[Nix-dev] Re: Tahoe-LAFS in NixOS

[Zooko Wilcox-O'Hearn]

On Sunday, 2009-12-13, at 15:54 , Ludovic Courtès wrote:

>> http://allmydata.org/pipermail/tahoe-dev/2009-December/003279.html
>
> At first sight it seems like a bit of overhead I’d like to avoid  
> these days.

Ah, too bad.  It really isn't that much work, but it kind of "looks"  
like a lot of work when you look at the instructions.

> Indeed, that seems to be an interesting approach.  However, is it  
> 100% automatic or 90%ish?  If the latter (which I suspect from my  
> experience packaging several Python libs), I wonder whether it’s a  
> big win in terms of the time spent packaging a given piece of  
> software.  What do you think?

The declarations of dependencies within the Python code [1] are 100%  
accurate -- they list all the Python packages (which Python calls  
"distributions" instead of "packages") that Tahoe-LAFS needs.  The  
question is how to map from Python "distributions" to NixOS  
packages.  For example, given that Tahoe-LAFS requires a Python  
"distribution" named "Twisted >= 2.4.0", how does this hypothetical  
automated tool determine that the Nixpkg named  
"pythonPackages.Twisted 8.2.0" will satisfy?

I suspect that a heuristic like prepending "pythonPackages." to the  
distribution name would be one of those 90% solutions, because  
occasionally a Python distribution will have a name different from  
the name of the operating system package that houses it.  Unless I'm  
wrong and NixOS has a strong policy about making them always match.

It is certainly not a 100% solution for Debian/Ubuntu, so the way we  
did this in stdeb [3] was to use a database which has all of the  
paths and filenames of all of the packages (the "apt-file" database),  
and look for a file named "Twisted-8.2.0.egg-info".  A well-packaged  
Python distribution should have such a file if and only if it  
provides the "Twisted" distribution, v8.2.0.  For the uses that I  
have put it to, this hack works 100%.

Regards,

Zooko

[1] http://allmydata.org/trac/tahoe/browser/_auto_deps.py
[2] https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/top-level/ 
python-packages.nix
[3] http://github.com/astraw/stdeb