feat(nix): remove devenv, build backend with nix

flake.nix

@@ -1,57 +1,69 @@
 {
   inputs = {
-    nixpkgs.url = "github:cachix/devenv-nixpkgs/rolling";
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
     alejandra = {
       url = "github:kamadorueda/alejandra/4.0.0";
       inputs.nixpkgs.follows = "nixpkgs";
     };
-    devenv = {
-      url = "github:cachix/devenv";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
     rust-overlay = {
       url = "github:oxalica/rust-overlay";
       inputs.nixpkgs.follows = "nixpkgs";
     };
-    devenv-root = {
-      url = "file+file:///dev/null";
-      flake = false;
-    };
   };
 
   nixConfig = {
     extra-trusted-public-keys = [
-      "devenv.cachix.org-1:w1cLUi8dv3hnoSPGAuibQv+f9TZLr6cv/Hm9XgU50cw="
+      "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+      "phundrak.cachix.org-1:osJAkYO0ioTOPqaQCIXMfIRz1/+YYlVFkup3R2KSexk="
+      "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
     ];
     extra-substituters = [
-      "https://devenv.cachix.org"
+      "https://phundrak.cachix.org?priority=10"
+      "https://nix-community.cachix.org?priority=20"
+      "https://cache.nixos.org?priority=30"
     ];
   };
 
   outputs = {
-    self,
     nixpkgs,
     flake-utils,
     rust-overlay,
     alejandra,
     ...
-  } @ inputs:
+  }:
     flake-utils.lib.eachDefaultSystem (
       system: let
         overlays = [(import rust-overlay)];
         pkgs = import nixpkgs {inherit system overlays;};
         rustVersion = pkgs.rust-bin.stable.latest.default;
-        rustPlatform = pkgs.makeRustPlatform {
-          cargo = rustVersion;
-          rustc = rustVersion;
+        targets = {
+          linux-x86_64 = {
+            crossPkgs = pkgs;
+            triple = "x86_64-unknown-linux-gnu";
+          };
+          linux-aarch64 = {
+            crossPkgs = pkgs.pkgsCross.aarch64-multiplatform;
+            triple = "aarch64-unknown-linux-gnu";
+          };
+        };
+        mkRustBuild = import ./nix/backend.nix;
+        packages = {
+          linux-x86_64 = mkRustBuild targets.linux-x86_64;
+          linux-aarch64 = mkRustBuild targets.linux-aarch64;
+        };
+        defaultBySystem = {
+          "x86_64-linux" = packages.linux-x86_64;
+          "aarch64-linux" = packages.linux-aarch64;
         };
       in {
         formatter = alejandra.defaultPackage.${system};
-        packages = import ./nix/package.nix {inherit pkgs rustPlatform;};
-        devShell = import ./nix/shell.nix {
-          inherit inputs pkgs self rustVersion system;
-        };
+        packages.backend =
+          packages
+          // {
+            default = defaultBySystem.${system} or packages.linux-x86_64;
+          };
+        devShell = import ./nix/shell.nix {inherit pkgs rustVersion;};
       }
     );
 }