fix: unwrap identity Date cast in comparison unwrapping

datafusion/expr-common/src/casts.rs

@@ -98,7 +98,19 @@ fn is_date_type(data_type: &DataType) -> bool {
 /// For example, `CAST(ts AS DATE) = DATE '2024-01-01'` means "any timestamp
 /// during that day", but unwrapping it to `ts = TIMESTAMP '2024-01-01
 /// 00:00:00'` matches only midnight.
+///
+/// An identity cast (`from_type == to_type`, e.g. `Date32 -> Date32`) never
+/// changes comparison semantics and is therefore not lossy. This has to be
+/// handled explicitly because `DataType::is_temporal()` is true for both
+/// `Date32` and `Date64`, so `is_date_type(from) && to.is_temporal()` would
+/// otherwise report an identity `Date -> Date` cast as lossy and block the
+/// rewrite. Note this is deliberately limited to *identical* types: a genuine
+/// `Date32 <-> Date64` cast changes units (days vs milliseconds) and must
+/// still be treated as lossy here.
 fn is_lossy_temporal_cast(from_type: &DataType, to_type: &DataType) -> bool {
+    if from_type == to_type {
+        return false;
+    }
     (is_date_type(from_type) && to_type.is_temporal())
         || (is_date_type(to_type) && from_type.is_temporal())
 }
@@ -813,6 +825,57 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_try_cast_identity_date_allowed() {
+        // An identity Date cast (e.g. `CAST(date_col AS DATE)` where the column
+        // is already Date32) must fold: it never changes comparison semantics,
+        // so `try_cast_literal_to_type` should return the same value rather than
+        // treating it as a lossy temporal cast.
+        expect_cast(
+            ScalarValue::Date32(Some(19_723)),
+            DataType::Date32,
+            ExpectedCast::Value(ScalarValue::Date32(Some(19_723))),
+        );
+
+        expect_cast(
+            ScalarValue::Date64(Some(1_704_067_200_000)),
+            DataType::Date64,
+            ExpectedCast::Value(ScalarValue::Date64(Some(1_704_067_200_000))),
+        );
+
+        // is_lossy_temporal_cast must classify an identity cast as non-lossy.
+        assert!(!is_lossy_temporal_cast(
+            &DataType::Date32,
+            &DataType::Date32
+        ));
+        assert!(!is_lossy_temporal_cast(
+            &DataType::Date64,
+            &DataType::Date64
+        ));
+    }
+
+    #[test]
+    fn test_try_cast_date32_date64_still_blocked() {
+        // `Date32` counts days and `Date64` counts milliseconds, but
+        // try_cast_numeric_literal uses mul = 1 for both, so a cross cast would
+        // convert units wrongly. The identity short-circuit must NOT open this
+        // up: Date32 <-> Date64 has to stay blocked.
+        assert!(is_lossy_temporal_cast(&DataType::Date32, &DataType::Date64));
+        assert!(is_lossy_temporal_cast(&DataType::Date64, &DataType::Date32));
+
+        expect_cast(
+            ScalarValue::Date32(Some(1)),
+            DataType::Date64,
+            ExpectedCast::NoValue,
+        );
+
+        expect_cast(
+            ScalarValue::Date64(Some(86_400_000)),
+            DataType::Date32,
+            ExpectedCast::NoValue,
+        );
+    }
+
     #[test]
     fn test_timestamp_precision_narrowing_cast() {
         let ts_ns = DataType::Timestamp(TimeUnit::Nanosecond, None);

datafusion/sqllogictest/test_files/simplify_expr.slt

@@ -146,3 +146,36 @@ logical_plan
 physical_plan
 01)ProjectionExec: expr=[column1@0 = 1 as opt1, column1@0 = 2 AND column1@0 != 2 as noopt1, column1@0 = 4 as opt2, column1@0 != 5 AND column1@0 = 5 as noopt2]
 02)--DataSourceExec: partitions=1, partition_sizes=[1]
+
+# Identity Date cast in a comparison predicate.
+# `cast(d AS date)` where `d` is already Date32 is an identity cast and should
+# fold away, so the predicate compares against the bare column `d`. This enables
+# downstream pruning / filter pushdown that expects a bare-column comparison.
+statement ok
+create table dates(d date) as values (DATE '2024-01-01'), (DATE '2024-01-02');
+
+query TT
+explain select d from dates where cast(d as date) = DATE '2024-01-01';
+----
+logical_plan
+01)Filter: dates.d = Date32("2024-01-01")
+02)--TableScan: dates projection=[d]
+physical_plan
+01)FilterExec: d@0 = 2024-01-01
+02)--DataSourceExec: partitions=1, partition_sizes=[1]
+
+# Identity Date cast inside an `IN` predicate. `IN` goes through a separate
+# validation and rewrite path but relies on the same literal-cast helper, so the
+# identity `cast(d AS date)` should likewise fold to a bare-column comparison.
+query TT
+explain select d from dates where cast(d as date) in (DATE '2024-01-01');
+----
+logical_plan
+01)Filter: dates.d = Date32("2024-01-01")
+02)--TableScan: dates projection=[d]
+physical_plan
+01)FilterExec: d@0 = 2024-01-01
+02)--DataSourceExec: partitions=1, partition_sizes=[1]
+
+statement ok
+drop table dates;