Tools fail to build with clang due to incompatibility with C++20: `error: no type named 'result_of' in namespace 'std'`

[barracuda156]

[100%] Building CXX object tools/CMakeFiles/tiledb-cli.dir/src/commands/info_command.cc.o
cd /opt/local/var/macports/build/tiledb-ef19584d/work/build/tools && /opt/local/bin/clang++-mp-17 -DFMT_SHARED -DNDEBUG -DSPDLOG_COMPILED_LIB -DSPDLOG_FMT_EXTERNAL -DSPDLOG_SHARED_LIB -D_FILE_OFFSET_BITS=64 -I/opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/.. -I/opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src -isystem /opt/local/include -isystem /opt/local/include/libfmt11 -isystem /opt/local/libexec/openssl3/include -pipe -I/opt/local/libexec/openssl3/include -Os -DNDEBUG -I/opt/local/libexec/openssl3/include -isystem/opt/local/include -stdlib=libc++ -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk -std=c++20 -arch arm64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk -mmacosx-version-min=14.0 -fvisibility=hidden -Wall -Wextra -Wno-unqualified-std-cast-call -fexperimental-library -MD -MT tools/CMakeFiles/tiledb-cli.dir/src/commands/help_command.cc.o -MF CMakeFiles/tiledb-cli.dir/src/commands/help_command.cc.o.d -o CMakeFiles/tiledb-cli.dir/src/commands/help_command.cc.o -c /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/help_command.cc
. . .
[100%] Built target tiledb
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/main/tiledb.cc:33:
/opt/local/include/clipp.h:163:40: error: no type named 'result_of' in namespace 'std'
  163 |         std::is_same<Ret,typename std::result_of<Fn(Args...)>::type>::value>{} );
      |                          ~~~~~~~~~~~~~~^~~~~~~~~
/opt/local/include/clipp.h:163:76: error: initializer list cannot be used on the right hand side of operator '>'
  163 |         std::is_same<Ret,typename std::result_of<Fn(Args...)>::type>::value>{} );
      |                                                                            ^~~
/opt/local/include/clipp.h:174:40: error: no type named 'result_of' in namespace 'std'
  174 |         std::is_same<Ret,typename std::result_of<Fn()>::type>::value>{} );
      |                          ~~~~~~~~~~~~~~^~~~~~~~~
/opt/local/include/clipp.h:174:69: error: initializer list cannot be used on the right hand side of operator '>'
  174 |         std::is_same<Ret,typename std::result_of<Fn()>::type>::value>{} );
      |                                                                     ^~~
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/info_command.cc:33:
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/info_command.h:36:
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/command.h:36:
/opt/local/include/clipp.h:163:40: error: no type named 'result_of' in namespace 'std'
  163 |         std::is_same<Ret,typename std::result_of<Fn(Args...)>::type>::value>{} );
      |                          ~~~~~~~~~~~~~~^~~~~~~~~
/opt/local/include/clipp.h:163:76: error: initializer list cannot be used on the right hand side of operator '>'
  163 |         std::is_same<Ret,typename std::result_of<Fn(Args...)>::type>::value>{} );
      |                                                                            ^~~
/opt/local/include/clipp.h:174:40: error: no type named 'result_of' in namespace 'std'
  174 |         std::is_same<Ret,typename std::result_of<Fn()>::type>::value>{} );
      |                          ~~~~~~~~~~~~~~^~~~~~~~~
/opt/local/include/clipp.h:174:69: error: initializer list cannot be used on the right hand side of operator '>'
  174 |         std::is_same<Ret,typename std::result_of<Fn()>::type>::value>{} );
      |                                                                     ^~~
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/help_command.cc:35:
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/help_command.h:39:
In file included from /opt/local/var/macports/build/tiledb-ef19584d/work/TileDB-2.28.1/tools/src/commands/command.h:36:
/opt/local/include/clipp.h:163:40: error: no type named 'result_of' in namespace 'std'
  163 |         std::is_same<Ret,typename std::result_of<Fn(Args...)>::type>::value>{} );
      |                          ~~~~~~~~~~~~~~^~~~~~~~~
/opt/local/include/clipp.h:163:76: error: initializer list cannot be used on the right hand side of operator '>'
  163 |         std::is_same<Ret,typename std::result_of<Fn(Args...)>::type>::value>{} );
      |                                                                            ^~~
/opt/local/include/clipp.h:174:40: error: no type named 'result_of' in namespace 'std'
  174 |         std::is_same<Ret,typename std::result_of<Fn()>::type>::value>{} );
      |                          ~~~~~~~~~~~~~~^~~~~~~~~
/opt/local/include/clipp.h:174:69: error: initializer list cannot be used on the right hand side of operator '>'
  174 |         std::is_same<Ret,typename std::result_of<Fn()>::type>::value>{} );
      |                                                                     ^~~
4 errors generated.
make[2]: *** [tools/CMakeFiles/tiledb-cli.dir/src/commands/help_command.cc.o] Error 1
make[2]: *** Waiting for unfinished jobs....
4 errors generated.
make[2]: *** [tools/CMakeFiles/tiledb-cli.dir/src/main/tiledb.cc.o] Error 1
4 errors generated.
make[2]: *** [tools/CMakeFiles/tiledb-cli.dir/src/commands/info_command.cc.o] Error 1
make[2]: Leaving directory `/opt/local/var/macports/build/tiledb-ef19584d/work/build'
make[1]: *** [tools/CMakeFiles/tiledb-cli.dir/all] Error 2
make[1]: Leaving directory `/opt/local/var/macports/build/tiledb-ef19584d/work/build'
make: *** [all] Error 2

Apparently result_of has been removed in C++20: opencv/opencv#21109
Same failure with Apple clang of macOS 14.

[barracuda156]

Upd. Fixed in clipp in FreeBSD: freebsd/freebsd-ports@e0f09a5

[teo-tsirpanis]

As you noticed, this is a problem of clipp, which you can remedy by applying to it a patch like the one you linked.

We can fix this on our side by compiling the tools with C++17, but they are not very much maintained (or mentioned in any documentation), so this is not a priority at this moment.

[barracuda156]

@teo-tsirpanis Ok, thanks for clarifying. I borrowed the patch into my fork, it worked fine for macOS build either.
P. S. I wanted to mention that tools seem not to have install target (I had to add a manual post-destroot phase), but now it is understandable why it is the case.