Generate appropriate schema doc comments from .proto files

- Add parse handling of .proto struct and field doc comments (enums and
their values were already handled)
- Add FBS generation handling of doc comments for structs, their
fields, enums, and their values (requires linking idl_gen_general in
the test binary build)
- Tested using test.proto|golden with doc comments added.  Xcode run of
flattest passes.

Change-Id: Idff64dd8064afba227174ab77d2c7be22d006628

src/idl_gen_fbs.cpp

@@ -61,11 +61,13 @@ std::string GenerateFBS(const Parser &parser, const std::string &file_name,
   for (auto enum_def_it = parser.enums_.vec.begin();
            enum_def_it != parser.enums_.vec.end(); ++enum_def_it) {
     EnumDef &enum_def = **enum_def_it;
+    GenComment(enum_def.doc_comment, &schema, nullptr);
     schema += "enum " + enum_def.name + " : ";
     schema += GenType(enum_def.underlying_type) + " {\n";
     for (auto it = enum_def.vals.vec.begin();
          it != enum_def.vals.vec.end(); ++it) {
       auto &ev = **it;
+      GenComment(ev.doc_comment, &schema, nullptr, "  ");
       schema += "  " + ev.name + " = " + NumToString(ev.value) + ",\n";
     }
     schema += "}\n\n";
@@ -74,10 +76,12 @@ std::string GenerateFBS(const Parser &parser, const std::string &file_name,
   for (auto it = parser.structs_.vec.begin();
            it != parser.structs_.vec.end(); ++it) {
     StructDef &struct_def = **it;
+    GenComment(struct_def.doc_comment, &schema, nullptr);
     schema += "table " + struct_def.name + " {\n";
     for (auto field_it = struct_def.fields.vec.begin();
              field_it != struct_def.fields.vec.end(); ++field_it) {
       auto &field = **field_it;
+      GenComment(field.doc_comment, &schema, nullptr, "  ");
       schema += "  " + field.name + ":" + GenType(field.value.type);
       if (field.value.constant != "0") schema += " = " + field.value.constant;
       if (field.required) schema += " (required)";

src/idl_parser.cpp

@@ -991,10 +991,13 @@ void Parser::ParseProtoDecl() {
     // These are identical in syntax to FlatBuffer's namespace decl.
     ParseNamespace();
   } else if (attribute_ == "message") {
+    std::vector<std::string> struct_comment = doc_comment_;
     Next();
     auto &struct_def = StartStruct();
+    struct_def.doc_comment = struct_comment;
     Expect('{');
     while (token_ != '}') {
+      std::vector<std::string> field_comment = doc_comment_;
       // Parse the qualifier.
       bool required = false;
       bool repeated = false;
@@ -1021,6 +1024,7 @@ void Parser::ParseProtoDecl() {
       Expect('=');
       Expect(kTokenIntegerConstant);
       auto &field = AddField(struct_def, name, type);
+      field.doc_comment = field_comment;
       field.required = required;
       // See if there's a default specified.
       if (IsNext('[')) {