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Motivation

We start with rust/cargo on linux to make it work with nix as backend, see https://github.com/NixOS/nix/pull/8699 for this

• https://lastlog.de/blog/libnix_roadmap.html#cargo-with-nix-support
• https://github.com/NixOS/nix/pull/8699
• https://github.com/Anillc/nixrs/pull/1

Working branch

https://github.com/nixcloud/cargo/tree/libnix-0.79.0

parts of both folders ~/.cargo and target have been replaced by the nix store.

Let's see what is in them!

~/.cargo

[nixos@nixos:~/cargo]$ du -sh ~/.cargo
239M    /home/nixos/.cargo

[nixos@nixos:~/cargo]$ ls ~/.cargo/
registry

[nixos@nixos:~/cargo]$ ls ~/.cargo/registry/
cache  CACHEDIR.TAG  index  src

cargo/target

The example is the cargo project itself, the tool coming with the rust toolchain, since we hack on it.

[nixos@nixos:~/cargo]$ du -sh target/
2.3G    target/

[nixos@nixos:~/cargo]$ ls target/
CACHEDIR.TAG  debug

[nixos@nixos:~/cargo]$ ls target/debug/
build  cargo  cargo.d  deps  examples  incremental  libcargo.d  libcargo.rlib

Plan

libnix backend in cargo needs to get these things working:

• no use of ~/.cargo, everything in /nix/store
• target/debug/* needs to come from /nix/store, eventually symlinked or transparently from the store

figure out what these are:

• target/debug/build

.fingerprint

target/debug/.fingerprint -> https://doc.rust-lang.org/nightly/nightly-rustc/cargo/core/compiler/fingerprint/index.html

[nixos@nixos:~/cargo]$ ls target/debug/.fingerprint/der-d0714c795318982b/
dep-lib-der  invoked.timestamp  lib-der  lib-der.json

[nixos@nixos:~/cargo]$ cat target/debug/.fingerprint/der-d0714c795318982b/lib-der
6b2cf10d51d11828

[nixos@nixos:~/cargo]$ cat target/debug/.fingerprint/der-d0714c795318982b/lib-der.json  | jq
{
  "rustc": 18217185010275080438,
  "features": "[\"alloc\", \"oid\", \"pem\", \"std\", \"zeroize\"]",
  "declared_features": "",
  "target": 4346314333490370059,
  "profile": 12206360443249279867,
  "path": 16879011525611689376,
  "deps": [
    [
      1724196337906130016,
      "pem_rfc7468",
      false,
      5466269655917579261
    ],
    [
      2676387858222833023,
      "const_oid",
      false,
      2852573652909154018
    ],
    [
      15098350142499636151,
      "zeroize",
      false,
      14469829910961900562
    ]
  ],
  "local": [
    {
      "CheckDepInfo": {
        "dep_info": "debug/.fingerprint/der-d0714c795318982b/dep-lib-der"
      }
    }
  ],
  "rustflags": [],
  "metadata": 12456048820742377390,
  "config": 2202906307356721367,
  "compile_kind": 0
}

[nixos@nixos:~/cargo]$ cat target/debug/.fingerprint/der-d0714c795318982b/dep-lib-der

finally:

• get a crate compiled without dependencies
• get one with nested dependencies
• get one with c library usage (like cargo itself)

how nix builds rust packages ATM

• https://github.com/cargo2nix/cargo2nix
• https://github.com/nix-community/crate2nix
• https://github.com/nix-community/carnix (obsoleted by create2nix)
• https://github.com/anirudhb/rust2nix

BuildContext

Some fields that might be interesting:

let bcx : BuildContext = create_bcx(ws, options, &interner)? // Line 153 in cargo/ops/cargo_compile/mod.rs
bcx.ws.gctx.home_path;
bcx.ws.gctx.cwd;
bcx.ws.gctx.ws_roots;
bcx.ws.current_manifest;
bcx.ws.packages.gctx;
bcx.ws.packages.packages; // HashMap<PackageId, LazyCell<Package>>