jonathanc-n commented on code in PR #16423:
URL: https://github.com/apache/datafusion/pull/16423#discussion_r2150374823


##########
datafusion/functions-nested/src/reverse.rs:
##########
@@ -175,3 +182,45 @@ fn general_array_reverse<O: OffsetSizeTrait + 
TryFrom<i64>>(
         Some(nulls.into()),
     )?))
 }
+
+fn fixed_size_array_reverse(
+    array: &FixedSizeListArray,
+    field: &FieldRef,
+) -> Result<ArrayRef> {
+    let values = array.values();
+    let original_data = values.to_data();
+    let capacity = Capacities::Array(original_data.len());
+    let mut nulls = vec![];

Review Comment:
   Instead of creating another null array you can use the `.extend_null` 
function that is inside `MutableArrayData`



##########
datafusion/functions-nested/src/reverse.rs:
##########
@@ -175,3 +182,45 @@ fn general_array_reverse<O: OffsetSizeTrait + 
TryFrom<i64>>(
         Some(nulls.into()),
     )?))
 }
+
+fn fixed_size_array_reverse(
+    array: &FixedSizeListArray,
+    field: &FieldRef,
+) -> Result<ArrayRef> {
+    let values = array.values();
+    let original_data = values.to_data();
+    let capacity = Capacities::Array(original_data.len());
+    let mut nulls = vec![];
+    let mut mutable =
+        MutableArrayData::with_capacities(vec![&original_data], false, 
capacity);
+    let value_length = array.value_length();
+
+    for row_index in 0..(array.len() as i32) {
+        // skip the null value
+        if array.is_null(row_index as usize) {
+            nulls.push(false);
+            mutable.extend(0, 0, 1);
+            continue;
+        } else {
+            nulls.push(true);
+        }
+
+        let start = row_index * value_length;
+        let end = (row_index + 1) * value_length;
+
+        let mut index = end - 1;
+
+        while index >= start {
+            mutable.extend(0, index as usize, index as usize + 1);
+            index -= 1;
+        }
+    }

Review Comment:
   This can be refactored, instead of converting to usize later we can convert 
this to usize first. `rev` function can also be used for the reverse logic
   ```suggestion
       let value_length = array.value_length() as usize;
       
       for row_index in 0..array.len() {
           // skip the null value
           if array.is_null(row_index) {
               mutable.extend_nulls(1);
           } else {
               let start = row_index * value_length;
               let end = start + value_length;
               for idx in (start..end).rev() {
                   mutable.extend(0, idx, idx + 1);
               }
           }
       }
   ```



##########
datafusion/sqllogictest/test_files/array.slt:
##########
@@ -7853,11 +7853,10 @@ select array_reverse(arrow_cast(make_array(1, 2, 3), 
'LargeList(Int64)')), array
 ----
 [3, 2, 1] [1]
 
-#TODO: support after FixedSizeList type coercion
-#query ??
-#select array_reverse(arrow_cast(make_array(1, 2, 3), 'FixedSizeList(3, 
Int64)')), array_reverse(arrow_cast(make_array(1), 'FixedSizeList(1, Int64)'));
-#----
-#[3, 2, 1] [1]
+query ??
+select array_reverse(arrow_cast(make_array(1, 2, 3), 'FixedSizeList(3, 
Int64)')), array_reverse(arrow_cast(make_array(1), 'FixedSizeList(1, Int64)'));
+----
+[3, 2, 1] [1]
 

Review Comment:
   Lets add a test for null values as well



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