buildRustPackage is broken

[dermetfan]

Issue description

pkgs.rust.buildRustPackage fails every time since I upgraded to nixpkgs 17.03pre101839.53a2baa.

This is perhaps also a chance to fix #22737.

In this example project:

❯ nix-build
these derivations will be built:
  /nix/store/7z80g4d5cc4n621vl28wzd23265cgcsz-cursedlife.drv
building path(s) ‘/nix/store/j2ify6k0kfay56mhwpzasdl1w46bqk3r-cursedlife’
unpacking sources
unpacking source archive /nix/store/9r24d70n0kzxx3zrlwp8jnnkai92giqn-cursedlife
source root is cursedlife
Using cargo deps from /nix/store/hyj7wbcfirjdx8min1wxdfaizsdsy617-cursedlife-fetch
Using indexHash '-ba82b75dd6681d6f'
Using rust registry from /nix/store/p07f0q58fvszdgjfg73i73g03jaxkfx8-rustRegistry-2017-02-19-d822c58
warning: custom registry support via the `registry.index` configuration is being removed, this functionality will not work in the future
error: failed to load source for a dependency on `ncurses`

Caused by:
  Unable to update registry file:///dev/null

Caused by:
  failed to open: /tmp/nix-build-cursedlife.drv-0/deps/registry/index/-ba82b75dd6681d6f/.cargo-index-lock

To learn more, run the command again with --verbose.
builder for ‘/nix/store/7z80g4d5cc4n621vl28wzd23265cgcsz-cursedlife.drv’ failed with exit code 101
error: build of ‘/nix/store/7z80g4d5cc4n621vl28wzd23265cgcsz-cursedlife.drv’ failed

The error message (Unable to update registry file:///dev/null) indicates that the behavior described in this code comment has changed. @wizeman?

Technical details

• System: 17.03pre101839.53a2baa (Gorilla)
• Nix version: nix-env (Nix) 1.11.6
• Nixpkgs version: 17.03pre101839.53a2baa

[grahamc]

I'm experiencing this same problem while building the NixOS/Security tools.

[globin]

ping @wizeman

[grahamc]

This was broken here: #22987 and I'm seeing extremely suspicious behavior:

1. With master, build NixOS/security, see it fail (note you'll need to update the depsSha.)
2. Revert PR buildRustPackage: fix deprecated use of registry.index config key #22987
3. Build NixOS/security, see it pass
4. Unrevert PR buildRustPackage: fix deprecated use of registry.index config key #22987
5. Build NixOS/security, see it doesn't need to rebuild, the previous build worked fine!

[wizeman]

@grahamc: That's what is supposed to happen if, for example, the change in #22987 broke the fetching of cargo dependencies.

Since the cargo dependencies get fetched as a fixed-output derivation, even if you change how the dependencies are fetched, Nix reuses the previously-succeeding fetch and says the build succeeded. It won't try to fetch the dependencies again unless depsSha256 is also changed.

[wizeman]

Perhaps the change in #22987 can be reverted temporarily until this is fixed.

[grahamc]

I think I understand what you're saying, except with master, NixOS/security first fails to build saying the sha doesn't match. Then I update the sha, then it fails to build. Does this still make sense?

[wizeman]

Yes, it still makes sense.

That could happen if the change in #22987 made the result of fetching the cargo dependencies incompatible with the "please-do-not-touch-the-network-just-reuse-what-we-downloaded-before" cargo fetch that happens in the postUnpack phase.

[grahamc]

I get it now: I suppose it isn't recalculating what the depsha SHOULD be, but instead simply finds it already present, and skips the calculation?

[wizeman]

@grahamc Yes (if I understand correctly what you're saying).

Anyway, maybe in the meantime we could just revert #22987?

Unfortunately I can't dedicate much time to these issues right now (or in the near future)...

[LnL7]

Yes indeed, I ran into a fetchurl a while back that had the sha of a different source. That will caused the derivation to use the wrong source because it was fetched before.

[anderspapitto]

hmm. I started looking at this (I broke it in #22987), and it's not something that's super trivial to me to fix. Can we revert for now? I was just getting rid of a deprecation warning anyway.

[anderspapitto]

hmm. I started looking at this (I broke it in #22987), and it's not something that's super trivial to me to fix. Can we revert for now? I was just getting rid of a deprecation warning anyway.