cargo clean (retain store paths during build)

[qknight]

Problem

It would be great if we could remove a bunch of irrelevant store paths without having to call "nix-collect-garbage" to clear all by using cargo clean.

This ticket is a draft.

~/.cargo

Legacy cargo clean removes the /target folder per project but leaves the ~/.cargo/ files untouched. For reference, my ~/.cargo has 5.8 Gb of files:

• git 1.3gb
• registry 4.0 gb
• bin 51 mb

These things should all be in the /nix/store and the bin should be a symlink. But this is not the topic of this ticket.

{{project_dir}}/target

The nix-backend in cargo already stores dep downloads like serde into /nix/store and also builds it in /nix/store but currently there exists no clear concept for tracking and removal.

current gc

Currently cargo build creates target/debug/nix/gc/result with the intent to prevent the removal:

• of download+intermediate build artifacts (deps)
• root crate artefacts

on nix-collect-garbage.

a list of store paths

At the moment the cargo toolchain consists of (target/debug/nix/cargo_build_caller.nix)

• fenix rustc
• build_parser
• nixpkgs checkout

The actual build dependencies are in:

• cargoPackages

Some of these can be discovered with: nix show-derivation

nix show-derivation /nix/store/4jqb4cjy6zp8c1pyqp0n2zy91d35b6in-cargo-0_88_0-bin-85e09d7d8299b1ad/bin/cargo | jq -r '.[].inputDrvs | keys[]'
...
/nix/store/xzirgb8m1zpfc496q91234c19pz13lm8-gix-lock-16_0_0-c0e4d3d42bd1d641.drv
/nix/store/y27n4zbylxiz8g0nm8br0rsnx1bsj6q9-logone-0_2_7-1eb55177eedd2e91.drv
/nix/store/y2qkszspj8sxvvj7fnahz7znf1h3cgph-darling-0_20_10-cbd8405b60358367.drv
/nix/store/ybidv07j6qz6b1d2hr7h552h1lrqkbv3-git2-0_20_0-a5a6e57aa11f1a77.drv
/nix/store/ywn37nmzl4jfdk06djwcibj91ds26mpg-gix-validate-0_9_3-5cd523d9060c9684.drv
/nix/store/ywzplrdm5324fssj0qrfyw48z40zahyd-nom-7_1_3-f13dd91924a7c5d9.drv
/nix/store/yzyd5kw1sl24cv69hc0ib6z5cfq33apz-openssl-probe-0_1_6-6d5d5ac82de655f5.drv
/nix/store/z44svagx0wh0y632mr8amva0gspn2n7l-parking_lot_core-0_9_10-e6343e9285ac5c5a.drv
/nix/store/z5a45f7jgw8c245c7w24a9389khdvqg4-overload-0_1_1-36d6dc4b2c1d5222.drv
/nix/store/zbhpk1rnsydn0z60m65yg38jk04hdz6s-sized-chunks-0_6_5-e757fe722119bf9b.drv
/nix/store/zjhhdydsc9igv2zhigv6qq22cm8im53z-fiat-crypto-0_2_9-92e05bb23b31efe5.drv
/nix/store/zl9xrvkl7814cw9w7hvr4wg4acdjj0cq-gix-hashtable-0_7_0-cf7f65c45ebb5acb.drv