Defined CodeGenerator Interface and implement C++ (#7771)

BUILD.bazel

@@ -44,6 +44,7 @@ filegroup(
         "include/flatbuffers/bfbs_generator.h",
         "include/flatbuffers/buffer.h",
         "include/flatbuffers/buffer_ref.h",
+        "include/flatbuffers/code_generator.h",
         "include/flatbuffers/code_generators.h",
         "include/flatbuffers/default_allocator.h",
         "include/flatbuffers/detached_buffer.h",

CMakeLists.txt

@@ -141,6 +141,7 @@ set(FlatBuffers_Library_SRCS
   include/flatbuffers/buffer_ref.h
   include/flatbuffers/default_allocator.h
   include/flatbuffers/detached_buffer.h
+  include/flatbuffers/code_generator.h
   include/flatbuffers/flatbuffer_builder.h
   include/flatbuffers/flatbuffers.h
   include/flatbuffers/flexbuffers.h

include/flatbuffers/code_generator.h

@@ -0,0 +1,73 @@
+/*
+ * 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.
+ */
+
+#ifndef FLATBUFFERS_CODE_GENERATOR_H_
+#define FLATBUFFERS_CODE_GENERATOR_H_
+
+#include <string>
+
+#include "flatbuffers/idl.h"
+
+namespace flatbuffers {
+
+// An code generator interface for producing converting flatbuffer schema into
+// code.
+class CodeGenerator {
+ public:
+  virtual ~CodeGenerator() = default;
+
+  enum Status {
+    OK = 0,
+    ERROR = 1,
+    NOT_IMPLEMENTED = 2,
+  };
+
+  // Generate code from the provided `parser`.
+  //
+  // DEPRECATED: prefer using the other overload of GenerateCode for bfbs.
+  virtual Status GenerateCode(const Parser &parser, const std::string &path,
+                              const std::string &filename) = 0;
+
+  // Generate code from the provided `buffer` of given `length`. The buffer is a
+  // serialized reflection.fbs.
+  virtual Status GenerateCode(const uint8_t *buffer, int64_t length) = 0;
+
+  virtual Status GenerateMakeRule(const Parser &parser, const std::string &path,
+                                  const std::string &filename,
+                                  std::string &output) = 0;
+
+  virtual Status GenerateGrpcCode(const Parser &parser, const std::string &path,
+                                  const std::string &filename) = 0;
+
+  virtual bool IsSchemaOnly() const = 0;
+
+  virtual bool SupportsBfbsGeneration() const = 0;
+
+  virtual IDLOptions::Language Language() const = 0;
+  virtual std::string LanguageName() const = 0;
+
+ protected:
+  CodeGenerator() = default;
+
+ private:
+  // Copying is not supported.
+  CodeGenerator(const CodeGenerator &) = delete;
+  CodeGenerator &operator=(const CodeGenerator &) = delete;
+};
+
+}  // namespace flatbuffers
+
+#endif  // FLATBUFFERS_CODE_GENERATOR_H_

include/flatbuffers/flatc.h

@@ -20,15 +20,21 @@
 #include <functional>
 #include <limits>
 #include <list>
+#include <memory>
 #include <string>
 
 #include "flatbuffers/bfbs_generator.h"
+#include "flatbuffers/code_generator.h"
 #include "flatbuffers/flatbuffers.h"
 #include "flatbuffers/idl.h"
 #include "flatbuffers/util.h"
 
 namespace flatbuffers {
 
+// TODO(derekbailey): It would be better to define these as normal includes and
+// not as extern functions. But this can be done at a later time.
+extern std::unique_ptr<flatbuffers::CodeGenerator> NewCppCodeGenerator();
+
 extern void LogCompilerWarn(const std::string &warn);
 extern void LogCompilerError(const std::string &err);
 
@@ -54,6 +60,8 @@ struct FlatCOptions {
   bool schema_binary = false;
   bool grpc_enabled = false;
   bool requires_bfbs = false;
+
+  std::vector<std::shared_ptr<CodeGenerator>> generators;
 };
 
 struct FlatCOption {
@@ -110,10 +118,13 @@ class FlatCompiler {
 
   explicit FlatCompiler(const InitParams &params) : params_(params) {}
 
+  bool RegisterCodeGenerator(const std::string& flag,
+                             std::shared_ptr<CodeGenerator> code_generator);
+
   int Compile(const FlatCOptions &options);
 
-  std::string GetShortUsageString(const std::string& program_name) const;
-  std::string GetUsageString(const std::string& program_name) const;
+  std::string GetShortUsageString(const std::string &program_name) const;
+  std::string GetUsageString(const std::string &program_name) const;
 
   // Parse the FlatC options from command line arguments.
   FlatCOptions ParseFromCommandLineArguments(int argc, const char **argv);
@@ -141,7 +152,9 @@ class FlatCompiler {
   Parser GetConformParser(const FlatCOptions &options);
 
   std::unique_ptr<Parser> GenerateCode(const FlatCOptions &options,
-                    Parser &conform_parser);
+                                       Parser &conform_parser);
+
+  std::map<std::string, std::shared_ptr<CodeGenerator>> code_generators_;
 
   InitParams params_;
 };

src/flatc.cpp

@@ -24,6 +24,7 @@
 
 #include "annotated_binary_text_gen.h"
 #include "binary_annotator.h"
+#include "flatbuffers/code_generator.h"
 #include "flatbuffers/idl.h"
 #include "flatbuffers/util.h"
 
@@ -308,6 +309,7 @@ std::string FlatCompiler::GetShortUsageString(
     const std::string &program_name) const {
   std::stringstream ss;
   ss << "Usage: " << program_name << " [";
+  // TODO(derekbailey): These should be generated from this.generators
   for (size_t i = 0; i < params_.num_generators; ++i) {
     const Generator &g = params_.generators[i];
     AppendShortOption(ss, g.option);
@@ -330,6 +332,7 @@ std::string FlatCompiler::GetUsageString(
   std::stringstream ss;
   ss << "Usage: " << program_name
      << " [OPTION]... FILE... [-- BINARY_FILE...]\n";
+  // TODO(derekbailey): These should be generated from this.generators
   for (size_t i = 0; i < params_.num_generators; ++i) {
     const Generator &g = params_.generators[i];
     AppendOption(ss, g.option, 80, 25);
@@ -613,20 +616,41 @@ FlatCOptions FlatCompiler::ParseFromCommandLineArguments(int argc,
         if (++argi >= argc) Error("missing path following: " + arg, true);
         options.annotate_schema = flatbuffers::PosixPath(argv[argi]);
       } else {
-        for (size_t i = 0; i < params_.num_generators; ++i) {
-          if (arg == "--" + params_.generators[i].option.long_opt ||
-              arg == "-" + params_.generators[i].option.short_opt) {
-            options.generator_enabled[i] = true;
-            options.any_generator = true;
-            opts.lang_to_generate |= params_.generators[i].lang;
-            if (params_.generators[i].bfbs_generator) {
-              opts.binary_schema_comments = true;
-              options.requires_bfbs = true;
+        // Look up if the command line argument refers to a code generator.
+        auto code_generator_it = code_generators_.find(arg);
+        if (code_generator_it != code_generators_.end()) {
+          std::shared_ptr<CodeGenerator> code_generator =
+              code_generator_it->second;
+
+          // TODO(derekbailey): remove in favor of just checking if
+          // generators.empty().
+          options.any_generator = true;
+          opts.lang_to_generate |= code_generator->Language();
+
+          if (code_generator->SupportsBfbsGeneration()) {
+            opts.binary_schema_comments = true;
+            options.requires_bfbs = true;
+          }
+
+          options.generators.push_back(std::move(code_generator));
+        } else {
+          // TODO(derekbailey): deprecate the following logic in favor of the
+          // code generator map above.
+          for (size_t i = 0; i < params_.num_generators; ++i) {
+            if (arg == "--" + params_.generators[i].option.long_opt ||
+                arg == "-" + params_.generators[i].option.short_opt) {
+              options.generator_enabled[i] = true;
+              options.any_generator = true;
+              opts.lang_to_generate |= params_.generators[i].lang;
+              if (params_.generators[i].bfbs_generator) {
+                opts.binary_schema_comments = true;
+                options.requires_bfbs = true;
+              }
+              goto found;
             }
-            goto found;
           }
+          Error("unknown commandline argument: " + arg, true);
         }
-        Error("unknown commandline argument: " + arg, true);
 
       found:;
       }
@@ -789,6 +813,57 @@ std::unique_ptr<Parser> FlatCompiler::GenerateCode(const FlatCOptions &options,
       bfbs_length = parser->builder_.GetSize();
     }
 
+    for (const std::shared_ptr<CodeGenerator> &code_generator :
+         options.generators) {
+      if (options.print_make_rules) {
+        std::string make_rule;
+        const CodeGenerator::Status status = code_generator->GenerateMakeRule(
+            *parser, options.output_path, filename, make_rule);
+        if (status == CodeGenerator::Status::OK && !make_rule.empty()) {
+          printf("%s\n",
+                 flatbuffers::WordWrap(make_rule, 80, " ", " \\").c_str());
+        } else {
+          Error("Cannot generate make rule for " +
+                code_generator->LanguageName());
+        }
+      } else {
+        flatbuffers::EnsureDirExists(options.output_path);
+
+        // Prefer bfbs generators if present.
+        if (code_generator->SupportsBfbsGeneration()) {
+          const CodeGenerator::Status status =
+              code_generator->GenerateCode(bfbs_buffer, bfbs_length);
+          if (status != CodeGenerator::Status::OK) {
+            Error("Unable to generate " + code_generator->LanguageName() +
+                  " for " + filebase + " using bfbs generator.");
+          }
+        } else {
+          if ((!code_generator->IsSchemaOnly() ||
+               (is_schema || is_binary_schema)) &&
+              code_generator->GenerateCode(*parser, options.output_path,
+                                           filebase) !=
+                  CodeGenerator::Status::OK) {
+            Error("Unable to generate " + code_generator->LanguageName() +
+                  " for " + filebase);
+          }
+        }
+      }
+
+      if (options.grpc_enabled) {
+        const CodeGenerator::Status status = code_generator->GenerateGrpcCode(
+            *parser, options.output_path, filebase);
+
+        if (status == CodeGenerator::Status::NOT_IMPLEMENTED) {
+          Warn("GRPC interface generator not implemented for " +
+               code_generator->LanguageName());
+        } else if (status == CodeGenerator::Status::ERROR) {
+          Error("Unable to generate GRPC interface for " +
+                code_generator->LanguageName());
+        }
+      }
+    }
+
+    // TODO(derekbailey): Deprecate the following in favor to the above.
     for (size_t i = 0; i < params_.num_generators; ++i) {
       if (options.generator_enabled[i]) {
         if (!options.print_make_rules) {
@@ -934,4 +1009,14 @@ int FlatCompiler::Compile(const FlatCOptions &options) {
   return 0;
 }
 
+bool FlatCompiler::RegisterCodeGenerator(
+    const std::string &flag, std::shared_ptr<CodeGenerator> code_generator) {
+  if (code_generators_.find(flag) != code_generators_.end()) {
+    Error("multiple generators registered under: " + flag, false, false);
+    return false;
+  }
+  code_generators_[flag] = std::move(code_generator);
+  return true;
+}
+
 }  // namespace flatbuffers

src/flatc_main.cpp

@@ -20,9 +20,12 @@
 #include "bfbs_gen_lua.h"
 #include "bfbs_gen_nim.h"
 #include "flatbuffers/base.h"
+#include "flatbuffers/code_generator.h"
 #include "flatbuffers/flatc.h"
 #include "flatbuffers/util.h"
 
+
+
 static const char *g_program_name = nullptr;
 
 static void Warn(const flatbuffers::FlatCompiler *flatc,
@@ -159,6 +162,12 @@ int main(int argc, const char *argv[]) {
 
   flatbuffers::FlatCompiler flatc(params);
 
+  std::shared_ptr<flatbuffers::CodeGenerator> cpp_generator =
+      flatbuffers::NewCppCodeGenerator();
+
+  flatc.RegisterCodeGenerator("--cpp", cpp_generator);
+  flatc.RegisterCodeGenerator("-c", cpp_generator);
+
   // Create the FlatC options by parsing the command line arguments.
   const flatbuffers::FlatCOptions &options =
       flatc.ParseFromCommandLineArguments(argc, argv);

src/idl_gen_cpp.cpp

@@ -17,6 +17,7 @@
 // independent from idl_parser, since this code is not needed for most clients
 
 #include <limits>
+#include <memory>
 #include <string>
 #include <unordered_set>
 
@@ -3871,4 +3872,50 @@ std::string CPPMakeRule(const Parser &parser, const std::string &path,
   return make_rule;
 }
 
+namespace {
+
+class CppCodeGenerator : public CodeGenerator {
+ public:
+  Status GenerateCode(const Parser &parser, const std::string &path,
+                      const std::string &filename) override {
+    if (!GenerateCPP(parser, path, filename)) { return Status::ERROR; }
+    return Status::OK;
+  }
+
+  // Generate code from the provided `buffer` of given `length`. The buffer is a
+  // serialized reflection.fbs.
+  Status GenerateCode(const uint8_t *buffer, int64_t length) override {
+    (void) buffer;
+    (void) length;
+    return Status::NOT_IMPLEMENTED;
+  }
+
+  Status GenerateMakeRule(const Parser &parser, const std::string &path,
+                          const std::string &filename,
+                          std::string &output) override {
+    output = CPPMakeRule(parser, path, filename);
+    return Status::OK;
+  }
+
+  Status GenerateGrpcCode(const Parser &parser, const std::string &path,
+                          const std::string &filename) override {
+    if (!GenerateCppGRPC(parser, path, filename)) { return Status::ERROR; }
+    return Status::OK;
+  }
+
+  bool IsSchemaOnly() const override { return true; }
+
+  bool SupportsBfbsGeneration() const override { return false; }
+
+  IDLOptions::Language Language() const override { return IDLOptions::kCpp; }
+
+  std::string LanguageName() const override { return "C++"; }
+};
+
+}  // namespace
+
+std::unique_ptr<CodeGenerator> NewCppCodeGenerator() {
+  return std::unique_ptr<CppCodeGenerator>(new CppCodeGenerator());
+}
+
 }  // namespace flatbuffers