Re: Goals for 0.4

[Amirouche Boubekki]

I will just add that this feature is available in nixos http://nixos.org/wiki/Nix%28OS%29_related_repositories_and_work

2013/8/30 Cyprien Nicolas <address@hidden>

Il y a 20 heures, Ludovic Courtès écrivit :

> Amirouche Boubekki <address@hidden> skribis:
>
> > What about the possiblity to use overlays ?
>
> Could you elaborate?
>
> I hear this comes from the Gentoo jargon, but I’m not sure what
> that means.

I like the idea.  I'll try to elaborate myself, as a Gentoo user for
years ;-) I describe them from my own experience, official
documentation can be found there [1]

In Gentoo, ebuilds (the files that specify how to build a package from
source) are stored in the "portage tree", which is the official
repository.  The tree consists of directories, one per category, plus
one sub-directory par package, where package directories contains one
or more ebuilds, one ebuild per package version.  (plus some
additional files, like patches.)

"Portage" (the tool used to install packages from source, through the
"emerge" command) looks for ebuild in that directory, but it can also
looks from other directories which follow the same structure, those
directories are called "overlays", as they can mask packages from the
official tree, but also extend it.

They are plenty of overlays usage: experimental packages,
user-contributed packages, locally used packages for testing purposes…


However, overlay create new concerns.  First, priority of overlays, if
two provide the same package-version combination, which one to choose?
If Overlay A provide Package P, which depends on Library L, not in
Overlay A but in the "base" repository, and that Overlay B provide
a newer version of Library L, which L to choose?

Handling build failure of packages using overlays can be quite tricky
too. ;-)

And last, how and where to "centralize" overlays, in order to give
user a tool to easily add, remove, update overlays.


1. http://www.gentoo.org/proj/en/overlays/userguide.xml

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Cyprien/Fulax