Re: Where should dynamic modules be installed?

[Paul Eggert <eggert@cs.ucla.edu>]

On 10/21/19 3:45 AM, Ulrich Mueller wrote:
> We are going to include the first package with a dynamically loaded
> module (emacs-libvterm) in Gentoo. The question arose where the .so file
> should be installed? Since it is a system dependent binary, installing
> it under /usr/share/emacs/ looks wrong. I cannot find anything about a
> recommended install location in the documentation.

There isn't one. We haven't thought through the issues here. Thanks for 
bringing up the topic.

> Would /usr/lib{,64}/emacs/site-modules/ be a reasonable place for this?

Where do you put executables like hexl, movemail, and profile? I suggest 
puting .so files near there. In Fedora 30, this directory is 
/usr/libexec/emacs/26.2/x86_64-redhat-linux-gnu (which is the value of 
the exec-directory variable). Since modules can be version-specific, it 
makes sense to have the Emacs version number somewhere in the directory 
name. Do you do that with other Emacs directories?

Also, why have "site-" in the name? Do you have "site-" in other 
Emacs-related directory names?

> Also, wouldn't it be cleaner if Emacs had a separate variable (analog to
> image-load-path, custom-theme-load-path, etc.) for loading of dynamic
> modules, instead of reusing load-path?

Emacs should do that, yes. How about if we use a variable named 
'module-directory' for that? It would work like exec-directory, except 
for modules.

I expect that the main reason Emacs doesn't have a variable like 
module-directory now, is that packagers haven't yet encountered the 
Emacs module system (it has been off by default, though that will change 
in Emacs 27) and so haven't run into problems like the one you mention.