buildRustPackage: add overrideRust attribute

[9999years]

This lets you write code like this:

let
  pkgs = import <nixpkgs> {};
  version = "0.1.15";
in
pkgs.ruff.overrideRust {
  inherit version;

  src = pkgs.fetchFromGitHub {
    owner = "astral-sh";
    repo = "ruff";
    rev = "v${version}";
    hash = "sha256-DzdzMO9PEwf4HmpG8SxRJTmdrmkXuQ8RsIchvsKstH8=";
  };

  cargoHash = "sha256-MpiWdNUs66OGYfOJo1kJQTCqjrk/DAYecaLf6GUUKew=";

  patches = [];
}

Previously, it was essentially impossible to override cargoHash.

[winterqt]

Functionality-wise, this looks like a dupe of #194475.

[9999years]

It doesn't look like #194475 is moving forward (it hasn't been reviewed in over a year). Can we get this merged as a stopgap measure and plan to replace it with a better solution when one becomes available?

The perfect is the enemy of the good, and this PR is small and addresses a very inconvenient missing feature in rustPlatform.

[r-vdp]

Tried it out and it worked well! This makes it so much easier to override rust packages.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-do-you-override-the-commit-rev-used-by-a-rust-package/47698/5

[Mic92]

Some motivation would be nice.

Suggested change

	# `buildRustPackage`.
	# `buildRustPackage`. This is useful for ...