Simplify excluding ProtobufWriter from compilation when USE_PROTOBUF=0.

dbms/src/Formats/ProtobufWriter.cpp

-#include "ProtobufWriter.h"
+#include <Common/config.h>
 #if USE_PROTOBUF
 
 #include <cassert>
-#include <optional>
 #include <math.h>
+#include <optional>
 #include <AggregateFunctions/IAggregateFunction.h>
-#include <IO/ReadHelpers.h>
-#include <IO/WriteHelpers.h>
 #include <boost/numeric/conversion/cast.hpp>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/descriptor.pb.h>
+#include <IO/ReadHelpers.h>
+#include <IO/WriteHelpers.h>
+#include "ProtobufWriter.h"
 
 
 namespace DB
@@ -797,5 +798,4 @@ void ProtobufWriter::writeAggregateFunction(const AggregateFunctionPtr & functio
 }
 
 }
-
 #endif

dbms/src/Formats/ProtobufWriter.h

 #pragma once
 
+#include <common/DayNum.h>
+#include <Common/UInt128.h>
 #include <Core/UUID.h>
+
+#include <Common/config.h>
+#if USE_PROTOBUF
+
 #include <Formats/ProtobufSimpleWriter.h>
 #include <boost/noncopyable.hpp>
-#include <Common/PODArray.h>
-#include <Common/UInt128.h>
-#include <common/DayNum.h>
-#include <Common/config.h>
 
 
 namespace google
@@ -18,20 +20,6 @@ namespace protobuf
 }
 }
 
-#if USE_PROTOBUF
-#   define EMPTY_DEF
-#   define EMPTY_DEF_RET(a)
-#else
-#   define EMPTY_DEF {}
-#   define EMPTY_DEF_RET(a) {return a;}
-#   pragma GCC diagnostic push
-#   pragma GCC diagnostic ignored "-Wunused-parameter"
-#   if defined(__clang__)
-#      pragma GCC diagnostic ignored "-Wextra-semi"
-#   endif
-#endif
-
-
 namespace DB
 {
 class IAggregateFunction;
@@ -44,57 +32,53 @@ using ConstAggregateDataPtr = const char *;
 class ProtobufWriter : private boost::noncopyable
 {
 public:
-    ProtobufWriter(WriteBuffer & out, const google::protobuf::Descriptor * message_type) EMPTY_DEF;
-    ~ProtobufWriter() EMPTY_DEF;
+    ProtobufWriter(WriteBuffer & out, const google::protobuf::Descriptor * message_type);
+    ~ProtobufWriter();
 
     /// Returns fields of the protobuf schema sorted by their numbers.
     const std::vector<const google::protobuf::FieldDescriptor *> & fieldsInWriteOrder() const;
 
     /// Should be called when we start writing a new message.
-    void newMessage() EMPTY_DEF;
+    void newMessage();
 
     /// Should be called when we start writing a new field.
     /// Returns false if there is no more fields in the message type.
-    bool nextField() EMPTY_DEF_RET(false);
+    bool nextField();
 
     /// Returns the current field of the message type.
     /// The value returned by this function changes after calling nextField() or newMessage().
-#if USE_PROTOBUF
     const google::protobuf::FieldDescriptor * currentField() const { return current_field; }
-#endif
 
-    void writeNumber(Int8 value) EMPTY_DEF;
-    void writeNumber(UInt8 value) EMPTY_DEF;
-    void writeNumber(Int16 value) EMPTY_DEF;
-    void writeNumber(UInt16 value) EMPTY_DEF;
-    void writeNumber(Int32 value) EMPTY_DEF;
-    void writeNumber(UInt32 value) EMPTY_DEF;
-    void writeNumber(Int64 value) EMPTY_DEF;
-    void writeNumber(UInt64 value) EMPTY_DEF;
-    void writeNumber(UInt128 value) EMPTY_DEF;
-    void writeNumber(Float32 value) EMPTY_DEF;
-    void writeNumber(Float64 value) EMPTY_DEF;
+    void writeNumber(Int8 value);
+    void writeNumber(UInt8 value);
+    void writeNumber(Int16 value);
+    void writeNumber(UInt16 value);
+    void writeNumber(Int32 value);
+    void writeNumber(UInt32 value);
+    void writeNumber(Int64 value);
+    void writeNumber(UInt64 value);
+    void writeNumber(UInt128 value);
+    void writeNumber(Float32 value);
+    void writeNumber(Float64 value);
 
-    void writeString(const StringRef & value) EMPTY_DEF;
+    void writeString(const StringRef & value);
 
-    void prepareEnumMapping(const std::vector<std::pair<std::string, Int8>> & name_value_pairs) EMPTY_DEF;
-    void prepareEnumMapping(const std::vector<std::pair<std::string, Int16>> & name_value_pairs) EMPTY_DEF;
-    void writeEnum(Int8 value) EMPTY_DEF;
-    void writeEnum(Int16 value) EMPTY_DEF;
+    void prepareEnumMapping(const std::vector<std::pair<std::string, Int8>> & name_value_pairs);
+    void prepareEnumMapping(const std::vector<std::pair<std::string, Int16>> & name_value_pairs);
+    void writeEnum(Int8 value);
+    void writeEnum(Int16 value);
 
-    void writeUUID(const UUID & value) EMPTY_DEF;
-    void writeDate(DayNum date) EMPTY_DEF;
-    void writeDateTime(time_t tm) EMPTY_DEF;
+    void writeUUID(const UUID & value);
+    void writeDate(DayNum date);
+    void writeDateTime(time_t tm);
 
-    void writeDecimal(Decimal32 decimal, UInt32 scale) EMPTY_DEF;
-    void writeDecimal(Decimal64 decimal, UInt32 scale) EMPTY_DEF;
-    void writeDecimal(const Decimal128 & decimal, UInt32 scale) EMPTY_DEF;
+    void writeDecimal(Decimal32 decimal, UInt32 scale);
+    void writeDecimal(Decimal64 decimal, UInt32 scale);
+    void writeDecimal(const Decimal128 & decimal, UInt32 scale);
 
-    void writeAggregateFunction(const AggregateFunctionPtr & function, ConstAggregateDataPtr place) EMPTY_DEF;
+    void writeAggregateFunction(const AggregateFunctionPtr & function, ConstAggregateDataPtr place);
 
 private:
-#if USE_PROTOBUF
-
     void enumerateFieldsInWriteOrder(const google::protobuf::Descriptor * message_type);
     void createConverters();
 
@@ -115,14 +99,45 @@ private:
 
     std::vector<std::unique_ptr<Converter>> converters;
     Converter * current_converter = nullptr;
-
-#endif
 };
 
 }
 
-#if !USE_PROTOBUF
-#   undef EMPTY_DEF
-#   undef EMPTY_DEF_RET
-#   pragma GCC diagnostic pop
+#else
+
+namespace DB
+{
+class IAggregateFunction;
+using AggregateFunctionPtr = std::shared_ptr<IAggregateFunction>;
+using ConstAggregateDataPtr = const char *;
+
+class ProtobufWriter
+{
+public:
+    void writeNumber(Int8 value) {}
+    void writeNumber(UInt8 value) {}
+    void writeNumber(Int16 value) {}
+    void writeNumber(UInt16 value) {}
+    void writeNumber(Int32 value) {}
+    void writeNumber(UInt32 value) {}
+    void writeNumber(Int64 value) {}
+    void writeNumber(UInt64 value) {}
+    void writeNumber(UInt128 value) {}
+    void writeNumber(Float32 value) {}
+    void writeNumber(Float64 value) {}
+    void writeString(const StringRef & value) {}
+    void prepareEnumMapping(const std::vector<std::pair<std::string, Int8>> & name_value_pairs) {}
+    void prepareEnumMapping(const std::vector<std::pair<std::string, Int16>> & name_value_pairs) {}
+    void writeEnum(Int8 value) {}
+    void writeEnum(Int16 value) {}
+    void writeUUID(const UUID & value) {}
+    void writeDate(DayNum date) {}
+    void writeDateTime(time_t tm) {}
+    void writeDecimal(Decimal32 decimal, UInt32 scale) {}
+    void writeDecimal(Decimal64 decimal, UInt32 scale) {}
+    void writeDecimal(const Decimal128 & decimal, UInt32 scale) {}
+    void writeAggregateFunction(const AggregateFunctionPtr & function, ConstAggregateDataPtr place) {}
+};
+
+}
 #endif