Issue #2997100 by claudiu.cristea, alexpott, penyaskito, tstoeckler, Pancho,...

Issue #2997100 by claudiu.cristea, alexpott, penyaskito, tstoeckler, Pancho, longwave, xjm: Introduce a way to deprecate config schemas

core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php

@@ -79,7 +79,15 @@ public function checkConfigSchema(TypedConfigManagerInterface $typed_config, $co
    */
   protected function checkValue($key, $value) {
     $error_key = $this->configName . ':' . $key;
+    /** @var \Drupal\Core\TypedData\TypedDataInterface $element */
     $element = $this->schema->get($key);
+
+    // Check if this type has been deprecated.
+    $data_definition = $element->getDataDefinition();
+    if (!empty($data_definition['deprecated'])) {
+      @trigger_error($data_definition['deprecated'], E_USER_DEPRECATED);
+    }
+
     if ($element instanceof Undefined) {
       return [$error_key => 'missing schema'];
     }

core/modules/config/tests/config_schema_deprecated_test/config/schema/config_schema_deprecated_test.schema.yml

+config_schema_deprecated_test.settings:
+  type: config_object
+  mapping:
+    complex_structure_deprecated:
+      type: mapping
+      deprecated: "The 'complex_structure_deprecated' config schema is deprecated in drupal:9.1.0 and is removed from drupal 10.0.0. Use the 'complex_structure' config schema instead. See http://drupal.org/node/the-change-notice-nid."
+      mapping:
+        type:
+          type: string
+        products:
+          type: sequence
+          sequence:
+            type: string

core/modules/config/tests/config_schema_deprecated_test/config_schema_deprecated_test.info.yml

+name: 'Deprecated configuration schema test'
+type: module
+package: Testing
+version: VERSION
+hidden: true

core/tests/Drupal/KernelTests/Core/Config/ConfigSchemaDeprecationTest.php

+<?php
+
+namespace Drupal\KernelTests\Core\Config;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests config schema deprecation.
+ *
+ * @group config
+ * @group legacy
+ */
+class ConfigSchemaDeprecationTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'config_schema_deprecated_test',
+  ];
+
+  /**
+   * Tests config schema deprecation.
+   *
+   * @expectedDeprecation The 'complex_structure_deprecated' config schema is deprecated in drupal:9.1.0 and is removed from drupal 10.0.0. Use the 'complex_structure' config schema instead. See http://drupal.org/node/the-change-notice-nid.
+   */
+  public function testConfigSchemaDeprecation() {
+    $config = $this->config('config_schema_deprecated_test.settings');
+    $config
+      ->set('complex_structure_deprecated.type', 'fruits')
+      ->set('complex_structure_deprecated.products', ['apricot', 'apple'])
+      ->save();
+    $this->assertSame(['type' => 'fruits', 'products' => ['apricot', 'apple']], $config->get('complex_structure_deprecated'));
+  }
+
+}