Remove hook_page_build(), it no longer exists

No need to fix this issue as drupal_get_destination() used in hook_page_build() that can no longer be used.

Yes, looks like we need to remove this hook.

As per Drupal 8: hook_page_build() is replace with hook_page_attachments() -- see this CR: https://www.drupal.org/node/2357755

It looks like hook_page_attachments() is the right one to go with.

Removed unused hook_page_build() and implemented functionality with Route Subscriber

Interesting approach, I think we need a test to make sure this functionality works and doesn't break anything.

Updated patch with tests.

I think the problem with this approach is that it only works with the default 404 page. Most people have a custom 404 page with content I think.

Can't we use hook_menu_local_tasks_alter() for this? I've checked that this is called also if there are no local tasks yet, so we should be able to dynamically insert one.

I have checked and hook_menu_local_tasks_alter() do not called if there are no local tasks yet, so lets only remove unused hook_page_build() (also redirect_is_current_page_404() which was used in hook) in this task and implement an action on 404 pages to create a redirect in new one if needed.

Agree with #26. Hook hook_page_build does not exist in D8/9/10. So these functions can be removed. If this functionality was required, new bugs would be opened.

Reroll patch #26

I've reviewed and retested the last patch form #28 and it works well and successfully redirects on 404 pages to the configured target URL, on Drupal 8.x and 9.x too. So looks good to me and should be ready to commit!

The issue is about finding a suitable replacement for this feature, not just removing the code. It served a purpose, there's little to gain from just removing it.

I changed my opinion on this, also due to #3035665: Remove hook_page_build(), it no longer exists. Doesn't look like people are that interested in it, so lets remove it.

It does need a rebase though and should be converted to a MR.

Created MR

Merged.