Remove from outline button goes to node/x/delete instead

I can confirm this issue on Drupal-8-beta-12. In addition it isn't possible to remove a node from books in the form display of the node.

I was pointed here from #2650756: [Regression] No UI to remove nodes from books., which I've just closed as a duplicate. I took a slightly different approach, and replaced the button with a link to node/x/outline/remove. Here's my reasoning:

• $actions['delete'] in EntityForm was turned into a link as part of #216064: Entity form "Delete" button triggers server-side + HTML5 form validation; change "Delete" button to a link. The reason behind that change was that delete buttons trigger form validation, whereas the delete link does not. I think that argument applies to the 'Remove from outline' operation.
• Using a delete link instead of a delete button adds a confirmation step, which matches the workflow from Drupal 7.
• Nothing in core uses the entity.node.book_remove_form route. It appears that \Drupal\book\Form\BookRemoveForm is dead code, in the sense that it is not linked from anywhere in the UI.

Of course either fix would be better than what we have currently. If you've got a counter-argument, I'd be happy to RTBC this approach instead.

Apologies: I've just run this through simplytest.me, and that's exactly what this patch does. Screenshots attached.

RTBC!

Re-uploading a patch, can't see another way to get it through the new bots.

Tested manually, works as described. Code makes sense. \o/

+++ b/core/modules/book/src/Form/BookOutlineForm.php
@@ -91,8 +91,14 @@ public function form(array $form, FormStateInterface $form_state) {
+    $actions['delete']['#type'] = 'submit';

@coleman.sean.c is correct that this should be a link and not a submit button for the reasons given in #6. The BookOutlineForm::delete() method should be removed and we should just make a link to the book-remove-form.

Attached patch removes the delete method, and replaces the button with a link, as per @alexpott in #10.

Since the delete button is no longer part of the form, drupalPostForm can't be used to click it, and the test-only patch from #1 won't pass. Instead, I've used assertLink: Is that sufficient?

Looking good.

+++ b/core/modules/book/src/Tests/BookTest.php
@@ -583,6 +584,7 @@ public function testBookOutline() {
+    $this->assertLink(t('Remove from book outline'));

It'd be good to click the link here and do the delete and confirm that this has worked. Yes this the functionality of the delete form is tested elsewhere but it would be good to have a test that actually does the same things as a user would.

Okay.

I won't have time to work on this for a few weeks, so if someone wants to write that test, please feel free.

Not sure what's happened in #16. I suspect it reverted some changes...

Here's a new patch with the clickLink() and an assert to make sure we've ended up on the right page. There's no point actually removing the book from the outline as that is tested elsewhere.

Tested issue by applying patch.
Looks good. Redirects to node/nid/outline/remove page.

Committed/pushed to 8.1.x and cherry-picked to 8.0.x. Thanks!