add a nix fmt/flake check action

.github/workflows/nix.yml

@@ -0,0 +1,37 @@
+---
+name: "Nix checks"
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+jobs:
+  nixflake:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v29
+        with:
+          github_access_token: ${{ secrets.GITHUB_TOKEN }}
+      - run: nix build
+      - run: nix flake check
+  nixfmt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: nixbuild/nix-quick-install-action@v29
+      - name: nix fmt
+        run: nix fmt $(find . -name \*nix -type f -not -path "./.git/*")
+      - name: Changed files
+        id: dirty
+        run: |
+          echo "Checking nix files with: nix fmt ..."
+          git diff --exit-code
+        continue-on-error: true
+      - name: Failure case
+        if: steps.dirty.outcome != 'success'
+        run: |
+          echo "Please fix formatting with nix fmt (file)"
+          exit 1
+      - name: Success
+        run: echo "All nix files passed format check"

flake.nix

@@ -14,7 +14,7 @@
           src = self;
           name = "aws-lc";
           inherit system;
-          nativeBuildInputs = [ pkgs.ninja pkgs.cmake pkgs.perl pkgs.golang ];
+          nativeBuildInputs = [ pkgs.ninja pkgs.cmake pkgs.perl pkgs.go ];
           cmakeFlags = [
             "-GNinja"
             "-DBUILD_SHARED_LIBS=ON"

nix/devshell.nix

@@ -1,7 +1,7 @@
-{pkgs}:
+{ pkgs }:
 pkgs.mkShell rec {
   buildInputs = [ pkgs.cmake ];
-  packages = [ pkgs.gdb pkgs.nixfmt pkgs.ninja pkgs.cmake pkgs.perl pkgs.go ];
+  packages = [ pkgs.nixfmt-classic pkgs.ninja pkgs.cmake pkgs.perl pkgs.go ];
   shellHook = ''
     echo "Entering a devShell..."
     export PS1="[awslc nix] $PS1"
@@ -20,5 +20,5 @@ pkgs.mkShell rec {
     function unit {
         ninja -C build run_tests
     }
-    '';
+  '';
 }