Re: Automatically saving package sources

[Stefan Kangas]

sbaugh@catern.com writes:

> It is nice for installed ELPA packages to be reinstalled when Emacs is
> upgraded or changed, since there can be changes to autoload generation,
> the byte compiler, the native compiler, or other things which will
> change the output from the package installation.

Yup, this is a long-standing problem.

I think there are some bugs in the bug tracker about it too.  Maybe they
can give some ideas.

> Furthermore, it is nice (where possible) for this reinstallation to
> happen with the same version of the package rather than by fetching the
> latest version from ELPA.  This minimizes the number of changes that
> happen at once.
>
> However, right now there is no easy way to reinstall a package from the
> same sources it was originally installed from, because those sources are
> not saved separately from the package itself.  They are all mixed
> together in the installed package directory.  This makes it impossible
> to produce a "clean slate" environment for reinstalling the package,
> which (since packages can create arbitrary files during
> byte-compilation) means the package can't be reinstalled in a way that's
> identical to its original installation.
>
> If package.el supported saving the package source separately, however,
> it could simply reinstall from that.
>
> I would like to add an option package-save-sources which makes
> package.el automatically save the package source for the currently
> installed package version in a separate directory.  Perhaps in
> ~/.emacs.d/elpa-sources.
>
> When package-save-sources is enabled, then package-reinstall would
> reinstall a package from the saved source rather than upgrading the
> package.  package-upgrade would delete the saved source and fetch a new
> version.
>
> Does this seem like a reasonable feature to add?

Yes, I think it could be useful.  I'm copying in Stefan Monnier too.

One complication that immediately comes to mind is how to find the
sources of those packages from *Help*.  I think it will expect to find
them in ~/.emacs.d/elpa rather than ~/.emacs.d/elpa-sources if the
package is loaded from there.  Maybe some special handling is needed.

Also, do we need to put it behind an option?  I guess I don't understand
the use-case for _not_ wanting this feature.

> As an additional benefit, elpa-sources would be useful for reviewing
> changes in the source when upgrading packages.  It could be optionally
> maintained as a VCS repository, with packages saved to a constant path
> based on their name (e.g. elpa-sources/xref.el instead of
> elpa-sources/xref-1.2.3/xref.el).  Then a VCS could be used to review
> the diff resulting from an upgrade.  This would be useful for any user
> who wants to scrutinize package code changes before installing them.