From 386d56af2817cbeeaea174b3f0c2431f66d75565 Mon Sep 17 00:00:00 2001
From: Seth Flynn <getchoo@tuta.io>
Date: Sat, 10 May 2025 22:27:44 -0400
Subject: [PATCH] modules: add `users.<user>.files.<name>.{generator,value}`
 options

---
 README.md               |  9 ++++++++
 modules/common/user.nix | 49 ++++++++++++++++++++++++++++++++---------
 tests/basic.nix         | 19 ++++++++++++++--
 3 files changed, 65 insertions(+), 12 deletions(-)

diff --git a/README.md b/README.md
index 7941173..a744515 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,15 @@ may use to manage individual users' homes by leveraging the module system.
       # This can be used to generate config files with various
       # formats expected by different programs.
       ".config/bar".source = pkgs.writeTextFile "file-foo" "file contents";
+
+      # You can also use generators to transform Nix values
+      ".config/baz" = {
+        # Works with `pkgs.formats` too!
+        generator = lib.generators.toJSON { };
+        value = {
+          some = "contents";
+        };
+      };
     };
   };
 }
diff --git a/modules/common/user.nix b/modules/common/user.nix
index 3a80057..ac593d7 100644
--- a/modules/common/user.nix
+++ b/modules/common/user.nix
@@ -10,10 +10,10 @@
 }: let
   inherit (lib.attrsets) mapAttrsToList;
   inherit (lib.strings) concatMapStringsSep concatLines;
-  inherit (lib.modules) mkIf mkDefault mkDerivedConfig;
+  inherit (lib.modules) mkIf mkDefault mkDerivedConfig mkMerge;
   inherit (lib.options) mkOption literalExpression mkEnableOption;
   inherit (lib.strings) hasPrefix;
-  inherit (lib.types) attrsOf bool lines listOf nullOr package path str submodule oneOf int;
+  inherit (lib.types) anything attrsOf bool either functionTo lines listOf nullOr package path str submodule oneOf int;
   inherit (builtins) isList;
 
   cfg = config;
@@ -58,6 +58,22 @@
           description = "Path of the source file or directory";
         };
 
+        generator = lib.mkOption {
+          type = nullOr (functionTo (either options.source.type options.text.type));
+          default = null;
+          description = "Function that when applied to `value` will create the `text` of the file.";
+          example = literalExpression "lib.generators.toGitINI";
+        };
+
+        value = lib.mkOption {
+          type = nullOr (attrsOf anything);
+          default = null;
+          description = "Value passed to the `generator`.";
+          example = {
+            user.email = "me@example.com";
+          };
+        };
+
         executable = mkOption {
           type = bool;
           default = false;
@@ -90,14 +106,27 @@
         };
       };
 
-      config = {
-        target = mkDefault name;
-        source = mkIf (config.text != null) (mkDerivedConfig options.text (text:
-          pkgs.writeTextFile {
-            inherit name text;
-            inherit (config) executable;
-          }));
-      };
+      config = let
+        generatedValue = config.generator config.value;
+      in
+        mkMerge [
+          {
+            target = mkDefault name;
+            source = mkIf (config.text != null) (mkDerivedConfig options.text (text:
+              pkgs.writeTextFile {
+                inherit name text;
+                inherit (config) executable;
+              }));
+          }
+
+          (lib.mkIf (config.generator != null && options.source.type.check generatedValue) {
+            source = mkDefault generatedValue;
+          })
+
+          (lib.mkIf (config.generator != null && options.text.type.check generatedValue) {
+            text = mkDefault generatedValue;
+          })
+        ];
     });
 in {
   imports = [
diff --git a/tests/basic.nix b/tests/basic.nix
index 029f6c3..8f5698b 100644
--- a/tests/basic.nix
+++ b/tests/basic.nix
@@ -6,6 +6,7 @@ in
     nodes = {
       node1 = {
         self,
+        lib,
         pkgs,
         ...
       }: {
@@ -22,8 +23,20 @@ in
           alice = {
             enable = true;
             packages = [pkgs.hello];
-            files.".config/foo" = {
-              text = "Hello world!";
+            files = {
+              ".config/foo" = {
+                text = "Hello world!";
+              };
+
+              ".config/bar.json" = {
+                generator = lib.generators.toJSON {};
+                value = {bar = true;};
+              };
+
+              ".config/baz.toml" = {
+                generator = (pkgs.formats.toml {}).generate "baz.toml";
+                value = {baz = true;};
+              };
             };
           };
         };
@@ -47,6 +60,8 @@ in
 
       # Test file created by Hjem
       machine.succeed("[ -L ~alice/.config/foo ]")
+      machine.succeed("[ -L ~alice/.config/bar.json ]")
+      machine.succeed("[ -L ~alice/.config/baz.toml ]")
 
       # Test regular files, created by systemd-tmpfiles
       machine.succeed("[ -d ~alice/user_tmpfiles_created ]")