ci: add nix and lix parse checks

Co-authored-by: Wolfgang Walther <walther@technowledgy.de>
Co-authored-by: piegames <git@piegames.de>

.github/workflows/test.yml

@@ -13,6 +13,7 @@ jobs:
       docs: ${{ steps.changes.outputs.docs }}
       format: ${{ steps.changes.outputs.format }}
       hm: ${{ steps.changes.outputs.hm }}
+      parse: ${{ steps.changes.outputs.parse }}
       tests: ${{ steps.changes.outputs.tests }}
     steps:
       - uses: actions/checkout@v6
@@ -39,6 +40,9 @@ jobs:
               - 'flake.lock'
               - 'flake.nix'
               - 'home-manager/**'
+            parse:
+              - '**/*.nix'
+              - 'flake.lock'
   tests:
     needs: changes
     strategy:
@@ -59,6 +63,12 @@ jobs:
       - name: Build docs
         if: github.event_name == 'schedule' || needs.changes.outputs.docs == 'true'
         run: nix build --show-trace .#docs-jsonModuleMaintainers
+      - name: Parse Nix files with latest nix
+        if: github.event_name == 'schedule' || needs.changes.outputs.parse == 'true'
+        run: nix build --show-trace .#ci-parse
+      - name: Parse Nix files with latest Lix
+        if: github.event_name == 'schedule' || needs.changes.outputs.parse == 'true'
+        run: nix build --show-trace .#ci-parse-lix
       - name: Format Check
         if: github.event_name == 'schedule' || needs.changes.outputs.format == 'true'
         run: nix fmt -- --ci
@@ -93,6 +103,12 @@ jobs:
             echo "- ☑️ **Format Check:** Skipped (no relevant files changed)" >> $GITHUB_STEP_SUMMARY
           fi
 
+          if [[ "${{ needs.changes.outputs.parse }}" == "true" ]]; then
+            echo "- ✅ **Nix Parse (nix + Lix):** Triggered" >> $GITHUB_STEP_SUMMARY
+          else
+            echo "- ☑️ **Nix Parse (nix + Lix):** Skipped (no relevant files changed)" >> $GITHUB_STEP_SUMMARY
+          fi
+
           if [[ "${{ needs.changes.outputs.hm }}" == "true" ]]; then
             echo "- ✅ **Home Manager Tests:** Triggered" >> $GITHUB_STEP_SUMMARY
           else

ci/parse.nix

@@ -0,0 +1,45 @@
+{
+  lib,
+  nix,
+  runCommand,
+}:
+let
+  home-manager =
+    with lib.fileset;
+    toSource {
+      root = ../.;
+      fileset = (fileFilter (file: file.hasExt "nix") ../.);
+    };
+  parseLog = "$TMPDIR/nix-parse.log";
+in
+runCommand "nix-parse-${nix.name}"
+  {
+    nativeBuildInputs = [
+      nix
+    ];
+  }
+  ''
+    export NIX_STORE_DIR=$TMPDIR/store
+    export NIX_STATE_DIR=$TMPDIR/state
+    nix-store --init
+
+    cd "${home-manager}"
+
+    # This will only show the first parse error, not all of them. That's fine, because
+    # the other CI jobs will report in more detail. This job is about checking parsing
+    # across different implementations / versions, not about providing the best DX.
+    # Returning all parse errors requires significantly more resources.
+    if ! find . -type f -iname '*.nix' | xargs -P $(nproc) nix-instantiate --parse 2> "${parseLog}" > /dev/null; then
+      cat "${parseLog}" >&2
+      echo "Parse failed in nix-instantiate." >&2
+      exit 1
+    fi
+
+    if grep "warning" "${parseLog}"; then
+      cat "${parseLog}" >&2
+      echo "Failing due to warnings in stderr" >&2
+      exit 1
+    fi
+
+    touch $out
+  ''

flake.nix

@@ -189,6 +189,11 @@
             default = hmPkg;
             home-manager = hmPkg;
 
+            ci-parse = pkgs.callPackage ./ci/parse.nix { nix = pkgs.nixVersions.latest; };
+            ci-parse-lix = pkgs.callPackage ./ci/parse.nix {
+              nix = pkgs.lixPackageSets.latest.lix;
+            };
+
             create-news-entry = pkgs.writeShellScriptBin "create-news-entry" ''
               ./modules/misc/news/create-news-entry.sh
             '';