Issue #2934517 by Berdir: Setting a revision ID on a new entity sets the newRevision flag to false

core/lib/Drupal/Core/Entity/ContentEntityBase.php

@@ -768,7 +768,7 @@ public function onChange($name) {
         // If the revision identifier field is being populated with the original
         // value, we need to make sure the "new revision" flag is reset
         // accordingly.
-        if ($key === 'revision' && $this->getRevisionId() == $this->getLoadedRevisionId()) {
+        if ($key === 'revision' && $this->getRevisionId() == $this->getLoadedRevisionId() && !$this->isNew()) {
           $this->newRevision = FALSE;
         }
       }

core/modules/system/tests/src/Functional/Entity/EntityRevisionsTest.php

@@ -256,6 +256,16 @@ public function testNewRevisionRevert() {
     $this->assertNull($entity->getRevisionId());
     $this->assertEquals($revision_id, $entity->getLoadedRevisionId());
     $this->assertTrue($entity->isNewRevision());
+
+    // Check that calling setNewRevision() on a new entity without a revision ID
+    // and then with a revision ID does not unset the revision ID.
+    $entity = EntityTestMulRev::create(['name' => 'EntityLoadedRevisionTest']);
+    $entity->set('revision_id', NULL);
+    $entity->set('revision_id', 5);
+    $this->assertTrue($entity->isNewRevision());
+    $entity->setNewRevision();
+    $this->assertEquals(5, $entity->get('revision_id')->value);
+
   }
 
 }