Re: Retrieving the "include" directory for Emacs Modules

["Björn Bidar" <bjorn.bidar@thaodan.de>]

Stefan Monnier via Users list for the GNU Emacs text editor
<help-gnu-emacs@gnu.org> writes:

>>> > As I tried to explain, if emacs-module.h is not installed in its
>>> > intended place, we cannot know where it is installed.
>>> The patch below would make sure that `emacs-module.h` is always
>>> available at `$(data-directory)/include/emacs-module.h`.
>> Sorry, this is wrong. [...] this is a change that will break previous
>> (and correct) behavior.
>
> I don't see how it would break anything: the .h file is still *also*
> copied to the $(includedir) for those people who want to compile their
> module outside of Emacs.
>
>> No compiler will look in that directory without a suitable -I option,
>
> That's OK: the sole purpose of the change is to let ELPA packages call
> `gcc` with such a `-I`!
>

Which is wrong for Unix-like systems except on macOS.

It's debatable if packages should compile their native modules
themselves but if they do they shouldn't change all systems just to
accommodate macOS and Windows.

Why not install the Emacs module header to PREFIX/include on these
platforms and deduct the path of the header similarly to how
eln-dest-dir is determined?