feature: prefer local build in nix (patch)

nixos/modules/flake.nix

···
     programs.command-not-found.dbPath = programsdb.packages.${pkgs.system}.programs-sqlite;
 
     nix = {
-      package = lib.mkDefault nix.packages.${pkgs.system}.nix; # pkgs.nixUnstable;
+      package = lib.mkDefault (nix.packages.${pkgs.system}.nix.overrideAttrs (oa: {
+        version = "${oa.version}_patched";
+        patches = [./prefer-local.patch];
+      }));
       settings.experimental-features = ["nix-command" "flakes"];
 
       registry.nixpkgs.flake = unstable;

nixos/modules/prefer-local.patch

···
+diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
+index cfc4baaca..4fbaae4fa 100644
+--- a/src/build-remote/build-remote.cc
++++ b/src/build-remote/build-remote.cc
+@@ -122,6 +122,8 @@ static int main_build_remote(int argc, char * * argv)
+             /* It's possible to build this locally right now: */
+             bool canBuildLocally = amWilling && couldBuildLocally;
+ 
++            if (canBuildLocally) continue;
++
+             /* Error ignored here, will be caught later */
+             mkdir(currentLoad.c_str(), 0777);
+