feat: allow resetting settings to default

framework/core/src/Extend/Settings.php

@@ -22,6 +22,7 @@ class Settings implements ExtenderInterface
     private array $settings = [];
     private array $defaults = [];
     private array $lessConfigs = [];
+    private array $forget = [];
 
     /**
      * Serialize a setting value to the ForumSerializer attributes.
@@ -60,6 +61,18 @@ public function default(string $key, mixed $value): self
         return $this;
     }
 
+    /**
+     * Reset a setting to default when callback returns true.
+     * @param string $key: The key of the setting.
+     * @param (callable(mixed $value): bool)|bool $callback: Boolean to determine whether the setting needs deleted.
+     */
+    public function forget(string $key, callable|bool $callback): self
+    {
+        $this->forget[$key] = $callback;
+
+        return $this;
+    }
+
     /**
      * Register a setting as a LESS configuration variable.
      *
@@ -98,6 +111,20 @@ public function extend(Container $container, Extension $extension = null): void
             });
         }
 
+        if (! empty($this->forget)) {
+            $settings = $container->make(SettingsRepositoryInterface::class);
+
+            foreach ($this->forget as $key => $callback) {
+                $value = $settings->get($key);
+                $callback = ContainerUtil::wrapCallback($callback, $container);
+                $shouldForget = $callback($value);
+
+                if ($shouldForget) {
+                    $settings->delete($key);
+                }
+            }
+        }
+
         if (! empty($this->settings)) {
             AbstractSerializer::addAttributeMutator(
                 ForumSerializer::class,

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

@@ -177,6 +177,29 @@ public function null_custom_setting_returns_null()
         $this->assertEquals(null, $value);
     }
 
+    /**
+     * @test
+     */
+    public function forgetting_setting_returns_default_value()
+    {
+        $this->setting('custom-prefix.forget_this_setting', '');
+
+        $this->extend(
+            (new Extend\Settings())
+                ->default('custom-prefix.forget_this_setting', 'extenderDefault')
+                ->forget('custom-prefix.forget_this_setting', function (mixed $value): bool {
+                    return $value === '';
+                })
+        );
+
+        $value = $this->app()
+            ->getContainer()
+            ->make('flarum.settings')
+            ->get('custom-prefix.forget_this_setting');
+
+        $this->assertEquals('extenderDefault', $value);
+    }
+
     /**
      * @test
      */