Reapply "nixos/seerr: use lib.mkStateRevisionOption"

This reverts commit 8820b84c40.

nixos/doc/manual/development/state-revision.section.md

@@ -0,0 +1,57 @@
+# State revision {#sec-state-revision}
+
+NixOS includes a {option}`system.stateVersion` option, used by some modules for a
+variety of reasons related to non-backward-compatible changes to software or
+the module itself.
+Module authors are discouraged from adding new uses of
+{option}`system.stateVersion` to their module.
+
+However, when the alternatives are impractical, modules that wish to consume
+{option}`system.stateVersion` should instead define their own `stateRevision`
+option using `utils.mkStateRevisionOption`.
+There should be no uses of `config.system.stateVersion` directly in the module.
+
+(Note the name difference: the {option}`system.stateVersion` option, with a V,
+takes a value that looks like "YY.MM".
+A `stateRevision` option, with an R, takes a non-negative integer value.)
+
+Modules should also add the value of their `stateRevision` option to
+`system.moduleStateRevisions."your.module.stateRevision"`, when the module is
+enabled.
+This is a purely informative option that exists to help describe the effects of
+changing {option}`system.stateVersion`.
+
+Example:
+
+```nix
+{
+  lib,
+  config,
+  utils,
+  ...
+}:
+let
+  cfg = config.services.whatever;
+in
+{
+  options.services.whatever = {
+    enable = lib.mkEnableOption "whatever, a service that does whatever";
+    stateRevision = utils.mkStateRevisionOption {
+      descriptionName = "the whatever service";
+      migrations = {
+        "26.05" = "Rename `/var/lib/old_name` to `/var/lib/new_name`.";
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.services.whatever = {
+      # ...
+      serviceConfig.StateDirectory = if cfg.stateRevision < 1 then "old_name" else "new_name";
+    };
+
+    # Important: this is inside the `lib.mkIf cfg.enable`
+    system.moduleStateRevisions."services.whatever.stateRevision" = cfg.stateRevision;
+  };
+}
+```

nixos/doc/manual/development/writing-modules.chapter.md

@@ -220,4 +220,5 @@ importing-modules.section.md
 replace-modules.section.md
 freeform-modules.section.md
 settings-options.section.md
+state-revision.section.md
 ```

nixos/doc/manual/redirects.json

@@ -253,6 +253,9 @@
   "sec-override-nixos-test": [
     "index.html#sec-override-nixos-test"
   ],
+  "sec-state-revision": [
+    "index.html#sec-state-revision"
+  ],
   "sec-wireless-declarative": [
     "index.html#sec-wireless-declarative"
   ],

nixos/lib/utils.nix

@@ -6,8 +6,10 @@
 
 let
   inherit (lib)
+    all
     any
     attrNames
+    concatImapStringsSep
     concatMapStringsSep
     concatStringsSep
     elem
@@ -27,8 +29,11 @@ let
     isList
     isPath
     isString
+    length
     listToAttrs
+    literalMD
     mapAttrs
+    mkOption
     nameValuePair
     optionalString
     removePrefix
@@ -36,8 +41,10 @@ let
     splitString
     stringToCharacters
     types
+    versionOlder
     ;
 
+  inherit (lib.lists) findFirstIndex;
   inherit (lib.strings) toJSON escapeC;
 in
 
@@ -604,6 +611,123 @@ let
         lib.listToAttrs
       ];
     };
+
+    /**
+      Creates a per-module `stateRevision` option that takes an int value, with a
+      default that is derived from `system.stateVersion`.
+
+      # Inputs
+
+      `descriptionName`
+      : A human-friendly name for your module, used for the description of the
+        created option.
+
+      `migrations`
+      : Attribute set that maps from values of `system.stateVersion`
+        (representing the breakpoints at which the default value of this option
+        will change) to Markdown instructions to users for manually migrating
+        their data to this breakpoint. The migration instructions will be
+        included in the NixOS documentation for this option. (These instructions
+        must only contain Markdown inlines, because they will be rendered in a
+        table. In particular, lists will not render correctly.)
+
+        `migrations` will also be exposed as an attribute on the result.
+
+      # Examples
+      :::{.example}
+      ## `lib.options.mkStateRevisionOption` usage example
+
+      ```nix
+      exampleModule =
+        { lib, config, utils, ... }:
+        {
+          options.services.whatever = {
+            stateRevision = utils.mkStateRevisionOption {
+              descriptionName = "the whatever service";
+              migrations = {
+                "26.05" = "Rename `/var/lib/old_name` to `/var/lib/new_name`.";
+                "26.11" = "Run the `upgrade_whatever` utility.";
+                };
+              };
+            };
+          };
+        }
+
+      (pkgs.nixos [
+        exampleModule
+        { system.stateVersion = "25.11"; }
+      ]).config.services.whatever.stateRevision # => 0
+      (pkgs.nixos [
+        exampleModule
+        { system.stateVersion = "26.05"; }
+      ]).config.services.whatever.stateRevision # => 1
+      (pkgs.nixos [
+        exampleModule
+        { system.stateVersion = "27.05"; }
+      ]).config.services.whatever.stateRevision # => 2
+      ```
+
+      :::
+
+      Modules should use this function when they change how data managed by the
+      module is persisted on the system between NixOS releases.
+
+      The default value of the option will be the number of attributes in the
+      `migrations` parameter with name less than or equal to the value of
+      `system.stateVersion`.
+
+      When using this function, don't forget to add the option's value to
+      `system.moduleStateRevisions."your.module.stateRevision"` when your module is
+      enabled.
+    */
+    mkStateRevisionOption =
+      {
+        descriptionName,
+        migrations,
+      }:
+      let
+        versions = attrNames migrations;
+        maxVal = length versions;
+      in
+      assert all (v: builtins.match "[0-9]{2}\\.[0-9]{2}" v != null) versions;
+      mkOption {
+        type = types.ints.between 0 maxVal;
+        description = ''
+          This option versions the format of state persisted by
+          ${descriptionName}. Its default value depends on the value of
+          {option}`system.stateVersion`.
+
+          Users who wish to increment this option will need to take manual
+          migration steps to preserve their data. **If you perform these
+          migrations, rolling back to an older generation will require also
+          reversing the migrations to the state expected by that generation.**
+          The migrations needed to advance to each value of this option are as
+          follows (perform all instructions after the row for the current
+          `stateRevision`, up to and including the row for the new
+          `stateRevision`):
+
+          | `stateRevision` | Migration instructions |
+          |-----------------|------------------------|
+          | 0               | (none)                 |
+          ${concatImapStringsSep "\n" (
+            v: sv: "| ${toString v} | ${replaceStrings [ "\n" ] [ " " ] migrations.${sv}} |"
+          ) versions}
+
+          Note that you do **not** need to change {option}`system.stateVersion`
+          in order to update this option. {option}`system.stateVersion` only
+          determines the default value of this option. Most users should not
+          change {option}`system.stateVersion` at all.
+        '';
+        default = findFirstIndex (versionOlder config.system.stateVersion) maxVal versions;
+        defaultText = literalMD ''
+          If {option}`system.stateVersion` is:
+          ${concatImapStringsSep "\n" (v: sv: "* <${sv}: ${toString (v - 1)}") versions}
+          * otherwise: ${toString maxVal}
+        '';
+      }
+      // {
+        inherit migrations;
+      };
   };
 in
 utils

nixos/modules/misc/version.nix

@@ -254,6 +254,30 @@ in
       '';
     };
 
+    moduleStateRevisions = mkOption {
+      type =
+        let
+          baseType = types.attrsOf types.ints.unsigned;
+          isStateRevisionOption = x: lib.isOption x && x ? migrations;
+        in
+        types.addCheck baseType (
+          attrs:
+          builtins.all (
+            attrPath: isStateRevisionOption (lib.attrByPath (lib.splitString "." attrPath) null options)
+          ) (builtins.attrNames attrs)
+        )
+        // {
+          description = "${baseType.description}, in which every attribute name is the path to an option created with mkStateRevisionOption";
+        };
+      default = { };
+      internal = true;
+      description = ''
+        NixOS modules should set attributes on this option. Users should leave
+        it alone. Future tooling may use it to determine the consequences of
+        updating {option}`system.stateVersion`.
+      '';
+    };
+
     configurationRevision = mkOption {
       type = types.nullOr types.str;
       default = null;

nixos/modules/services/misc/seerr.nix

@@ -2,13 +2,14 @@
   config,
   pkgs,
   lib,
+  utils,
   ...
 }:
 let
   cfg = config.services.seerr;
-  # 26.05 introduced a breaking change which is guarded behind stateVersion to avoid
-  # breaking users.
-  useNewConfigLocation = lib.versionAtLeast config.system.stateVersion "26.05";
+  # 26.05 introduced a breaking change which is guarded behind stateRevision to
+  # avoid breaking users.
+  useNewConfigLocation = cfg.stateRevision >= 1;
 in
 {
   imports = [
@@ -39,8 +40,23 @@ in
     configDir = lib.mkOption {
       type = lib.types.path;
       default = if useNewConfigLocation then "/var/lib/seerr/" else "/var/lib/jellyseerr/config";
+      defaultText = lib.literalMD "{file}`/var/lib/seerr` (or {file}`/var/lib/jellyseerr/config` if {option}`services.seerr.stateRevision` < 1)";
       description = "Config data directory";
     };
+
+    stateRevision = utils.mkStateRevisionOption {
+      descriptionName = "Seerr";
+      migrations = {
+        "26.05" = ''
+          Move {file}`/var/lib/private/jellyseerr/config` to
+          {file}`/var/lib/private/seerr`, if you have not set
+          {option}`services.seerr.configDir`. (If you have set
+          {option}`services.seerr.configDir`, you should also have forced
+          {option}`systemd.services.seerr.serviceConfig.StateDirectory`, and in
+          that case `stateRevision` does not affect your configuration.)
+        '';
+      };
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -81,5 +97,7 @@ in
     networking.firewall = lib.mkIf cfg.openFirewall {
       allowedTCPPorts = [ cfg.port ];
     };
+
+    system.moduleStateRevisions."services.seerr.stateRevision" = cfg.stateRevision;
   };
 }

nixos/tests/all-tests.nix

@@ -1059,6 +1059,7 @@ in
   modularService = pkgs.callPackage ../modules/system/service/systemd/test.nix {
     inherit evalSystem;
   };
+  moduleStateRevisions = pkgs.callPackage ./moduleStateRevisions.nix { };
   molly-brown = runTest ./molly-brown.nix;
   mollysocket = runTest ./mollysocket.nix;
   monado = runTest ./monado.nix;
@@ -1842,7 +1843,7 @@ in
   userborn-mutable-users = runTest ./userborn-mutable-users.nix;
   userborn-static = runTest ./userborn-static.nix;
   ustreamer = runTest ./ustreamer.nix;
-  utils = import ./utils { inherit runTest; };
+  utils = pkgs.callPackage ./utils { inherit runTest; };
   utmp = runTest ./utmp.nix;
   uwsgi = runTest ./uwsgi.nix;
   v2ray = runTest ./v2ray.nix;

nixos/tests/moduleStateRevisions.nix

@@ -0,0 +1,25 @@
+{
+  lib,
+  emptyFile,
+  nixos,
+}:
+let
+  evalModuleStateRevisions =
+    cfg:
+    (nixos [
+      { system.stateVersion = lib.trivial.release; }
+      cfg
+    ]).config.system.moduleStateRevisions;
+
+  # For modules that follow the <module>.enable, <module>.stateRevision pattern:
+  testModule =
+    path:
+    evalModuleStateRevisions (lib.setAttrByPath path { enable = true; })
+    ? "${builtins.concatStringsSep "." path}.stateRevision";
+in
+assert evalModuleStateRevisions { } == { };
+assert testModule [
+  "services"
+  "seerr"
+];
+emptyFile

nixos/tests/utils/default.nix

@@ -1,5 +1,9 @@
-{ runTest }:
+{
+  callPackage,
+  runTest,
+}:
 
 {
   genJqSecretsReplacement = runTest ./genJqSecretsReplacement.nix;
+  mkStateRevisionOption = callPackage ./mkStateRevisionOption.nix { };
 }

nixos/tests/utils/mkStateRevisionOption.nix

@@ -0,0 +1,39 @@
+{
+  emptyFile,
+  nixos,
+}:
+let
+  result = nixos (
+    { utils, ... }:
+    {
+      options = {
+        stateRevision1 = utils.mkStateRevisionOption {
+          descriptionName = "...";
+          migrations = {
+            "27.05" = "...";
+          };
+        };
+        stateRevision2 = utils.mkStateRevisionOption {
+          descriptionName = "...";
+          migrations = {
+            "26.11" = "...";
+          };
+        };
+        stateRevision3 = utils.mkStateRevisionOption {
+          descriptionName = "...";
+          migrations = {
+            "24.05" = "...";
+            "27.05" = "...";
+          };
+        };
+      };
+      config.system.stateVersion = "26.11";
+    }
+  );
+  inherit (result) config options;
+in
+assert config.stateRevision1 == 0;
+assert config.stateRevision2 == 1;
+assert config.stateRevision3 == 1;
+assert options.stateRevision1.migrations == { "27.05" = "..."; };
+emptyFile