nix: switch to flake

Author: phip1611

.envrc

@@ -1 +1 @@
-use nix
+use flake

.github/workflows/integrationtest.yml

@@ -26,13 +26,7 @@ jobs:
     steps:
       - name: Check out
         uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
-        with:
-          # This channel is only required to invoke "nix-shell".
-          # Everything inside that nix-shell will use a pinned version of
-          # nixpkgs.
-          nix_path: nixpkgs=channel:nixos-23.11
-      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - uses: cachix/install-nix-action@v31
       - name: Set up cargo cache
         uses: actions/cache@v4
         continue-on-error: false
@@ -48,6 +42,6 @@ jobs:
           key: ${{ runner.os }}-${{ github.job }}-${{ hashFiles('integration-test/**/Cargo.toml', 'integration-test/**/Cargo.lock', 'integration-test/bins/rust-toolchain.toml') }}
       # Have all the "copying into Nix store" messages in a dedicated step for
       # better log visibility.
-      - run: nix-shell --run "echo OK"
+      - run: nix develop --command bash -c "echo OK"
       # Now, run the actual test.
-      - run: nix-shell --run run-integrationtest
+      - run: nix develop --command bash -c "run-integrationtest"

flake.lock

@@ -0,0 +1,29 @@
+{
+  description = "multiboot2-rs";
+
+  inputs = {
+    # We follow the latest stable release of nixpkgs
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-25.05";
+  };
+
+  outputs =
+    inputs@{ self, nixpkgs, ... }:
+    let
+      # Systems definition for dev shells and exported packages,
+      # independent of the NixOS configurations and modules defined here. We
+      # just use "every system" here to not restrict any user. However, it
+      # likely happens that certain packages don't build for/under certain
+      # systems.
+      systems = nixpkgs.lib.systems.flakeExposed;
+      forAllSystems =
+        function: nixpkgs.lib.genAttrs systems (system: function nixpkgs.legacyPackages.${system});
+    in
+    {
+      formatter = forAllSystems (pkgs: pkgs.nixfmt-rfc-style);
+      devShells = forAllSystems (pkgs: {
+        default = import ./shell.nix {
+          inherit pkgs;
+        };
+      });
+    };
+}

flake.nix

@@ -1,7 +1,5 @@
-let
-  sources = import ./nix/sources.nix;
-  pkgs = import sources.nixpkgs {};
-in
+{ pkgs ? import <nixpkgs> {} }:
+
 pkgs.mkShell rec {
   packages = with pkgs; [
     # general
@@ -18,9 +16,4 @@ pkgs.mkShell rec {
     ./integration-test/run.sh
     '')
   ];
-
-  # To invoke "nix-shell" in the CI-runner, we need a global Nix channel.
-  # For better reproducibility inside the Nix shell, we override this channel
-  # with the pinned nixpkgs version.
-  NIX_PATH = "nixpkgs=${sources.nixpkgs}";
 }