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/BUILD.bazel

@@ -69,6 +69,9 @@ cc_library(
         "bfbs_gen_nim.cpp",
         "bfbs_gen_nim.h",
         "bfbs_namer.h",
+        "file_binary_writer.cpp",
+        "file_name_saving_file_manager.cpp",
+        "file_writer.cpp",
         "flatc_main.cpp",
         "idl_gen_binary.cpp",
         "idl_gen_binary.h",

src/file_binary_writer.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 FileBinaryWriter : public FileManager {
+ public:
+  bool SaveFile(const std::string &absolute_file_name,
+                const std::string &content) override {
+    std::ofstream ofs(absolute_file_name, std::ofstream::binary);
+    if (!ofs.is_open()) return false;
+    ofs.write(content.c_str(), content.size());
+    return !ofs.bad();
+  }
+
+  bool Loadfile(const std::string &absolute_file_name, std::string *output) {
+    if (DirExists(absolute_file_name.c_str())) return false;
+    std::ifstream ifs(absolute_file_name, std::ifstream::binary);
+    if (!ifs.is_open()) return false;
+    // The fastest way to read a file into a string.
+    ifs.seekg(0, std::ios::end);
+    auto size = ifs.tellg();
+    (*output).resize(static_cast<size_t>(size));
+    ifs.seekg(0, std::ios::beg);
+    ifs.read(&(*output)[0], (*output).size());
+    return !ifs.bad();
+  }
+};
+
+}  // namespace flatbuffers

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

src/file_writer.cpp

@@ -0,0 +1,47 @@
+/*
+ * 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 FileWriter : public FileManager {
+ public:
+  bool SaveFile(const std::string &absolute_file_name,
+                const std::string &content) override {
+    std::ofstream ofs(absolute_file_name, std::ofstream::out);
+    if (!ofs.is_open()) return false;
+    ofs.write(content.c_str(), content.size());
+    return !ofs.bad();
+  }
+
+  bool Loadfile(const std::string &absolute_file_name, std::string *output) {
+    if (DirExists(absolute_file_name.c_str())) return false;
+    std::ifstream ifs(absolute_file_name, std::ifstream::in);
+    if (!ifs.is_open()) return false;
+    // This is slower, but works correctly on all platforms for text files.
+    std::ostringstream oss;
+    oss << ifs.rdbuf();
+    *output = oss.str();
+    return !ifs.bad();
+  }
+};
+
+}  // namespace flatbuffers

src/flatc.cpp

@@ -250,6 +250,8 @@ const static FlatCOption flatc_options[] = {
   { "", "no-leak-private-annotation", "",
     "Prevents multiple type of annotations within a Fbs SCHEMA file. "
     "Currently this is required to generate private types in Rust" },
+  { "", "file-names-only", "",
+    "Print out generated file names without writing to the files"},
 };
 
 auto cmp = [](FlatCOption a, FlatCOption b) { return a.long_opt < b.long_opt; };
@@ -653,6 +655,9 @@ FlatCOptions FlatCompiler::ParseFromCommandLineArguments(int argc,
       } else if (arg == "--annotate") {
         if (++argi >= argc) Error("missing path following: " + arg, true);
         options.annotate_schema = flatbuffers::PosixPath(argv[argi]);
+      } else if(arg == "--file-names-only") {
+        // TODO (khhn): Provide 2 implementation
+        options.file_names_only = true;
       } else {
         if (arg == "--proto") { opts.proto_mode = true; }