nixos/config: add defaultPackages option

readd perl (used in shell scripts), rsync (needed for NixOps) and strace (common debugging tool)

they where previously removed in NixOS#91213

Co-authored-by: Timo Kaufmann <timokau@zoho.com>
Co-authored-by: 8573 <8573@users.noreply.github.com>
(cherry picked from commit 74b3d66)

nixos/doc/manual/release-notes/rl-2009.xml

@@ -1315,7 +1315,11 @@ services.transmission.settings.rpc-bind-address = "0.0.0.0";
  <para>
  Nginx module <literal>nginxModules.fastcgi-cache-purge</literal> renamed to official name <literal>nginxModules.cache-purge</literal>.
  Nginx module <literal>nginxModules.ngx_aws_auth</literal> renamed to official name <literal>nginxModules.aws-auth</literal>.
- The packages <package>perl</package>, <package>rsync</package> and <package>strace</package> were removed from <option>systemPackages</option>. If you need them, install them again with <code><xref linkend="opt-environment.systemPackages"/> = with pkgs; [ perl rsync strace ];</code> in your <filename>configuration.nix</filename>.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The option <option>defaultPackages</option> was added. It installs the packages <package>perl</package>, <package>rsync</package> and <package>strace</package> for now. They were added unconditionally to <option>systemPackages</option> before, but are not strictly necessary for a minimal NixOS install. You can set it to an empty list to have a more minimal system. Be aware that some functionality might still have an impure dependency on those packages, so things might break.
  </para>
  </listitem>
  <listitem>

nixos/modules/config/system-path.nix

@@ -41,6 +41,12 @@ let
  pkgs.zstd
  ];
 
+ defaultPackages = map (pkg: setPrio ((pkg.meta.priority or 5) + 3) pkg)
+ [ pkgs.perl
+ pkgs.rsync
+ pkgs.strace
+ ];
+
 in
 
 {
@@ -63,6 +69,21 @@ in
  '';
  };
 
+ defaultPackages = mkOption {
+ type = types.listOf types.package;
+ default = defaultPackages;
+ example = literalExample "[]";
+ description = ''
+ Set of packages users expect from a minimal linux istall.
+ Like systemPackages, they appear in
+ /run/current-system/sw. These packages are
+ automatically available to all users, and are
+ automatically updated every time you rebuild the system
+ configuration.
+ If you want a more minimal system, set it to an empty list.
+ '';
+ };
+
  pathsToLink = mkOption {
  type = types.listOf types.str;
  # Note: We need `/lib' to be among `pathsToLink' for NSS modules
@@ -102,7 +123,7 @@ in
 
  config = {
 
- environment.systemPackages = requiredPackages;
+ environment.systemPackages = requiredPackages ++ config.environment.defaultPackages;
 
  environment.pathsToLink =
  [ "/bin"