flake: use stock Nixpkgs Rust toolchain

This makes it easier to use Nixpkgs’ cross‐compilation machinery
and simplifies the flake.

.cargo/config.toml

@@ -1,3 +0,0 @@
-# For -Zbuild-std
-[target.aarch64-unknown-linux-musl]
-rustflags = ["-C", "target-feature=+crt-static", "-C", "link-arg=-lgcc"]

flake.lock

@@ -15,26 +15,6 @@
         "type": "github"
       }
     },
-    "fenix": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs"
-        ],
-        "rust-analyzer-src": "rust-analyzer-src"
-      },
-      "locked": {
-        "lastModified": 1738391509,
-        "narHash": "sha256-TC3xA++KgprECm/WPsLUd+a77MObZPElCW6eAsjVW1k=",
-        "rev": "de3ea31eb651b663449361f77d9c1e8835290470",
-        "revCount": 2156,
-        "type": "tarball",
-        "url": "https://api.flakehub.com/f/pinned/nix-community/fenix/0.1.2156%2Brev-de3ea31eb651b663449361f77d9c1e8835290470/0194c095-0041-7b9c-b19e-cf1c4a2adaad/source.tar.gz"
-      },
-      "original": {
-        "type": "tarball",
-        "url": "https://flakehub.com/f/nix-community/fenix/0.1.1727.tar.gz"
-      }
-    },
     "flake-compat": {
       "flake": false,
       "locked": {
@@ -190,27 +170,9 @@
     "root": {
       "inputs": {
         "crane": "crane",
-        "fenix": "fenix",
         "nix": "nix",
         "nixpkgs": "nixpkgs_2"
       }
-    },
-    "rust-analyzer-src": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1738224931,
-        "narHash": "sha256-1zhfA5NBqin0Z79Se85juvqQteq7uClJMEb7l2pdDUY=",
-        "owner": "rust-lang",
-        "repo": "rust-analyzer",
-        "rev": "3c2aca1e5e9fbabb4e05fc4baa62e807aadc476a",
-        "type": "github"
-      },
-      "original": {
-        "owner": "rust-lang",
-        "ref": "nightly",
-        "repo": "rust-analyzer",
-        "type": "github"
-      }
     }
   },
   "root": "root",

flake.nix

@@ -4,11 +4,6 @@
   inputs = {
     nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.tar.gz";
 
-    fenix = {
-      url = "https://flakehub.com/f/nix-community/fenix/0.1.1727.tar.gz";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-
     # Pinned to `master` until a release containing
     # <https://github.com/ipetkov/crane/pull/792> is cut.
     crane.url = "github:ipetkov/crane";
@@ -16,7 +11,7 @@
     nix.url = "https://flakehub.com/f/NixOS/nix/2.tar.gz";
   };
 
-  outputs = { self, nixpkgs, fenix, crane, ... }@inputs:
+  outputs = { self, nixpkgs, crane, ... }@inputs:
     let
       supportedSystems = [
         "aarch64-linux"
@@ -35,27 +30,12 @@
         inherit (pkgs) lib;
         inherit system;
       });
-
-      fenixToolchain = system: with fenix.packages.${system};
-        combine ([
-          stable.clippy
-          stable.rustc
-          stable.cargo
-          stable.rustfmt
-          stable.rust-src
-          stable.rust-analyzer
-        ] ++ nixpkgs.lib.optionals (system == "x86_64-linux") [
-          targets.x86_64-unknown-linux-musl.stable.rust-std
-        ] ++ nixpkgs.lib.optionals (system == "aarch64-linux") [
-          targets.aarch64-unknown-linux-musl.stable.rust-std
-        ]);
     in
     {
 
       overlays.default = final: prev:
       let
-          toolchain = fenixToolchain final.hostPlatform.system;
+          craneLib = crane.mkLib final;
-          craneLib = (crane.mkLib final).overrideToolchain toolchain;
           crateName = craneLib.crateNameFromCargoToml {
             cargoToml = ./magic-nix-cache/Cargo.toml;
           };
@@ -122,14 +102,14 @@
           createChain 200 startFile;
       });
 
-      devShells = forEachSupportedSystem ({ system, pkgs, lib }:
+      devShells = forEachSupportedSystem ({ system, pkgs, lib }: {
-      let
-          toolchain = fenixToolchain system;
-      in
-      {
         default = pkgs.mkShell {
           packages = with pkgs; [
-            toolchain
+            rustc
+            cargo
+            clippy
+            rustfmt
+            rust-analyzer
 
             nix # for linking attic
             boost # for linking attic
@@ -149,7 +129,7 @@
           ];
 
           NIX_CFLAGS_LINK = lib.optionalString pkgs.stdenv.isDarwin "-lc++abi";
-          RUST_SRC_PATH = "${toolchain}/lib/rustlib/src/rust/library";
+          RUST_SRC_PATH = "${pkgs.rustPlatform.rustcSrc}/library";
         };
       });
     };