make gcrootsdir optional again

.github/workflows/nix-github-actions.yml

@@ -1,6 +1,7 @@
 name: Nix actions
 on:
   pull_request:
+  merge_group:
   push:
     branches:
       - main
@@ -47,7 +48,6 @@ jobs:
       - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v31
       - uses: cachix/cachix-action@v16
-        if: ${{ ! env.NAMESPACE_RUNNER }}
         with:
           name: nix-community
           authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
@@ -68,7 +68,6 @@ jobs:
           extra_nix_config: |
             accept-flake-config = true
       - uses: cachix/cachix-action@v16
-        if: ${{ ! env.NAMESPACE_RUNNER }}
         with:
           name: nix-community
           authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "Hydra's builtin hydra-eval-jobs as a standalone";
 
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  inputs.nixpkgs.url = "https://nixos.org/channels/nixpkgs-unstable/nixexprs.tar.xz";
   inputs.flake-parts.url = "github:hercules-ci/flake-parts";
   inputs.flake-parts.inputs.nixpkgs-lib.follows = "nixpkgs";
   inputs.treefmt-nix.url = "github:numtide/treefmt-nix";

src/nix-eval-jobs.cc

@@ -465,11 +465,7 @@ auto main(int argc, char **argv) -> int {
             throw nix::UsageError("no expression specified");
         }
 
-        if (myArgs.gcRootsDir.empty()) {
-            const nix::Path tmpDir = nix::createTempDir();
-            gcRootsDir.emplace(tmpDir, true);
-            myArgs.gcRootsDir = tmpDir;
-        } else {
+        if (!myArgs.gcRootsDir.empty()) {
             myArgs.gcRootsDir = std::filesystem::absolute(myArgs.gcRootsDir);
         }
 
@@ -570,15 +566,16 @@ auto main(int argc, char **argv) -> int {
                             nix::writeDerivation(*store, drvAggregate);
                         auto newDrvPathS = store->printStorePath(newDrvPath);
 
-                        assert(!myArgs.gcRootsDir.empty());
-                        const nix::Path root =
-                            myArgs.gcRootsDir + "/" +
-                            std::string(nix::baseNameOf(newDrvPathS));
+                        if (!myArgs.gcRootsDir.empty()) {
+                            const nix::Path root =
+                                myArgs.gcRootsDir + "/" +
+                                std::string(nix::baseNameOf(newDrvPathS));
 
-                        if (!nix::pathExists(root)) {
-                            auto localStore =
-                                store.dynamic_pointer_cast<nix::LocalFSStore>();
-                            localStore->addPermRoot(newDrvPath, root);
+                            if (!nix::pathExists(root)) {
+                                auto localStore = store.dynamic_pointer_cast<
+                                    nix::LocalFSStore>();
+                                localStore->addPermRoot(newDrvPath, root);
+                            }
                         }
 
                         nix::logger->log(

tests/test_eval.py

@@ -124,6 +124,27 @@ def test_eval_error() -> None:
         assert "this is an evaluation error" in attrs["error"]
 
 
+def test_no_gcroot_dir() -> None:
+    cmd = [
+        str(BIN),
+        "--meta",
+        "--workers",
+        "1",
+        "--flake",
+        ".#legacyPackages.x86_64-linux.brokenPkgs",
+    ]
+    res = subprocess.run(
+        cmd,
+        cwd=TEST_ROOT.joinpath("assets"),
+        text=True,
+        stdout=subprocess.PIPE,
+    )
+    print(res.stdout)
+    attrs = json.loads(res.stdout)
+    assert attrs["attr"] == "brokenPackage"
+    assert "this is an evaluation error" in attrs["error"]
+
+
 def test_constituents() -> None:
     with TemporaryDirectory() as tempdir:
         cmd = [