consolidate Avro default scalar into AvroExtraAttributes with checked_cast

Author: huan233usc

src/iceberg/avro/avro_data_util.cc

@@ -590,12 +590,11 @@ Status PrepareStructDefaultScalars(std::span<FieldProjection> projections,
     auto* field_builder = struct_builder->field_builder(static_cast<int>(i));
 
     if (field_projection.kind == FieldProjection::Kind::kDefault) {
-      if (dynamic_cast<const AvroDefaultAttributes*>(field_projection.attributes.get()) !=
-          nullptr) {
+      if (field_projection.attributes != nullptr) {
         continue;
       }
-      auto attrs = std::make_shared<AvroDefaultAttributes>();
-      ICEBERG_ASSIGN_OR_RAISE(attrs->scalar,
+      auto attrs = std::make_shared<AvroExtraAttributes>();
+      ICEBERG_ASSIGN_OR_RAISE(attrs->default_scalar,
                               MakeDefaultScalar(std::get<Literal>(field_projection.from),
                                                 field_builder->type()));
       field_projection.attributes = std::move(attrs);
@@ -624,11 +623,15 @@ Status AppendDefaultToBuilder(const Literal& literal, ::arrow::ArrayBuilder* bui
 
 Status AppendDefaultToBuilder(const FieldProjection& projection,
                               ::arrow::ArrayBuilder* builder) {
-  if (const auto* attrs =
-          dynamic_cast<const AvroDefaultAttributes*>(projection.attributes.get());
-      attrs != nullptr && attrs->scalar != nullptr) {
-    ICEBERG_ARROW_RETURN_NOT_OK(builder->AppendScalar(*attrs->scalar));
-    return {};
+  // Avro projections carry a single attributes type, so once one is attached it is an
+  // AvroExtraAttributes; use checked_cast instead of a per-row dynamic_cast.
+  if (projection.attributes != nullptr) {
+    const auto& attrs =
+        internal::checked_cast<const AvroExtraAttributes&>(*projection.attributes);
+    if (attrs.default_scalar != nullptr) {
+      ICEBERG_ARROW_RETURN_NOT_OK(builder->AppendScalar(*attrs.default_scalar));
+      return {};
+    }
   }
   return AppendDefaultToBuilder(std::get<Literal>(projection.from), builder);
 }

src/iceberg/avro/avro_data_util_internal.h

@@ -31,19 +31,22 @@
 
 namespace iceberg::avro {
 
-/// \brief Cached Arrow scalar for a `kDefault` field projection.
+/// \brief Avro-specific per-field projection attributes.
 ///
-/// Materialized once (see `PrepareDefaultScalars`) so row-by-row Avro decode only
-/// needs `AppendScalar` instead of repeating `ToArrowScalar` / `CastTo` per row.
-struct AvroDefaultAttributes : FieldProjection::ExtraAttributes {
-  std::shared_ptr<::arrow::Scalar> scalar;
+/// `FieldProjection` has a single attributes slot, so all Avro-side attributes live in
+/// one container (mirroring `ParquetExtraAttributes`) rather than separate subclasses
+/// that could not coexist. `default_scalar` is the Arrow scalar for a `kDefault` field,
+/// materialized once (see `PrepareDefaultScalars`) so row-by-row decode only needs
+/// `AppendScalar` instead of repeating `ToArrowScalar` / `CastTo` per row.
+struct AvroExtraAttributes : FieldProjection::ExtraAttributes {
+  std::shared_ptr<::arrow::Scalar> default_scalar;
 };
 
 /// \brief Precompute cast Arrow scalars for every `kDefault` field under `projection`.
 ///
 /// Walks `root_builder` in lockstep with the projection so each default is cast to the
 /// builder's Arrow type once per scan. Safe to call repeatedly; existing
-/// `AvroDefaultAttributes` entries are left unchanged.
+/// `AvroExtraAttributes` entries are left unchanged.
 Status PrepareDefaultScalars(SchemaProjection& projection,
                              ::arrow::ArrayBuilder* root_builder);
 

src/iceberg/test/avro_data_test.cc

@@ -801,7 +801,7 @@ TEST(AppendDefaultToBuilderTest, ReusesPreparedScalar) {
   SchemaProjection schema_projection;
   schema_projection.fields.push_back(projection);
   ASSERT_THAT(PrepareDefaultScalars(schema_projection, &struct_builder), IsOk());
-  ASSERT_NE(dynamic_cast<const AvroDefaultAttributes*>(
+  ASSERT_NE(dynamic_cast<const AvroExtraAttributes*>(
                 schema_projection.fields[0].attributes.get()),
             nullptr);
 
@@ -852,8 +852,7 @@ TEST(AppendDefaultToBuilderTest, PreparesScalarUnderNestedCollections) {
   ASSERT_THAT(PrepareDefaultScalars(schema_projection, &root_builder), IsOk());
 
   const auto& prepared = schema_projection.fields[0].children[0].children[0].children[0];
-  ASSERT_NE(dynamic_cast<const AvroDefaultAttributes*>(prepared.attributes.get()),
-            nullptr);
+  ASSERT_NE(dynamic_cast<const AvroExtraAttributes*>(prepared.attributes.get()), nullptr);
 }
 
 TEST(AppendDatumToBuilderTest, NestedStructWithMissingOptionalFields) {