[SOLVED] Cmake execute_process at build time to get git commit hash at build time

Issue

I want to use cmake execute_process, or similar, to get the git hash at build time not at configure time. I have it working and populating the git hash at configure time, but I would like to have it update at build time.

Here is an example of what I have to get the git hash at configure time.

(this is an example from Profession Cmake https://crascit.com/professional-cmake/)

foobar_version.cpp.in

std::string getFooBarGitHash()
{
   return "@FooBar_GIT_HASH@";
}

CMakeLists.txt

find_package(Git REQUIRED)
execute_process(
   COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
   RESULT_VARIABLE result
   OUTPUT_VARIABLE FooBar_GIT_HASH
   OUTPUT_STRIP_TRAILING_WHITESPACE
)
if(result)
    message(FATAL_ERROR "Failed to get git hash: ${result}")
endif()

configure_file(foobar_version.cpp.in foobar_version.cpp @ONLY)

This works and populates a foobar_version.cpp file with the git hash as expected, but I want to have this run at build time. Is there a convenient way to do this?

Solution

I solved this problem by generating a custom version.h header file with a python script GitHashExtractor and the following snippet in my cmake file.

set(PROJECT_SOURCES
        [... your files ...]
        GitHashExtractor/firmwareVersion.py
        GitHashExtractor/version.h
)

# START github.com/ni-m/gitHashExtractor
set(VERSION_FILE "./GitHashExtractor/version.h")
set(VERSION_PYTHON "./GitHashExtractor/firmwareVersion.py")
set_property(SOURCE ${VERSION_FILE} PROPERTY SKIP_AUTOGEN ON) #Qt Framework
add_custom_command(OUTPUT ${VERSION_FILE}
    COMMAND python ${VERSION_PYTHON} [ARGS] [Qt.h]
    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
    COMMENT "Creating ${VERSION_FILE}"
)

# target GitHashExtractor is always built
add_custom_target(GitHashExtractor ALL DEPENDS ${VERSION_FILE})
# END github.com/ni-m/gitHashExtractor

The last line makes sure to always build this target. This snipped is tested unter the Qt framework with cmake. You may want to remove the set_property(SOURCE ${VERSION_FILE} PROPERTY SKIP_AUTOGEN ON) line if you're not using Qt.

Answered By - Marco

Answer Checked By - Mary Flores (WPSolving Volunteer)