flake.nix: make checks friendly for non-x86_64-linux systems

          );

      });

      checks.x86_64-linux = {

        tarball = jobs.x86_64-linux.tarball;

      checks = forAllSystems (system: {

        tarball = jobs.${system}.tarball;

      } // lib.optionalAttrs (self.legacyPackages.${system}.stdenv.isLinux) {

        # Test that ensures that the nixosSystem function can accept a lib argument

        # Note: prefer not to extend or modify `lib`, especially if you want to share reusable modules

        #       alternatives include: `import` a file, or put a custom library in an option or in `_module.args.<libname>`

        nixosSystemAcceptsLib = (self.lib.nixosSystem {

          pkgs = self.legacyPackages.x86_64-linux;

          pkgs = self.legacyPackages.${system};

          lib = self.lib.extend (final: prev: {

            ifThisFunctionIsMissingTheTestFails = final.id;

          });

            })

          ];

        }).config.system.build.toplevel;

      };

      });

      htmlDocs = {

        nixpkgsManual = jobs.x86_64-linux.manual;

        nixpkgsManual = builtins.mapAttrs (_: jobSet: jobSet.manual) jobs;

        nixosManual = (import ./nixos/release-small.nix {

          nixpkgs = self;

        }).nixos.manual.x86_64-linux;

        }).nixos.manual;

      };

      # The "legacy" in `legacyPackages` doesn't imply that the packages exposed