_experimental-update-script-combinators.sequence: handle silent scripts

    let

      scripts = scriptsNormalized;

      hasCommitSupport = lib.findSingle ({ supportedFeatures, ... }: supportedFeatures == [ "commit" ]) null null scripts != null;

      hasSilentSupport = lib.findFirst ({ supportedFeatures, ... }: supportedFeatures == [ "silent" ]) null scripts != null;

      # Supported features currently only describe the format of the standard output of the update script.

      # Here we ensure that the standard output of the combined update script is well formed.

      validateFeatures =

        if hasCommitSupport then

          # Exactly one update script declares only “commit” feature and all the rest declare only “silent” feature.

          ({ supportedFeatures, ... }: supportedFeatures == [ "commit" ] || supportedFeatures == [ "silent" ])

        else if hasSilentSupport then

          # All update scripts declare only “silent” feature.

          ({ supportedFeatures, ... }: supportedFeatures == [ "silent" ])

        else

          # No update script declares any supported feature to fail loudly on unknown features rather than silently discard them.

          ({ supportedFeatures, ... }: supportedFeatures == [ ]);

    in

    assert lib.assertMsg (lib.all validateFeatures scripts) "Combining update scripts with features enabled (other than a single script with “commit” and all other with “silent”) is currently unsupported.";

    assert lib.assertMsg (lib.all validateFeatures scripts) "Combining update scripts with features enabled (other than “silent” scripts and an optional single script with “commit”) is currently unsupported.";

    assert lib.assertMsg (builtins.length (lib.unique (builtins.map ({ attrPath ? null, ... }: attrPath) scripts)) == 1) "Combining update scripts with different attr paths is currently unsupported.";

    {

      command = commandsToShellInvocation (builtins.map ({ command, ... }: command) scripts);

      supportedFeatures = lib.optionals hasCommitSupport [

        "commit"

      ];

      supportedFeatures =

        if hasCommitSupport then

          [ "commit" ]

        else if hasSilentSupport then

          [ "silent" ]

        else

          [ ];

    };

  /*