[Nix-dev] Rust prebuilt package overlay.

[Nicolas Pierron]

Hi list,

# Motivation

I saw an issue on github the other day about Rust packaging #23291.  I
have faced the problem that Rust nightly version was not enough for
building rustc out of the repository.

Rust nightly is probably changing too frequently to be maintained
within Nixpkgs #8697.  Also, Firefox developer, I will need to follow
Rust versions as soon as they are packaged and updated in Firefox.

The recommended way for developing Firefox is to periodically run
rustup (every ~6 weeks), which is sad from my point of view.  As I
rely on nixpkgs-mozilla [1] repository to generate the build
environment I use, I decided to tackle the issue inherent of having
recent version of rustc & cargo.

# What

I created an overlay which mimic rustup behaviour, and allow you to
spawn a nix-shell with the latest nightly, beta, or stable version of
rustc & cargo.

To use this overlay, checkout nixpkgs-mozilla [1], and create a
symbolic link to the file rust-overlay.nix [2] in the
~/.config/nixpkgs/overlays

  $ cd ~/
  $ git clone https://github.com/mozilla/nixpkgs-mozilla.git
  $ mkdir -p  ~/.config/nixpkgs/overlays
  $ ln -s ~/nixpkgs-mozilla/rust-overlay.nix
~/.config/nixpkgs/overlays/rust-overlay.nix

Once installed, you can install the latest versions with the following commands:

  $ nix-env -Ai nixos.rustChannels.stable.rust

Or use this attribute to build a nix-shell environment which pull the
latest version of rust for you when you enter it.

You can substitute the "stable" channel by "nightly" and "beta", or
use the function provided by this overlay to pull a version based on a
build date.

# How

This overlay should auto-update it-self as if you were running rustup
each time you go through the rustChannels attributes.  It works by
using the fetchurl builtin function to pull the same file as rustup do
through https.

The *.toml manifest file is then parsed (yes, in Nix [3]) to extract
the sha256 and the location of all the packages indexed by the
manifest file.  Then, some logic is used [2] to convert the *.toml
file into proper derivations which are used to pull the prebuilt
binaries and to change the interpreter of the binaries using patchelf.

If you encounter issue, feel free to report them on the
nixpkgs-mozilla repository [1], and to fix them as well ;)

Have fun and enjoy.

#23291: https://github.com/NixOS/nixpkgs/issues/23291
#8697: https://github.com/NixOS/nixpkgs/issues/8697
[1] https://github.com/mozilla/nixpkgs-mozilla
[2] https://github.com/mozilla/nixpkgs-mozilla/blob/master/rust-overlay.nix
[3] https://github.com/mozilla/nixpkgs-mozilla/blob/master/lib/parseTOML.nix

-- 
Nicolas Pierron
http://www.linkedin.com/in/nicolasbpierron - http://nbp.name/