From 98aed87aaa66bd593152ca2414493f51a9ea2108 Mon Sep 17 00:00:00 2001
From: Liang-Chi Hsieh <viirya@gmail.com>
Date: Fri, 22 Apr 2022 19:29:11 -0700
Subject: [PATCH 1/2] Read/Write nested dictionaries under FixedSizeList in IPC

---
 arrow/src/ipc/reader.rs | 39 +++++++++++++++++++++++++++++++++++++++
 arrow/src/ipc/writer.rs | 16 ++++++++++++++--
 2 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/arrow/src/ipc/reader.rs b/arrow/src/ipc/reader.rs
index 33d6085764be..a3ccf902c624 100644
--- a/arrow/src/ipc/reader.rs
+++ b/arrow/src/ipc/reader.rs
@@ -1573,4 +1573,43 @@ mod tests {
             offsets,
         );
     }
+
+    #[test]
+    fn test_roundtrip_stream_dict_of_fixed_size_list_of_dict() {
+        let values = StringArray::from(vec![Some("a"), None, Some("c"), None]);
+        let keys = Int8Array::from_iter_values([0, 0, 1, 2, 0, 1, 3, 1, 2]);
+        let dict_array = DictionaryArray::<Int8Type>::try_new(&keys, &values).unwrap();
+        let dict_data = dict_array.data();
+
+        let list_data_type = DataType::FixedSizeList(
+            Box::new(Field::new_dict(
+                "item",
+                DataType::Dictionary(Box::new(DataType::Int8), Box::new(DataType::Utf8)),
+                true,
+                1,
+                false,
+            )),
+            3,
+        );
+        let list_data = ArrayData::builder(list_data_type.clone())
+            .len(3)
+            .add_child_data(dict_data.clone())
+            .build()
+            .unwrap();
+        let list_array = FixedSizeListArray::from(list_data);
+
+        let keys_for_dict = Int8Array::from_iter_values([0, 1, 0, 1, 1, 2, 0, 1, 2]);
+        let dict_dict_array =
+            DictionaryArray::<Int8Type>::try_new(&keys_for_dict, &list_array).unwrap();
+
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "f1",
+            dict_dict_array.data_type().clone(),
+            false,
+        )]));
+        let input_batch =
+            RecordBatch::try_new(schema, vec![Arc::new(dict_dict_array)]).unwrap();
+        let output_batch = roundtrip_ipc_stream(&input_batch);
+        assert_eq!(input_batch, output_batch);
+    }
 }
diff --git a/arrow/src/ipc/writer.rs b/arrow/src/ipc/writer.rs
index 1f73d16d2b74..efc878a12109 100644
--- a/arrow/src/ipc/writer.rs
+++ b/arrow/src/ipc/writer.rs
@@ -27,7 +27,7 @@ use flatbuffers::FlatBufferBuilder;
 
 use crate::array::{
     as_large_list_array, as_list_array, as_map_array, as_struct_array, as_union_array,
-    make_array, Array, ArrayData, ArrayRef,
+    make_array, Array, ArrayData, ArrayRef, FixedSizeListArray,
 };
 use crate::buffer::{Buffer, MutableBuffer};
 use crate::datatypes::*;
@@ -147,7 +147,6 @@ impl IpcDataGenerator {
         dictionary_tracker: &mut DictionaryTracker,
         write_options: &IpcWriteOptions,
     ) -> Result<()> {
-        // TODO: Handle other nested types (FixedSizeList)
         match column.data_type() {
             DataType::Struct(fields) => {
                 let s = as_struct_array(column);
@@ -181,6 +180,19 @@ impl IpcDataGenerator {
                     write_options,
                 )?;
             }
+            DataType::FixedSizeList(field, _) => {
+                let list = column
+                    .as_any()
+                    .downcast_ref::<FixedSizeListArray>()
+                    .expect("Unable to downcast to fixed size list array");
+                self.encode_dictionaries(
+                    field,
+                    &list.values(),
+                    encoded_dictionaries,
+                    dictionary_tracker,
+                    write_options,
+                )?;
+            }
             DataType::Map(field, _) => {
                 let map_array = as_map_array(column);
 

From f645b649944d22ac07b8b2b1676bd457b1914cef Mon Sep 17 00:00:00 2001
From: Liang-Chi Hsieh <viirya@gmail.com>
Date: Fri, 22 Apr 2022 19:43:47 -0700
Subject: [PATCH 2/2] Fix clippy

---
 arrow/src/ipc/reader.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arrow/src/ipc/reader.rs b/arrow/src/ipc/reader.rs
index a3ccf902c624..8a26167dbae8 100644
--- a/arrow/src/ipc/reader.rs
+++ b/arrow/src/ipc/reader.rs
@@ -1591,7 +1591,7 @@ mod tests {
             )),
             3,
         );
-        let list_data = ArrayData::builder(list_data_type.clone())
+        let list_data = ArrayData::builder(list_data_type)
             .len(3)
             .add_child_data(dict_data.clone())
             .build()