just upgrade GoogleTest and go to C++14

CMakeLists.txt

@@ -41,6 +41,12 @@ endif()
 
 project(lightgbm LANGUAGES C CXX)
 
+if(BUILD_CPP_TEST)
+  set(CMAKE_CXX_STANDARD 14)
+else()
+  set(CMAKE_CXX_STANDARD 11)
+endif()
+
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake/modules")
 
 #-- Sanitizer
@@ -327,11 +333,6 @@ if(${MM_MALLOC})
 endif()
 
 if(UNIX OR MINGW OR CYGWIN)
-  if(BUILD_CPP_TEST)
-    set(CMAKE_CXX_STANDARD 20)
-  else()
-    set(CMAKE_CXX_STANDARD 11)
-  endif()
   set(
     CMAKE_CXX_FLAGS
     "${CMAKE_CXX_FLAGS} -pthread -Wextra -Wall -Wno-ignored-attributes -Wno-unknown-pragmas -Wno-return-type"

include/LightGBM/utils/common.h

@@ -1197,11 +1197,9 @@ inline static std::vector<T> StringToArray(const std::string& str, char delimite
 *       This safety check serves to prevent incorrect internal API usage.
 *       Correct usage will never incur in this problem:
 *         - The received buffer size shall be sufficient at all times for the input format string and value.
-* /Users/jlamb/repos/LightGBM/include/LightGBM/utils/common.h:1203:35:   in 'constexpr' expansion of 'fmt::v8::basic_format_string<char, const unsigned int&>(format)'
-* /Users/jlamb/repos/LightGBM/include/LightGBM/utils/common.h:1203:35: error: 'format' is not a constant expression
 */
 template <typename T>
-inline static void format_to_buf(char* buffer, const size_t buf_len, fmt::format_string<T> format, const T value) {
+inline static void format_to_buf(char* buffer, const size_t buf_len, const char* format, const T value) {
     auto result = fmt::format_to_n(buffer, buf_len, format, value);
     if (result.size >= buf_len) {
       Log::Fatal("Numerical conversion failed. Buffer is too small.");
@@ -1212,29 +1210,29 @@ inline static void format_to_buf(char* buffer, const size_t buf_len, fmt::format
 template<typename T, bool is_float, bool high_precision>
 struct __TToStringHelper {
   void operator()(T value, char* buffer, size_t buf_len) const {
-    format_to_buf(buffer, buf_len, fmt::format_string<T>("{}"), value);
+    format_to_buf(buffer, buf_len, "{}", value);
   }
 };
 
 template<typename T>
 struct __TToStringHelper<T, true, false> {
   void operator()(T value, char* buffer, size_t buf_len) const {
-    format_to_buf(buffer, buf_len, fmt::format_string<T>("{:g}"), value);
+    format_to_buf(buffer, buf_len, "{:g}", value);
   }
 };
 
 template<typename T>
 struct __TToStringHelper<T, true, true> {
   void operator()(T value, char* buffer, size_t buf_len) const {
-    format_to_buf(buffer, buf_len, fmt::format_string<T>("{:.17g}"), value);
+    format_to_buf(buffer, buf_len, "{:.17g}", value);
   }
 };
 
 /*!
 * Converts an array to a string with with values separated by the space character.
 * This method replaces Common's ``ArrayToString`` and ``ArrayToStringFast`` functionality
 * and is locale-independent.
-*
+* 
 * \note If ``high_precision_output`` is set to true,
 *       floating point values are output with more digits of precision.
 */

src/io/dense_bin.hpp

@@ -614,7 +614,7 @@ class DenseBin : public Bin {
 #endif
   std::vector<uint8_t> buf_;
 
-  DenseBin(const DenseBin& other)
+  DenseBin<VAL_T, IS_4BIT>(const DenseBin<VAL_T, IS_4BIT>& other)
       : num_data_(other.num_data_), data_(other.data_) {}
 };
 

src/io/multi_val_dense_bin.hpp

@@ -343,10 +343,7 @@ class MultiValDenseBin : public MultiValBin {
   std::vector<uint32_t> offsets_;
   std::vector<VAL_T, Common::AlignmentAllocator<VAL_T, 32>> data_;
 
-  // https://oleksandrkvl.github.io/2021/04/02/cpp-20-overview.html
-  // https://github.com/PixarAnimationStudios/OpenUSD/issues/2183
-  // https://github.com/PixarAnimationStudios/OpenUSD/pull/2242/files
-  MultiValDenseBin(const MultiValDenseBin& other)
+  MultiValDenseBin<VAL_T>(const MultiValDenseBin<VAL_T>& other)
     : num_data_(other.num_data_), num_bin_(other.num_bin_), num_feature_(other.num_feature_),
       offsets_(other.offsets_), data_(other.data_) {
   }

src/io/multi_val_sparse_bin.hpp

@@ -430,8 +430,8 @@ class MultiValSparseBin : public MultiValBin {
   std::vector<INDEX_T> t_size_;
   std::vector<uint32_t> offsets_;
 
-  MultiValSparseBin(
-      const MultiValSparseBin& other)
+  MultiValSparseBin<INDEX_T, VAL_T>(
+      const MultiValSparseBin<INDEX_T, VAL_T>& other)
       : num_data_(other.num_data_),
         num_bin_(other.num_bin_),
         estimate_element_per_row_(other.estimate_element_per_row_),

src/io/sparse_bin.hpp

@@ -782,7 +782,7 @@ class SparseBin : public Bin {
 
   SparseBin<VAL_T>* Clone() override;
 
-  SparseBin(const SparseBin& other)
+  SparseBin<VAL_T>(const SparseBin<VAL_T>& other)
       : num_data_(other.num_data_),
         deltas_(other.deltas_),
         vals_(other.vals_),