Issue comparing revisions with '?view_mode=full'

Thanks for the bug report. Unfortunately, I wasn't able to reproduce a White Screen of Death as in #2962941, but I was able to trigger an E_WARNING by manually editing the view mode to a nonsensical value.

Warning: Undefined array key "this-view-mode-does-not-exist" in Drupal\diff_plus\Plugin\diff\Layout\VisualInlineHtml5DiffLayout->getDisplayModeOptions() (line 154 of modules/contrib/diff_plus/src/Plugin/diff/Layout/VisualInlineHtml5DiffLayout.php).
Drupal\diff_plus\Plugin\diff\Layout\VisualInlineHtml5DiffLayout->getDisplayModeOptions(Object, Object, Object, 'this-view-mode-does-not-exist') (Line: 234)
Drupal\diff_plus\Plugin\diff\Layout\VisualInlineHtml5DiffLayout->build(Object, Object, Object) (Line: 168)
Drupal\diff\Controller\PluginRevisionController->compareEntityRevisions(Object, Object, Object, 'visual_inline_html5') (Line: 49)
Drupal\diff\Controller\NodeRevisionController->compareNodeRevisions(Object, Object, Object, 'visual_inline_html5')
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 592)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 181)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 53)
Asm89\Stack\Cors->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 704)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Is this what you were seeing?

In order to fix a bug, we'll first need a failing test. Can you update the steps to reproduce so that I can write such a test case?

Thanks!

Hi luke.leber!
Right now i dont remember well if this was exaclty the message but could be.
Anyway thanks for your time, i think that we can close it and review it if we reproduce it in the future!