GH-43911: [C++] Compute Row: ListKeyEncoder Supports

cpp/src/arrow/compute/row/row_encoder_internal.cc

@@ -29,6 +29,51 @@ using internal::FirstTimeBitmapWriter;
 namespace compute {
 namespace internal {
 
+Result<std::shared_ptr<KeyEncoder>> MakeKeyEncoder(const TypeHolder& column_type, std::shared_ptr<ExtensionType>* extension_type, MemoryPool* pool) {
+  const bool is_extension = column_type.id() == Type::EXTENSION;
+  const TypeHolder& type =
+      is_extension
+          ? arrow::internal::checked_cast<const ExtensionType*>(column_type.type)
+                ->storage_type()
+          : column_type;
+
+  if (is_extension) {
+    *extension_type = arrow::internal::checked_pointer_cast<ExtensionType>(
+        column_type.GetSharedPtr());
+  }
+  if (type.id() == Type::BOOL) {
+    return std::make_shared<BooleanKeyEncoder>();
+  }
+
+  if (type.id() == Type::DICTIONARY) {
+    return std::make_shared<DictionaryKeyEncoder>(type.GetSharedPtr(), pool);
+  }
+
+  if (is_fixed_width(type.id())) {
+    return std::make_shared<FixedWidthKeyEncoder>(type.GetSharedPtr());
+  }
+
+  if (is_binary_like(type.id())) {
+    return std::make_shared<VarLengthKeyEncoder<BinaryType>>(type.GetSharedPtr());
+  }
+
+  if (is_large_binary_like(type.id())) {
+    return std::make_shared<VarLengthKeyEncoder<LargeBinaryType>>(type.GetSharedPtr());
+  }
+
+  if (is_list(type.id())) {
+    auto element_type = ::arrow::checked_cast<BaseListType*>(type.type)->value_type();
+    if (is_nested(element_type->id())) {
+      return Status::NotImplemented("Unsupported nested type in List for row encoder", type.ToString());
+    }
+    std::shared_ptr<ExtensionType> element_extension_type;
+    ARROW_ASSIGN_OR_RAISE(auto element_encoder, MakeKeyEncoder(element_type, &element_extension_type, pool));
+    return std::make_shared<ListKeyEncoder>(std::move(element_type), std::move(element_encoder));
+  }
+
+  return Status::NotImplemented("Unsupported type for row encoder", type.ToString());
+}
+
 // extract the null bitmap from the leading nullity bytes of encoded keys
 Status KeyEncoder::DecodeNulls(MemoryPool* pool, int32_t length, uint8_t** encoded_bytes,
                                std::shared_ptr<Buffer>* null_bitmap,
@@ -256,53 +301,32 @@ Result<std::shared_ptr<ArrayData>> DictionaryKeyEncoder::Decode(uint8_t** encode
   return data;
 }
 
-void RowEncoder::Init(const std::vector<TypeHolder>& column_types, ExecContext* ctx) {
-  ctx_ = ctx;
-  encoders_.resize(column_types.size());
-  extension_types_.resize(column_types.size());
+ListKeyEncoder::ListKeyEncoder(std::shared_ptr<DataType> element_type, std::shared_ptr<KeyEncoder> element_encoder)
+    : element_type_(std::move(element_type)), element_encoder_(std::move(element_encoder)) {}
 
-  for (size_t i = 0; i < column_types.size(); ++i) {
-    const bool is_extension = column_types[i].id() == Type::EXTENSION;
-    const TypeHolder& type =
-        is_extension
-            ? arrow::internal::checked_cast<const ExtensionType*>(column_types[i].type)
-                  ->storage_type()
-            : column_types[i];
-
-    if (is_extension) {
-      extension_types_[i] = arrow::internal::checked_pointer_cast<ExtensionType>(
-          column_types[i].GetSharedPtr());
-    }
-    if (type.id() == Type::BOOL) {
-      encoders_[i] = std::make_shared<BooleanKeyEncoder>();
-      continue;
-    }
+void ListKeyEncoder::AddLength(const ExecValue& exec_value, int64_t batch_length, int32_t* lengths) {}
 
-    if (type.id() == Type::DICTIONARY) {
-      encoders_[i] =
-          std::make_shared<DictionaryKeyEncoder>(type.GetSharedPtr(), ctx->memory_pool());
-      continue;
-    }
+void ListKeyEncoder::AddLengthNull(int32_t* length) {}
 
-    if (is_fixed_width(type.id())) {
-      encoders_[i] = std::make_shared<FixedWidthKeyEncoder>(type.GetSharedPtr());
-      continue;
-    }
+Status ListKeyEncoder::Encode(const ExecValue& data, int64_t batch_length,
+              uint8_t** encoded_bytes) {
+  return Status::NotImplemented("ListKeyEncoder::Encode");
+}
 
-    if (is_binary_like(type.id())) {
-      encoders_[i] =
-          std::make_shared<VarLengthKeyEncoder<BinaryType>>(type.GetSharedPtr());
-      continue;
-    }
+void ListKeyEncoder::EncodeNull(uint8_t** encoded_bytes) {}
 
-    if (is_large_binary_like(type.id())) {
-      encoders_[i] =
-          std::make_shared<VarLengthKeyEncoder<LargeBinaryType>>(type.GetSharedPtr());
-      continue;
-    }
+Result<std::shared_ptr<ArrayData>> ListKeyEncoder::Decode(uint8_t** encoded_bytes, int32_t length,
+                                          MemoryPool* pool) {
+  return std::shared_ptr<ArrayData>(nullptr);
+}
+
+Status RowEncoder::Init(const std::vector<TypeHolder>& column_types, ExecContext* ctx) {
+  ctx_ = ctx;
+  encoders_.resize(column_types.size());
+  extension_types_.resize(column_types.size());
 
-    // We should not get here
-    ARROW_DCHECK(false);
+  for (size_t i = 0; i < column_types.size(); ++i) {
+    ARROW_ASSIGN_OR_RAISE(encoders_[i], MakeKeyEncoder(column_types[i], &extension_types_[i], ctx->memory_pool()));
   }
 
   int32_t total_length = 0;
@@ -314,6 +338,7 @@ void RowEncoder::Init(const std::vector<TypeHolder>& column_types, ExecContext*
   for (size_t i = 0; i < column_types.size(); ++i) {
     encoders_[i]->EncodeNull(&buf_ptr);
   }
+  return Status::OK();
 }
 
 void RowEncoder::Clear() {

cpp/src/arrow/compute/row/row_encoder_internal.h

@@ -269,6 +269,28 @@ struct ARROW_EXPORT NullKeyEncoder : KeyEncoder {
   }
 };
 
+struct ARROW_EXPORT ListKeyEncoder : KeyEncoder {
+  explicit ListKeyEncoder(std::shared_ptr<DataType> element_type, std::shared_ptr<KeyEncoder> element_encoder);
+
+  void AddLength(const ExecValue&, int64_t batch_length, int32_t* lengths) override;
+
+  void AddLengthNull(int32_t* length) override;
+
+  Status Encode(const ExecValue& data, int64_t batch_length,
+                uint8_t** encoded_bytes) override;
+
+  void EncodeNull(uint8_t** encoded_bytes) override;
+
+  Result<std::shared_ptr<ArrayData>> Decode(uint8_t** encoded_bytes, int32_t length,
+                                            MemoryPool* pool) override;
+
+  std::shared_ptr<DataType> element_type_;
+  std::shared_ptr<KeyEncoder> element_encoder_;
+  // extension_type_ is used to store the extension type of the list element.
+  // It would be nullptr if the list element is not an extension type.
+  std::shared_ptr<ExtensionType> extension_type_;
+};
+
 /// RowEncoder encodes ExecSpan to a variable length byte sequence
 /// created by concatenating the encoded form of each column. The encoding
 /// for each column depends on its data type.
@@ -328,14 +350,23 @@ struct ARROW_EXPORT NullKeyEncoder : KeyEncoder {
 /// Null string Would be encoded as:
 /// 1 ( 1 byte for null) + 0 ( 4 bytes for length )
 ///
+/// ## List Type
+///
+/// List Type is encoded as:
+/// [null byte, list element count, [element 1, element 2, ...]]
+/// Element count uses 4 bytes.
+///
+/// Currently, we only support encoding of primitive types, dictionary types
+/// in the list, the nested list is not supported.
+///
 /// # Row Encoding
 ///
 /// The row format is the concatenation of the encodings of each column.
 class ARROW_EXPORT RowEncoder {
  public:
   static constexpr int kRowIdForNulls() { return -1; }
 
-  void Init(const std::vector<TypeHolder>& column_types, ExecContext* ctx);
+  Status Init(const std::vector<TypeHolder>& column_types, ExecContext* ctx);
   void Clear();
   Status EncodeAndAppend(const ExecSpan& batch);
   Result<ExecBatch> Decode(int64_t num_rows, const int32_t* row_ids);