[cmake-developers] why can target_include_directories() not be applied to custom targets?

[Attila Krasznahorkay]

Hi,

Just to say that setting INCLUDE_DIRECTORIES on a custom target is indeed a bit of an obscure thing, but we do use it. You can find the full reasoning in:

https://gitlab.kitware.com/cmake/cmake/issues/16830

Because of that, I understood that CMake will provide this functionality in the future as well, so we can rely on this build setup.

Cheers,
          Attila

> On 8 Jul 2018, at 12:16, Petr Kmoch <petr.kmoch at gmail.com> wrote:
> 
> Hi Drew,
> 
> a custom target can do literally anything, it's just a buildsystem wrapper for running arbitrary executables; or often not even that, and is just a collection of custom commands. There is nothing CMake automatically does with the properties [INTERFACE_]INCLUDE_DIRECTORIES set on a custom command.
> 
> Note that if you need the properties set for some reason (i.e. if your custom command/target code uses them for something), you can still set them just fine using set_property() or set_target_properties(). However, I expect this to be a very rare thing to do, so I think it's OK target_include_directories() actually errors out on custom targets. IMO it's much more likely that a non-custom target was intended.
> 
> (Note that I am just an ordinary CMake user, so the above is in no way "official.")
> 
> Petr
> 
> On 7 July 2018 at 21:27, Drew Parsons <dparsons at debian.org> wrote:
> Commit 510fdcb18801076e2041eaae2941375eecc93ec2 at
> https://gitlab.kitware.com/cmake/cmake/commit/510fdcb18801076e2041eaae2941375eecc93ec2
> prevents custom targets from using target_include_directories().
> 
> This makes no sense to me.  A custom target is still a target. It needs
> to be compiled, it uses -I flags.
> 
> Can you explain the ban on applying target_include_directories() to
> custom targets?
> 
> Drew
> 
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