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

[Elvis Stansvik]

2017-05-30 15:59 GMT+02:00 Robert Maynard <robert.maynard at kitware.com>:
> 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.

Ah right, I realized afterwards that older CMake support might be the reason.

Did not know about the minimum version bump, but that sounds promising then.

Thanks,
Elvis

>
> 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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>