[CMake] Dependencies to generated C header files in another CMake project

[Stefan Granqvist]

Hi,

I have the situation where one CMake project generates a couple of header 
files, placing the resulting header files in ${PROJECT_BINARY_DIR} for the 
project. The files are generated using one ADD_CUSTOM_COMMAND for each 
header files to generate. In addition I also have a corresponding 
ADD_CUSTOM_TARGET with a dummy target which depends on the generated header 
file. My experiences is that the custom target is needed to make the 
generated file to be produced also when if there is no other target in the 
project using the generated file.  Let us call this project P1.

I also have another CMake project (here called P2) that would also like to 
use the generated header files from the P1. But I have failed to setup a 
dependency in P2 that uses P1 to build the generated files. It would be very 
nice if I could build P2 using make without having to build P1 manually, 
prior to P2.

Both these projects are subdirectories in a CMake "main" CMake project (P0). 
However, I  would like to have the possibility to go directly to P2 (after 
using CMake to generate the make files) and run "make" without first have 
run make from P0's make file and thereby rely on the subdirectory order.

Similar inter-project dependencies seem to works when I have a dependency 
between an executable in one project and a library in anther project. 
However when using generated files and custom targets, it seems impossible 
to get the same dependency to work. I think I have tried everything that is 
described in the CMake book... I have tried using ADD_DEPENDENCIES between 
targets in the two projects. I have also tried to use 
SET_SOURCE_FILE_PROPERTIES both using GENERATED on the generated header 
files, and the OBJECT_DEPENDS property. I also tested to add a dependency 
from a target in P2 to the link library that P1 produces. In this case, P1 
is forced to be created before the target in P2 is linked, but the generated 
file might be produced too late, since a header file in P2 needs the 
generated header file in P1.

The only solution I can think of is to change P1 to generate the file in a 
fix location, and add the same rule in P2 (using ADD_CUSTOM_COMMAND) that 
will produce the same generated file at the same location. This will 
probably work, but the beauty of the inter-project dependencies from 
built-in CMake targets is gone...

Does anyone have any advice how to solve this problem? Any comments are 
welcome. I am using CMake version 2.0.3 on cygwin/x86 and Solaris/Sparc 
hosts.

Best Regards
Stefan

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