Add advance feature indicators to reflection (#6546)

* Add advance feature indicators to reflection

* deserialize too

* model advanced features as bitflags

* use uint64_t instead of AdvancedFeatures

* git clang format

* initialize advanced_features_

* remove whitespace

Co-authored-by: Casper Neo <cneo@google.com>

5 files changed, 88 insertions, 15 deletions

diff --git a/include/flatbuffers/idl.h b/include/flatbuffers/idl.h
index 6ae07ab2..29bf6215 100644
--- a/include/flatbuffers/idl.h
+++ b/include/flatbuffers/idl.h
@@ -780,6 +780,7 @@ class Parser : public ParserState {
         root_struct_def_(nullptr),
         opts(options),
         uses_flexbuffers_(false),
+        advanced_features_(0),
         source_(nullptr),
         anonymous_counter_(0),
         parse_depth_counter_(0) {
@@ -1011,6 +1012,8 @@ class Parser : public ParserState {
   IDLOptions opts;
   bool uses_flexbuffers_;
 
+  uint64_t advanced_features_;
+
  private:
   const char *source_;
 
diff --git a/include/flatbuffers/reflection_generated.h b/include/flatbuffers/reflection_generated.h
index b98afd65..235146e1 100644
--- a/include/flatbuffers/reflection_generated.h
+++ b/include/flatbuffers/reflection_generated.h
@@ -114,6 +114,44 @@ inline const char *EnumNameBaseType(BaseType e) {
   return EnumNamesBaseType()[index];
 }
 
+enum AdvancedFeatures {
+  AdvancedArrayFeatures = 1ULL,
+  AdvancedUnionFeatures = 2ULL,
+  OptionalScalars = 4ULL,
+  DefaultVectorsAndStrings = 8ULL
+};
+
+inline const AdvancedFeatures (&EnumValuesAdvancedFeatures())[4] {
+  static const AdvancedFeatures values[] = {
+    AdvancedArrayFeatures,
+    AdvancedUnionFeatures,
+    OptionalScalars,
+    DefaultVectorsAndStrings
+  };
+  return values;
+}
+
+inline const char * const *EnumNamesAdvancedFeatures() {
+  static const char * const names[9] = {
+    "AdvancedArrayFeatures",
+    "AdvancedUnionFeatures",
+    "",
+    "OptionalScalars",
+    "",
+    "",
+    "",
+    "DefaultVectorsAndStrings",
+    nullptr
+  };
+  return names;
+}
+
+inline const char *EnumNameAdvancedFeatures(AdvancedFeatures e) {
+  if (flatbuffers::IsOutRange(e, AdvancedArrayFeatures, DefaultVectorsAndStrings)) return "";
+  const size_t index = static_cast<size_t>(e) - static_cast<size_t>(AdvancedArrayFeatures);
+  return EnumNamesAdvancedFeatures()[index];
+}
+
 struct Type FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
   typedef TypeBuilder Builder;
   enum FlatBuffersVTableOffset FLATBUFFERS_VTABLE_UNDERLYING_TYPE {
@@ -1063,7 +1101,8 @@ struct Schema FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
     VT_FILE_IDENT = 8,
     VT_FILE_EXT = 10,
     VT_ROOT_TABLE = 12,
-    VT_SERVICES = 14
+    VT_SERVICES = 14,
+    VT_ADVANCED_FEATURES = 16
   };
   const flatbuffers::Vector<flatbuffers::Offset<reflection::Object>> *objects() const {
     return GetPointer<const flatbuffers::Vector<flatbuffers::Offset<reflection::Object>> *>(VT_OBJECTS);
@@ -1083,6 +1122,9 @@ struct Schema FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
   const flatbuffers::Vector<flatbuffers::Offset<reflection::Service>> *services() const {
     return GetPointer<const flatbuffers::Vector<flatbuffers::Offset<reflection::Service>> *>(VT_SERVICES);
   }
+  reflection::AdvancedFeatures advanced_features() const {
+    return static_cast<reflection::AdvancedFeatures>(GetField<uint64_t>(VT_ADVANCED_FEATURES, 0));
+  }
   bool Verify(flatbuffers::Verifier &verifier) const {
     return VerifyTableStart(verifier) &&
            VerifyOffsetRequired(verifier, VT_OBJECTS) &&
@@ -1100,6 +1142,7 @@ struct Schema FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
            VerifyOffset(verifier, VT_SERVICES) &&
            verifier.VerifyVector(services()) &&
            verifier.VerifyVectorOfTables(services()) &&
+           VerifyField<uint64_t>(verifier, VT_ADVANCED_FEATURES) &&
            verifier.EndTable();
   }
 };
@@ -1126,6 +1169,9 @@ struct SchemaBuilder {
   void add_services(flatbuffers::Offset<flatbuffers::Vector<flatbuffers::Offset<reflection::Service>>> services) {
     fbb_.AddOffset(Schema::VT_SERVICES, services);
   }
+  void add_advanced_features(reflection::AdvancedFeatures advanced_features) {
+    fbb_.AddElement<uint64_t>(Schema::VT_ADVANCED_FEATURES, static_cast<uint64_t>(advanced_features), 0);
+  }
   explicit SchemaBuilder(flatbuffers::FlatBufferBuilder &_fbb)
         : fbb_(_fbb) {
     start_ = fbb_.StartTable();
@@ -1146,8 +1192,10 @@ inline flatbuffers::Offset<Schema> CreateSchema(
     flatbuffers::Offset<flatbuffers::String> file_ident = 0,
     flatbuffers::Offset<flatbuffers::String> file_ext = 0,
     flatbuffers::Offset<reflection::Object> root_table = 0,
-    flatbuffers::Offset<flatbuffers::Vector<flatbuffers::Offset<reflection::Service>>> services = 0) {
+    flatbuffers::Offset<flatbuffers::Vector<flatbuffers::Offset<reflection::Service>>> services = 0,
+    reflection::AdvancedFeatures advanced_features = static_cast<reflection::AdvancedFeatures>(0)) {
   SchemaBuilder builder_(_fbb);
+  builder_.add_advanced_features(advanced_features);
   builder_.add_services(services);
   builder_.add_root_table(root_table);
   builder_.add_file_ext(file_ext);
@@ -1164,7 +1212,8 @@ inline flatbuffers::Offset<Schema> CreateSchemaDirect(
     const char *file_ident = nullptr,
     const char *file_ext = nullptr,
     flatbuffers::Offset<reflection::Object> root_table = 0,
-    std::vector<flatbuffers::Offset<reflection::Service>> *services = nullptr) {
+    std::vector<flatbuffers::Offset<reflection::Service>> *services = nullptr,
+    reflection::AdvancedFeatures advanced_features = static_cast<reflection::AdvancedFeatures>(0)) {
   auto objects__ = objects ? _fbb.CreateVectorOfSortedTables<reflection::Object>(objects) : 0;
   auto enums__ = enums ? _fbb.CreateVectorOfSortedTables<reflection::Enum>(enums) : 0;
   auto file_ident__ = file_ident ? _fbb.CreateString(file_ident) : 0;
@@ -1177,7 +1226,8 @@ inline flatbuffers::Offset<Schema> CreateSchemaDirect(
       file_ident__,
       file_ext__,
       root_table,
-      services__);
+      services__,
+      advanced_features);
 }
 
 inline const reflection::Schema *GetSchema(const void *buf) {
diff --git a/reflection/reflection.fbs b/reflection/reflection.fbs
index d9e2dc47..36230b20 100644
--- a/reflection/reflection.fbs
+++ b/reflection/reflection.fbs
@@ -102,6 +102,14 @@ table Service {
     documentation:[string];
 }
 
+// New schema language features that are not supported by old code generators.
+enum AdvancedFeatures : ulong (bit_flags) {
+    AdvancedArrayFeatures,
+    AdvancedUnionFeatures,
+    OptionalScalars,
+    DefaultVectorsAndStrings,
+}
+
 table Schema {
     objects:[Object] (required);    // Sorted.
     enums:[Enum] (required);        // Sorted.
@@ -109,6 +117,7 @@ table Schema {
     file_ext:string;
     root_table:Object;
     services:[Service];             // Sorted.
+    advanced_features:AdvancedFeatures;
 }
 
 root_type Schema;
diff --git a/src/idl_parser.cpp b/src/idl_parser.cpp
index 88ecf81c..f04e5a3d 100644
--- a/src/idl_parser.cpp
+++ b/src/idl_parser.cpp
@@ -765,10 +765,13 @@ CheckedError Parser::ParseField(StructDef &struct_def) {
   if (!struct_def.fixed && IsArray(type))
     return Error("fixed-length array in table must be wrapped in struct");
 
-  if (IsArray(type) && !SupportsAdvancedArrayFeatures()) {
-    return Error(
-        "Arrays are not yet supported in all "
-        "the specified programming languages.");
+  if (IsArray(type)) {
+    advanced_features_ |= reflection::AdvancedArrayFeatures;
+    if (!SupportsAdvancedArrayFeatures()) {
+      return Error(
+          "Arrays are not yet supported in all "
+          "the specified programming languages.");
+    }
   }
 
   FieldDef *typefield = nullptr;
@@ -778,6 +781,7 @@ CheckedError Parser::ParseField(StructDef &struct_def) {
     ECHECK(AddField(struct_def, name + UnionTypeFieldSuffix(),
                     type.enum_def->underlying_type, &typefield));
   } else if (IsVector(type) && type.element == BASE_TYPE_UNION) {
+    advanced_features_ |= reflection::AdvancedUnionFeatures;
     // Only cpp, js and ts supports the union vector feature so far.
     if (!SupportsAdvancedUnionFeatures()) {
       return Error(
@@ -802,11 +806,16 @@ CheckedError Parser::ParseField(StructDef &struct_def) {
       return Error(
           "default values are not supported for struct fields, table fields, "
           "or in structs.");
-    if ((IsString(type) || IsVector(type)) && field->value.constant != "0" &&
-        field->value.constant != "null" && !SupportsDefaultVectorsAndStrings())
-      return Error(
-          "Default values for strings and vectors are not supported in one of "
-          "the specified programming languages");
+    if (IsString(type) || IsVector(type)) {
+      advanced_features_ |= reflection::DefaultVectorsAndStrings;
+      if (field->value.constant != "0" && field->value.constant != "null" &&
+          !SupportsDefaultVectorsAndStrings()) {
+        return Error(
+            "Default values for strings and vectors are not supported in one "
+            "of the specified programming languages");
+      }
+    }
+
     if (IsVector(type) && field->value.constant != "0" &&
         field->value.constant != "[]") {
       return Error("The only supported default for vectors is `[]`.");
@@ -891,6 +900,7 @@ CheckedError Parser::ParseField(StructDef &struct_def) {
   }
 
   if (field->IsScalarOptional()) {
+    advanced_features_ |= reflection::OptionalScalars;
     if (type.enum_def && type.enum_def->Lookup("null")) {
       FLATBUFFERS_ASSERT(IsInteger(type.base_type));
       return Error(
@@ -3498,7 +3508,8 @@ void Parser::Serialize() {
   auto serv__ = builder_.CreateVectorOfSortedTables(&service_offsets);
   auto schema_offset = reflection::CreateSchema(
       builder_, objs__, enum__, fiid__, fext__,
-      (root_struct_def_ ? root_struct_def_->serialized_location : 0), serv__);
+      (root_struct_def_ ? root_struct_def_->serialized_location : 0), serv__,
+      static_cast<reflection::AdvancedFeatures>(advanced_features_));
   if (opts.size_prefixed) {
     builder_.FinishSizePrefixed(schema_offset, reflection::SchemaIdentifier());
   } else {
@@ -3915,7 +3926,7 @@ bool Parser::Deserialize(const reflection::Schema *schema) {
       }
     }
   }
-
+  advanced_features_ = schema->advanced_features();
   return true;
 }
 
diff --git a/tests/arrays_test.bfbs b/tests/arrays_test.bfbs
index fe24507f..d6b6f731 100644
--- a/tests/arrays_test.bfbs
+++ b/tests/arrays_test.bfbs