flake: fix patch for nix-eval-jobs

We carry a custom patch for nix-eval-jobs that causes the tool to not
unset the `NIX_PATH` environment variable anymore. The patch does not
apply anymore starting with d0bcdae (clang-tidy: use trailing return
type, 2024-11-10) because surrounding code has changed. Other than that
the patch still applies.

The mentioned commit was released with nix-eval-jobs v2.25.0, which
nixos-unstable has recently upgraded to. Adapt the patch to unbreak the
build.

Fixes #255.

flake.nix

@@ -36,11 +36,11 @@
       patched = prev.nix-eval-jobs.overrideAttrs (old: {
         version = old.version + "-colmena";
         patches = (old.patches or []) ++ [
-          # Allows NIX_PATH to be honored
-          (final.fetchpatch {
-            url = "https://github.com/zhaofengli/nix-eval-jobs/commit/6ff5972724230ac2b96eb1ec355cd25ca512ef57.patch";
-            hash = "sha256-2NiMYpw27N+X7Ixh2HkP3fcWvopDJWQDVjgRdhOL2QQ";
-          })
+          (if builtins.compareVersions old.version "2.25.0" >= 0 then
+            ./nix-eval-jobs-unstable.patch
+          else
+            ./nix-eval-jobs-stable.patch
+          )
         ];
       });
     in {

nix-eval-jobs-stable.patch

@@ -0,0 +1,25 @@
+From 6ff5972724230ac2b96eb1ec355cd25ca512ef57 Mon Sep 17 00:00:00 2001
+From: Zhaofeng Li <hello@zhaofeng.li>
+Date: Sat, 5 Oct 2024 17:59:04 -0600
+Subject: [PATCH] Allow NIX_PATH environment variable
+
+---
+ src/nix-eval-jobs.cc | 5 -----
+ 1 file changed, 5 deletions(-)
+
+diff --git a/src/nix-eval-jobs.cc b/src/nix-eval-jobs.cc
+index de7a2bcf..30de4c53 100644
+--- a/src/nix-eval-jobs.cc
++++ b/src/nix-eval-jobs.cc
+@@ -342,11 +342,6 @@ void collector(Sync<State> &state_, std::condition_variable &wakeup) {
+ }
+
+ int main(int argc, char **argv) {
+-
+-    /* Prevent undeclared dependencies in the evaluation via
+-       $NIX_PATH. */
+-    unsetenv("NIX_PATH");
+-
+     /* We are doing the garbage collection by killing forks */
+     setenv("GC_DONT_GC", "1", 1);
+

nix-eval-jobs-unstable.patch

@@ -0,0 +1,16 @@
+diff --git a/src/nix-eval-jobs.cc b/src/nix-eval-jobs.cc
+index 13d610c..e5e6a0f 100644
+--- a/src/nix-eval-jobs.cc
++++ b/src/nix-eval-jobs.cc
+@@ -376,11 +376,6 @@ void collector(nix::Sync<State> &state_, std::condition_variable &wakeup) {
+ } // namespace
+
+ auto main(int argc, char **argv) -> int {
+-
+-    /* Prevent undeclared dependencies in the evaluation via
+-       $NIX_PATH. */
+-    unsetenv("NIX_PATH"); // NOLINT(concurrency-mt-unsafe)
+-
+     /* We are doing the garbage collection by killing forks */
+     setenv("GC_DONT_GC", "1", 1); // NOLINT(concurrency-mt-unsafe)
+