[CMake] How to specify that CMake build time configuration depends on a certain file?

[Daniel Dunbar]

Hi all,

I've been searching for an answer to the following problem, with no luck:

I have a CMake build that reads in some data from an external
(non-CMake) file during configuration.

I want to tell CMake that the configuration depends on this file, so
that the --check-build-system / check_cache steps will know to
automatically rebuild the project files / Makefiles / etc., whenever I
edit the external file.

Is this possible?

Here is an example test case to demonstrate the problem, I want the
project to know to rebuild when I change the version.txt file:
--
# Here is the test CMakeLists file that uses an external file:
$ cat CMakeLists.txt
cmake_minimum_required(VERSION 2.6)

file(STRINGS "version.txt" VERSION)
add_library(test t.cpp)
add_definitions("-DVERSION=@VERSION@")

# And here is the external file:
$ cat version.txt
1

# Do our first build.
$ make
[100%] Building CXX object CMakeFiles/test.dir/t.cpp.o
Linking CXX static library libtest.a
[100%] Built target test

# Modify the external file.
$ echo 2 > version.txt

# Now we rerun make, but nothing is rebuilt because CMake
# doesn't know the configuration depends on version.txt
$ make
[100%] Built target test
--

Thanks in advance,
 - Daniel