refactor: update Snapshot structure to remove default initializations for optional fields

Author: Joe-Abraham

src/iceberg/snapshot.h

@@ -390,19 +390,19 @@ struct ICEBERG_EXPORT Snapshot {
   /// A unique long ID.
   int64_t snapshot_id;
   /// The snapshot ID of the snapshot's parent. Omitted for any snapshot with no parent.
-  std::optional<int64_t> parent_snapshot_id = std::nullopt;
+  std::optional<int64_t> parent_snapshot_id;
   /// A monotonically increasing long that tracks the order of changes to a table.
-  int64_t sequence_number = 0;
+  int64_t sequence_number;
   /// A timestamp when the snapshot was created, used for garbage collection and table
   /// inspection.
-  TimePointMs timestamp_ms{};
+  TimePointMs timestamp_ms;
   /// The location of a manifest list for this snapshot that tracks manifest files with
   /// additional metadata.
   std::string manifest_list;
   /// A string map that summaries the snapshot changes, including operation.
   std::unordered_map<std::string, std::string> summary;
   /// ID of the table's current schema when the snapshot was created.
-  std::optional<int32_t> schema_id = std::nullopt;
+  std::optional<int32_t> schema_id;
 
   /// \brief Create a new Snapshot instance with validation on the inputs.
   static Result<std::unique_ptr<Snapshot>> Make(

src/iceberg/test/table_update_test.cc

@@ -379,9 +379,12 @@ TEST(TableUpdateTest, SetSnapshotRefApplyUpdate) {
     // Add a snapshot that the ref will point to
     auto snapshot = std::make_shared<Snapshot>(
         Snapshot{.snapshot_id = 123456789,
+                 .parent_snapshot_id = std::nullopt,
                  .sequence_number = 1,
                  .timestamp_ms = TimePointMsFromUnixMs(1000000),
-                 .manifest_list = "s3://bucket/manifest-list.avro"});
+                 .manifest_list = "s3://bucket/manifest-list.avro",
+                 .summary = {},
+                 .schema_id = std::nullopt});
     builder->AddSnapshot(snapshot);
 
     // Apply SetSnapshotRef update for a branch
@@ -414,9 +417,12 @@ TEST(TableUpdateTest, SetSnapshotRefApplyUpdate) {
     // Add a snapshot that the ref will point to
     auto snapshot = std::make_shared<Snapshot>(
         Snapshot{.snapshot_id = 987654321,
+                 .parent_snapshot_id = std::nullopt,
                  .sequence_number = 1,
                  .timestamp_ms = TimePointMsFromUnixMs(2000000),
-                 .manifest_list = "s3://bucket/manifest-list.avro"});
+                 .manifest_list = "s3://bucket/manifest-list.avro",
+                 .summary = {},
+                 .schema_id = std::nullopt});
     builder->AddSnapshot(snapshot);
 
     // Apply SetSnapshotRef update for a tag