How can I include a dependency file generated by a custom command in cmake for GNU make?

Question

I have integrated a tool that generates some code from a text file in CMake based build environment.

This tool is also able to generate the dependency file in the GNU make format (pretty much like gcc -MD does it for c files).

I would like to include this dependency file in makefiles generated by CMake in order to correctly rebuild when necessary. Unfortunately, I could not find the correct way to do this.

I tried:

• Generated Dependency Files in CMake , but there was no answer
• https://cmake.org/cmake/help/latest/command/add_custom_command.html?highlight=add_custom_command has the DEPFILE option but it only works for Ninja

Has anyone had a similar issue?

Answer 1

try to define your file as dependency of your add_custom_target:

cmake_minimum_required(VERSION 3.0)
project(Custom_Command_TEST)
add_custom_command(OUTPUT "${CMAKE_BINARY_DIR}/your_gen_file.txt"
                   COMMAND /bin/date > "${CMAKE_BINARY_DIR}/your_gen_file.txt"
                   COMMAND /bin/echo "RUNNING COMMAND")

add_custom_target(GenerateFile
                  /bin/echo "RUNNING TARGET"
                  DEPENDS "${CMAKE_BINARY_DIR}/your_gen_file.txt")

add_executable(${PROJECT_NAME} main.cpp)
add_dependencies(${PROJECT_NAME} GenerateFile)

will only rebuild the target GenerateFile. You could put your .txt generation step as COMMAND in add_custom_command.

output of first make:

[ 33%] Generating your_gen_file.txt
RUNNING COMMAND
RUNNING TARGET
[ 33%] Built target GenerateFile
[ 66%] Building CXX object CMakeFiles/Custom_Command_TEST.dir/main.cpp.o
[100%] Linking CXX executable Custom_Command_TEST
[100%] Built target Custom_Command_TEST

output second make:

RUNNING TARGET
[ 33%] Built target GenerateFile
[100%] Built target Custom_Command_TEST

In case you want to rebuild everything again, you'll want to make clean.

You could also check this older post