flake.nix

{
  description = ''
    Pure and reproducible overlay for binary distributed rust toolchains.
    A compatible but better replacement for rust overlay of github:mozilla/nixpkgs-mozilla.
  '';

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  };

  outputs = { self, nixpkgs }@inputs: let
    inherit (nixpkgs) lib;
    inherit (lib) filterAttrs mapAttrs' replaceStrings;

    forEachSystem = lib.genAttrs lib.systems.flakeExposed;

    overlay = import ./.;

    defaultDistRoot = import ./lib/dist-root.nix;
    mkManifests = distRoot: import ./lib/manifests.nix { inherit lib distRoot; };

    # Builder to construct `rust-bin` interface on an existing `pkgs`.
    # This would be immutable, non-intrusive and (hopefully) can benefit from
    # flake eval-cache.
    #
    # Note that this does not contain compatible attrs for mozilla-overlay.
    mkRustBin =
      { distRoot ? defaultDistRoot }:
      pkgs:
      lib.fix (rust-bin: import ./lib/rust-bin.nix {
        inherit lib pkgs;
        inherit (pkgs.rust) toRustTarget;
        inherit (rust-bin) nightly;
        manifests = mkManifests distRoot;
      });

  in {
    lib = {
      # Internal use only!
      _internal = {
        defaultManifests = mkManifests defaultDistRoot;
      };

      inherit mkRustBin;
    };

    overlays = {
      default = overlay;
      rust-overlay = overlay;
    };

    # TODO: Flake outputs except `overlay[s]` are not stabilized yet.

    packages =
      let
        select = version: comps:
          if comps ? default then
            comps.default // {
              minimal = comps.minimal or (throw "missing profile 'minimal' for ${version}");
            }
          else
            null;
        result = rust-bin:
          mapAttrs' (version: comps: {
            name = if version == "latest"
              then "rust"
              else "rust_${replaceStrings ["."] ["_"] version}";
            value = select version comps;
          }) rust-bin.stable //
          mapAttrs' (version: comps: {
            name = if version == "latest"
              then "rust-nightly"
              else "rust-nightly_${version}";
            value = select version comps;
          }) rust-bin.nightly //
          mapAttrs' (version: comps: {
            name = if version == "latest"
              then "rust-beta"
              else "rust-beta_${version}";
            value = select version comps;
          }) rust-bin.beta;
        result' = rust-bin: filterAttrs (name: drv: drv != null) (result rust-bin);
      in
      forEachSystem (system:
        result' (mkRustBin {} nixpkgs.legacyPackages.${system})
        // { default = self.packages.${system}.rust; }
      );

    checks = forEachSystem (import ./tests inputs);
  };
}