Add a FileWriter interface (#7821)

* Add a FileWriter interface

* Change interface

* Provide 2 impl for File interface: FileManager & FileNameManager

* Update

* update

* Update

* Add file_writer file

* Update

* Format files

* Update based on review

* Update

* Format bzl file

* Add LoadFile function

* Format

---------

Co-authored-by: Derek Bailey <derekbailey@google.com>

src/file_name_saving_file_manager.cpp

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 Google Inc. All rights reserved.
+ *
+ * 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.
+ */
+
+#include <fstream>
+#include <set>
+#include <string>
+
+#include "flatbuffers/file_manager.h"
+
+namespace flatbuffers {
+
+class FileNameSavingFileManager : public FileManager {
+ public:
+  FileNameSavingFileManager(std::set<std::string> file_names)
+      : file_names_(file_names) {}
+
+  bool SaveFile(const std::string &absolute_file_name,
+                const std::string &content) override {
+    (void)content;
+    auto pair = file_names_.insert(absolute_file_name);
+    // pair.second indicates whether the insertion is
+    // successful or not.
+    return pair.second;
+  }
+
+  bool Loadfile(const std::string &absolute_file_name, std::string *content) {
+    (void) absolute_file_name;
+    (void) content;
+    return false;
+  }
+
+ private:
+  std::set<std::string> file_names_;
+};
+
+}  // namespace flatbuffers