makes the return value of --help same as official abseil library

src/init.h

@@ -18,6 +18,7 @@
 #include "common.h"
 #include "third_party/absl/flags/flag.h"
 #include "third_party/absl/flags/parse.h"
+#include "third_party/absl/flags/usage.h"
 
 #ifdef _USE_EXTERNAL_PROTOBUF
 #include "google/protobuf/message_lite.h"
@@ -30,6 +31,7 @@ ABSL_DECLARE_FLAG(int32, minloglevel);
 namespace sentencepiece {
 inline void ParseCommandLineFlags(const char *usage, int *argc, char ***argv,
                                   bool remove_arg = true) {
+  absl::SetProgramUsageMessage(*argv[0]);
   const auto unused_args = absl::ParseCommandLine(*argc, *argv);
 
   if (remove_arg) {

third_party/absl/flags/flag.cc

@@ -211,7 +211,7 @@ std::vector<char *> ParseCommandLine(int argc, char *argv[]) {
 
   if (absl::GetFlag(FLAGS_help)) {
     std::cout << internal::PrintHelp(argv[0]);
-    sentencepiece::error::Exit(0);
+    sentencepiece::error::Exit(1);
   } else if (absl::GetFlag(FLAGS_version)) {
     std::cout << PACKAGE_STRING << " " << VERSION << std::endl;
     sentencepiece::error::Exit(0);

third_party/absl/flags/usage.h

@@ -0,0 +1,28 @@
+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.!
+
+#ifndef ABSL_FLAGS_USAGE_H_
+#define ABSL_FLAGS_USAGE_H_
+
+#include <vector>
+
+#include "third_party/absl/strings/string_view.h"
+
+namespace absl {
+
+inline void SetProgramUsageMessage(absl::string_view new_usage_message) {}
+
+}  // namespace absl
+
+#endif  // ABSL_FLAGS_USAGE_H_