-isystem /usr/include doesn't work with gcc6 about openvdb HOT 6 CLOSED

I can reproduce this with gcc 9.1.
To fix it, just set option in CMake to not use isystem from imported targets, I found the reference in the CMake maillist here:

cmake ../src -DCMAKE_NO_SYSTEM_FROM_IMPORTED:BOOL=TRUE 

This is the first time I faced this in CMake, probably has to do with the way (non standard?) OpenVDB is importing targets.

from openvdb.

Since /usr/include/ is searched by default, you can set *_INCL_DIR to some nonexistent directory, or to an existing directory that contains no headers. Or just change -isystem to -I, if you don't mind seeing lots of compiler warnings.

from openvdb.

Thanks for the trick @phcerdan, same happens here for llvm builds on openSUSE Tumbleweed (a rolling release). Here's the public build: https://build.opensuse.org/package/live_build_log/home:frispete:blender/openvdb/openSUSE_Tumbleweed/x86_64
BTW, the build triggers (a few too) many warnings due to some openexr/tbb deprecations.

A further note on packaging: it happens, that the library base is not /usr/lib for some 64bit distributions.
check the less than optimal %prep section of: https://build.opensuse.org/package/view_file/home:frispete:blender/openvdb/openvdb.spec?expand=1

from openvdb.

Shouldn't the usage of concerned cmake flag be mentioned in README building section?

from openvdb.

More proper fix may be removing ${IlmBase_INCLUDE_DIR}/../
in

https://github.com/AcademySoftwareFoundation/openvdb/blob/master/cmake/FindIlmBase.cmake#L325

(and do same thing for FindOpenEXR.cmake)

This path is expanded to /usr/include/OpenEXR/.. in apt installed OpenEXR(IlmBase) on Ubuntu 18.04.

I have confirmed OpenVDB compiles fine at least on Ubuntu 18.04 by deleting these include paths.

from openvdb.

Same issue on master commit f077a14
The fix -DCMAKE_NO_SYSTEM_FROM_IMPORTED:BOOL=TRUE works but can't compile without

from openvdb.