modules/version: init with nixpkgsReleaseCheck

Inspired by `home.version` and `home.enableNixpkgsReleaseCheck` in Home
Manager. Print a warning when `lib` or `pkgs` are from a different
release to Nixvim.

modules/misc/default.nix

@@ -4,5 +4,6 @@
     ./context.nix
     ./meta.nix
     ./nixvim-info.nix
+    ./version.nix
   ];
 }

modules/misc/version.nix

@@ -0,0 +1,74 @@
+{
+  lib,
+  pkgs,
+  config,
+  options,
+  ...
+}:
+let
+  versionInfo = lib.importTOML ../../version-info.toml;
+in
+{
+  options.version = {
+    release = lib.mkOption {
+      type = lib.types.str;
+      default = versionInfo.release;
+      description = "The Nixvim release.";
+      internal = true;
+      readOnly = true;
+    };
+
+    isUnstable = lib.mkOption {
+      type = lib.types.bool;
+      default = versionInfo.unstable;
+      description = "Whether Nixvim is from an unstable branch.";
+      internal = true;
+      readOnly = true;
+    };
+
+    enableNixpkgsReleaseCheck = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      example = false;
+      description = ''
+        Whether to check for release version mismatch between Nixvim and Nixpkgs.
+
+        Using mismatched versions is likely to cause errors and unexpected behavior.
+        It is highly recommended to use corresponding Nixvim and Nixpkgs releases.
+
+        When this option is enabled and a mismatch is detected,
+        a warning will be printed when the Nixvim configuration is evaluated.
+      '';
+    };
+
+  };
+
+  config = {
+    warnings =
+      let
+        nixvimRelease = config.version.release;
+        libRelease = lib.trivial.release;
+        pkgsRelease = pkgs.lib.trivial.release;
+        releaseMismatch = nixvimRelease != libRelease || nixvimRelease != pkgsRelease;
+      in
+      lib.optional (config.version.enableNixpkgsReleaseCheck && releaseMismatch) ''
+        You are using${
+          if libRelease == pkgsRelease then
+            " Nixvim version ${nixvimRelease} and Nixpkgs version ${libRelease}."
+          else
+            ''
+              :
+              - Nixvim version: ${nixvimRelease}
+              - Nixpkgs version used to evaluate Nixvim: ${libRelease}
+              - Nixpkgs version used for packages (`pkgs`): ${pkgsRelease}''
+        }
+
+        Using mismatched versions is likely to cause errors and unexpected behavior.
+        It is highly recommended to use corresponding Nixvim and Nixpkgs releases.
+
+        If you insist, you can disable this warning using:
+
+          ${options.version.enableNixpkgsReleaseCheck} = false;
+      '';
+  };
+}