buildRustPackage fails with cargo 0.10.0

[the-kenny]

Issue description

buildRustPackage fails with cargo-0.10.0. I located two issues:

• Cargo tries to create a lockfile in $CARGO_HOME/registry/index/$indexHash/.cargo-index.lock

This is easily fixed by creating a symlink-tree instead of linking $indexHash to the nix-store directly.

• Cargo tries to fetch the registry from file:///dev/null

I don't seem to be able to track this one down. See the following output (with RUST_LOG=debug set):

these derivations will be built:
  /nix/store/xmhh0dypjnhcd49ykss8c3x4bxjvp9xi-rustfmt-0.4.drv
building path(s) ‘/nix/store/dlch40w9lvia203zyk8qnqn8mh97m7lf-rustfmt-0.4’
unpacking sources
unpacking source archive /nix/store/i0q0g2fg3xhhzcyv4y95gh74zkn9j2gc-rustfmt-19768da5c97c108a05e6f545b73ba4b76d1b1788-src
source root is rustfmt-19768da5c97c108a05e6f545b73ba4b76d1b1788-src
Using cargo deps from /nix/store/k3mxzp6n0sp4bszhklp02y8g2vrrb2zs-rustfmt-0.4-fetch
Using indexHash '-2304f9dd481834b8'
DEBUG:cargo::core::registry: load/missing  file:///tmp/nix-build-rustfmt-0.4.drv-0/rustfmt-19768da5c97c108a05e6f545b73ba4b76d1b1788-src
DEBUG:cargo::core::registry: load/missing  registry file:///dev/null
    Updating registry `file:///dev/null`
DEBUG:cargo: handle_error; err=CliError { error: ChainedError { error: failed to fetch `file:///dev/null`, cause: Error { code: -1, klass: 6, message: "Could not find repository from \'/dev/null\'" } }, unknown:
true, exit_code: 101 }
error: An unknown error occurred

The source for rustfmt is at /tmp/nix-build-rustfmt-0.4.drv-0/rustfmt-19768da5c97c108a05e6f545b73ba4b76d1b1788-src - I don't know why cargo thinks it's missing. Looking at the implementation of cargo (registry.rs:93) doesn't really help.

Steps to reproduce

git clone git@github.com:the-kenny/nixpkgs.git --branch rust-cargo-0.10.0
cd nixpkgs
nix-build . -A rustfmt

[dvc94ch]

This worked for me:

runCommand "rustRegistry-${version}-${builtins.substring 0 7 rev}" { inherit src; } ''
  # For some reason, cargo doesn't like fetchgit's git repositories, not even
  # if we set leaveDotGit to true, set the fetchgit branch to 'master' and clone
  # the repository (tested with registry rev
  # 965b634156cc5c6f10c7a458392bfd6f27436e7e), failing with the message:
  #
  # "Target OID for the reference doesn't exist on the repository"
  #
  # So we'll just have to create a new git repository from scratch with the
  # contents downloaded with fetchgit...

  mkdir -p $out

  cp -r ${src}/* $out/

  cd $out

  git="${git}/bin/git"

  $git init
  $git config --local user.email "example@example.com"
  $git config --local user.name "example"
  $git add .
  $git commit -m 'Rust registry commit'

  touch $out/touch . "$out/.cargo-index-lock"
''

[the-kenny]

@dvc94ch I'll give it a try, thanks.

[the-kenny]

Looks good - I'll test a bit more and push it if everything works.

[the-kenny]

Just a note: Before merging I'd like to give rust-lang/cargo#2361 a try and see if we can use it. Might be a cleaner and upstream-supported solution.

[the-kenny]

Pushed the updates with the workaround shown above. They seem to work fine with the packages rust tools and my personal packages.

[dvc94ch]

unrelated question, if you're not too busy, do you mind merging my PR #15606? :) It would be greatly appreciated...