There were two problems here:

1. On the JS side, the reference to $widgetBody didn't refer to the
   right DOM element any more. This might be because it was replaced by
   the `getMergeStatus` method. Even if it wasn't, ensuring we have the
   right element means that the content gets updated.

2. On the Ruby side, the `log_merge_error` method didn't update the
   `merge_error` column of the merge request. Change that to update if
   requested, and update in the most common cases by default.

   Additionally, this would sometimes return an error hash, but it
   doesn't look like this was ever used (the return value of
   `MergeService#execute` appears to be unused everywhere).

Introduce Gitlab::Database.with_connection_pool

See merge request !9192

Move /projects/fork/:id to /projects/:id/fork in V4 API

Closes #14492

See merge request !8940

Fix ActiveRecord connection leaks

Closes #27949 and gitlab-com/infrastructure#1139

See merge request !9109

Add discussion events to contributions calendar

Closes #22645

See merge request !8821

Display loading indicator when filtering ref switcher dropdown

Closes #27966

See merge request !9144

Add omniauth-oauth2-generic strategy

Closes #26744

See merge request !9048

Add GFM support to nested groups

See merge request !9184

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9192#note_23293693

Fix UX Guide apostrophe use for singular common nouns

See merge request !9190

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Replace static fixture for behaviors/quick_submit_spec.js

See merge request !9086

Replace static fixture for merge_request_tabs_spec.js

See merge request !9172

Make deploy key not show in User's keys list

Closes #27480

See merge request !9024

- Allows configurable Single Sign On with most simple OAuth2 providers
- Adds documentation for the new strategy

Closes #26744

Remove deprecated templates endpoints in V4

Closes #22818

See merge request !8853

Add option to receive email notifications about your own activity

See merge request !8836

Show mentioned/issues being closed from a Merge Requests title

Closes #24333

See merge request !9194

Resolve "GroupsController#activity.json is REALLY slow due to SQL"

Closes #27395

See merge request !9088

Enable Style/RedundantException, Lint/EmptyWhen, and RSpec/ExpectActual cops

See merge request !9151

Respect autocrlf setting when creating/updating file through web UI

Closes gitlab-com/www-gitlab-com#1152

See merge request !9198

Add indices to improve loading of labels page

Closes #25413

See merge request !9121

Signed-off-by: Rémy Coutable <remy@rymai.me>

only print errors and warnings from webpack dev server

See merge request !9118

Fix current build arrow

Closes #27939

See merge request !9154

Show directory hierarchy when listing wiki pages

Closes #23535

See merge request !8133

We don't need to connect when requesting the name of the database
adapter. This in turn should prevent us from requesting/leaking
connections just by asking whether we're using PostgreSQL or MySQL.