feat: improve rust template

templates/rust/flake.nix

@@ -1,58 +1,59 @@
 {
   inputs = {
-    crane = {
-      url = "github:ipetkov/crane";
-      inputs = {
-        flake-utils.follows = "flake-utils";
-        nixpkgs.follows = "nixpkgs";
-      };
-    };
-    fenix = {
-      url = "github:nix-community/fenix";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
+    crane.url = "github:ipetkov/crane";
+    crane.inputs.nixpkgs.follows = "nixpkgs";
+    fenix.url = "github:nix-community/fenix";
+    fenix.inputs.nixpkgs.follows = "nixpkgs";
     flake-utils.url = "github:numtide/flake-utils";
     nixpkgs.url = "nixpkgs/nixos-unstable";
   };
 
-  outputs = { self, crane, fenix, flake-utils, nixpkgs }:
+  outputs = { self, crane, flake-utils, nixpkgs, ... }@inputs:
     flake-utils.lib.eachDefaultSystem (system:
       let
-        pkgs = (import nixpkgs) {
-          inherit system;
-        };
-        toolchain = fenix.packages.${system}.stable;
+        inherit (pkgs) lib;
+        pkgs = import nixpkgs { inherit system; };
+        fenix = inputs.fenix.packages.${system};
         craneLib = crane.lib.${system}.overrideToolchain toolchain.toolchain;
+        mkSrc = extraPaths: with lib.fileset; let
+          root = ./.;
+          rustFiles = fromSource (craneLib.cleanCargoSource root);
+          fileset = union rustFiles (unions extraPaths);
+        in
+        toSource { inherit root fileset; };
+
+        ## Customize here ##
+        toolchain = fenix.complete; # or fenix.stable;
         stdenv = pkgs.stdenvAdapters.useMoldLinker pkgs.stdenv;
       in
       {
-        packages =
-          let
-            inherit (pkgs.lib) fileset;
-            without = fs: fileset.difference ./. fs;
-            nixFiles = fileset.unions [ ./flake.nix ./flake.lock ./.envrc ];
-            gitFiles = fileset.gitTracked ./.;
-            src = fileset.toSource {
-              root = ./.;
-              fileset = fileset.intersection (without nixFiles) gitFiles;
-            };
-          in
-          {
-            default =
-              craneLib.buildPackage {
-                inherit src stdenv;
-              };
-          };
+        packages.default = craneLib.buildPackage {
+          inherit stdenv;
+          src = mkSrc [ ];
+          strictDeps = true;
+          buildInputs = [
+            # Add additional build inputs here
+          ] ++ lib.optionals pkgs.stdenv.isDarwin [
+            # Additional darwin specific inputs can be set here
+            pkgs.libiconv
+          ];
+          # Additional environment variables can be set directly
+          # MY_CUSTOM_VAR = "some value";
+        };
 
-        devShell = pkgs.mkShell.override
+        devShells.default = pkgs.mkShell.override { inherit stdenv; }
           {
-            inherit stdenv;
-          }
-          {
-            nativeBuildInputs = with toolchain;
-              [ rustc cargo rust-analyzer clippy ] ++ (with pkgs;
-              [ ]
-              );
+            nativeBuildInputs = with pkgs; [
+              # Add additional build inputs here
+            ] ++ (with toolchain; [
+              cargo
+              clippy
+              rustfmt
+              rustc
+              fenix.rust-analyzer
+            ]);
+            RUST_SRC_PATH = "${toolchain.rust-src}/lib/rustlib/src/rust/library";
           };
-      });
+      }
+    );
 }