fix(storage): preserve ABI compatibility by adding explicit Finalize overloads without default arguments

Author: v-pratap

google/cloud/storage/async/writer.cc

@@ -69,6 +69,11 @@ future<StatusOr<AsyncToken>> AsyncWriter::Write(AsyncToken token,
       });
 }
 
+future<StatusOr<google::storage::v2::Object>> AsyncWriter::Finalize(
+    AsyncToken token, WritePayload payload) {
+  return Finalize(std::move(token), std::move(payload), absl::nullopt);
+}
+
 future<StatusOr<google::storage::v2::Object>> AsyncWriter::Finalize(
     AsyncToken token, WritePayload payload,
     absl::optional<Crc32cChecksumValue> const& expected_checksum) {
@@ -82,6 +87,11 @@ future<StatusOr<google::storage::v2::Object>> AsyncWriter::Finalize(
       .then([impl = impl_](auto f) { return f.get(); });
 }
 
+future<StatusOr<google::storage::v2::Object>> AsyncWriter::Finalize(
+    AsyncToken token) {
+  return Finalize(std::move(token), WritePayload{}, absl::nullopt);
+}
+
 future<StatusOr<google::storage::v2::Object>> AsyncWriter::Finalize(
     AsyncToken token,
     absl::optional<Crc32cChecksumValue> const& expected_checksum) {

google/cloud/storage/async/writer.h

@@ -116,18 +116,19 @@ class AsyncWriter {
   future<StatusOr<AsyncToken>> Write(AsyncToken token, WritePayload payload);
 
   /// Finalize the upload with the existing data.
+  future<StatusOr<google::storage::v2::Object>> Finalize(AsyncToken token);
   future<StatusOr<google::storage::v2::Object>> Finalize(
       AsyncToken token,
-      absl::optional<Crc32cChecksumValue> const& expected_checksum =
-          absl::nullopt);
+      absl::optional<Crc32cChecksumValue> const& expected_checksum);
 
   /**
    * Upload @p payload and then finalize the upload.
    */
+  future<StatusOr<google::storage::v2::Object>> Finalize(AsyncToken token,
+                                                         WritePayload payload);
   future<StatusOr<google::storage::v2::Object>> Finalize(
       AsyncToken token, WritePayload payload,
-      absl::optional<Crc32cChecksumValue> const& expected_checksum =
-          absl::nullopt);
+      absl::optional<Crc32cChecksumValue> const& expected_checksum);
 
   /**
    * Flush any buffered data to the service.