fix: correct partition field handling for non-partitioned tables

- Fix ManifestEntry::operator== logic with proper parentheses grouping
- Add null pointer safety in DataFile::Type() for non-partitioned tables
- Change partition field type validation from list to struct in manifest reader
- Support empty partition structs for non-partitioned tables (n_children == 0)
- Update test bounds values to match actual manifest file data

This resolves issues with non-partitioned table support and fixes
critical bugs in object comparison and type validation.

Author: HeartLinked

src/iceberg/manifest_entry.cc

@@ -29,13 +29,16 @@ namespace iceberg {
 
 bool ManifestEntry::operator==(const ManifestEntry& other) const {
   return status == other.status && snapshot_id == other.snapshot_id &&
-             sequence_number == other.sequence_number &&
-             file_sequence_number == other.file_sequence_number &&
-             (data_file && other.data_file && *data_file == *other.data_file) ||
-         (!data_file && !other.data_file);
+         sequence_number == other.sequence_number &&
+         file_sequence_number == other.file_sequence_number &&
+         ((data_file && other.data_file && *data_file == *other.data_file) ||
+          (!data_file && !other.data_file));
 }
 
 std::shared_ptr<StructType> DataFile::Type(std::shared_ptr<StructType> partition_type) {
+  if (!partition_type) {
+    partition_type = std::make_shared<StructType>(std::vector<SchemaField>{});
+  }
   return std::make_shared<StructType>(std::vector<SchemaField>{
       kContent,
       kFilePath,

src/iceberg/manifest_reader_internal.cc

@@ -368,15 +368,17 @@ Status ParseDataFile(const std::shared_ptr<StructType>& data_file_schema,
         break;
       case 3: {
         if (view_of_file_field->storage_type != ArrowType::NANOARROW_TYPE_STRUCT) {
-          return InvalidManifest("Field:{} should be a list.", field_name);
+          return InvalidManifest("Field:{} should be a struct.", field_name);
         }
-        auto view_of_partition = view_of_file_field->children[0];
-        for (size_t row_idx = 0; row_idx < view_of_partition->length; row_idx++) {
-          if (ArrowArrayViewIsNull(view_of_partition, row_idx)) {
-            break;
+        if (view_of_file_field->n_children > 0) {
+          auto view_of_partition = view_of_file_field->children[0];
+          for (size_t row_idx = 0; row_idx < view_of_partition->length; row_idx++) {
+            if (ArrowArrayViewIsNull(view_of_partition, row_idx)) {
+              break;
+            }
+            ICEBERG_RETURN_UNEXPECTED(
+                ParseLiteral(view_of_partition, row_idx, manifest_entries));
           }
-          ICEBERG_RETURN_UNEXPECTED(
-              ParseLiteral(view_of_partition, row_idx, manifest_entries));
         }
       } break;
       case 4:

test/manifest_reader_test.cc

@@ -142,7 +142,6 @@ class ManifestReaderV2Test : public TempFileTestBase {
     std::vector<int64_t> file_sizes = {1344};
     std::vector<int64_t> record_counts = {4};
 
-    // Real bounds data extracted from the manifest
     std::vector<std::map<int32_t, std::vector<uint8_t>>> lower_bounds = {
         {{1, {0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}},
          {2, {'r', 'e', 'c', 'o', 'r', 'd', '_', 'f', 'o', 'u', 'r'}},