From d3281688bf9f1d69da5eab3ca795e9df6e489292 Mon Sep 17 00:00:00 2001
From: Austin Horstman <khaneliman12@gmail.com>
Date: Fri, 13 Mar 2026 14:42:33 -0500
Subject: [PATCH] gtk: warn on gtk4 theme inheritance change

The gtk4 theme option still inherits from gtk.theme for users pinned
before 26.05, but that fallback was previously silent. Move the
default through the shared state-version helper so the compatibility
branch emits the standard deprecation warning and stays consistent
with other future cleanups.

Add a focused test that covers the legacy inheritance path alongside
the existing current-state-version test for the null default.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>
---
 modules/misc/gtk/gtk4.nix                     | 20 +++++++++++++++++--
 tests/modules/misc/gtk/default.nix            |  1 +
 .../gtk4-stateversion-theme-inheritance.nix   | 19 ++++++++++++++++++
 3 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 tests/modules/misc/gtk/gtk4/gtk4-stateversion-theme-inheritance.nix

diff --git a/modules/misc/gtk/gtk4.nix b/modules/misc/gtk/gtk4.nix
index 9d71f76e0..98a7e8181 100644
--- a/modules/misc/gtk/gtk4.nix
+++ b/modules/misc/gtk/gtk4.nix
@@ -45,8 +45,24 @@ in
           packageExample = "pkgs.gnome.gnome-themes-extra";
         }
       );
-      default = if lib.versionOlder config.home.stateVersion "26.05" then cfg.theme else null;
-      defaultText = literalExpression ''if lib.versionOlder config.home.stateVersion "26.05" then cfg.theme else null'';
+      inherit
+        (lib.hm.deprecations.mkStateVersionOptionDefault {
+          inherit (config.home) stateVersion;
+          since = "26.05";
+          optionPath = [
+            "gtk"
+            "gtk4"
+            "theme"
+          ];
+          legacy = {
+            value = cfg.theme;
+            text = "config.gtk.theme";
+          };
+          current.value = null;
+        })
+        default
+        defaultText
+        ;
       description = ''
         Theme for GTK 4 applications.
 
diff --git a/tests/modules/misc/gtk/default.nix b/tests/modules/misc/gtk/default.nix
index 69a772424..c206173ed 100644
--- a/tests/modules/misc/gtk/default.nix
+++ b/tests/modules/misc/gtk/default.nix
@@ -15,6 +15,7 @@
 
   # GTK4
   gtk4-basic-settings = ./gtk4/gtk4-basic-settings.nix;
+  gtk4-stateversion-theme-inheritance = ./gtk4/gtk4-stateversion-theme-inheritance.nix;
   gtk4-theme-css-injection = ./gtk4/gtk4-theme-css-injection.nix;
   gtk4-no-theme-css-injection = ./gtk4/gtk4-no-theme-css-injection.nix;
   gtk4-stateversion-no-theme-inheritance = ./gtk4/gtk4-stateversion-no-theme-inheritance.nix;
diff --git a/tests/modules/misc/gtk/gtk4/gtk4-stateversion-theme-inheritance.nix b/tests/modules/misc/gtk/gtk4/gtk4-stateversion-theme-inheritance.nix
new file mode 100644
index 000000000..785d48bdf
--- /dev/null
+++ b/tests/modules/misc/gtk/gtk4/gtk4-stateversion-theme-inheritance.nix
@@ -0,0 +1,19 @@
+{ pkgs, ... }:
+{
+  home.stateVersion = "25.11";
+
+  gtk = {
+    enable = true;
+    theme = {
+      name = "Adwaita-dark";
+      package = pkgs.gnome-themes-extra;
+    };
+  };
+
+  nmt.script = ''
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini \
+      '^gtk-theme-name=Adwaita-dark$'
+    assertFileContains home-files/.config/gtk-4.0/gtk.css \
+      'share/themes/Adwaita-dark/gtk-4.0/gtk.css'
+  '';
+}