Re: Suppressing native compilation (short and long term)

[Eli Zaretskii]

> From: David Bremner <david@tethera.net>
> Cc: emacs-devel@gnu.org, akrl@sdf.org, rlb@defaultvalue.org
> Date: Fri, 30 Sep 2022 10:13:56 -0300
> 
> 
> > The reason stated by Rob was that they want to prevent "writing to
> > user's HOME directory".  I don't think I understand the rationale well
> > enough, and I asked some questions about it.  I hope Rob will answer,
> > and then we could continue discussing what is reasonable for that use
> > case.
> 
> For package builds, Debian has the following policy 
> 
>     
> https://www.debian.org/doc/debian-policy/ch-source.html#main-building-script-debian-rules
> 
> in particular
> 
>     Required targets must not attempt to write outside of the unpacked
>     source package tree. There are two exceptions. Firstly, the binary
>     targets may write the binary packages to the parent directory of the
>     unpacked source package tree. Secondly, required targets may write
>     to /tmp, /var/tmp and to the directory specified by the TMPDIR
>     environment variable, but must not depend on the contents of any of
>     these.
> 
>     This restriction is intended to prevent source package builds
>     creating and depending on state outside of themselves, thus
>     affecting multiple independent rebuilds. In particular, the required
>     targets must not attempt to write into HOME.
> 
> Some additional byte compilation happens at package install time.

This is what I'm asking about: what exactly triggers the compilation?
Just installing a package shouldn't do that, only loading it into
Emacs should.

The other part of what I asked is that if for some reason installation
does need to compile files (something that I still need to understand
why it happens), there's nothing that hard-codes HOME in the directory
list used for that.  You can set native-comp-eln-load-path to anything
you want, and only the directories in that list will be used.

> In my
> view the same restrictions should apply there. In addition to the
> unintentional sharing of state mentioned in policy, there is also the
> issue of cleaning up after a package on uninstall. This is manageable
> now because any generated .elc files go in a package specific directory,
> which can just be removed on purging the package.

See above: you can do the same with *.eln files, if, for some reason,
they are produced by the installation.

> I think just turning off native compilation when HOME is not writeable
> would be sensible from a Debian point of view. Emacs did not previously
> require a writable HOME (although maybe most users never tested
> this). It would be unfortunate if this changed for Emacs with native
> compilation support.

Emacs doesn't require a writable HOME, it requires a writable
directory to store *.eln files.  It doesn't have to be HOME.  And once
again, I still don't understand why *.eln files are produced at
installation time in the first place.