Include runtime files in output

flake.nix

@@ -8,7 +8,21 @@
       (system:
         let pkgs = nixpkgs.legacyPackages.${system}; in
         {
-          defaultPackage = pkgs.callPackage ./package.nix {};
+          packages.default = pkgs.callPackage ./package.nix {};
+
+          checks = {
+            # I used to put these into $out/lib, but justStaticExecutables
+            # removes that directory. Now I feel like I'm just getting lucky. So
+            # let's double check the files are there.
+            file-check = pkgs.runCommand "check-runtime-files" {} ''
+              if [ -e ${self.packages.${system}.default}/run/config/settings.yml ]; then
+                touch $out
+              else
+                2>&1 echo "Runtime files are missing"
+                exit 1
+              fi
+            '';
+          };
         }
       );
 }

package.nix

@@ -9,6 +9,12 @@ let
         preConfigure = ''
           ${pkgs.hpack}/bin/hpack .
         '';
+        # During build, static files are generated into the source tree's
+        # static/ dir. Plus, config/ is needed at runtime.
+        postInstall = ''
+          mkdir -p $out/run
+          cp -a {static,config} $out/run
+        '';
         src = pkgs.lib.cleanSource old.src;
       });