[CMake] Is there a way to delay "find_package" until link-time when the package is actually needed?

[Timothy Wrona]

The problem is it is very likely that there are some circular dependencies
in the build tree -- which is why it was broken up to generation of all,
then build all, then link all in the first place.

With circular dependencies there's no real way to sort these dependencies
out without just running generation twice, but the first run will get a
bunch of errors for missing packages.

On Thu, Feb 14, 2019 at 12:38 PM Eric Noulard <eric.noulard at gmail.com>
wrote:

>
>
> Le jeu. 14 févr. 2019 à 18:22, Timothy Wrona <tjwrona1992 at gmail.com> a
> écrit :
>
>> I have a collection of interdependent CMake projects (lots of legacy
>> code) that I want to convert to using CMake targets for linking. The code
>> is built in such a way that all projects run cmake generation, then all
>> projects build, then all projects link.
>>
>> I would like to export a CMake target from one of the projects and link
>> to it in another, but the issue is the project I am exporting from runs its
>> cmake generation AFTER the project I am linking the target in. This causes
>> "find_package" to fail because the target has not been exported yet, but
>> realistically the exported target is not needed until link-time.
>>
>
> This heavily depends on the target. Modern CMake target convey compile
> time information as well like compile flags, include directory etc...
>
> Can't you re-order the cmake generation order of your projects?
> If you [ever] have the graph dependency of your projects you may
> topologically sort them in order to avoid this issue and superbuild them in
> appropriate order.
>
>
>> Is there a way to delay "find_package" to not look for the package until
>> link-time?
>>
>
> I don't think so.
>
>
>> At link-time the package will have been exported already and if
>> "find_package" was not called until then, it would be found successfully
>> and the target could be pulled in and linked to.
>>
>
> But the build compile line options used to generate build system files are
> computed during CMake configuration/generation step.
> So I don't think what you ask is possible.
>
> --
> Eric
>
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