[enum_parser] generate ToStringBuf specialization

IGNIETFERRO-1350

ref:bb9bb1755b6abfc5a27639daf049b8a7cd748fe4

tools/enum_parser/enum_parser/main.cpp

@@ -310,6 +310,9 @@ void GenerateEnum(
     // outer ToString
     if (headerOutPtr) {
         (*headerOutPtr) << "const TString& ToString(" << name << ");\n";
+        (*headerOutPtr) << "Y_FORCE_INLINE TStringBuf ToStringBuf(" << name << " e) {\n";
+        (*headerOutPtr) << "    return ::NEnumSerializationRuntime::ToStringBuf<" << name << ">(e);\n";
+        (*headerOutPtr) << "}\n";
     }
     out << "const TString& ToString(" << name << " x) {\n";
     out << "    const " << nsNameBufsClass << "& names = " << nsNameBufsClass << "::Instance();\n";
@@ -352,6 +355,12 @@ void GenerateEnum(
 
     // specializations for NEnumSerializationRuntime function family
     out << "namespace NEnumSerializationRuntime {\n";
+    // template<> ToStringBuf
+    out << "    template<>\n";
+    out << "    TStringBuf ToStringBuf<" << name << ">(" << name << " e) {\n";
+    out << "        return ::NEnumSerializationRuntime::DispatchToStringBufFn<" << nsNameBufsClass << ">(e);\n";
+    out << "    }\n\n";
+
     // template<> GetEnumAllValues
     out << "    template<>\n";
     out << "    TMappedArrayView<" << name <<"> GetEnumAllValuesImpl<" << name << ">() {\n";

tools/enum_parser/enum_serialization_runtime/dispatch_methods.h

@@ -26,6 +26,21 @@ namespace NEnumSerializationRuntime {
         }
     }
 
+    template <class TNameBufs, typename EEnum>
+    inline TStringBuf DispatchToStringBufFn(EEnum n) {
+        constexpr auto order = TNameBufs::NamesOrder;
+        if constexpr (order >= ::NEnumSerializationRuntime::ESortOrder::DirectMapping) {
+            return TNameBufs::ToStringBufDirect(n, TNameBufs::EnumInitializationData);
+        } else if constexpr (std::size(TNameBufs::EnumInitializationData.NamesInitializer) <= LINEAR_SEARCH_KEYS_SIZE_THRESHOLD) {
+            return TNameBufs::ToStringBufFullScan(n, TNameBufs::EnumInitializationData);
+        } else if constexpr (order >= ::NEnumSerializationRuntime::ESortOrder::Ascending) {
+            return TNameBufs::ToStringBufSorted(n, TNameBufs::EnumInitializationData);
+        } else {
+            const TNameBufs& names = TNameBufs::Instance();
+            return names.ToStringBuf(n);
+        }
+    }
+
     template <class TNameBufs, typename EEnum>
     inline EEnum DispatchFromStringImplFn(const char* data, size_t len) {
         const TStringBuf name{data, len};

tools/enum_parser/enum_serialization_runtime/enum_runtime.h

@@ -102,34 +102,51 @@ namespace NEnumSerializationRuntime {
     public:
         using TBase::TBase;
 
+        // ToString
+        // Return reference to singleton preallocated string
         const TString& ToString(const EEnum key) const {
             return TBase::ToString(TCast::CastToRepresentationType(key));
         }
 
-        bool FromString(const TStringBuf name, EEnum& ret) const {
-            return MapFindResult(TBase::TryFromString(name), ret);
+        // ToStringBuf
+        TStringBuf ToStringBuf(EEnum key) const {
+            return TBase::ToStringBuf(TCast::CastToRepresentationType(key));
         }
-
-        EEnum FromString(const TStringBuf name) const {
-            return TCast::CastFromRepresentationType(TBase::FromString(name));
+        static TStringBuf ToStringBufFullScan(const EEnum key, const TInitializationData& enumInitData) {
+            return TBase::ToStringBufFullScan(TCast::CastToRepresentationType(key), enumInitData);
+        }
+        static TStringBuf ToStringBufSorted(const EEnum key, const TInitializationData& enumInitData) {
+            return TBase::ToStringBufSorted(TCast::CastToRepresentationType(key), enumInitData);
+        }
+        static TStringBuf ToStringBufDirect(const EEnum key, const TInitializationData& enumInitData) {
+            return TBase::ToStringBufDirect(TCast::CastToRepresentationType(key), enumInitData);
         }
 
+        // TryFromString-like functons
+        // Return false for unknown enumeration names
+        bool FromString(const TStringBuf name, EEnum& ret) const {
+            return MapFindResult(TBase::TryFromString(name), ret);
+        }
         static bool TryFromStringFullScan(const TStringBuf name, EEnum& ret, const TInitializationData& enumInitData) {
             return MapFindResult(TBase::TryFromStringFullScan(name, enumInitData), ret);
         }
-
         static bool TryFromStringSorted(const TStringBuf name, EEnum& ret, const TInitializationData& enumInitData) {
             return MapFindResult(TBase::TryFromStringSorted(name, enumInitData), ret);
         }
 
+        // FromString
+        // Throw exception for unknown enumeration names
+        EEnum FromString(const TStringBuf name) const {
+            return TCast::CastFromRepresentationType(TBase::FromString(name));
+        }
         static EEnum FromStringFullScan(const TStringBuf name, const TInitializationData& enumInitData) {
             return TCast::CastFromRepresentationType(TBase::FromStringFullScan(name, enumInitData));
         }
-
         static EEnum FromStringSorted(const TStringBuf name, const TInitializationData& enumInitData) {
             return TCast::CastFromRepresentationType(TBase::FromStringSorted(name, enumInitData));
         }
 
+        // Inspection
         TMappedDictView<EEnum, TString> EnumNames() const noexcept {
             return {TBase::TypelessEnumNames()};
         }
@@ -138,18 +155,16 @@ namespace NEnumSerializationRuntime {
             return {TBase::TypelessEnumValues()};
         }
 
+        // Out
         void Out(IOutputStream* os, const EEnum key) const {
             TBase::Out(os, TCast::CastToRepresentationType(key));
         }
-
         static void OutFullScan(IOutputStream* os, const EEnum key, const TInitializationData& enumInitData) {
             TBase::OutFullScan(os, TCast::CastToRepresentationType(key), enumInitData);
         }
-
         static void OutSorted(IOutputStream* os, const EEnum key, const TInitializationData& enumInitData) {
             TBase::OutSorted(os, TCast::CastToRepresentationType(key), enumInitData);
         }
-
         static void OutDirect(IOutputStream* os, const EEnum key, const TInitializationData& enumInitData) {
             TBase::OutDirect(os, TCast::CastToRepresentationType(key), enumInitData);
         }

util/generic/serialized_enum.h

@@ -81,6 +81,14 @@ namespace NEnumSerializationRuntime {
      */
     template <typename EnumT>
     const TVector<TString>& GetEnumAllCppNamesImpl();
+
+    /**
+     * Converts @c e to a string. Works like @c ToString(e) function, but returns @c TStringBuf instead of @c TString.
+     * Thus works slightly faster and usually avoids any dynamic memory allocation.
+     * @throw yexception is case of unknown enum value
+     */
+    template <typename EnumT>
+    TStringBuf ToStringBuf(EnumT e);
 }
 
 /**