micros_val, &mut builder, trunc_date_to_week)
+                        }
+                        "DAY" | "DD" => {
+                            timestamp_trunc_ntz_single(micros_val, &mut builder, trunc_date_to_day)
+                        }
+                        "HOUR" => {
+                            timestamp_trunc_ntz_single(micros_val, &mut builder, trunc_date_to_hour)
+                        }
+                        "MINUTE" => timestamp_trunc_ntz_single(
+                            micros_val,
+                            &mut builder,
+                            trunc_date_to_minute,
+                        ),
+                        "SECOND" => timestamp_trunc_ntz_single(
+                            micros_val,
+                            &mut builder,
+                            trunc_date_to_second,
+                        ),
+                        "MILLISECOND" => {
+                            timestamp_trunc_ntz_single(micros_val, &mut builder, trunc_date_to_ms)
+                        }
+                        "MICROSECOND" => timestamp_trunc_ntz_single(
+                            micros_val,
+                            &mut builder,
+                            trunc_date_to_microsec,
+                        ),
+                        _ => Err(SparkError::Internal(format!(
+                            "Unsupported format: {:?} for function 'timestamp_trunc'",
+                            $formats.value(index)
+                        ))),
+                    };
+                    op_result?
+                }
+                Ok(builder.finish())
+            }
             DataType::Timestamp(TimeUnit::Microsecond, Some(tz)) => {
                 let tz: Tz = tz.parse()?;
                 for (index, val) in iter.enumerate() {

spark/src/main/scala/org/apache/comet/serde/datetime.scala

@@ -295,11 +295,9 @@ object CometSecond extends CometExpressionSerde[Second] {
 object CometUnixTimestamp extends CometExpressionSerde[UnixTimestamp] {
 
   private def isSupportedInputType(expr: UnixTimestamp): Boolean = {
-    // Note: TimestampNTZType is not supported because Comet incorrectly applies
-    // timezone conversion to TimestampNTZ values. TimestampNTZ stores local time
-    // without timezone, so no conversion should be applied.
     expr.children.head.dataType match {
       case TimestampType | DateType => true
+      case dt if dt.typeName == "timestamp_ntz" => true
       case _ => false
     }
   }

spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst.sql

@@ -0,0 +1,62 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+-- Exercise Comet's native date_trunc on a timezone that observes DST.
+-- CometTruncTimestamp marks non-UTC as Incompatible, so enable allowIncompatible
+-- to force the native path and verify correctness against Spark.
+
+-- Config: spark.comet.expression.TruncTimestamp.allowIncompatible=true
+-- Config: spark.sql.session.timeZone=America/Los_Angeles
+
+statement
+CREATE TABLE test_trunc_dst(ts timestamp) USING parquet
+
+statement
+INSERT INTO test_trunc_dst VALUES
+  (timestamp('2024-11-03 06:30:00')),
+  (timestamp('2024-11-03 14:30:00')),
+  (timestamp('2024-03-10 05:30:00')),
+  (timestamp('2024-03-10 12:30:00')),
+  (timestamp('2024-11-15 12:00:00')),
+  (timestamp('2024-12-15 23:30:00')),
+  (timestamp('2024-07-15 10:00:00')),
+  (NULL)
+
+-- DAY truncation on a time after fall-back (PST) produces midnight of the same
+-- day, which is BEFORE the fall-back transition and should be in PDT.
+query
+SELECT ts, date_trunc('DAY', ts) FROM test_trunc_dst ORDER BY ts
+
+-- HOUR truncation crossing DST boundaries.
+query
+SELECT ts, date_trunc('HOUR', ts) FROM test_trunc_dst ORDER BY ts
+
+-- WEEK truncation can span DST transitions (the week of Nov 3 2024 starts Oct 28 PDT).
+query
+SELECT ts, date_trunc('WEEK', ts) FROM test_trunc_dst ORDER BY ts
+
+-- MONTH truncation: Nov 15 PST truncated to MONTH gives Nov 1, which is PDT.
+query
+SELECT ts, date_trunc('MONTH', ts) FROM test_trunc_dst ORDER BY ts
+
+-- QUARTER truncation: the motivating case from the PR (Dec PST -> Oct PDT).
+query
+SELECT ts, date_trunc('QUARTER', ts) FROM test_trunc_dst ORDER BY ts
+
+-- YEAR truncation: Dec 15 PST truncated to YEAR gives Jan 1, which is PST too, so no DST crossing.
+query
+SELECT ts, date_trunc('YEAR', ts) FROM test_trunc_dst ORDER BY ts

spark/src/test/scala/org/apache/comet/CometCastSuite.scala

@@ -1594,7 +1594,13 @@ class CometCastSuite extends CometTestBase with AdaptiveSparkPlanHelper {
   // CAST from TimestampNTZType
 
   test("cast TimestampNTZType to StringType") {
-    castTest(generateTimestampNTZ(), DataTypes.StringType)
+    // TimestampNTZ is timezone-independent, so casting to string should produce
+    // the same result regardless of the session timezone.
+    for (tz <- representativeTimezones) {
+      withSQLConf(SQLConf.SESSION_LOCAL_TIMEZONE.key -> tz) {
+        castTest(generateTimestampNTZ(), DataTypes.StringType)
+      }
+    }
   }
 
   test("cast TimestampNTZType to DateType") {