[Nix-dev] Updating emacs-snapshot package

[Phil Hagelberg]

Shea Levy <shea at shealevy.com> writes:

>>> It’s not Nixpkgs, it’s Emacs.  :-)  So it has its own channel, at
>>> <http://hydra.nixos.org/jobset/gnu/emacs-trunk/channel/latest/MANIFEST>.
>>> But you can’t really use it easily.
>> I don't understand the distinction. Is keeping it in its own channel
>> comparable to the way PPAs (Personal Package Archives) work in Ubuntu?
>
> Not quite. Nixpkgs is a package repository (well, a package recipe
> repository), emacs is a text editor, and hydra is a continuous build
> system that, among other things, makes its build results available via
> a nix channel. AFAIK, the primary purpose of building nixpkgs with
> hydra is to have the latest packages easily downloadable for nixpkgs
> users. AFAIK, the primary purpose of building emacs with hydra is to
> do continuous integration testing of the latest emacs source code,
> with the existence of the emacs-trunk channel being just a happy
> side-effect.

Oh, OK; so the whole purpose is different. I guess what I don't
understand is why the Emacs hydra build .nix file isn't also used by the
emacs-snapshot package in nixpkgs, since that package is extremely out
of date.

Is it just discouraged to package prerelease versions of software in
general? If it's merely a question of stability then it shouldn't be a
problem; the Emacs 24 pretest is very stable.

> In the example in the manual, the path downloaded corresponds to the
> highest-versioned package named 'firefox' in the nixpkgs repo. In
> other words, nix has access to a nix expression that defines that
> firefox, it tries to build it, and sees its already built. In your
> example, you haven't told nix where to find the nix expression
> defining emacs, so nix has no way to see that the path you downloaded
> corresponds to 'emacs', so you have to specify the path directly.
> Trying 'nix-env -i emacs' will just build the version of emacs
> specified in nixpkgs, which is obviously not the snapshot version you
> downloaded.

Thanks, that makes sense.

-Phil