nix: use nixfmt instead of nixpkgs-fmt

nixpkgs-fmt is deprecated

Author: phip1611

shell.nix

@@ -11,7 +11,8 @@ pkgs.mkShell {
   nativeBuildInputs = with pkgs; [
     # nix related stuff (such as dependency management)
     niv
-    nixpkgs-fmt
+    # TODO use "nixfmt" once it is stable - likely in nixpkgs @ NixOS 24.11
+    nixfmt-rfc-style
 
     # Integration test dependencies
     swtpm

xtask/src/main.rs

@@ -261,9 +261,9 @@ fn run_fmt_project(fmt_opt: &FmtOpt) -> Result<()> {
     }
 
     // fmt nix
-    if has_cmd("nixpkgs-fmt") {
+    if has_cmd("nixfmt") {
         eprintln!("Formatting: nix");
-        let mut command = Command::new("nixpkgs-fmt");
+        let mut command = Command::new("nixfmt");
         if fmt_opt.check {
             command.arg("--check");
         }