build failure with robin_map 1.4.0

[emollier]

Hi César,

As noted in Debian bug #1118378, veryfasttree fails to build with robin_map 1.4.0 with the following error:

/usr/bin/c++ -DCLI11_BOOST_OPTIONAL=0 -DNDEBUG -I/build/reproducible-path/veryfasttree-4.0.5+dfsg/libs/CLI11/include -I/build/reproducible-path/veryfasttree-4.0.5+dfsg/libs/bxzstr/include -g -O2 -ffile-prefix-map=/build/reproducible-path/veryfasttree-4.0.5+dfsg=. -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -Wdate-time -D_FORTIFY_SOURCE=2 -Wall -O3 -DUSE_CUDA=0 -mavx512f -std=gnu++11 -fopenmp -MD -MT CMakeFiles/VeryFastTree.dir/src/impl/VeryFastTreeDoubleSSE128.cpp.o -MF CMakeFiles/VeryFastTree.dir/src/impl/VeryFastTreeDoubleSSE128.cpp.o.d -o CMakeFiles/VeryFastTree.dir/src/impl/VeryFastTreeDoubleSSE128.cpp.o -c /build/reproducible-path/veryfasttree-4.0.5+dfsg/src/impl/VeryFastTreeDoubleSSE128.cpp
In file included from /usr/include/tsl/robin_map.h:34,
                 from /build/reproducible-path/veryfasttree-4.0.5+dfsg/src/impl/../HashTable.h:7,
                 from /build/reproducible-path/veryfasttree-4.0.5+dfsg/src/impl/../VeyFastTreeImpl.h:13,
                 from /build/reproducible-path/veryfasttree-4.0.5+dfsg/src/impl/VeryFastTreeDouble.cpp:3:
/usr/include/tsl/robin_hash.h: In member function ‘tsl::detail_robin_hash::bucket_entry<ValueType, StoreHash>::value_type& tsl::detail_robin_hash::bucket_entry<ValueType, StoreHash>::value()’:
/usr/include/tsl/robin_hash.h:251:18: error: ‘launder’ is not a member of ‘std’ [-Wtemplate-body]
  251 |     return *std::launder(
      |                  ^~~~~~~
/usr/include/tsl/robin_hash.h:251:18: note: ‘std::launder’ is only available from C++17 onwards
/usr/include/tsl/robin_hash.h: In member function ‘const tsl::detail_robin_hash::bucket_entry<ValueType, StoreHash>::value_type& tsl::detail_robin_hash::bucket_entry<ValueType, StoreHash>::value() const’:
/usr/include/tsl/robin_hash.h:257:18: error: ‘launder’ is not a member of ‘std’ [-Wtemplate-body]
  257 |     return *std::launder(
      |                  ^~~~~~~
/usr/include/tsl/robin_hash.h:257:18: note: ‘std::launder’ is only available from C++17 onwards
/usr/include/tsl/robin_hash.h: In member function ‘void tsl::detail_robin_hash::robin_hash<ValueType, KeySelect, ValueSelect, Hash, KeyEqual, Allocator, StoreHash, GrowthPolicy>::min_load_factor(float)’:
/usr/include/tsl/robin_hash.h:1020:30: error: ‘clamp’ is not a member of ‘std’ [-Wtemplate-body]
 1020 |     m_min_load_factor = std::clamp(ml, float(MINIMUM_MIN_LOAD_FACTOR),
      |                              ^~~~~
/usr/include/tsl/robin_hash.h: In member function ‘void tsl::detail_robin_hash::robin_hash<ValueType, KeySelect, ValueSelect, Hash, KeyEqual, Allocator, StoreHash, GrowthPolicy>::max_load_factor(float)’:
/usr/include/tsl/robin_hash.h:1025:30: error: ‘clamp’ is not a member of ‘std’ [-Wtemplate-body]
 1025 |     m_max_load_factor = std::clamp(ml, float(MINIMUM_MAX_LOAD_FACTOR),
      |                              ^~~~~

On quick analysis, this looks to be caused by robin_map's usage of capabilities introduced in standard C++ 2017, but veryfasttree encodes instructions in the CMakeLists.txt to stick to C++ 2011. See the reference documentation:

• https://en.cppreference.com/w/cpp/utility/launder.html
• https://en.cppreference.com/w/cpp/algorithm/clamp.html

I considered the option of uploading a modified veryfasttree with the below patch to address the release critical bug, but I thought that a bump of C++ version might have other implications, in which case you want to be aware of such change:

--- veryfasttree.orig/CMakeLists.txt
+++ veryfasttree/CMakeLists.txt
@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.5...3.27)
 project(VeryFastTree)
 
-set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD 17)
 
 option(USE_SHARED "enable/disable linking of system shared libraries" OFF)
 option(USE_NATIVE "enable/disable system's processor architecture optimization (linux)" ON)

This does not directly impact your tree upstream, given that you vendor the robin_map along your libs/, which is why I have not pushed a merge request, but that should be useful to be aware of, when you will wish to bump your local copy of the library.

Have a nice day, :)
Étienne.