build: use nightly toolchain

This change adds `fenix` to the nix flake to enable the use of nightly
toolchains.

Using nightly rust toolchains enables the use of the features behind the
`exit_status_error`[^1] feature flag, which allows the use of
`ExitStatusError`[^2].

[^1]: rust-lang/rust#84908
[^2]: https://doc.rust-lang.org/std/process/struct.ExitStatusError.html

flake.nix

@@ -5,12 +5,17 @@
       url = "github:ipetkov/crane";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs = {
     self,
     nixpkgs,
     crane,
+    fenix,
   }: let
     forEachSystem = nixpkgs.lib.genAttrs [
       "aarch64-darwin"
@@ -21,7 +26,7 @@
   in {
     packages = forEachSystem (system: let
       craneDerivations = nixpkgs.legacyPackages.${system}.callPackage ./nix/default.nix {
-        inherit crane;
+        inherit crane fenix;
       };
     in {
       default = craneDerivations.myCrate;

nix/default.nix

@@ -2,14 +2,27 @@
   pkgs,
   system,
   crane,
+  fenix,
 }: let
-  craneLib = crane.lib.${system};
+  fenix-channel = fenix.packages.${system}.latest;
+  fenix-toolchain = fenix-channel.withComponents [
+    "cargo"
+    "clippy"
+    "rust-analyzer"
+    "rust-src"
+    "rustc"
+    "rustfmt"
+  ];
+
+  craneLib = crane.lib.${system}.overrideToolchain fenix-toolchain;
 
   # Common derivation arguments used for all builds
   commonArgs = {
     src = craneLib.cleanCargoSource ../.;
 
     nativeBuildInputs = pkgs.lib.optionals pkgs.stdenv.isDarwin [
+      pkgs.darwin.apple_sdk.frameworks.Security
+      pkgs.darwin.apple_sdk.frameworks.SystemConfiguration
       pkgs.libiconv
     ];
   };
@@ -51,5 +64,6 @@ in {
     myCrate
     myCrateClippy
     myCrateCoverage
+    fenix-toolchain
     ;
 }

nix/flake.nix

@@ -5,6 +5,10 @@
       url = "github:ipetkov/crane";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     pre-commit-hooks = {
       url = "github:cachix/pre-commit-hooks.nix";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -15,6 +19,7 @@
     self,
     nixpkgs,
     crane,
+    fenix,
     pre-commit-hooks,
   }: let
     forEachSystem = nixpkgs.lib.genAttrs [
@@ -25,7 +30,8 @@
     ];
   in {
     checks = forEachSystem (system: let
-      craneDerivations = nixpkgs.legacyPackages.${system}.callPackage ./default.nix {inherit crane;};
+      pkgs = import nixpkgs {inherit system;};
+      craneDerivations = pkgs.callPackage ./default.nix {inherit crane fenix;};
       pre-commit-check = pre-commit-hooks.lib.${system}.run {
         src = ../.;
         hooks = {
@@ -46,17 +52,13 @@
     });
 
     devShells = forEachSystem (system: let
-      pkgs = nixpkgs.legacyPackages.${system};
-      craneDerivations = pkgs.callPackage ./default.nix {inherit crane;};
+      pkgs = import nixpkgs {inherit system;};
+      craneDerivations = pkgs.callPackage ./default.nix {inherit crane fenix;};
     in {
       default = pkgs.mkShell {
-        nativeBuildInputs = with pkgs;
+        packages = with pkgs;
           [
-            cargo
-            clippy
-            rust-analyzer
-            rustc
-            rustfmt
+            craneDerivations.fenix-toolchain
           ]
           ++ craneDerivations.commonArgs.nativeBuildInputs;