feat: add environment.extraInit option

nix/modules/environment.nix

@@ -16,6 +16,12 @@
       type = lib.types.listOf lib.types.str;
       default = [ ];
     };
+
+    extraInit = lib.mkOption {
+      type = lib.types.lines;
+      default = "";
+      description = "Shell script code which should be called before any shell session through the host /etc/profile.";
+    };
   };
 
   config =
@@ -31,6 +37,7 @@
         etc = {
           "profile.d/system-manager-path.sh".source = pkgs.writeText "system-manager-path.sh" ''
             export PATH=${pathDir}/bin/:''${PATH}
+            ${config.environment.extraInit}
           '';
 
           # TODO: figure out how to properly add fish support. We could start by

testFlake/container-tests.nix

@@ -119,6 +119,41 @@ in
       '';
   };
 
+  container-extra-init = makeContainerTestFor "extra-init" {
+    modules = [
+      (
+        { ... }:
+        {
+          environment.etc."nix/nix.conf".replaceExisting = true;
+
+          environment.extraInit = ''
+            export MY_CUSTOM_VAR="hello-from-extraInit"
+          '';
+        }
+      )
+    ];
+    testScriptFunction =
+      { toplevel, hostPkgs, ... }:
+      ''
+        start_all()
+
+        machine.wait_for_unit("multi-user.target")
+
+        activation_logs = machine.activate()
+        for line in activation_logs.split("\n"):
+            assert not "ERROR" in line, line
+        machine.wait_for_unit("system-manager.target")
+
+        with subtest("extraInit code is present in profile script"):
+            content = machine.succeed("cat /etc/profile.d/system-manager-path.sh")
+            assert "MY_CUSTOM_VAR" in content, f"Expected extraInit content in profile script, got: {content}"
+
+        with subtest("extraInit variable is set in login shell"):
+            value = machine.succeed("bash --login -c 'echo $MY_CUSTOM_VAR'").strip()
+            assert value == "hello-from-extraInit", f"Expected 'hello-from-extraInit', got: '{value}'"
+      '';
+  };
+
   container-masked-units = makeContainerTestFor "masked-units" {
     modules = [
       (