All poll actions should use ajax, drop confirmation form for cancel

Yeah, this is a lot better :)

1. +++ b/src/Form/PollViewForm.php
   @@ -101,7 +102,7 @@ class PollViewForm extends FormBase {
      /**
   -   * Handles vote submit.
   +   * Handles replace form.
       *
       * @param array $form
       *   The previous form.
   

   More something like "Ajax callback to replace the poll form."

   Also, drop the @param and @return, those are usually left out for callbacks like this. And they're wrong now anyway (we no longer return an array)

2. +++ b/src/Form/PollViewForm.php
   @@ -111,12 +112,16 @@ class PollViewForm extends FormBase {
   +    $form = ['messages' => ['#type' => 'status_messages']] + $form;
   +    /** @var \Drupal\Core\Render\RendererInterface $renderer */
   +    $renderer = \Drupal::service('renderer');
   +    $output = $renderer->renderRoot($form);
   

   We should add some inline docs to describe what we are doing here (embed status messages into the form and then render and return it, replacing the existing form completely)

3. +++ b/src/Form/PollViewForm.php
   @@ -111,12 +112,16 @@ class PollViewForm extends FormBase {
   +    return $response->addCommand(new ReplaceCommand('.poll-view-form-' . $this->poll->id() . '', $output));
   

   useless ". ''"

4. +++ b/src/Form/PollViewForm.php
   @@ -256,21 +268,23 @@ class PollViewForm extends FormBase {
   +    \Drupal::logger('poll')->notice('%user\'s vote in Poll #%poll deleted.', array(
   +      '%user' => $this->currentUser()->id(),
   +      '%poll' => $this->poll->id(),
   +    ));
   

   Follow-up: Improve log message, this is pretty useless for an anonymous user currently.

5. +++ b/src/Form/PollViewForm.php
   @@ -256,21 +268,23 @@ class PollViewForm extends FormBase {
   +    if ($this->getRequest()->query->get('ajax_form')) {
   +      $form_state->setRebuild(TRUE);
   +    }
   

   Add a comment here and below, explaining this:

   // In case of an ajax submission, trigger a form rebuild so that we can return an updated form through the ajax callback.

6. +++ b/src/Form/PollViewForm.php
   @@ -325,6 +339,9 @@ class PollViewForm extends FormBase {
        // be the poll form or another page that is displaying this poll, for
        // example as a block.
   +    if ($this->getRequest()->query->get('ajax_form')) {
   

   Same here, additionally, the comment above doesn't really make sense here. Maybe move that below the new code.

7. +++ b/src/Tests/PollVoteTest.php
   @@ -123,7 +120,7 @@ class PollVoteTest extends PollTestBase {
       */
   -  public function testAjaxPollVote() {
   +  /*public function testAjaxPollVote() {
   

   Sorry, I wasn't aware that this *only* tests ajax and needs to be disabled. Yes, in that case, add a @todo.

8. +++ b/templates/poll-results.html.twig
   @@ -18,7 +18,7 @@
    #}
   -<div class="poll">
   +<div id="poll-{{ poll.id.value }}" class="poll">
   

   I think we no longer need this. Same in the vote form. can also be dropped from preprocess then.

Very nice. Committed!