> On Aug 25, 2017, at 11:21 AM, Robert Dailey <rcdailey.li...@gmail.com> wrote:
>
> So I've been studying the find_package[1] and "creating packages"[2]
> documentation, as well as the CMakePackageConfigHelpers[3] page.
>
> Based on the current offerings of configuration packages, I do not
> understand the need for the relocatable config.cmake file when all it
> really contains is:
>
> include(${CMAKE_CURRENT_LIST_DIR}/foo-config.cmake)
In general, if the library does not have any dependencies, you can just export
the targets directly to the config.cmake file:
install(TARGETS foo EXPORT foo-config)
install(EXPORT foo-config DESTINATION lib/cmake/foo)
However, if the library has dependencies, you will need to iterate over them in
the config.cmake file. That is if `foo` uses zlib, like this:
find_package(ZLIB)
target_link_libraries(foo ZLIB::ZLIB)
Then the foo-config.cmake needs to do this(assuming the export targets are
written to foo-targets):
include(CMakeFindDependencyMacro)
find_dependency(ZLIB)
include("${CMAKE_CURRENT_LIST_DIR}/foo-targets.cmake”)
The reason for this is that the imported foo target will link against
ZLIB::ZLIB, but it will not define it. Actually, the generated
foo-targets.cmake will create an error if ZLIB::ZLIB doesn’t exists, which is
why `find_dependency(ZLIB)`(which is really just `find_package` underneath)
needs to be called before including the foo-targets.cmake.
Hopefully that makes sense.
>
> However, what I'm wondering is even though the import targets should
> contain all information about include directories, libraries, etc,
> should I still define the typical Foo_INCLUDE_DIRS, Foo_LIBRARIES
> variables? Example of what foo-config.cmake would be like:
>
> include(${CMAKE_CURRENT_LIST_DIR}/foo-config.cmake)
> set( Foo_INCLUDE_DIRS "... path here...." )
> set( Foo_LIBRARIES "List of libraries here...” )
In general, defining relocatable variables like `Foo_INCLUDE_DIRS` was more
common in with cmake 2.8. With modern cmake using just the imported targets is
much better then dealing with all those variables and trying to make them
relocatable.
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