Re: Retrieving the "include" directory for Emacs Modules

[Eli Zaretskii <eliz@gnu.org>]

> From: Marco Antoniotti <marcoxa@gmail.com>
> Date: Sun, 8 Dec 2024 16:18:15 +0100
> 
> sorry again: the behavior on Mac and Windows is different w.r.t.
> data-directory (see previous message).  I can try on a Linux machine
> tomorrow.  Note that I installed Emacs with brew on my Mac
> 
> Case in point: if I try to install 'pq' from the package manager I get the
> following error.
> 
> gcc -I/Users/marcoxa/.emacs.d/elpa/pq-0.2 -I -I/usr/share/emacs/29.4
> -I/usr/local/include/postgresql@14 -std=gnu99 -ggdb3 -Wall -fPIC -c
> pq-core.c
> 
> pq-core.c:19:10: fatal error: 'emacs-module.h' file not found
>    19 | #include <emacs-module.h>
>       |          ^~~~~~~~~~~~~~~~
> 1 error generated.
> make: *** [pq-core.o] Error 1
> 
> which is not surprising as the include directory is not listed in the -I
> options.

It shouldn't be: if the compiler cannot find emacs-module.h, then your
Emacs is installed incorrectly.  The installation should put
emacs-module.h where the compiler looks for include files.

> Of course, I can muck around and ensure that the C_INCLUDE_PATH has the
> right things in it, but the issue, as is, IMHO remains.

You shouldn't need to mess with C_INCLUDE_PATH, because emacs-module.h
is supposed to be in the C include path to begin with.

> Having said that, another reason for needing a reliable
> include-directory variable,
> is to query Emacs in batch mode (I know: iti is expensive), to run a build
> system outside Emacs for testing.

Sorry, I don't understand that: what do you mean by "to run a build
system"?