constexpr called in a constant expression compilation error

[shtsai-zz]

Dear all,

I used git clone to obtain the source code for hemelb and tried to compile it on a 64-bit Rocky 8 Linux system using GCC 11.3.0. The compilation uses zlib 1.2.12, ParMETIS 4.0.3, TinyXML 2.6.2, Boost 1.79.0, and CMake 3.24.3 installed on the system.

Basically, the steps followed were:

git clone https://github.com/hemelb-codes/hemelb.git
cd hemelb
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr/local/src/st/HemeLB/install ../
make

The compilation is running into errors like this:

[ 75%] Performing build step for 'hemelb'
[  1%] Building CXX object reporting/CMakeFiles/hemelb_reporting.dir/BuildInfo.cc.o
[  1%] Building CXX object reporting/CMakeFiles/hemelb_reporting.dir/Reporter.cc.o
[  2%] Building CXX object reporting/CMakeFiles/hemelb_reporting.dir/Timers.cc.o
[  3%] Building CXX object reporting/CMakeFiles/hemelb_reporting.dir/Dict.cc.o
[  3%] Built target hemelb_reporting
[  3%] Building CXX object configuration/CMakeFiles/hemelb_configuration.dir/CommandLine.cc.o
[  4%] Building CXX object configuration/CMakeFiles/hemelb_configuration.dir/SimConfig.cc.o
[  5%] Building CXX object configuration/CMakeFiles/hemelb_configuration.dir/SimBuilder.cc.o
In file included from /usr/local/src/st/HemeLB/20231211/hemelb/Code/extraction/LocalPropertyOutput.h:11,
                 from /usr/local/src/st/HemeLB/20231211/hemelb/Code/extraction/PropertyWriter.h:9,
                 from /usr/local/src/st/HemeLB/20231211/hemelb/Code/extraction/PropertyActor.h:9,
                 from /usr/local/src/st/HemeLB/20231211/hemelb/Code/configuration/SimBuilder.h:11,
                 from /usr/local/src/st/HemeLB/20231211/hemelb/Code/configuration/SimBuilder.cc:6:
/usr/local/src/st/HemeLB/20231211/hemelb/Code/lb/Lattices.h: In function ‘constexpr auto hemelb::lb::detail::get_default_lattice()’:
/usr/local/src/st/HemeLB/20231211/hemelb/Code/lb/Lattices.h:19:31: error: ‘constexpr auto hemelb::operator==(const hemelb::ct_string<M>&, const char*) [with long unsigned int N = 5]’ called in a constant expression
   19 |             if constexpr (LAT == "D3Q15") {
      |                           ~~~~^~~~~~~~~~

The same error happens when I tried the compilation using GCC 11.2.0, GCC 8.3.0 and Intel compilers v. 2021.4.0.

What compiler version and compilation options are recommended for building hemelb?

Any thoughts why this error occurs and how to get it resolved?

Thank you very much in advance.

[rupertnash]

HemeLB needs a C++20 compiler.

The particular feature you're missing is constexpr support for std::basic_string in libstdc++. GCC 12 is the minimum version.

Several people have hit this now. I will investigate if there is a relatively easy fix.

[shtsai-zz]

Good to know, thanks! I was able to compile hemelb successfully using GCC 12.2.0. Thank you so much!

[rupertnash]

Just merged #807 which should make everything work back to GCC 11. Not going to try and support anything older than that.