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

[Eric Noulard]

Le jeu. 14 févr. 2019 à 18:57, Timothy Wrona <tjwrona1992 at gmail.com> a
écrit :

> 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.
>

Yes, wrong solution to a real design issue :-)


>
> 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.
>

I understand the situation, I did face that too in the past.
If there is not too much circular deps you may either break them by writing
(by hand) a bunch of imported target or you can merge in the same CMake
project the sub-projects belonging to the same cycle.
Feasibility depends on the amount of projects (and cycle) you have.




>
> 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
>>
>

-- 
Eric
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