[vtk-developers] Should VTK targets have INTERFACE_{INCLUDE_DIRECTORIES, COMPILE_DEFINITIONS} set?

[Robert Maynard]

Hi Elvis,

The VTK module system was developed to support versions of CMake that
didn't support INTERFACE_ properties and all the other nice features of
Modern CMake. Now that VTK requires CMake 3.3+ it would be possible to
update the module system to provide this support. I believe that other
developers are interested in this effort, but I am not aware of an explicit
timeline.

On Sun, May 28, 2017 at 11:53 AM, Elvis Stansvik <
elvis.stansvik at orexplore.com> wrote:

> 2017-05-28 17:30 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> > Hi all,
> >
> > When linking against a VTK module through an imported target, e.g
> >
> >   find_package(VTK 8.0.0 REQUIRED COMPONENTS vtkCommonCore)
> >   ...
> >   target_link_libraries(myapp vtkCommonCore)
> >
> > I must still manually make sure I use
> >
> >   target_include_directories(myapp PUBLIC ${VTK_INCLUDE_DIRS})
> >   ...
> >   target_compile_definitions(myapp PUBLIC ${VTK_DEFINITIONS})
> >
> > to get the include directories and definitions.
> >
> > This is in contrast to e.g. Qt's CMake files, which makes sure targets
> > have INTERFACE_INCLUDE_DIRECTORIES and INTERFACE_COMPILE_DEFINITIONS
> > set on its targets. For example, QtSvg (from Qt5SvgConfig.cmake):
> >
> >     set_property(TARGET Qt5::Svg PROPERTY
> >       INTERFACE_INCLUDE_DIRECTORIES ${_Qt5Svg_OWN_INCLUDE_DIRS})
> >     set_property(TARGET Qt5::Svg PROPERTY
> >       INTERFACE_COMPILE_DEFINITIONS QT_SVG_LIB)
> >
> > Now, this is not really a bit inconvenience, I just have to make sure
> > to add ${VTK_INCLUDE_DIRS} and ${VTK_DEFINITIONS}.
> >
> > However, I recently started using the libclang-based
> > include-what-you-use tool [1] to help sanitize my header inclusions.
> > The tool will make suggestions such as (taking a Qt header as example
> > here):
> >
> > /home/estan/orexplore/insight/src/model/HoleLoader.cpp should add these
> lines:
> > #include <QFileInfo> // for QFileInfo
> >
> > I noticed that for a VTK header, it'll instead suggest e.g:
> >
> > /home/estan/orexplore/insight/src/model/Hole.cpp should add these lines:
> > #include "vtkSmartPointer.h" // for vtkSmartPointer
> >
> > Notice the "" instead of <>.
> >
> > I dug into include-what-you-use to find out why this is happening, and
> > it's because on the compile line, the Qt include directories are given
> > with -isystem, while the VTK include directories are given with -I,
> > and -isystem vs -I is what the tool uses (for lack of other
> > information) to determine whether to suggest the inclusion with <> or
> > with "".
> >
> > I believe that maybe the -I flags added for VTK would become -isystem,
> > if they were brought in through the INTERFACE_INCLUDE_DIRECTORIES
> > mechanism, same as Qt.
> >
> > So all this lead me to two questions regarding VTK:
> >
> > 1. Should VTK's installed CMake files perhaps make sure
> > INTERFACE_INCLUDE_DIRECTORIES and INTERFACE_INCLUDE_DEFINITIONS are
> > set on its exported targets?
> >
> > 2. If not, anyone know if there's something that could be done to make
> > the flags end up as -isystem flags instead of -I when using
> > ${VTK_INCLUDE_DIRS}?
>
> Disregard this question: I realized that I could simply use SYSTEM in
> my target_include_directories(...) to make CMake treat it as a system
> include directory, which makes it use -isystem on compilers that
> support it.
>
> So then it's only question 1 left. I think it would be nice to have
> INTERFACE_{INCLUDE_DIRECTORIES,DEFINITIONS} set on the targets, just
> to avoid having to add ${VTK_INCLUDE_DIRS} and ${VTK_DEFINITIONS}
> manually.
>
> Elvis
>
> >
> > Cheers,
> > Elvis
> >
> > [1] https://github.com/include-what-you-use/include-what-you-use
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