ConfigEntityBase::preSave() tries to load the original entity but instead loads itself

Created #2226037: Change signature of Entity::loadUnchanged() to accept an EntityInterface instead of random ID

1. +++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
   @@ -336,9 +348,6 @@ public function save(EntityInterface $entity) {
          $return = SAVED_NEW;
   
   @@ -348,6 +357,9 @@ public function save(EntityInterface $entity) {
          $this->invokeHook('insert', $entity);
   ...
   +    // Immediately update the original ID.
   +    $entity->setOriginalId($entity->id());
   

   Does it make sense to have an original ID on entity inserts?

2. +++ b/core/modules/breakpoint/lib/Drupal/breakpoint/Entity/Breakpoint.php
   @@ -106,6 +106,16 @@ class Breakpoint extends ConfigEntityBase implements BreakpointInterface {
   +   */
   +  public function id() {
   +    if (!isset($this->id)) {
   +      $this->id = $this->sourceType . '.' . $this->source . '.' . $this->name;
   +    }
   +    return $this->id;
   
   @@ -114,13 +124,6 @@ public function save() {
   -    // Build an id if none is set.
   -    // Since a particular name can be used by multiple theme/modules we need
   -    // to make a unique id.
   -    if (empty($this->id)) {
   -      $this->id = $this->sourceType . '.' . $this->source . '.' . $this->name;
   -    }
   -
   
   +++ b/core/modules/breakpoint/lib/Drupal/breakpoint/Entity/BreakpointGroup.php
   @@ -104,15 +104,22 @@ public function save() {
   -    if (empty($this->id)) {
   -      $this->id = $this->sourceType . '.' . $this->source . '.' . $this->name;
   -    }
   ...
      /**
       * {@inheritdoc}
       */
   +  public function id() {
   +    if (!isset($this->id)) {
   +      $this->id = $this->sourceType . '.' . $this->source . '.' . $this->name;
   +    }
   +    return $this->id;
   +  }
   +
   +  /**
   +   * {@inheritdoc}
   +   */
   

   I really like this

3. +++ b/core/tests/Drupal/Tests/Core/Config/Entity/ConfigEntityStorageTest.php
   @@ -0,0 +1,723 @@
   +class ConfigEntityStorageTest extends UnitTestCase {
   

   MOAAAAAAAAH!

Excellent.

Thank you so much to improve the documentation here!

Committed/pushed to 8.x, thanks!