[FC-32491] get rid of userenv

The old userenv module relied on nix envs, which are prone to breakage
on system upgrades. the new approach will function the same, but
eliminate the possibility of breakage while also being more discoverable
in the `/etc/local/nixos` directory

src/batou_ext/nix.py

@@ -102,37 +102,36 @@ class UserEnv(batou.component.Component):
                     "yarn",
                     "zip",
                 ],
-                channel="<nixos-channel-base-url-to-be-put-in>/nixexprs.tar.xz"
                 shellInit="# additional shell init")
 
     A list of available channels can be found at e.g.
     https://nixos.org/channels/
     """
 
     namevar = "profile_name"
-    channel = batou.component.Attribute(str)
     shellInit = ""
     packages = ()
     let_extra = ""
+    channel = None
 
     def configure(self):
-        self.checksum = hashlib.sha256()
+        if self.channel:
+            batou.output.step(
+                "WARNING",
+                "using `channel` with UserEnv is deprecated, please remove it from your deployment code.",
+                yellow=True,
+            )
+
         template = pkg_resources.resource_string(
             __name__, "resources/userenv.nix"
         ).decode("UTF-8")
         self.profile = self.expand(template).encode("UTF-8")
-        self.checksum.update(self.profile)
-        self.nix_env_name = self.expand(
-            "{{component.profile_name}}-1.{{component.checksum.hexdigest()}}"
-        )
+
         self += batou.lib.file.File(
-            self.profile_name + ".nix", content=self.profile
-        )
-        self += Package(self.nix_env_name, file=self._.path)
-        self.user_profile_path = os.path.expanduser(
-            "~/.nix-profile/etc/profile.d/{}.sh".format(self.profile_name)
+            f"/etc/local/nixos/profile-{self.profile_name}.nix",
+            content=self.profile,
         )
-        self.user_bin_path = os.path.expanduser("~/.nix-profile/bin")
+        self.user_profile_path = "/etc/profile"
 
 
 class Rebuild(batou.component.Component):

src/batou_ext/resources/userenv.nix

@@ -1,27 +1,14 @@
-let
-  # see https://nixos.org/channels/
-  nixpkgs = fetchTarball {{component.channel}};
-
-in
-{ pkgs ? import nixpkgs { } }:
-
-with pkgs;
-let
+{ pkgs, ... }: let
+  {{component.let_extra}}
 
-  shellInit = writeText "shellInit"''
+in {
+  users.users."{{component.environment.service_user}}".packages = with pkgs; [
+    # {%- for name in component.packages %}
+    {{name}}
+    # {%- endfor %}
+  ];
 
+  environment.shellInit = ''
     {{component.shellInit.replace('\n', '\n    ').strip()}}
   '';
-
-  {{component.let_extra}}
-
-in buildEnv {
-    name = "{{ '{{' }}component.nix_env_name{{ '}}' }}";
-    paths = [
-      (runCommand "profile" { } "install -D ${shellInit} $out/etc/profile.d/{{component.profile_name}}.sh")
-      {%- for name in component.packages %}
-      {{name}}
-      {%- endfor %}
-    ];
-    extraOutputsToInstall = [ "bin" "dev" "lib" "man" "out" ];
 }