[CMake] Why is XXX_INCLUDE_DIRS plural and should it be deep?

[Rolf Eike Beer]

esatel wrote:

> 2. The other sets a similar variable but then does find_package on HDF5 and
> loads the dependencies into NetCDF_INCLUDE_DIRS and NetCDF_LIBRARIES.
> 
> This design (2) cascades. FindHDF5.cmake represents a similar decision about
> whether to find_package its dependencies like the zlib compression library.
> I believe the one in the cmake distro doesn't do that.
> 
> What is the best practice here? To handle dual locations for the library at
> hand or to accumulate or both? The first seems unavoidable ... the second
> seems to be an unevenly applied standard.

My personal vote on this is: if the public headers of package X include 
headers from one of it's dependencies then you should cascade. So if 
<netcdf.h> does

#ifdef WITH_HDF5
#include <hdf5.h>
#endif

then you would get a compile error if the HDF5 include directories are not 
set. If this is just an internal dependency or you would explicitely need to 
include e.g. netcdf/hdf5.h to get that sort of stuff then I would vote for not 
becoming recursive. Which is a "sane" default as most packages will not need 
that recursive approach then.

Eike
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