Six months ago or so it clearly stated in the Drupal docs to NOT create D8 modules do to the API not being finished. But still right and left there were people developing and porting D8 modules, clients were asking for it as experience and I needed to catch up. I decided to try my hand at it and had a working module. When I finally got GIT access 6 months later to push my changes to Fancy Login, It had stopped working on the latest D8 build. This article covers how I dealt with the changes to the API made during this period and the updates I had to make since the D8 API has changed yet again.
UPDATE: this article is quite old and D8 core is now complete.
1. moved file FancyLoginSettingsForm.php from folder fancy_login/src to fancy_login/src/Form folder
2. in FancyLoginSettingsForm.php file changed translate functions t(). for example
t('Text !url.', array('!url' => 'background-
color')) to t('Text background-color', array('@url' =>
3. Moved the function user_login_block_ajax_callback from file FancyLoginSettingsForm.php to
4. Moved libraries such as