Execute git describe in custom_target

Question

I would like to write output of git describe as a string to a file, so I can embed the information in my binary (C++). This has to work across platforms.

The best I can yet come up with was:

add_custom_target( SubmarineGitVersion
    COMMAND cmd /c "${CMAKE_EXECUTABLE}" echo czstring GIT_VERSION = STRINGIFY\( > "${CMAKE_CURRENT_BINARY_DIR}/GitVersion.hpp"
    COMMAND cmd /c "${GIT_EXECUTABLE}" describe --tags --always >> "${CMAKE_CURRENT_BINARY_DIR}/GitVersion.hpp"
    COMMAND cmd /c "${CMAKE_EXECUTABLE}" echo \) >> "${CMAKE_CURRENT_BINARY_DIR}/GitVersion.hpp"
)

This roughly works on Windows (is missing a ; at the end):

czstring GIT_VERSION = STRINGIFY(
tag-343434
)

Is there any better/more cross-platform way of doing this?

Answer 1

Common way for create "version" files is using configure_file command. Such way file will be created at configure stage:

GitVersion.hpp.in:

czstring GIT_VERSION = STRINGIFY(
${GIT_REPO_VERSION}
)

CMakeLists.txt:

# Store version into variable
execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --always
    OUTPUT_VARIABLE GIT_REPO_VERSION)
# The variable will be used when file is configured
configure_file("GitVersion.hpp.in" "GitVersion.hpp")

If you want to create version file on build stage, move above cmake commands into some file, and execute this file in CMake script mode:

generate_version.cmake:

# Git executable is extracted from parameters.
execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --always
    OUTPUT_VARIABLE GIT_REPO_VERSION)
# Input and output files are extracted from parameters.
configure_file(${INPUT_FILE} ${OUTPUT_FILE})

CMakeLists.txt:

add_custom_target( SubmarineGitVersion
    COMMAND ${CMAKE_COMMAND}
        -D GIT_EXECUTABLE=${GIT_EXECUTABLE}
        -D INPUT_FILE=${CMAKE_CURRENT_SOURCE_DIR}/GitVersion.hpp.in
        -D OUTPUT_FILE=${CMAKE_CURRENT_BINARY_DIR}/GitVersion.hpp
        -P ${CMAKE_CURRENT_SOURCE_DIR}/generate_version.cmake
)