clean install

web/core/tests/fixtures/plugins/CustomPlugin.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace com\example\PluginNamespace;
+
+use Drupal\Component\Plugin\Attribute\Plugin;
+
+/**
+ * Custom plugin attribute.
+ */
+#[\Attribute(\Attribute::TARGET_CLASS)]
+class CustomPlugin extends Plugin {
+
+  /**
+   * Constructs a CustomPlugin attribute object.
+   *
+   * @param string $id
+   *   The attribute class ID.
+   * @param string $title
+   *   The title.
+   */
+  public function __construct(
+    public readonly string $id,
+    public readonly string $title,
+  ) {}
+
+}
+
+/**
+ * Custom plugin attribute.
+ */
+#[\Attribute(\Attribute::TARGET_CLASS)]
+class CustomPlugin2 extends Plugin {}

web/core/tests/fixtures/plugins/Plugin/PluginNamespace/AttributeDiscoveryTest1.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace com\example\PluginNamespace;
+
+use Drupal\Component\Plugin\Attribute\Plugin;
+
+/**
+ * Provides a custom test plugin.
+ */
+#[Plugin(
+  id: "discovery_test_1",
+)]
+#[CustomPlugin(
+  id: "discovery_test_1",
+  title: "Discovery test plugin"
+)]
+class AttributeDiscoveryTest1 {}

web/core/tests/fixtures/plugins/Plugin/PluginNamespace/AttributeDiscoveryTest2.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace com\example\PluginNamespace;
+
+use Drupal\a_module_that_does_not_exist\Plugin\Custom;
+
+/**
+ * Provides a custom test plugin that extends from a missing dependency.
+ */
+#[CustomPlugin(
+  id: "discovery_test_2",
+  title: "Discovery test plugin 2"
+)]
+class AttributeDiscoveryTest2 extends Custom {}