refactor: prepare for breaking change in Protobuf C++ API. (#14828)

Author: evalon32

google/cloud/spanner/internal/status_utils.cc

@@ -14,6 +14,7 @@
 
 #include "google/cloud/spanner/internal/status_utils.h"
 #include "google/cloud/grpc_error_delegate.h"
+#include "google/cloud/internal/absl_str_cat_quiet.h"
 #include "google/cloud/internal/status_payload_keys.h"
 #include "absl/strings/match.h"
 #include <google/rpc/error_details.pb.h>
@@ -38,7 +39,8 @@ bool IsSessionNotFound(google::cloud::Status const& status) {
     for (google::protobuf::Any const& any : proto.details()) {
       if (any.UnpackTo(&resource_info)) {
         google::spanner::v1::Session session;
-        auto session_url = "type.googleapis.com/" + session.GetTypeName();
+        auto session_url =
+            absl::StrCat("type.googleapis.com/", session.GetTypeName());
         return resource_info.resource_type() == session_url;
       }
     }

google/cloud/spanner/proto_enum.h

@@ -57,7 +57,10 @@ class ProtoEnum {
   explicit operator enum_type() const { return v_; }
 
   /// The fully-qualified name of the enum type, scope delimited by periods.
-  static std::string const& TypeName() { return Descriptor()->full_name(); }
+  static std::string const& TypeName() {
+    static std::string const kName(Descriptor()->full_name());
+    return kName;
+  }
 
   /// @name Relational operators
   ///@{

google/cloud/spanner/proto_message.h

@@ -74,7 +74,8 @@ class ProtoMessage {
 
   /// The fully-qualified name of the message type, scope delimited by periods.
   static std::string const& TypeName() {
-    return message_type::GetDescriptor()->full_name();
+    static std::string const kName(message_type::GetDescriptor()->full_name());
+    return kName;
   }
 
   /// @name Relational operators

google/cloud/spanner/testing/status_utils.cc

@@ -14,6 +14,7 @@
 
 #include "google/cloud/spanner/testing/status_utils.h"
 #include "google/cloud/grpc_error_delegate.h"
+#include "google/cloud/internal/absl_str_cat_quiet.h"
 #include <google/rpc/error_details.pb.h>
 #include <google/rpc/status.pb.h>
 #include <google/spanner/v1/spanner.pb.h>
@@ -25,7 +26,8 @@ GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
 
 grpc::Status SessionNotFoundRpcError(std::string name) {
   google::spanner::v1::Session session;
-  auto session_url = "type.googleapis.com/" + session.GetTypeName();
+  auto session_url =
+      absl::StrCat("type.googleapis.com/", session.GetTypeName());
 
   google::rpc::ResourceInfo resource_info;
   resource_info.set_resource_type(session_url);