feat: allow resetting settings to default

framework/core/src/Api/Controller/SetSettingsController.php

@@ -13,13 +13,16 @@
 use Flarum\Settings\Event;
 use Flarum\Settings\SettingsRepositoryInterface;
 use Illuminate\Contracts\Events\Dispatcher;
+use Illuminate\Support\Arr;
 use Laminas\Diactoros\Response\EmptyResponse;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\RequestHandlerInterface;
 
 class SetSettingsController implements RequestHandlerInterface
 {
+    public static array $resetWhen = [];
+
     public function __construct(
         protected SettingsRepositoryInterface $settings,
         protected Dispatcher $dispatcher
@@ -37,7 +40,11 @@ public function handle(ServerRequestInterface $request): ResponseInterface
         foreach ($settings as $k => $v) {
             $this->dispatcher->dispatch(new Event\Serializing($k, $v));
 
-            $this->settings->set($k, $v);
+            if (! is_null($resetWhen = Arr::get(static::$resetWhen, $k)) && $resetWhen($v)) {
+                $this->settings->delete($k);
+            } else {
+                $this->settings->set($k, $v);
+            }
         }
 
         $this->dispatcher->dispatch(new Event\Saved($settings));

framework/core/src/Extend/Settings.php

@@ -10,12 +10,14 @@
 namespace Flarum\Extend;
 
 use Flarum\Admin\WhenSavingSettings;
+use Flarum\Api\Controller\SetSettingsController;
 use Flarum\Api\Resource\ForumResource;
 use Flarum\Api\Schema\Attribute;
 use Flarum\Extension\Extension;
 use Flarum\Foundation\ContainerUtil;
 use Flarum\Settings\SettingsRepositoryInterface;
 use Illuminate\Contracts\Container\Container;
+use Illuminate\Support\Arr;
 use Illuminate\Support\Collection;
 
 class Settings implements ExtenderInterface
@@ -24,6 +26,7 @@ class Settings implements ExtenderInterface
     private array $defaults = [];
     private array $lessConfigs = [];
     private array $resetJsCacheFor = [];
+    private array $resetWhen = [];
 
     /**
      * Serialize a setting value to the ForumSerializer attributes.
@@ -62,6 +65,20 @@ public function default(string $key, mixed $value): self
         return $this;
     }
 
+    /**
+     * Delete a custom setting value when the callback returns true.
+     * This allows the setting to be reset to its default value.
+     *
+     * @param string $key: The key of the setting.
+     * @param (callable(mixed $value): bool) $callback: The callback to determine if the setting should be reset.
+     */
+    public function resetWhen(string $key, callable|string $callback): self
+    {
+        $this->resetWhen[$key] = $callback;
+
+        return $this;
+    }
+
     /**
      * Register a setting as a LESS configuration variable.
      *
@@ -113,6 +130,16 @@ public function extend(Container $container, Extension $extension = null): void
             });
         }
 
+        if (! empty($this->resetWhen)) {
+            foreach ($this->resetWhen as $key => $callback) {
+                Arr::set(
+                    SetSettingsController::$resetWhen,
+                    $key,
+                    ContainerUtil::wrapCallback($callback, $container)
+                );
+            }
+        }
+
         if (! empty($this->settings)) {
             (new ApiResource(ForumResource::class))
                 ->fields(function () use ($container) {

framework/core/tests/integration/extenders/SettingsTest.php

@@ -187,6 +187,54 @@ public function null_custom_setting_returns_null()
         $this->assertEquals(null, $value);
     }
 
+    #[Test]
+    public function resetting_setting_returns_default_value()
+    {
+        $this->extend(
+            (new Extend\Settings())
+                ->default('custom-prefix.filter_this_setting', 'extenderDefault')
+                ->resetWhen('custom-prefix.filter_this_setting', function (mixed $value): bool {
+                    return $value === '';
+                })
+        );
+
+        $this->send(
+            $this->request('POST', '/api/settings', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'custom-prefix.filter_this_setting' => ''
+                ]
+            ])
+        );
+
+        $value = $this->app()
+            ->getContainer()
+            ->make('flarum.settings')
+            ->get('custom-prefix.filter_this_setting');
+
+        $this->assertEquals('extenderDefault', $value);
+    }
+
+    #[Test]
+    public function not_resetting_setting_returns_value()
+    {
+        $this->send(
+            $this->request('POST', '/api/settings', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'custom-prefix.filter_this_setting' => ''
+                ]
+            ])
+        );
+
+        $value = $this->app()
+            ->getContainer()
+            ->make('flarum.settings')
+            ->get('custom-prefix.filter_this_setting');
+
+        $this->assertEquals('', $value);
+    }
+
     #[Test]
     public function custom_less_var_does_not_work_by_default()
     {