ci: add nix and lix parse checks

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

.github/workflows/lint.yml

@@ -7,7 +7,6 @@ on:
       - "**.svg"
       - ".gitignore"
       - "LICENSE"
-      - "flake.lock"
 
 defaults:
   run:
@@ -21,5 +20,7 @@ jobs:
         uses: actions/checkout@v6
       - name: Install Nix
         uses: cachix/install-nix-action@v31
+      - name: Run nix and Lix parse checks
+        run: nix build --show-trace --keep-going .#checks.x86_64-linux.parseNix .#checks.x86_64-linux.parseLix --accept-flake-config
       - name: Run treefmt check
         run: nix build .#checks.x86_64-linux.treefmt --accept-flake-config

ci/parse.nix

@@ -0,0 +1,50 @@
+{
+  lib,
+  nix,
+  pipeOperatorFlag,
+  runCommand,
+}:
+runCommand "nix-parse-${nix.name}"
+  {
+    nativeBuildInputs = [ nix ];
+    nixvim =
+      with lib.fileset;
+      toSource {
+        root = ../.;
+        fileset = fileFilter (file: file.hasExt "nix") ../.;
+      };
+    inherit pipeOperatorFlag;
+  }
+  ''
+    export HOME="$TMPDIR"
+    export XDG_CONFIG_HOME="$TMPDIR"
+    export NIX_CONF_DIR="$TMPDIR/nix-conf"
+    parseLog="$TMPDIR/nix-parse.log"
+    mkdir -p "$NIX_CONF_DIR"
+    : > "$NIX_CONF_DIR/nix.conf"
+
+    export NIX_STORE_DIR="$TMPDIR/store"
+    export NIX_STATE_DIR="$TMPDIR/state"
+    nix-store --init
+
+    cd "$nixvim"
+
+    # 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' -print0 | xargs -0 -P "$(nproc)" nix-instantiate --extra-experimental-features "$pipeOperatorFlag" --parse > /dev/null 2> "$parseLog"; then
+      cat "$parseLog" >&2
+      echo "Parse failed in nix-instantiate." >&2
+      exit 1
+    fi
+
+    if grep -q "^warning:" "$parseLog"; then
+      cat "$parseLog" >&2
+      echo "Failing due to warnings in stderr" >&2
+      exit 1
+    fi
+
+    touch "$out"
+  ''

flake/dev/default.nix

@@ -5,6 +5,7 @@
     ./generate-all-maintainers
     ./git-hooks.nix
     ./package-tests.nix
+    ./parse.nix
     ./template-tests.nix
     ./tests.nix
   ];

flake/dev/parse.nix

@@ -0,0 +1,16 @@
+_: {
+  perSystem =
+    { pkgs, ... }:
+    {
+      checks = {
+        parseNix = pkgs.callPackage ../../ci/parse.nix {
+          nix = pkgs.nixVersions.latest;
+          pipeOperatorFlag = "pipe-operators";
+        };
+        parseLix = pkgs.callPackage ../../ci/parse.nix {
+          nix = pkgs.lixPackageSets.latest.lix;
+          pipeOperatorFlag = "pipe-operator";
+        };
+      };
+    };
+}