sing-box: install shell completions directly

{

  lib,

  stdenv,

  buildGoModule,

  fetchFromGitHub,

  installShellFiles,

  buildPackages,

  coreutils,

  nix-update-script,

  nixosTests,

    "-X=github.com/sagernet/sing-box/constant.Version=${finalAttrs.version}"

  ];

  postInstall =

    let

      emulator = stdenv.hostPlatform.emulator buildPackages;

    in

    ''

      installShellCompletion --cmd sing-box \

        --bash <(${emulator} $out/bin/sing-box completion bash) \

        --fish <(${emulator} $out/bin/sing-box completion fish) \

        --zsh  <(${emulator} $out/bin/sing-box completion zsh )

  postInstall = ''

    installShellCompletion release/completions/sing-box.{bash,fish,zsh}

    substituteInPlace release/config/sing-box{,@}.service \

      --replace-fail "/usr/bin/sing-box" "$out/bin/sing-box" \