Option to automatically delete demo content

That's needs more discussion about is this really needed and a way to do that

Looks like there was some advice on the linked PR for how to handle this. If I re-do this with the suggested method, would the patch be accepted? We need this for our D8 distro.

I created a patch for current dev branch based in the PR mentioned in issue summary

1. +++ b/default_content.module
   @@ -16,3 +16,15 @@ function default_content_modules_installed($modules) {
   +  // @todo Move this to an event once we have HookEvent.
   +  foreach ($modules as $module) {
   +    if (!\Drupal::isConfigSyncing()) {
   +      \Drupal::service('default_content.deleter')->deleteContent($module);
   

   please move usage of \Drupal:: out of loop, also I suggest to use early return if config sync happening

   Also todo looks pointless

2. +++ b/src/Deleter.php
   @@ -0,0 +1,110 @@
   +      foreach ($this->entityTypeManager->getDefinitions() as $entity_type_id => $entity_type) {
   +        $reflection = new \ReflectionClass($entity_type->getClass());
   +        // We are only interested in deleting content entities.
   +        if ($reflection->implementsInterface(ConfigEntityInterface::class)) {
   +          continue;
   

   Please don't use reflection here, there's \Drupal\Core\Entity\EntityTypeInterface::entityClassImplements() for that

   Also not sure the check is right for config, so better to check for \Drupal\Core\Entity\FieldableEntityInterface or \Drupal\Core\Entity\ContentEntityInterface

3. +++ b/src/Deleter.php
   @@ -0,0 +1,110 @@
   +          $entity = $this->entityRepository->loadEntityByUuid($entity_type_id, $entity_uuid);
   +          $entity->delete();
   

   Better to load all entities and delete them multiple

+++ b/src/Deleter.php
@@ -0,0 +1,110 @@
+      $root_user = $this->entityTypeManager->getStorage('user')->load(1);
+      $this->accountSwitcher->switchTo($root_user);

You're missing to $this->accountSwitcher->switchBack(); at the end and not sure why it needs to login as UID1

Fixed comments in #5 and #6

+++ b/src/Deleter.php
@@ -98,13 +98,12 @@ class Deleter implements DeleterInterface {
+          $entities[] = $this->entityRepository->loadEntityByUuid($entity_type_id, $entity_uuid);

please index this array with uuid to prevent loading same entities and delete bugs

Fixed last comment

FWIW, in our workflow, putting this in uninstall would be very bad. We enable this module, import content, and then disable it, hal, and serialization.

More ideally this would be a drush command, see #3282547: Drush command to delete and reimporting default content,