[CMake] Subdirectories and FIND_LIBRARY routines

[Rolf Eike Beer]

Am Monday 26 July 2010 schrieb Michael Wild:

> The build_thirdparty macro
calls itself other macros, e.g. build_zlib. That
> one "guesses" the output
location of the zlib libraries, creates an
> IMPORTED library target and
sets XXX_LIBRARIES accordingly.
> 
> The problem of finding the output
location of external projects has been
> discussed quite a few times, and
there is only one really clean, although
> complex and confusing solution:
There is one "master" project which only
> makes calls to
ExternalProject_Add, even the main project is build as such
> an external
project.

Which sucks at other places: we some such "master" projects that
pull in a ton of other projects. But sometimes we just want to build one of
these subprojects and not a monster which 500+ projects (takes about an hour
to build on a recent DualCore with MSVC2008). So we have a macro
ADD_SUBDIRECTORY_ONCE that works like ADD_SUBDIRECTORY but checks the cache
if that directory has already been included. Now every subproject can
A_S_ONCE all of it's dependencies so you can start at many places in the
tree and get a correct build. Next problem is when the place where A_S_ONCE
was called first (and which pushed it's absolute path into the cache) get's
removed from the tree as noone then is including that needed dependency
anymore. Nightmare again. Luckyly that doesn't happen too often...

Eike
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