Use isSyncing flag to prevent creation of configuration entities on synchronisation

Good to go!

I'd like to commit this but I do not understand at all what's happening here. Maybe tests would help. But to me...

+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Entity/CustomBlockType.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Entity/CustomBlockType.php
@@ -87,7 +87,9 @@ public function postSave(EntityStorageControllerInterface $storage_controller, $

@@ -87,7 +87,9 @@ public function postSave(EntityStorageControllerInterface $storage_controller, $
 
     if (!$update) {
       entity_invoke_bundle_hook('create', 'custom_block', $this->id());
-      custom_block_add_body_field($this->id);
+      if (!$this->isSyncing()) {
+        custom_block_add_body_field($this->id);
+      }
     }

postSave() is effectively a hook, acting just after the block is saved. Then if (!$update) is basically saying "if it's a new block.." So far so good. But if the block is actively synching, and custom_block_add_body_field($this->id) is skipped, when does the code go back and add it again? Does CMI re-issue a postSave() again once the block is imported?

@webchick

When config is importing, we want the actual configuration to be imported. In case someone created a block type without a body field on his dev site (ie, the user has removed the body field), and only kept an image field, we don't want to suddenly see a body field popping up on the production site because that's not what the user wanted.

We introduced this isSyncing flag in #2069373: Race conditions on import if CUD on ConfigEntity A triggers changes in ConfigEntity B which tests it for the body field on content types. I talked with Alex asking whether we need additional tests here too, but he argued that we'll tests this more thoroughly, to begin with in #2108813: Add fancier config import/export test scenario. So this is still good to go imo.

All right, I still don't totally get it but let's give it a shot. :)

Committed and pushed to 8.x. Thanks!