Wim Leers · 7e270d1a
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
+    $possible_types = $this->getPossibleTypes($original_mapping_type);
+
+    // TRICKY: it is tempting to not consider this a dynamic type if only one
+    // concrete type exists. But that would lead to different validation errors
+    // when modules are installed or uninstalled.
+    assert(!empty($possible_types));
+
+    // Determine all valid keys, across all possible types.
+    $typed_data_manager = $this->getTypedDataManager();
+    $all_type_definitions = $typed_data_manager->getDefinitions();
+    $possible_type_definitions = array_intersect_key($all_type_definitions, array_fill_keys($possible_types, TRUE));
+    // TRICKY: \Drupal\Core\Config\TypedConfigManager::getDefinition() does the
+    // necessary resolving, but TypedConfigManager::getDefinitions() does not! 🤷‍♂️
+    // @see \Drupal\Core\Config\TypedConfigManager::getDefinitionWithReplacements()
+    // @see ::getValidKeys()
+    foreach (array_keys($possible_type_definitions) as $possible_type_name) {
-    foreach (array_keys($possible_type_definitions) as $possible_type_name) {
+    $valid_keys_per_type = [];
+    foreach (array_keys($possible_type_definitions) as $possible_type_name) {
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
+    // Expand the dynamic placeholders to find all mapping types derived from
+    // the original mapping type. To continue the previous example:
+    // - `editor.settings.unicorn`
+    // - `editor.image_upload_settings.*`
+    // - `editor.image_upload_settings.1`
+    $possible_types = $this->getPossibleTypes($original_mapping_type);
+
+    // TRICKY: it is tempting to not consider this a dynamic type if only one
+    // concrete type exists. But that would lead to different validation errors
+    // when modules are installed or uninstalled.
+    assert(!empty($possible_types));
+
+    // Determine all valid keys, across all possible types.
+    $typed_data_manager = $this->getTypedDataManager();
+    $all_type_definitions = $typed_data_manager->getDefinitions();
+    $possible_type_definitions = array_intersect_key($all_type_definitions, array_fill_keys($possible_types, TRUE));
-    $all_type_definitions = $typed_data_manager->getDefinitions();
-    $possible_type_definitions = array_intersect_key($all_type_definitions, array_fill_keys($possible_types, TRUE));
+    $possible_type_definitions = array_intersect_key($typed_data_manager->getDefinitions(), array_fill_keys($possible_types, TRUE));
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
+    // @see \Drupal\Core\Config\TypedConfigManager::replaceVariable()
+    $matches = [];
+    if (preg_match_all('/(\[[^\]]+\])/', $name, $matches) >= 1) {
+      $name = str_replace($matches[0], '[]', $name);
+    }
+    // Then, replace all `[]` occurrences with `.*` and escape all periods for
+    // use in a regex. So:
+    // `module\.something\.foo_.*`
+    // or
+    // `.*\.third_party\..*`
+    $regex = str_replace(['.', '[]'], ['\.', '.*'], $name);
+    // Now find all possible types:
+    // 1. `module.something.foo_foo`, `module.something.foo_bar`, etc.
+    $possible_types = array_filter(
+      array_keys($this->getTypedDataManager()->getDefinitions()),
+      fn (string $type) => preg_match("/^$regex$/", $type) === 1
-      array_keys($this->getTypedDataManager()->getDefinitions()),
-      fn (string $type) => preg_match("/^$regex$/", $type) === 1
+      $this->getTypedDataManager()->getDefinitions(),
+      fn (array $type) => preg_match("/^$regex$/", $type['id']) === 1
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
+    // ("statically") valid. Not all types have a fallback type.
+    // @see \Drupal\Core\Config\TypedConfigManager::getDefinitionWithReplacements()
+    $fallback_type = $typed_data_manager->findFallback($original_mapping_type);
+    $valid_keys_everywhere = array_intersect_key(
+      $valid_keys_per_type,
+      [$fallback_type => NULL],
+    );
+    assert(count($valid_keys_everywhere) <= 1);
+    $statically_required_keys = NestedArray::mergeDeepArray($valid_keys_everywhere);
+
+    // Now that statically valid keys are known, determine which valid keys are
+    // only valid in *some* cases: remove the statically valid keys from every
+    // per-type array of valid keys.
+    $valid_keys_some = array_diff_key($valid_keys_per_type, $valid_keys_everywhere);
+    $valid_keys_some_processed = array_map(
+      fn (array $keys) => array_values(array_filter($keys, fn (string $key) => !in_array($key, $statically_required_keys, TRUE))),
-      fn (array $keys) => array_values(array_filter($keys, fn (string $key) => !in_array($key, $statically_required_keys, TRUE))),
+      fn (array $keys) => array_values(array_diff($keys, $statically_required_keys)),