chore: update nix flake

flake.nix

@@ -1,52 +1,57 @@
 {
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
-    flake-utils.url = "github:numtide/flake-utils";
-    rust-overlay = {
-      url = "github:oxalica/rust-overlay";
-      inputs = {
-        nixpkgs.follows = "nixpkgs";
-      };
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
     };
     solc = {
       url = "github:hellwolf/solc.nix";
-      inputs = {
-        nixpkgs.follows = "nixpkgs";
-        flake-utils.follows = "flake-utils";
-      };
+      inputs = { nixpkgs.follows = "nixpkgs"; };
     };
   };
 
-  outputs = { self, nixpkgs, rust-overlay, flake-utils, solc }:
-    flake-utils.lib.eachDefaultSystem (system:
-      let
-        pkgs = import nixpkgs {
-          inherit system;
-          overlays = [ rust-overlay.overlays.default solc.overlay ];
-        };
-        lib = pkgs.lib;
-        toolchain = pkgs.rust-bin.stable.latest.default.override {
-          extensions = [ "rustfmt" "clippy" "rust-src" ];
-        };
-      in
-      {
-        devShells.default = pkgs.mkShell {
-          nativeBuildInputs = with pkgs; [
-            pkg-config
-            solc_0_8_23
-            (solc.mkDefault pkgs solc_0_8_23)
-            toolchain
-          ];
-          buildInputs = lib.optionals pkgs.stdenv.isDarwin [
-            pkgs.darwin.apple_sdk.frameworks.AppKit
-          ];
-          packages = with pkgs; [
-            rust-analyzer-unwrapped
-          ];
+  outputs = { self, nixpkgs, fenix, solc }:
+    let eachSystem = nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed;
+    in {
+      devShells = eachSystem (system:
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+            overlays = [ fenix.overlays.default solc.overlay ];
+          };
 
-          # Environment variables
-          RUST_SRC_PATH = "${toolchain}/lib/rustlib/src/rust/library";
-          LD_LIBRARY_PATH = lib.makeLibraryPath [ pkgs.libusb1 ];
-        };
-      });
+          lib = pkgs.lib;
+          toolchain = fenix.packages.${system}.stable.toolchain;
+        in {
+          default = pkgs.mkShell {
+            nativeBuildInputs = with pkgs; [
+              pkg-config
+              solc_0_8_27
+              # default for foundry's tests
+              (solc.mkDefault pkgs solc_0_8_27)
+              toolchain
+            ];
+            buildInputs = lib.optionals pkgs.stdenv.isDarwin
+              [ pkgs.darwin.apple_sdk.frameworks.AppKit ];
+
+            packages = with pkgs; [ rust-analyzer-unwrapped ];
+
+            shellHook = ''
+              # Directly set CFLAGS to what we need.
+              # This will overwrite any CFLAGS inherited from the parent environment.
+              # -O2: Enable optimization (for _FORTIFY_SOURCE and jemalloc performance).
+              # -DJEMALLOC_STRERROR_R_RETURNS_CHAR_P: Hint for jemalloc's strerror_r usage.
+              export CFLAGS="-O2 -DJEMALLOC_STRERROR_R_RETURNS_CHAR_P"
+
+              # Simple trim of whitespace
+              export CFLAGS=$(echo "$CFLAGS" | xargs)
+            '';
+
+            # Environment variables
+            RUST_SRC_PATH = "${toolchain}/lib/rustlib/src/rust/library";
+            LD_LIBRARY_PATH = lib.makeLibraryPath [ pkgs.libusb1 ];
+          };
+        });
+    };
 }