Ensure empty plugin settings are saved correctly (#22891)

* Send and process empty setting arrays as __empty__ value
* Add integration test for an empty settings array

plugins/CorePluginsAdmin/SettingsMetadata.php

@@ -20,6 +20,8 @@ class SettingsMetadata
 {
     public const PASSWORD_PLACEHOLDER = '******';
 
+    public const EMPTY_ARRAY = '__empty__';
+
     /**
      * @param Settings[]  $settingsInstances
      * @param array $settingValues   array('pluginName' => array('settingName' => 'settingValue'))
@@ -34,6 +36,11 @@ public function setPluginSettings($settingsInstances, $settingValues)
 
                     $fieldConfig = $setting->configureField();
 
+                    // empty arrays are sent as __empty__ value, so we need to convert it here back to an array
+                    if ($setting->getType() === FieldConfig::TYPE_ARRAY && $value === self::EMPTY_ARRAY) {
+                        $value = [];
+                    }
+
                     if (
                         isset($value) && (
                         $fieldConfig->uiControl !== FieldConfig::UI_CONTROL_PASSWORD ||

plugins/CorePluginsAdmin/tests/Integration/ApiTest.php

@@ -29,6 +29,12 @@ class ApiTest extends IntegrationTestCase
         ],
     ];
 
+    private $testSystemSettingsEmptyValuePayload = [
+        'ExampleSettingsPlugin' => [
+            ['name' => 'browsers', 'value' => '__empty__'],
+        ],
+    ];
+
     protected static function beforeTableDataCached()
     {
         parent::beforeTableDataCached();
@@ -113,6 +119,26 @@ public function testGetSystemSettingsRedactsPasswordValues()
         self::assertTrue(password_verify('newPassword', $pluginSettings->getSetting('password')->getValue()));
     }
 
+    public function testSetSystemSettingsCorrectlySetsEmptyValue()
+    {
+        $pluginSettings = StaticContainer::get(\Piwik\Plugins\ExampleSettingsPlugin\SystemSettings::class);
+        $settings = $this->getPluginSettings('ExampleSettingsPlugin', 'browsers');
+        $defaultValue = ['firefox', 'chromium', 'safari'];
+
+        self::assertEquals('browsers', $settings['name']);
+        self::assertEquals($defaultValue, $settings['value']);
+        self::assertEquals($defaultValue, $pluginSettings->getSetting('browsers')->getValue());
+
+        $settingValues = $this->testSystemSettingsEmptyValuePayload;
+        \Piwik\Plugins\CorePluginsAdmin\API::getInstance()->setSystemSettings($settingValues, self::TEST_PASSWORD);
+
+        $newSettings = $this->getPluginSettings('ExampleSettingsPlugin', 'browsers');
+
+        self::assertEquals('browsers', $newSettings['name']);
+        self::assertEquals([], $newSettings['value']);
+        self::assertEquals([], $pluginSettings->getSetting('browsers')->getValue());
+    }
+
     private function getPluginSettings(string $pluginName, string $settingName): array
     {
         $settings = \Piwik\Plugins\CorePluginsAdmin\API::getInstance()->getSystemSettings();