On 11/04/2017 18:24, Wouter Klouwen wrote:
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.
That's not an insurmountable problem. If your projects are buildable in
parallel with the third-party sources, you can add each third-party
source, plus each first-party project, as a separate external project
and then build the entire collection in parallel.
The only thing that's changed with the superbuild vs a completely
self-contained project is the location of the higher-level organisation.
With the superbuild, that is moved out into a separate project which
coordinates the building of everything with appropriate inter-project
dependencies.
Regards,
Roger
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