CMake Configure File Build Rule

Question

I'm using CMake for my build system and in the project, we will have a bunch of configuration files. Some of them will just need to be copied over, some will need to be modified per computer. I'm currently using CMake's "configure_file" command to copy/replace parts of the file. This works great, and I love how I can use any variable from CMake in the configure routine.

But if you change the original file, CMake will not pick this up and you have to rerun cmake for it to configure the directory. When I run "make", I want it to pick up that I've changed the file and rerun configure.

It will also reconfigure files always, even if the file it is overwriting is newer. I want it to act like a custom target.

I think I can do this with add_custom_command, but I don't think I can run a CMake command from add_custom_command. So is there anyway to duplicate the behaviour that configure_file does in CMake?

Answer 1

I do not think this has an easy answer. I see two options:

1. To trigger a re-run of cmake if an input changes, you might be able to make your input file depend on CMakeLists.txt.

2. To run a cmake command as part of and add_custom_command, there is the variable ${CMAKE_COMMAND}, which will give you the path to the running cmake. You could, as part of the configure step, generate a fragment of CMake code (that calls configure_file) that is invoked using the -P option. Either pass substitutions on the command line using -D, or write them to the CMake fragment.