build(nix): fix flake builds

flake.nix

@@ -1,74 +1,56 @@
 {
-  inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs";
-    flake-utils.url = "github:numtide/flake-utils";
+  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  inputs.d2n.url = "github:nix-community/dream2nix";
+  inputs.d2n.inputs.nixpkgs.follows = "nixpkgs";
+  inputs.parts.url = "github:hercules-ci/flake-parts";
+  inputs.rust-overlay.url = "github:oxalica/rust-overlay";
+  inputs.rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
 
-    fenix = {
-      url = "github:nix-community/fenix";
-      inputs.nixpkgs.follows = "nixpkgs";
+  outputs = inp:
+    inp.parts.lib.mkFlake {inputs = inp;} {
+      systems = ["x86_64-linux"];
+      imports = [inp.d2n.flakeModuleBeta];
+      perSystem = {
+        config,
+        system,
+        pkgs,
+        ...
+      }: let
+        cargoToml = builtins.fromTOML (builtins.readFile ./Cargo.toml);
+        pkgsWithToolchain = pkgs.appendOverlays [inp.rust-overlay.overlays.default];
+
+        toolchains = pkgsWithToolchain.rust-bin.stable."${cargoToml.package.rust-version}";
+        # toolchain to use when building conduit, includes only cargo and rustc to reduce closure size
+        buildToolchain = toolchains.minimal;
+        # toolchain to use in development shell
+        # the "default" component set of toolchain adds rustfmt, clippy etc.
+        devToolchain = toolchains.default.override {
+          extensions = ["rust-src"];
+        };
+
+        # flake outputs for conduit project
+        conduitOutputs = config.dream2nix.outputs.conduit;
+      in {
+        dream2nix.inputs.conduit = {
+          source = inp.self;
+          projects.conduit = {
+            name = "conduit";
+            subsystem = "rust";
+            translator = "cargo-lock";
+          };
+          packageOverrides = {
+            "^.*".set-toolchain.overrideRustToolchain = _: {
+              cargo = buildToolchain;
+              rustc = buildToolchain;
+            };
+          };
+        };
+        devShells.conduit = conduitOutputs.devShells.conduit.overrideAttrs (old: {
+          # export default crate sources for rust-analyzer to read
+          RUST_SRC_PATH = "${devToolchain}/lib/rustlib/src/rust/library";
+          nativeBuildInputs = (old.nativeBuildInputs or []) ++ [devToolchain];
+        });
+        devShells.default = config.devShells.conduit;
+      };
     };
-    naersk = {
-      url = "github:nix-community/naersk";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-  };
-
-  outputs =
-    { self
-    , nixpkgs
-    , flake-utils
-
-    , fenix
-    , naersk
-    }: flake-utils.lib.eachDefaultSystem (system:
-    let
-      pkgs = nixpkgs.legacyPackages.${system};
-
-      # Nix-accessible `Cargo.toml`
-      cargoToml = builtins.fromTOML (builtins.readFile ./Cargo.toml);
-
-      # The Rust toolchain to use
-      toolchain = fenix.packages.${system}.toolchainOf {
-        # Use the Rust version defined in `Cargo.toml`
-        channel = cargoToml.package.rust-version;
-
-        # THE rust-version HASH
-        sha256 = "sha256-8len3i8oTwJSOJZMosGGXHBL5BVuGQnWOT2St5YAUFU=";
-      };
-
-      builder = (pkgs.callPackage naersk {
-        inherit (toolchain) rustc cargo;
-      }).buildPackage;
-    in
-    {
-      packages.default = builder {
-        src = ./.;
-
-        nativeBuildInputs = (with pkgs.rustPlatform; [
-          bindgenHook
-        ]);
-      };
-
-      devShells.default = pkgs.mkShell {
-        # Rust Analyzer needs to be able to find the path to default crate
-        # sources, and it can read this environment variable to do so
-        RUST_SRC_PATH = "${toolchain.rust-src}/lib/rustlib/src/rust/library";
-
-        # Development tools
-        nativeBuildInputs = (with pkgs.rustPlatform; [
-          bindgenHook
-        ]) ++ (with toolchain; [
-          cargo
-          clippy
-          rust-src
-          rustc
-          rustfmt
-        ]);
-      };
-
-      checks = {
-        packagesDefault = self.packages.${system}.default;
-        devShellsDefault = self.devShells.${system}.default;
-      };
-    });
 }