Add a config action to clone a config entity

This seems like a reasonable and useful feature, so +1.

I'm not sure that duplicateIfNotExists makes sense, though; by definition, you can't duplicate a thing if the duplicate already exists.

I would suggest we make this as simple as possible, where the action only takes a string, which is the ID of the duplicate to create. So:

config:
  actions:
    core.entity_view_display.node.page.default:
      # Duplicates the default display, and gives it the ID of node.page.search_result.
      duplicate: node.page.search_result

In other words, this action should only be able to work on config entities that already exist.

Also, I know this feature will be needed for Drupal CMS, so tagging as a Starshot blocker.

Up for discussion, but if I'm wanting to clone an existing config and it doesn't exist, I'd expect an error here rather than just not cloning as this could affect further actions.

I think I agree with you, on second thought. Adjusted!

Nice! Tested and working as designed. RTBC

Committed and pushed 520019bb2fe to 11.x and 36a124b2f5e to 10.4.x. Thanks!

diff --git a/core/tests/Drupal/KernelTests/Core/Recipe/EntityCloneConfigActionTest.php b/core/tests/Drupal/KernelTests/Core/Recipe/EntityCloneConfigActionTest.php
index 5a712a60ab9..dd9472d81f7 100644
--- a/core/tests/Drupal/KernelTests/Core/Recipe/EntityCloneConfigActionTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Recipe/EntityCloneConfigActionTest.php
@@ -32,6 +32,9 @@ protected function setUp(): void {
     $this->createRole(['access user profiles'], 'test');
   }
 
+  /**
+   * Tests error if original entity does not exist.
+   */
   public function testErrorIfOriginalDoesNotExist(): void {
     $this->expectException(ConfigActionException::class);
     $this->expectExceptionMessage("Cannot clone 'user.role.nope' because it does not exist.");
@@ -39,6 +42,9 @@ public function testErrorIfOriginalDoesNotExist(): void {
       ->applyAction('cloneAs', 'user.role.nope', 'user.role.yep');
   }
 
+  /**
+   * Tests successful clone.
+   */
   public function testSuccessfulClone(): void {
     $this->container->get('plugin.manager.config_action')
       ->applyAction('cloneAs', 'user.role.test', 'cloned');
@@ -48,7 +54,10 @@ public function testSuccessfulClone(): void {
     $this->assertTrue($clone->hasPermission('access user profiles'));
   }
 
-  public function testNoConflictWithExistingClone(): void {
+  /**
+   * Tests no error is thrown when an entity with the same ID already exists.
+   */
+  public function testNoErrorWithExistingEntity(): void {
     $this->createRole(['administer site configuration'], 'cloned');
 
     $this->container->get('plugin.manager.config_action')

Fixed on commit.

Are we not doing change records to announce the availability of this, and in which version it's available? 🤔

(Very cool BTW!)

Needs to be added to the docs also.

Change record written: https://www.drupal.org/node/3481718