Hi all, I'd like to set a CMake variable to the current git commit short hash. This variable will be used as part of the version string for my project (ex: "1.0.1+git.${SHORT_HASH}"). I can get at this short hash by using execute_process and setting the resulting output to a variable.
```cmake execute_process( COMMAND git rev-parse --short HEAD RESULT_VARIABLE SHORT_HASH_RESULT OUTPUT_VARIABLE SHORT_HASH) ``` My issue is that cmake will only run execute_process once, during the configure step. I need cmake to run this execute_process on every build and, if the output has changed, reconfigure to make sure SHORT_HASH is up to date. I came up with one solution to this issue: During the configure step, I can write the current short hash to a file named short_hash.txt. On every build, I'll re-compute the short hash and verify that the computed short hash is the same as what is in short_hash.txt. If its not, I'll write the new short hash to short_hash.txt. I then make short_hash.txt an input to configure_file. This will cause cmake to validate SHORT_HASH is properly set, and re-configure if its not. ```cmake execute_process( COMMAND git rev-parse --short HEAD RESULT_VARIABLE SHORT_HASH_RESULT OUTPUT_VARIABLE SHORT_HASH) # If running in script mode (this runs on every build) if (CMAKE_SCRIPT_MODE_FILE) if (EXISTS "${SHORT_HASH_FILE}") file(READ ${SHORT_HASH_FILE} READ_IN_SHORT_HASH) else() set(READ_IN_SHORT_HASH "") endif() if (NOT ("${READ_IN_SHORT_HASH}" STREQUAL "${SHORT_HASH}")) message(STATUS "Short hash is out of date") # This will update short_hash.txt, causing cmake to reconfigure file(WRITE ${SHORT_HASH_FILE} ${SHORT_HASH}) endif() # Else running as part of cmake configure else() set(SHORT_HASH_FILE ${CMAKE_CURRENT_BINARY_DIR}/short_hash.txt) file(WRITE ${SHORT_HASH_FILE} ${SHORT_HASH}) # The trick here is to make sure short_hash.txt is listed as a byproduct add_custom_target( git_short_hash BYPRODUCTS ${SHORT_HASH_FILE} COMMAND ${CMAKE_COMMAND} "-DSHORT_HASH_FILE=${SHORT_HASH_FILE}" "-P" "${CMAKE_CURRENT_LIST_FILE}" COMMENT "Re-checking short hash..." VERBATIM USES_TERMINAL) # This configure_file makes cmake reconfigure dependent on short_hash.txt configure_file(${SHORT_HASH_FILE} ${SHORT_HASH_FILE}.junk COPYONLY) message(STATUS "Short Hash: ${SHORT_HASH}") endif() ``` This works great with cmake 3.12 and ninja 1.8.2! (I was really happy with how well it worked. I tip my hat to the cmake developers for this). However, it doesn't work with Makefiles, and causes ninja 1.7.2 to get stuck in an infinite loop. On CMake 3.10 this will cause ninja 1.8.2 to generate a warning about a loop. Has anyone run into this issue before and have a better solution? Or is trying to execute a command before cmake checks if it should reconfigure a hack that should never be done? Thanks for the help! Matt -- Powered by www.kitware.com Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ Kitware offers various services to support the CMake community. For more information on each offering, please visit: CMake Support: http://cmake.org/cmake/help/support.html CMake Consulting: http://cmake.org/cmake/help/consulting.html CMake Training Courses: http://cmake.org/cmake/help/training.html Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Follow this link to subscribe/unsubscribe: https://cmake.org/mailman/listinfo/cmake