buildRustCrate: add support for renaming crates

[danieldk]

Motivation for this change

Before this change, buildRustCrate always called rustc with

--extern libName=[...]libName[...]

However, Cargo permits using a different name under which a dependency
is known to a crate. For example, rand 0.7.0 uses:

[dependencies]
getrandom_package = { version = "0.1.1", package = "getrandom", optional = true }

Which introduces the getrandom dependency such that it is known as
getrandom_package to the rand crate. In this case, the correct extern
flag is of the form

--extern getrandom_package=[...]getrandom[...]

which is currently not supported. In order to support such cases, this
change introduces a crateRenames argument to buildRustCrate. This
argument is an attribute set of dependencies that should be
renamed. In this case, crateRenames would be:

{
  "getrandom" = "getrandom_package";
}

The extern options are then built such that if the libName occurs as
an attribute in this set, it value will be used as the local
name. Otherwise libName will be used as before.

This change should not affect existing derivations that use buildRustCrate --
an empty attrset is used for crateRenames when this argument is not provided,
applying the old behavior.

Please review very carefully, I have never looked at the buildRustCrate
code before ;).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

ping @P-E-Meunier @kolloch

cc @

[andir]

Added @gilligan as I had a conversation about this feature with him during the week.

[andir]

After a first glance it looks okay. Could you add a testcase to the buildRustCrateTests attribute?

The tests currently pass and are even cached meaning you are really not causing any changes to "old" expressions 👍.

[gilligan]

The changes per se look good to me! It's in line with what I was also mentioning on the crates2nix repo. Thank you so much for taking the time and initiative to fix it :)

I agree with @andir that there should be some tests with this change. Maybe you can just use the same minimal example that I put in https://github.com/gilligan/rs-nix-test to verify that things are working.

With tests added i'd be happy to see this merged. Oh, and I think we should also get this into 18.09, right?

[danieldk]

Thanks for the comments! I have added a test case.

[danieldk]

The last two pushes were just replacing occurrences of buildRustPackage to buildRustCrate. Apparently, I was sleeping ;).

[danieldk]

Found and fixed a bug while preparing a PR for crate2nix to support renames: the lookup should be by crateName and not libName, otherwise this breaks when crateName != libName. I have also added a test for this case.

[gilligan]

Awesome work!

[oxalica]

I found it do renaming only over crate names, without considering crate version.

This seems to cause problem when a crate depends on multiple versions of the same named crate.
For example:

a = { version = "0.1", package = "libc" }
b = { version = "0.2", package = "libc" }

We cannot even provide a proper crateRenames in this case.

@danieldk

[danieldk]

For example:

a = { version = "0.1", package = "libc" }
b = { version = "0.2", package = "libc" }

We cannot even provide a proper crateRenames in this case.

Good find!

rustc extern flags:

--extern a=/home/daniel/rename-test/target/debug/deps/liblibc-da86144831204d21.rlib --extern b=/home/daniel/rename-test/target/debug/deps/liblibc-a4b0875e7e16a993.rlib

So, I guess crateRenames needs to be keyed on the version besides the crate name. Another problem is that upstream tools may not even create valid Nix. E.g. crate2nix (@kolloch):

        dependencies = {
          "libc" = {
            packageId = "libc 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)";
            rename = "b";
          };
          "libc" = {
            packageId = "libc 0.2.62 (registry+https://github.com/rust-lang/crates.io-index)";
            rename = "b";
          };
        };

[oxalica]

@danieldk I've opened a new issue #70270 for this.