buildRustPackage: use the same config file name for cargo-setup-hook and fetch-cargo-tarball

[P-E-Meunier]

Currently, fetch-cargo-tarball produces a config file named .cargo/config, while cargo-setup-hook uses a default config file whenever .cargo/config.toml isn't present.

This causes all configurations to be ignored, in particular private registries.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[alyssais]

This is going to break FODs. See previous attempts: #321095 (reverted in #321998), #339281.

[alyssais]

#349360 would possibly make this workable with the new interface.

[P-E-Meunier]

The point isn't to use config.toml, but rather to use the same in both places. I understand the point of keeping config, but the current situation is currently broken with private registries.

Do you think an alternative where cargo-setup-hook checks both places to decide whether to take a default config would work?

[alyssais]

I don't know. I do know that making them different happened on purpose (#331167), but maybe this wasn't considered.

cc @emilazy @mmlb

[mmlb]

I did the most I could without breaking FOD which as I learned (again) leads to silent breakage. I believe any further changes would have to be with a different api so that users can opt-into it. I have not looked at #349360.