tools: do not download build tools when linting Nix files

Signed-off-by: Antoine du Hamel <duhamelantoine1995@gmail.com>
PR-URL: #65961
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: aduh95

.github/workflows/nix-changes.yml

@@ -111,9 +111,10 @@ jobs:
       - uses: cachix/install-nix-action@13d8dd58da0234aa297dedd986986ccb8e7f3e24  # v31.11.1
       - name: Lint Nix files
         run: |
-          nix-shell -I nixpkgs=./tools/nix/pkgs.nix -p 'nixfmt-tree' --run '
-            treefmt --quiet --ci
-          ' && EXIT_CODE="$?" || EXIT_CODE="$?"
+          NIX_LINTER=$(nix-instantiate --eval --raw -E '(import ./shell.nix {}).NIX_LINTER')
+          # Attempt to get it from cache, and fallback to building `devTools.nix` otherwise.
+          nix-store --realise "${NIX_LINTER%/bin/*}" || nix-build -I nixpkgs=tools/nix/pkgs.nix ./tools/nix/devTools.nix --no-out-link
+          "$NIX_LINTER" --quiet --ci && EXIT_CODE="$?" || EXIT_CODE="$?"
           if [ "$EXIT_CODE" != "0" ]
           then
             git --no-pager diff || true

shell.nix

@@ -167,6 +167,14 @@ pkgs.mkShell {
       YAMLLINT = pkgs.lib.getExe yamllint;
     }
   )
+  // (
+    let
+      treefmt = pkgs.lib.lists.findFirst (p: p.meta.mainProgram == "treefmt") null devTools;
+    in
+    pkgs.lib.optionalAttrs (treefmt != null) {
+      NIX_LINTER = pkgs.lib.getExe treefmt;
+    }
+  )
   // pkgs.lib.optionalAttrs (!withSQLite) {
     NOSQLITE = "1";
   }

tools/nix/devTools.nix

@@ -7,6 +7,7 @@
   pkgs.gh
   pkgs.git
   pkgs.jq
+  pkgs.nixfmt-tree
   pkgs.ruff
   pkgs.shellcheck
   pkgs.yamllint

tools/nix/list-requisites.sh

@@ -58,7 +58,7 @@ DRV=$(
       ++ builtins.attrValues (
         {
           # Additional packages we are using across the codebase
-          inherit (pkgs) nixfmt-tree sccache;
+          inherit (pkgs) sccache;
         }
         // import ./tools/nix/openssl-matrix.nix { }
         // sharedLibDepsFn (