Coerce Array inner types

datafusion/expr-common/src/type_coercion/binary.rs

@@ -480,11 +480,6 @@ fn type_union_resolution_coercion(
             let new_value_type = type_union_resolution_coercion(value_type, other_type);
             new_value_type.map(|t| DataType::Dictionary(index_type.clone(), Box::new(t)))
         }
-        (DataType::List(lhs), DataType::List(rhs)) => {
-            let new_item_type =
-                type_union_resolution_coercion(lhs.data_type(), rhs.data_type());
-            new_item_type.map(|t| DataType::List(Arc::new(Field::new("item", t, true))))
-        }
         (DataType::Struct(lhs), DataType::Struct(rhs)) => {
             if lhs.len() != rhs.len() {
                 return None;
@@ -529,6 +524,7 @@ fn type_union_resolution_coercion(
             // Numeric coercion is the same as comparison coercion, both find the narrowest type
             // that can accommodate both types
             binary_numeric_coercion(lhs_type, rhs_type)
+                .or_else(|| list_coercion(lhs_type, rhs_type))
                 .or_else(|| temporal_coercion_nonstrict_timezone(lhs_type, rhs_type))
                 .or_else(|| string_coercion(lhs_type, rhs_type))
                 .or_else(|| numeric_string_coercion(lhs_type, rhs_type))
@@ -1138,27 +1134,46 @@ fn numeric_string_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<D
     }
 }
 
+/// Coerces two fields together, ensuring the field data (name and nullability) is correctly set.
+fn coerce_list_children(lhs_field: &FieldRef, rhs_field: &FieldRef) -> Option<FieldRef> {
+    let data_types = vec![lhs_field.data_type().clone(), rhs_field.data_type().clone()];
+    Some(Arc::new(
+        (**lhs_field)
+            .clone()
+            .with_data_type(type_union_resolution(&data_types)?)
+            .with_nullable(lhs_field.is_nullable() || rhs_field.is_nullable()),
+    ))
+}
+
 /// Coercion rules for list types.
 fn list_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
     use arrow::datatypes::DataType::*;
     match (lhs_type, rhs_type) {
-        (List(_), List(_)) => Some(lhs_type.clone()),
-        (LargeList(_), List(_)) => Some(lhs_type.clone()),
-        (List(_), LargeList(_)) => Some(rhs_type.clone()),
-        (LargeList(_), LargeList(_)) => Some(lhs_type.clone()),
-        (List(_), FixedSizeList(_, _)) => Some(lhs_type.clone()),
-        (FixedSizeList(_, _), List(_)) => Some(rhs_type.clone()),
+        (
+            LargeList(lhs_field),
+            List(rhs_field) | LargeList(rhs_field) | FixedSizeList(rhs_field, _),
+        )
+        | (List(lhs_field) | FixedSizeList(lhs_field, _), LargeList(rhs_field)) => {
+            Some(LargeList(coerce_list_children(lhs_field, rhs_field)?))
+        }
+
+        (List(lhs_field), List(rhs_field) | FixedSizeList(rhs_field, _))
+        | (FixedSizeList(lhs_field, _), List(rhs_field)) => {
+            Some(List(coerce_list_children(lhs_field, rhs_field)?))
+        }
+
         // Coerce to the left side FixedSizeList type if the list lengths are the same,
         // otherwise coerce to list with the left type for dynamic length
-        (FixedSizeList(lf, ls), FixedSizeList(_, rs)) => {
+        (FixedSizeList(lhs_field, ls), FixedSizeList(rhs_field, rs)) => {
             if ls == rs {
-                Some(lhs_type.clone())
+                Some(FixedSizeList(
+                    coerce_list_children(lhs_field, rhs_field)?,
+                    *rs,
+                ))
             } else {
-                Some(List(Arc::clone(lf)))
+                Some(List(coerce_list_children(lhs_field, rhs_field)?))
             }
         }
-        (LargeList(_), FixedSizeList(_, _)) => Some(lhs_type.clone()),
-        (FixedSizeList(_, _), LargeList(_)) => Some(rhs_type.clone()),
         _ => None,
     }
 }
@@ -2105,10 +2120,36 @@ mod tests {
             DataType::List(Arc::clone(&inner_field))
         );
 
+        // Negative test: inner_timestamp_field and inner_field are not compatible because their inner types are not compatible
+        let inner_timestamp_field = Arc::new(Field::new(
+            "item",
+            DataType::Timestamp(TimeUnit::Microsecond, None),
+            true,
+        ));
+        let result_type = get_input_types(
+            &DataType::List(Arc::clone(&inner_field)),
+            &Operator::Eq,
+            &DataType::List(Arc::clone(&inner_timestamp_field)),
+        );
+        assert!(result_type.is_err());
+
         // TODO add other data type
         Ok(())
     }
 
+    #[test]
+    fn test_list_coercion() {
+        let lhs_type = DataType::List(Arc::new(Field::new("lhs", DataType::Int8, false)));
+
+        let rhs_type = DataType::List(Arc::new(Field::new("rhs", DataType::Int64, true)));
+
+        let coerced_type = list_coercion(&lhs_type, &rhs_type).unwrap();
+        assert_eq!(
+            coerced_type,
+            DataType::List(Arc::new(Field::new("lhs", DataType::Int64, true)))
+        ); // nullable because the RHS is nullable
+    }
+
     #[test]
     fn test_type_coercion_logical_op() -> Result<()> {
         test_coercion_binary_rule!(

datafusion/functions-nested/src/make_array.rs

@@ -26,7 +26,7 @@ use arrow_array::{
     new_null_array, Array, ArrayRef, GenericListArray, NullArray, OffsetSizeTrait,
 };
 use arrow_buffer::OffsetBuffer;
-use arrow_schema::DataType::{LargeList, List, Null};
+use arrow_schema::DataType::{List, Null};
 use arrow_schema::{DataType, Field};
 use datafusion_common::{plan_err, utils::array_into_list_array_nullable, Result};
 use datafusion_expr::binary::{
@@ -198,7 +198,6 @@ pub(crate) fn make_array_inner(arrays: &[ArrayRef]) -> Result<ArrayRef> {
             let array = new_null_array(&DataType::Int64, length);
             Ok(Arc::new(array_into_list_array_nullable(array)))
         }
-        LargeList(..) => array_array::<i64>(arrays, data_type),
         _ => array_array::<i32>(arrays, data_type),
     }
 }

datafusion/sqllogictest/test_files/array.slt

@@ -1155,6 +1155,12 @@ select column1, column5 from arrays_values_without_nulls;
 [21, 22, 23, 24, 25, 26, 27, 28, 29, 30] [6, 7]
 [31, 32, 33, 34, 35, 26, 37, 38, 39, 40] [8, 9]
 
+# make array with arrays of different types
+query ?
+select make_array(make_array(1), arrow_cast(make_array(-1), 'LargeList(Int8)'))
+----
+[[1], [-1]]
+
 query ???
 select make_array(column1),
        make_array(column1, column5),

datafusion/sqllogictest/test_files/union.slt

@@ -761,3 +761,19 @@ SELECT NULL WHERE FALSE;
 ----
 0.5
 1
+
+# Test Union of List Types. Issue: https://github.com/apache/datafusion/issues/12291
+query error DataFusion error: type_coercion\ncaused by\nError during planning: Incompatible inputs for Union: Previous inputs were of type List(.*), but got incompatible type List(.*) on column 'x'
+SELECT make_array(2) x UNION ALL SELECT make_array(now()) x;
+
+query ?
+select make_array(arrow_cast(2, 'UInt8')) x UNION ALL SELECT make_array(arrow_cast(-2, 'Int8')) x;
+----
+[-2]
+[2]
+
+query ?
+select make_array(make_array(1)) x UNION ALL SELECT make_array(arrow_cast(make_array(-1), 'LargeList(Int8)')) x;
+----
+[[-1]]
+[[1]]