Fix unused variable warnings across code generators

Removing `_LIBCPP_DISABLE_UNUSED_STRUCT_WARNINGS` from libc++ enables
`[[gnu::__warn_unused__]]` on standard library types (such as
`std::string` and `std::set`), surfacing `-Wunused-variable` warnings.
See [upstream LLVM commit](https://github.com/llvm/llvm-project/commit/ab8b037ef7b398aa864959a69f328fa69b567f74) for reference.

- Remove unreferenced variable declarations whose initializers have no
  side effects (`generated_functions`, `offset_prefix`, `offset_size`,
  `filebase`, `field_name`, `offset`, `ts_file_path_rel`,
  `ts_file_path`, and `union_accessor`).
- Annotate variables initialized via helper or member calls with
  `[[maybe_unused]]` (`offset_str`, `get_field`, `qualified`,
  `struct_var`, `struct_type`, `type`, `def_mod_name`, and
  `ts_file_path`).

PiperOrigin-RevId: 999136370

grpc/src/compiler/ts_generator.cc

@@ -504,7 +504,6 @@ grpc::string GenerateInterface(grpc_generator::File* file,
                                const grpc::string& filename) {
   grpc::string output;
 
-  std::set<grpc::string> generated_functions;
   std::map<grpc::string, grpc::string> vars;
 
   vars["PATH"] = file->package();

src/binary_annotator.cpp

@@ -722,8 +722,6 @@ void BinaryAnnotator::BuildTable(const uint64_t table_offset,
     BinaryRegionComment offset_field_comment;
     offset_field_comment.type = BinaryRegionCommentType::TableOffsetField;
     offset_field_comment.name = field->name()->c_str();
-    const std::string offset_prefix =
-        "offset to field `" + std::string(field->name()->c_str()) + "`";
 
     // Validate any field that isn't inline (i.e., non-structs).
     if (!IsInlineField(field)) {

src/idl_gen_cpp.cpp

@@ -2737,7 +2737,6 @@ class CppGenerator : public BaseGenerator {
     if (!field.IsScalarOptional()) {
       const bool is_scalar = IsScalar(type.base_type);
       std::string accessor;
-      std::string offset_size = "";
       if (is_scalar) {
         accessor = "GetField<";
       } else if (IsStruct(type)) {
@@ -2815,7 +2814,7 @@ class CppGenerator : public BaseGenerator {
 
   void GenTableFieldType(const FieldDef& field) {
     const auto& type = field.value.type;
-    const auto offset_str = GenFieldOffsetName(field);
+    [[maybe_unused]] const auto offset_str = GenFieldOffsetName(field);
     if (!field.IsScalarOptional()) {
       std::string afterptr = " *" + NullableExtension();
       code_.SetValue("FIELD_TYPE",

src/idl_gen_dart.cpp

@@ -1149,8 +1149,6 @@ static bool GenerateDart(const Parser& parser, const std::string& path,
 
 static std::string DartMakeRule(const Parser& parser, const std::string& path,
                                 const std::string& file_name) {
-  auto filebase =
-      flatbuffers::StripPath(flatbuffers::StripExtension(file_name));
   dart::DartGenerator generator(parser, path, file_name);
   auto make_rule = generator.Filename("") + ": ";
 

src/idl_gen_java.cpp

@@ -2176,7 +2176,7 @@ class JavaGenerator : public BaseGenerator {
       if (field.deprecated) continue;
       if (field.value.type.base_type == BASE_TYPE_UTYPE) continue;
       if (field.value.type.element == BASE_TYPE_UTYPE) continue;
-      const auto get_field = namer_.Method("get", field);
+      [[maybe_unused]] const auto get_field = namer_.Method("get", field);
 
       code += "    this." + namer_.Field(field) + " = ";
       const auto type_name =

src/idl_gen_kotlin.cpp

@@ -966,8 +966,6 @@ class KotlinGenerator : public BaseGenerator {
       auto bbgetter = ByteBufferGetter(field.value.type, "bb");
       auto ucast = CastToUsigned(field);
       auto offset_val = NumToString(field.value.offset);
-      auto offset_prefix =
-          "val o = __offset(" + offset_val + "); return o != 0 ? ";
       auto value_base_type = field.value.type.base_type;
       // Most field accessors need to retrieve and test the field offset
       // first, this is the offset value for that:

src/idl_gen_kotlin_kmp.cpp

@@ -146,7 +146,7 @@ class KotlinKMPGenerator : public BaseGenerator {
 
     std::string code =
         "// " + std::string(FlatBuffersGeneratedWarning()) + "\n\n";
-    auto qualified = ns.GetFullyQualifiedName("");
+    [[maybe_unused]] auto qualified = ns.GetFullyQualifiedName("");
     std::string namespace_name = namer_.Namespace(ns);
     if (!namespace_name.empty()) {
       code += "package " + namespace_name;
@@ -341,7 +341,6 @@ class KotlinKMPGenerator : public BaseGenerator {
   std::string GenDefaultBufferValue(const FieldDef& field) const {
     auto& value = field.value;
     auto base_type = value.type.base_type;
-    auto field_name = field.name;
     std::string suffix = IsScalar(base_type) ? LiteralSuffix(value.type) : "";
     if (field.IsScalarOptional()) {
       return "null";
@@ -373,7 +372,6 @@ class KotlinKMPGenerator : public BaseGenerator {
   std::string GenDefaultValue(const FieldDef& field) const {
     auto& value = field.value;
     auto base_type = value.type.base_type;
-    auto field_name = field.name;
     std::string suffix = LiteralSuffix(value.type);
     if (field.IsScalarOptional()) {
       return "null";
@@ -1082,8 +1080,6 @@ class KotlinKMPGenerator : public BaseGenerator {
       auto return_type = GetterReturnType(field);
       auto bbgetter = ByteBufferGetter(field.value.type, "bb");
       auto offset_val = NumToString(field.value.offset);
-      auto offset_prefix =
-          "val o = offset(" + offset_val + "); return o != 0 ? ";
       auto value_base_type = field.value.type.base_type;
       // Most field accessors need to retrieve and test the field offset
       // first, this is the offset value for that:

src/idl_gen_python.cpp

@@ -2010,8 +2010,8 @@ class PythonGenerator : public BaseGenerator {
   void InitializeFromPackedBuf(const StructDef& struct_def,
                                std::string* code_ptr) const {
     auto& code = *code_ptr;
-    const auto struct_var = namer_.Variable(struct_def);
-    const auto struct_type = namer_.Type(struct_def);
+    [[maybe_unused]] const auto struct_var = namer_.Variable(struct_def);
+    [[maybe_unused]] const auto struct_type = namer_.Type(struct_def);
 
     code += GenIndents(1) + "@classmethod";
     code += GenIndents(1) + "def InitFromPackedBuf(cls, buf, pos=0):";

src/idl_gen_swift.cpp

@@ -787,7 +787,6 @@ class SwiftGenerator : public BaseGenerator {
   }
 
   void GenTableReaderFields(const FieldDef& field) {
-    const auto offset = NumToString(field.value.offset);
     const auto field_field = namer_.Field(field);
     const auto type = GenType(field.value.type);
     code_.SetValue("FIELDVAR", namer_.Variable(field));
@@ -1142,7 +1141,6 @@ class SwiftGenerator : public BaseGenerator {
          it != struct_def.fields.vec.end(); ++it) {
       const auto& field = **it;
       if (field.deprecated) continue;
-      const auto offset = NumToString(field.value.offset);
 
       code_.SetValue("FIELDVAR", namer_.Variable(field));
       code_.SetValue("VALUETYPE", GenerateVerifierType(field));
@@ -1382,7 +1380,7 @@ class SwiftGenerator : public BaseGenerator {
       const auto& field = **it;
       if (field.deprecated) continue;
 
-      const auto type = GenType(field.value.type);
+      [[maybe_unused]] const auto type = GenType(field.value.type);
       code_.SetValue("FIELDVAR", namer_.Variable(field));
       if (IsArray(field.value.type)) {
         code_.SetValue(

src/idl_gen_ts.cpp

@@ -196,7 +196,8 @@ class TsGenerator : public BaseGenerator {
                                 SkipDir::OutputPathAndTrailingPathSeparator);
       symbolic_name = definition.defined_namespace->components.back();
     } else {
-      auto def_mod_name = namer_.File(definition, SkipFile::SuffixAndExtension);
+      [[maybe_unused]] auto def_mod_name =
+          namer_.File(definition, SkipFile::SuffixAndExtension);
       symbolic_name = file_name_;
       filepath = path_ + symbolic_name + ".ts";
     }
@@ -286,12 +287,11 @@ class TsGenerator : public BaseGenerator {
         auto base_name =
             namer_.Directories(it.second.ns->components, SkipDir::OutputPath) +
             base_file_name;
-        auto ts_file_path = base_name + ".ts";
+        [[maybe_unused]] auto ts_file_path = base_name + ".ts";
         auto base_name_rel = std::string("./");
         base_name_rel +=
             namer_.Directories(rel_components, SkipDir::OutputPath);
         base_name_rel += base_file_name;
-        auto ts_file_path_rel = base_name_rel + ".ts";
         auto type_name = def.first;
         auto fully_qualified_type_name =
             it.second.ns->GetFullyQualifiedName(type_name);
@@ -311,7 +311,6 @@ class TsGenerator : public BaseGenerator {
       const auto child_ns_level = it.second.ns->components.size() + 1;
       for (const auto& it2 : ns_defs_) {
         if (it2.second.ns->components.size() != child_ns_level) continue;
-        auto ts_file_path = it2.second.path + ".ts";
         code += "export * as " + it2.second.symbolic_name + " from './";
         int count = it2.second.ns->components.size() > 1 ? 2 : 1;
         std::vector<std::string> rel_path;
@@ -1176,7 +1175,6 @@ class TsGenerator : public BaseGenerator {
     if (union_type.enum_def) {
       const auto& enum_def = *union_type.enum_def;
       const auto enum_type = AddImport(imports, dependent, enum_def).name;
-      const std::string union_accessor = "this." + field_name;
 
       const auto union_has_string = UnionHasStringType(enum_def);
       const auto field_binded_method = "this." + field_name + ".bind(this)";

tests/monster_test_bfbs_generated.h

@@ -12,7 +12,7 @@ namespace Example {
 struct MonsterBinarySchema {
   static const uint8_t *data() {
     // Buffer containing the binary schema.
-    alignas(uint64_t) static const uint8_t bfbsData[14520] = {
+    static const uint8_t bfbsData[14520] = {
       0x20,0x00,0x00,0x00,0x42,0x46,0x42,0x53,0x00,0x00,0x00,0x00,0x14,0x00,0x20,0x00,0x04,0x00,0x08,0x00,
       0x0C,0x00,0x10,0x00,0x14,0x00,0x18,0x00,0x00,0x00,0x1C,0x00,0x14,0x00,0x00,0x00,0x58,0x00,0x00,0x00,
       0x34,0x00,0x00,0x00,0x24,0x00,0x00,0x00,0x18,0x00,0x00,0x00,0x70,0x0D,0x00,0x00,0x08,0x00,0x00,0x00,