[cmake-developers] External projects & library dependencies

[Wouter Klouwen]

Hi Brad,

thanks for taking the time to reply.

On 11/04/17 18:00, Brad King wrote:
> On 04/11/2017 12:33 PM, Wouter Klouwen wrote:
>> So in order to create a mega project I want to put all of the third
>> party packages into the build system using ExternalProject_Add.
>> This function does provide for targets in terms of build dependencies,
>> but this isn't quite enough. I need these packages to convey information
>> in the same way as was done through pkg-config files and provide
>> COMPILE_OPTIONS, INCLUDE_DIRECTORIES and LINK_LIBRARIES.
>>
>> All of this information is present once the ExternalProject is built as
>> it would be possible to invoke pkg-config afterwards. This is of course
>> too late for CMake to resolve this information at configure/build rule
>> creation time.
>>
>> Is there a better way of solving this other than effectively duplicating
>> the information in the pkg-config files so that CMake can read it at
>> generation time?
>
> Make your outer project a "superbuild" that does not compile anything
> itself but instead just uses ExternalProject_Add to build everything
> else in dependency order.  That way each project won't configure until
> all its dependencies are built.

Unfortunately this isn't really an option for us. There's a non trivial
amount of third party packages that take a non trivial amount of time to
compile.
Waiting for all of these to compile while not yet starting on our own
projects would create a very long critical path before the build could
fan out for all targets. This would have a detrimental impact on our
build performance.

I appreciate it's not a usual problem as this is for an embedded
platform where we have to cross build everything from scratch.

Thanks,
     W


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