add command line argument for go namespace (#4222)

include/flatbuffers/idl.h

@@ -358,6 +358,7 @@ struct IDLOptions {
   bool allow_non_utf8;
   std::string include_prefix;
   bool binary_schema_comments;
+  std::string go_namespace;
 
   // Possible options for the more general generator below.
   enum Language {

src/flatc.cpp

@@ -90,6 +90,7 @@ std::string FlatCompiler::GetUsageString(const char* program_name) const {
       "                     T::c_str() and T::length() must be supported\n"
       "  --no-js-exports    Removes Node.js style export lines in JS.\n"
       "  --goog-js-export   Uses goog.exports* for closure compiler exporting in JS.\n"
+      "  --go-namespace     Generate the overrided namespace in Golang.\n"
       "  --raw-binary       Allow binaries without file_indentifier to be read.\n"
       "                     This may crash flatc given a mismatched schema.\n"
       "  --proto            Input is a .proto, translate to .fbs.\n"
@@ -160,6 +161,9 @@ int FlatCompiler::Compile(int argc, const char** argv) {
         opts.skip_js_exports = true;
       } else if(arg == "--goog-js-export") {
         opts.use_goog_js_export_format = true;
+      } else if(arg == "--go-namespace") {
+        if (++argi >= argc) Error("missing golang namespace" + arg, true);
+        opts.go_namespace = argv[argi];
       } else if(arg == "--defaults-json") {
         opts.output_default_scalars_in_json = true;
       } else if (arg == "--unknown-json") {

src/idl_gen_go.cpp

@@ -17,6 +17,7 @@
 // independent from idl_parser, since this code is not needed for most clients
 
 #include <string>
+#include <sstream>
 
 #include "flatbuffers/flatbuffers.h"
 #include "flatbuffers/idl.h"
@@ -740,9 +741,15 @@ static void GenStructBuilder(const StructDef &struct_def,
 class GoGenerator : public BaseGenerator {
  public:
   GoGenerator(const Parser &parser, const std::string &path,
-              const std::string &file_name)
-      : BaseGenerator(parser, path, file_name, "" /* not used*/,
-                      "" /* not used */){};
+              const std::string &file_name, const std::string &go_namespace)
+      : BaseGenerator(parser, path, file_name, "" /* not used*/, "" /* not used */) {
+    std::istringstream iss(go_namespace);
+    std::string component;
+    while (std::getline(iss, component, '.')) {
+      go_namespace_.components.push_back(component);
+    }
+  }
+
   bool generate() {
     for (auto it = parser_.enums_.vec.begin(); it != parser_.enums_.vec.end();
          ++it) {
@@ -780,19 +787,22 @@ class GoGenerator : public BaseGenerator {
                 bool needs_imports) {
     if (!classcode.length()) return true;
 
+    Namespace& ns = go_namespace_.components.empty() ? *def.defined_namespace : go_namespace_;
     std::string code = "";
-    BeginFile(LastNamespacePart(*def.defined_namespace), needs_imports, &code);
+    BeginFile(LastNamespacePart(ns), needs_imports, &code);
     code += classcode;
     std::string filename =
-        NamespaceDir(*def.defined_namespace) + def.name + ".go";
+        NamespaceDir(ns) + def.name + ".go";
     return SaveFile(filename.c_str(), code, false);
   }
+
+  Namespace go_namespace_;
 };
 }  // namespace go
 
 bool GenerateGo(const Parser &parser, const std::string &path,
                 const std::string &file_name) {
-  go::GoGenerator generator(parser, path, file_name);
+  go::GoGenerator generator(parser, path, file_name, parser.opts.go_namespace);
   return generator.generate();
 }