A @ variable reference on a line by itself, what does it mean and where can @ variable references occur?

EricGT · March 21, 2023, 11:59am

Creating a parser for CMake files and used the CMake files from the CMake GitHub repository for testing.

Kitware/CMake/blob/master/Modules/FindCUDA/run_nvcc.cmake#L104


      
          foreach(def ${CUDA_NVCC_COMPILE_DEFINITIONS})
            list(APPEND nvcc_flags "-D${def}")
          endforeach()
          
          if(build_cubin AND NOT generated_cubin_file)
            message(FATAL_ERROR "You must specify generated_cubin_file on the command line")
          endif()
          
          # This is the list of host compilation flags.  It C or CXX should already have
          # been chosen by FindCUDA.cmake.
          @CUDA_HOST_FLAGS@
          
          # Take the compiler flags and package them up to be sent to the compiler via -Xcompiler
          set(nvcc_host_compiler_flags "")
          # If we weren't given a build_configuration, use Debug.
          if(NOT build_configuration)
            set(build_configuration Debug)
          endif()
          string(TOUPPER "${build_configuration}" build_configuration)
          #message("CUDA_NVCC_HOST_COMPILER_FLAGS = ${CUDA_NVCC_HOST_COMPILER_FLAGS}")
          foreach(flag ${CMAKE_HOST_FLAGS} ${CMAKE_HOST_FLAGS_${build_configuration}})

@CUDA_HOST_FLAGS@

The syntax page from the web documentation does not note what this is however Professional CMake notes it as @-syntax and mentions configure_file for which the web documenation has a page.

https://cmake.org/cmake/help/latest/command/configure_file.html?highlight=configure_file

The web documentation for variable references only notes

A variable reference has the form ${<variable>} and is evaluated inside a Quoted Argument or an Unquoted Argument.

So where can these @-syntax varaible references appear in a CMake file before substituion occurs?

fenrir · March 21, 2023, 12:17pm

This file is actually an input to `configure_file´ (see FindCUDA.cmake). It’s just not reflected in the extension.

EricGT · March 21, 2023, 12:20pm

FYI

For others looking for findCUDA

https://cmake.org/cmake/help/latest/module/FindCUDA.html?highlight=findcuda

I take that to mean that a file name like run_nvcc.cmake.in would have made more sense to most programmers.

While the specifics of @CUDA_HOST_FLAGS@ have been noted, still have the main quesiton.

Where can these @-syntax varaible references appear in a CMake file before substituion occurs?

benthevining · March 21, 2023, 8:18pm

Nowhere. @ reference syntax is only valid in input files to configure_file.

ben.boeckel · March 22, 2023, 12:17pm

Technically, pre-CMP0053, @ variables work in normal CMake code too (with weird caveats as any unintentional behavior is wont to have). However, you can ignore that for anything modern.