feat: add persist module

flake.lock

@@ -551,6 +551,21 @@
         "type": "github"
       }
     },
+    "impermanence": {
+      "locked": {
+        "lastModified": 1737831083,
+        "narHash": "sha256-LJggUHbpyeDvNagTUrdhe/pRVp4pnS6wVKALS782gRI=",
+        "owner": "nix-community",
+        "repo": "impermanence",
+        "rev": "4b3e914cdf97a5b536a889e939fb2fd2b043a170",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "impermanence",
+        "type": "github"
+      }
+    },
     "libgit2": {
       "flake": false,
       "locked": {
@@ -1141,6 +1156,7 @@
         "flake-parts": "flake-parts_4",
         "flake-registry": "flake-registry",
         "home-manager": "home-manager",
+        "impermanence": "impermanence",
         "lite-config": "lite-config",
         "lix-module": "lix-module",
         "nixpkgs": "nixpkgs_8",

flake.nix

@@ -26,6 +26,7 @@
     };
 
     ataraxiasjel-nur.url = "github:AtaraxiaSjel/nur";
+    impermanence.url = "github:nix-community/impermanence";
     lix-module = {
       # url = "https://git.lix.systems/lix-project/nixos-module/archive/2.92.0.tar.gz";
       url = "github:ataraxiasjel/lix-nixos-module/2.92.0-1";

modules/home/default.nix

@@ -1,4 +1,11 @@
-{ ... }:
+{ lib, ... }:
+let
+  inherit (lib) filterAttrs;
+  inherit (builtins) attrNames readDir;
+  moduleDirs =
+    dir:
+    map (name: dir + "/${name}") (attrNames (filterAttrs (_: type: type == "directory") (readDir dir)));
+in
 {
-
+  imports = moduleDirs ./.;
 }

modules/home/persist/default.nix

@@ -0,0 +1,48 @@
+{
+  lib,
+  ...
+}:
+let
+  inherit (lib) mkOption mkEnableOption;
+  inherit (lib.types) listOf path str;
+in
+{
+  options =
+    let
+      common = {
+        directories = mkOption {
+          type = listOf str;
+          default = [ ];
+        };
+        files = mkOption {
+          type = listOf str;
+          default = [ ];
+        };
+      };
+    in
+    {
+      persist = {
+        enable = mkEnableOption "A tmpfs root with explicit opt-in state";
+        persistRoot = mkOption {
+          type = path;
+          default = "/persist";
+        };
+        # Stuff that matters
+        # TODO backups
+        state = {
+          # backup = {...};
+        } // common;
+        # Stuff that's just there to speed up the system
+        cache = {
+          clean = {
+            enable = mkEnableOption "cleaning the cache files and directories";
+            dates = mkOption {
+              type = str;
+              default = "weekly";
+              description = "A systemd.time calendar description of when to clean the cache files";
+            };
+          };
+        } // common;
+      };
+    };
+}

modules/nixos/persist/default.nix

@@ -0,0 +1,147 @@
+{
+  config,
+  lib,
+  inputs,
+  ...
+}:
+let
+  inherit (lib)
+    escapeShellArg
+    filterAttrs
+    mapAttrs
+    mapAttrs'
+    mkEnableOption
+    mkIf
+    mkMerge
+    mkOption
+    nameValuePair
+    ;
+  inherit (lib.types) listOf path str;
+  inherit (builtins) concatMap;
+  cfg = config.persist;
+in
+{
+  imports = [ inputs.impermanence.nixosModules.impermanence ];
+
+  options =
+    let
+      common = {
+        directories = mkOption {
+          type = listOf str;
+          default = [ ];
+        };
+        files = mkOption {
+          type = listOf str;
+          default = [ ];
+        };
+      };
+    in
+    {
+      persist = {
+        enable = mkEnableOption "A tmpfs root with explicit opt-in state";
+        persistRoot = mkOption {
+          type = path;
+          default = "/persist";
+        };
+        # Stuff that matters
+        # TODO backups
+        state = {
+          # backup = {...};
+        } // common;
+        # Stuff that's just there to speed up the system
+        cache = {
+          clean = {
+            enable = mkEnableOption "cleaning the cache files and directories";
+            dates = mkOption {
+              type = str;
+              default = "weekly";
+              description = "A systemd.time calendar description of when to clean the cache files";
+            };
+          };
+        } // common;
+      };
+    };
+
+  config =
+    let
+      # TODO: fix infinite recursion (can't get user home directory)
+      # userPersists = lib.mapAttrs (name: cfg:
+      #   cfg.persist // {
+      #     home = config.users.users.${name}.home;
+      #   }
+      # ) config.home-manager.users;
+      takeAll = what: concatMap (x: x.${what});
+      persists = with cfg; [
+        state
+        cache
+      ];
+      allFiles = takeAll "files" persists;
+      allDirectories = takeAll "directories" persists;
+
+      userPersists = mapAttrs (_: cfg: cfg.persist) config.home-manager.users;
+      usersFlatten = mapAttrs (
+        name: cfg:
+        let
+          persists = with cfg; [
+            state
+            cache
+          ];
+          allHomeFiles = takeAll "files" persists;
+          allHomeDirectories = takeAll "directories" persists;
+        in
+        {
+          home = "/home/${name}";
+          directories = allHomeDirectories;
+          files = allHomeFiles;
+        }
+      ) userPersists;
+    in
+    mkIf cfg.enable {
+      # Persist users uid by default
+      persist.state.directories = [ "/var/lib/nixos" ];
+
+      environment.persistence.${cfg.persistRoot} = {
+        hideMounts = true;
+        directories = allDirectories;
+        files = allFiles;
+        users = usersFlatten;
+      };
+
+      systemd.services =
+        let
+          filtered = filterAttrs (_: cfg: cfg.cache.clean.enable) userPersists;
+        in
+        mkMerge [
+          (mapAttrs' (
+            name: cfg:
+            let
+              absoluteHomePath = map (x: "/home/${name}/${x}");
+            in
+            nameValuePair "persist-cache-cleanup-${name}" {
+              description = "Cleaning up cache files and directories for user ${name}";
+              script = ''
+                  ${builtins.concatStringsSep "\n" (
+                    map (x: "rm ${escapeShellArg x}") (absoluteHomePath cfg.cache.files)
+                  )}
+
+                ${builtins.concatStringsSep "\n" (
+                  map (x: "rm -rf ${escapeShellArg x}") (absoluteHomePath cfg.cache.directories)
+                )}
+              '';
+              startAt = cfg.cache.clean.dates;
+            }
+          ) filtered)
+          {
+            persist-cache-cleanup = mkIf cfg.cache.clean.enable {
+              description = "Cleaning up cache files and directories";
+              script = ''
+                ${builtins.concatStringsSep "\n" (map (x: "rm ${escapeShellArg x}") cfg.cache.files)}
+
+                ${builtins.concatStringsSep "\n" (map (x: "rm -rf ${escapeShellArg x}") cfg.cache.directories)}
+              '';
+              startAt = cfg.cache.clean.dates;
+            };
+          }
+        ];
+    };
+}