Re: Sharing native-lisp system load-path between builds

[Andrea Corallo]

Björn Bidar <bjorn.bidar@thaodan.de> writes:

> Eli Zaretskii <eliz@gnu.org> writes:
>
>>> From: Björn Bidar <bjorn.bidar@thaodan.de>
>>> Date: Mon, 26 Jun 2023 03:14:17 +0300
>>> 
>>> I'm building Emacs master for OpenSUSE to provide testing.
>>> OpenSUSE packaging packages Emacs so that they have three builds with
>>> different feature sets: X11 without GTK, GTK and one build just without
>>> X11 or GTK.
>>> 
>>> This helps different users to chose their preferred builds and keeps
>>> build workers small for Emacs packages build.
>>> 
>>> The packages share the elisp, native-lisp ahead of time compilations and
>>> docs.
>>> 
>>> Recently the native-lisp load path changed to change per Emacs
>>> executable.
>>
>> It isn't a recent change, at least not in principle.
>
> What could have change this?
>
>>> I don't know the exact commit when this changed but it was
>>> between ref 3c8167ec0f9647e6fc33e65b0a0324f96cb795ee and
>>> d46a2fa319808963bbe8d3a90e7dbb13fcd844f5.
>>> 
>>> Now my questions: Is this a bug or can a different hash be used to
>>> determine the system load-path? It is very useful to precompile the
>>> lisp code once per emacs builds that share the same code.
>>
>> It's impossible to share native-compiled *.eln files between different
>> builds, because they depend on the primitives compiled into the build
>> and on the architecture of the host CPU.
>
>> So you must have a separate directory for each build configuration,
>> and any significant change in the Emacs C code will require
>> recompilation of all the *.eln files.
>
> Each build configuration is 100% the same except the optional
> dependencies they are build with.
>
> There's no change to any source they are build one after the other.
>
> See the spec file here:
> https://build.opensuse.org/package/view_file/home:Thaodan:emacs/emacs/emacs.spec?expand=1

The hash depends on the set of C primitives present in Emacs.  If the
hash differs it means your configurations are producing Emacsen with
different sets of primitives, and this makes eln files incompatible.

Best Regards

  Andrea