Improving how NGINX modules are used and built

[mirai <mirai@makinata.eu>]

Consider the following nginx-configuration modules field snippet from Guix docs:

--8<---------------cut here---------------start------------->8---
(modules
 (list
  (file-append nginx-accept-language-module "\
/etc/nginx/modules/ngx_http_accept_language_module.so")
  (file-append nginx-lua-module "\
/etc/nginx/modules/ngx_http_lua_module.so")))
--8<---------------cut here---------------end--------------->8---

It is unclear at all how an arbitrary nginx module should be added given that
one needs to append the package object with a path to the modules .so file.
This .so name can only be found by listing the files from the package object
which adds further obscurity to what should have been:

--8<---------------cut here---------------start------------->8---
(modules
 (list nginx-accept-language-module nginx-lua-module))
--8<---------------cut here---------------end--------------->8---

An oddity of how nginx modules are packaged in guix is that they all place
the .so file under /etc/nginx/modules which is an odd directory to place library object files.
Compared against other distributions, they tend to place the .so files under /usr/lib64/nginx
and a .conf file under /usr/share/nginx/modules that contains

--8<---------------cut here---------------start------------->8---
load_module "/usr/lib64/nginx/modules/ngx_foo_module.so";
--8<---------------cut here---------------end--------------->8---

My guess is that the intention behind
(file-append nginx-foo-module "/etc/nginx/modules/ngx_foo.so") is that
it was supposed to replicate the .conf behavior but inadvertently ended up being
used as a place for .so files.

Looking at how network-manager-configuration handles its vpn-plugins field, it seems doable
that a similar approach can be used here.
The existing nginx-modules should be changed to install their .so files under lib{64}/nginx
instead and they should drop a etc/nginx/modules/foo_module.conf file responsible for loading
the module from the .so file. Including modules through a .conf should be preferred as
there's no guarantee that a module is a .so file or that it is always a
_single_ .so file but in general this file should typically be a one-line .conf file containing:

--8<---------------cut here---------------start------------->8---
load_module "/gnu/store/......nginx-foo-module/usr/lib64/nginx/ngx_foo_module.so";
--8<---------------cut here---------------end--------------->8---

And nginx-configuration should serialize the modules field as a series of lines including
the module .conf files, that is:

--8<---------------cut here---------------start------------->8---
include "/gnu/store/......nginx-foo-module/etc/nginx/modules/ngx_foo_module.conf";
include "/gnu/store/......nginx-bar-module/etc/nginx/modules/ngx_bar_module.conf";
...
--8<---------------cut here---------------end--------------->8---
(note: a directory union could be used here as an alternative)


On a related note, given how nginx-modules are expected to be built and linked against the
same nginx build, a new nginx-build-system for nginx modules could be considered as the few
existing nginx modules in guix are for the most part a copy-paste of each other with some
modifications here-and-there.

Thoughts?

Regards,
Bruno