[gentoo-lisp] dev-scheme/guile:2.0 status update and migration plan

[Cyprien Nicolas]

Hi all. Here is a tentative guide for explaining how to move all
guile stuff in the overlay to the tree, and hope avoiding
forthcoming bugs. This guide is written according to what
I recall for the year and a half since I started slotting guile.

I should have written this a year ago, I was waiting for some Lisp
Project dev to get enough time to dig into guile, but it has not
happened, and more and more packages require their attention.  I did
not find the time to become myself a dev either, and time passes.


I CC proxy-maint@ here, as I volonteer to maintain guile for the time
being, and I think I'm currently the one using the lisp overlay having
the best knowledge in Gentoo's guile status.


Foreword
--------

I used SLOTted guile before I pushed it to the lisp overlay [1].
I had some issues regarding eselect-guile script that I fixed
since. I no longer have any Gentoo machine (my last and main laptop
died two weeks ago), I only have a Gentoo Alt/Prefix amd64-linux on my
work laptop, but I haven't really tested guile-2 on prefix yet. I am
confident with what I have done with guile, but it needs more
testing. Pushing it to the overlay with p.mask will benefit from
flameeyes' tinderbox.

1. http://git.overlays.gentoo.org/gitweb/?p=proj/lisp.git;a=commit;h=8409eb91bf10a18080d33cb0c69797335f5aeec9


Here is a short outline: first I list the new packages that need to be
added to the tree, then review the known issues, and propose
a migration plan.

New Ebuilds
===========


dev-scheme/guile-1.8.8-r2
-------------------------

Same version as in-tree guile-1.8.8-r1, but not compatible with.
I wrote it long ago, and the tree version has been updated since, and
I didn't get it in sync with. Changes summary:

- Bump to EAPI4
- Add +readline in IUSE and sys-libs/readline conditionnal dependency
  using a patch available in $FILESDIR
- It misses the ~arm-linux and ~x64-macos KEYWORDS
- R/Depends on app-admin/eselect-guile (see below)
- 3 configure changes --program-suffix, slotted --infodir and use_with
  readline
- einstall --infodir (I don't remember why it is here, seems redundant
  with configure's parameter)
- Rename the guile.m4 file to guile-1.8.m4
- Remove env file manipulation
- Add eselect guile update ifunset to src_post{inst,rm} phases.

dev-scheme/guile-2.0.9
----------------------

The main change compared to guile-1.8 is the removal of emacs support,
no longer supported by upstream. All the rest of the ebuild seems
mostly trivial.


app-admin/eselect-guile
-----------------------

An eselect module for managing slotted guile versions, barely tested.
Explicit block on <dev-scheme/guile-1.8.8-r2 which is not
properly slotted.


2. Known Issues
===============

app-text/texmacs
----------------

See https://bugs.gentoo.org/show_bug.cgi?id=436400

Won't support guile-2, said grozin. I patched the texmacs build system
to explicitly change all `guile-config` calls to
`guile-config-1.8`. This patch is gentoo-specific and unlikely to be
merged upstream anytime soon, as guile-1.8 does not provide any
pkgconfig interface (guile-2.0 does).

See texmacs-1.0.7.16-r2 in the overlay, here are the differences:
- Change guile dependency to specify the correct slotted version
  1.8.8-r2
- Add a patch (in FILESDIR) to force guile*-1.8 in the build system.

I haven't followed new texmacs releases (tree has 1.0.7.17 and
1.0.7.19).


dev-scheme/greg
---------------

See https://bugs.gentoo.org/show_bug.cgi?id=351991

Almost used by nothing (only one package in sci- needs greg when
FEATURE=test). Needs a proper fix, like texmacs maybe.

Others
------

I have not check all reverse deps, maybe there are more issue to
come. We won't find them until we get all guile stuff in the tree.


3. Migration Plan
=================

Here is how I would move all that, based on my experience, quizes and
documentation I read.

First push app-admin/eselect-guile, as nothing depends on it yet, and
won't block anything. Then push guile-1.8.8-r2, p.mask it, as it may
break several packages in ~arch. Maybe just drop keywords for testing
the slot system?. Then push guile-2.0.9, p.mask or w/o keywords, same
reasons.


This might mot be ideal, it will break texmacs and stuff, but I don't
know of a better way to achieve it yet. Some of you have more
experience here :-).


I hope this helps, feel free to ask any question regarding guile if
needed.  I thank the one who volonteer to make this happen.

Oh, as a sidenote, guile upstream does not really support 1.8 anymore,
they don't have time to, and concentrate all efforts on 2.0, so moving
to guile-2.0 is getting more and more urgent day after day.  I heard
remors that future autogen version will require guile-2.0. The earlier
we push guile-2.0, the more testing window we have.

Cheers,
-- 
Cyprien Nicolas (Fulax)
Gentoo Lisp project contrib