Compiler Explorer

Source code

foo: (forward item: _) = {
    std::print(" {}", std::is_rvalue_reference_v<decltype(item)>);
}

bar_fold: <Is...: std::size_t>() = {
    test := 42;
    ((Is, foo(test)), ...);
}

bar_loop: () = {
    test := 42;
    for 0..<2 do (_) {
        foo(test);
    }
}

bar_manual: () = {
    test := 42;
    foo(test);
    foo(test);
}

namespace cpp2 {
    template<bool Condition>
    constexpr decltype(auto) move_if(auto&& val) {
        if constexpr(Condition) {
            return move(val);
        } else {
            return val;
        }
    }
}
template<std::size_t... Is>
void bar_workaround() {
    auto test{ 42 };
    [&]<std::size_t... GeneratedIndices>(std::index_sequence<GeneratedIndices...>) -> decltype(auto) {
        return ((Is, foo(cpp2::move_if<GeneratedIndices + 1 == sizeof...(Is)>(test))), ...);
    }(std::make_index_sequence<sizeof...(Is)>{});
}

int main() {
    std::println("fold:");
    bar_fold<0, 1>();

std::println("\nloop:");
    bar_loop();

std::println("\nmanually unrolled:");
    bar_manual();

std::println("\nfold with workaround:");
    bar_workaround<0, 1>();
}

Source code

# https://libcxx.llvm.org/Modules.html#using-in-external-projects
if(CMAKE_VERSION VERSION_LESS "3.27.0")
  set(CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API "2182bf5c-ef0d-489a-91da-49dbc3090d2a")
else()
  set(CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API "aa1f7df0-828a-4fcd-9afc-2dc80491aca7")
endif()
set(CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP 1)

# https://github.com/huangqinjin/cxxmodules/blob/master/CMakeLists.txt
if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
    string(CONCAT CMAKE_EXPERIMENTAL_CXX_SCANDEP_SOURCE
      "/opt/compiler-explorer/clang-trunk/bin/clang-scan-deps"
      " -format=p1689"
      " --"
      " <CMAKE_CXX_COMPILER> <DEFINES> <INCLUDES> <FLAGS>"
      " -isystem /opt/compiler-explorer/gcc-snapshot/bin/../lib/gcc/x86_64-linux-gnu/${CMAKE_CXX_COMPILER_VERSION}/include"
      " -x c++ <SOURCE> -c -o <OBJECT>"
      " -MT <DYNDEP_FILE>"
      " -MD -MF <DEP_FILE>"
      " > <DYNDEP_FILE>")
    set(CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FORMAT "gcc")
    set(CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FLAG "-fmodules-ts -Mno-modules -fmodule-mapper=<MODULE_MAP_FILE> -x c++")
endif()

if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
  add_compile_options(-stdlib=libc++)
  add_link_options(-stdlib=libc++ -lc++abi)
endif()

set(JEGP_CXX2_COMPILER "/opt/compiler-explorer/cppfront-trunk/cppfront")
set(JEGP_CPPFRONT_INCLUDE_DIRECTORIES "${CMAKE_CURRENT_SOURCE_DIR}")

add_library(cppfront::cpp2util INTERFACE IMPORTED)
target_include_directories(cppfront::cpp2util INTERFACE "${JEGP_CPPFRONT_INCLUDE_DIRECTORIES}")

add_executable(cppfront::cppfront IMPORTED)
set_target_properties(cppfront::cppfront PROPERTIES IMPORTED_LOCATION "${JEGP_CXX2_COMPILER}")

include("JEGPCpp2.cmake")

Source code

function(_jegp_cpp2_generate cpp2_src)
  string(REGEX REPLACE "2$" "" cpp1_src "${cpp2_src}")

cmake_path(GET cpp1_src PARENT_PATH cpp1_src_parent_path)
  cmake_path(GET cpp1_src FILENAME cpp1_src_filename)
  cmake_path(RELATIVE_PATH cpp1_src_parent_path BASE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")
  string(PREPEND cpp1_src_parent_path "${CMAKE_CURRENT_BINARY_DIR}/${JEGP_CPPFRONT_BUILD_DIR}/")
  file(MAKE_DIRECTORY "${cpp1_src_parent_path}")
  set(cpp1_src "${cpp1_src_parent_path}/${cpp1_src_filename}")
  cmake_path(NORMAL_PATH cpp1_src)

add_custom_command(
    OUTPUT "${cpp1_src}" COMMAND "${JEGP_CXX2_COMPILER}" "${JEGP_CXX2_FLAGS}" "${cpp2_src}" -o "${cpp1_src}"
    DEPENDS "${JEGP_CXX2_COMPILER}" "${cpp2_src}" WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
  set_source_files_properties("${cpp1_src}" PROPERTIES INCLUDE_DIRECTORIES "${JEGP_CPPFRONT_INCLUDE_DIRECTORIES}")

return(PROPAGATE cpp1_src)
endfunction()

function(jegp_cpp2_target name)
  get_target_property(cpp2_sources "${name}" SOURCES)
  list(FILTER cpp2_sources INCLUDE REGEX "\\.(cpp|h)2$")

foreach(cpp2_src IN LISTS cpp2_sources)
    _jegp_cpp2_generate("${cpp2_src}")
    target_sources("${name}" PRIVATE "${cpp1_src}")
  endforeach()
endfunction()

function(jegp_cpp2_target_sources)
  set(args)
  foreach(i RANGE 0 ${ARGC})
    if(NOT (${ARGV${i}} MATCHES "\\.(cpp|h)2$"))
      list(APPEND args "\${ARGV${i}}")
      continue()
    endif()

_jegp_cpp2_generate("${ARGV${i}}")
    set(ARGV${i} "${cpp1_src}")
    list(APPEND args "\${ARGV${i}}")
  endforeach()
  cmake_language(EVAL CODE "target_sources(${args})")
endfunction()

Source code