[CMake] Using add_subdirectory to manage project dependencies that aren't actually in a subdirectory

[Joe]

Iosif Neitzke <iosif.neitzke+cmake at ...> writes:

> 
> Why not just go one directory up?  Add /path/to/CMakeLists.txt
> containing at least:
> 
> add_subdirectory(A)
> add_subdirectory(B)
> 
> https://github.com/toomuchatonce/cmake-examples/blob/master/staticlibs-
add_subdir/CMakeLists.txt
> 
> On Fri, Sep 18, 2015 at 5:42 PM, Joe <jtcacct at ...> wrote:
> > Hi.  I was hoping to get some guidance on if this is bad practice.  I am
> > simply trying to find a way to manage internal dependencies of my project
> > but with a file structure that is distributed.  It looks like this:
> >
> > /path/to/A
> >
> > /path/to/B
> >
> > B depends on A.  I cannot change this directory structure.  The solution we
> > have chose is to create the following:
> >
> > /path/to/modules/FindA.cmake:
> >
> > ...
> > if (NOT TARGET A)
> >    set(PATH_TO_A ${CMAKE_CURRENT_LIST_DIR}../A)
> >    add_subdirectory(${PATH_TO_A} ${PATH_TO_A}/build)
> > endif()
> > ...
> >
> > This way, A' CMakeLists is invoked and the library is compiled and built.
> > Then in B's CMakeLists.txt:
> >
> > ...
> > set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH}
> >    ${CMAKE_CURRENT_LIST_DIR}/../modules)
> >
> > find_package(A)
> > add_executable(main_B src/main_B.cpp)
> > target_link_libraries(main_B A)
> > ...
> >
> > Is this bad practice?  I tried to figure out find_package in CONFIG mode but
> > every example I've found seems complicated and obtuse.  Thank you.
> >
> >
> >
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Iosif, thanks for the reply. Unfortunately, I do not have control over that
(the long answer is that the projects are arranged in a Clearcase VOB
file structure).  Honestly, what I really need is just a way to invoke a
CMakeLists.txt for a project that lives in a completely arbitrary place
on the filesystem.  I tried to read the documentation, but I can't seem
to figure out if I'm supposed to use ExternalProject_Add or find_package.
If the answer is find_package, I can't seem to tell if I'm supposed to be
using it in MODULE mode or CONFIG mode.  CONFIG mode seems really
confusing, which is why I came up with the approach used in the first post.
Basically, I use add_subdirectory() simply a mechanism to invoke another 
project's CMakeLists.txt.  I could have used include(), but I 
liked the idea of distributing the build by using the second parameter of 
add_subdirectory to build the project in it's own area.