Re: [gentoo-dev] ebuild USE priority

[Matthew Kennedy <mkennedy@gentoo.org>]

On Tue, 2002-05-14 at 17:23, Erik Grinaker wrote:
> The ebuild is for the Unix Amiga Emulator, or uae for short. uae allows
> you to select which backend to compile against during ./configure, and
> you can choose *either* x, svgalib, ncurses or sdl.

When creating the xemacs-gamma ebuild I encountered the same dillema.
When you say "*either*", I assume you mean that X, svga, ncurse and sdl
are optional, but mutually exclusive.

> If a user has, say, both X and svga in his USE variable, how do I
> determine whether to use X or svgalib for backend?

XEmacs gamma supports gtk OR motif OR lucid interfaces (each of which
can be considered a use flag) in mutual exclusion. Of course, I don't
want to dictate one of those three to the user, since my preference may
not be theirs.

I thought of a priority scheme, but couldn't see clearly how that would
be done. How did you do it, BTW?

What I ended up doing was checking for an env. var. named USE_PREF which
is localized to xemacs-gamma. It allows the user to merge xemacs-gamma
like this:

   USE_PREF=gtk app-editors/xemacs-gamma

Inside the ebuild, I have a case statement which set the ./configure
flags based on the value of USE_PREF. If no USE_PREF is given, then it
defaults to a reasonable choice ("lucid" in xemacs-gamma's case).

*** Note: USE_PREF is undocumented of course, unused by any other
package AFAIK, and not an official Gentoo thing. ***

Personally, I think my USE_PREF implementation sucks still because it
really messes up RDEPEND/DEPEND. ie. RDEPEND/DEPEND become a function of
USE_PREF.

Perhaps I should have created the following?

   app-editors/xemacs-gamma-gtk
   app-editors/xemacs-gamma-lucid
   app-editors/xemacs-gamma-motif

Ugh. What if you have two sets of mutually exclusive USE flags -- just
multiply out the number of ebuilds you create.

Perhaps I could have one app-editors/xemacs-gamma and build xemacs
several times (one build for every use flag in gtk, motif, lucid),
renaming the final binaries to /usr/bin/xemacs-21.4.8-{gtk,motif,lucid}.
Even provide an xemacs-update script in the spirit of
opengl-update/java-config just to complete my madness :)

(ie. It's not possible to build a gtk, motif AND lucid based xemacs in a
single ./configure)

> According to what I believe is common sense I would prioritize them as
> X, sdl, svga, ncurses - but is there a better way to do this, or do I

Are you using the order in which X, sdl and svga appear in USE? What if
I have X and svga in USE, but I want an svga amiga emulator? That's kind
dillema I'm talking about.

Matt