GitLab

Currently, when a user wants to assign an issue/MR to himself, he needs
to type his full username or select it from the suggested ones in the
dropdown list.
This commits suggest a faster solution which is typing `/assign me`

Closes #35304.

The method User#projects_limit_left would run "personal_projects.count"
but such a query is not memoized. As a result multiple calls to
User#projects_limit_left would result in multiple COUNT(*) queries being
executed.

To work around this this commit adds User#personal_projects_count which
simply memoizes the result of the COUNT(*) in an instance variable.

In various places we check if the same relation would return projects.
This is done using "any?" which will run a COUNT query with any
LIMIT/OFFSET values still applied.

To work around all this we introduce 2 helper methods that take care of
doing the right thing. This leads to the produced queries being simpler
and fewer queries being executed.

Also fix the test because we no longer have :empty_project,
just use :project is the same as before

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2483

This reverts merge request !12761

Closes gitaly#433

Closes gitaly#421

added specs to sticky util file
added `No files found.` text when results are empty

To investigate gitlab-org/gitlab-ce#31599

TodoService should not call `.select(&:id)` on todos, because this is
bad performance. So instead use sub-queries, which will result in a
single SQL query to the database.

https://docs.gitlab.com/ee/development/sql.html#plucking-ids

`:mailer` is needed to pick it easily, while
`type: :mailer` is needed for picking it automatically for
tests located in spec/mailers/*_spec.rb

It's a bit complicated in spec/services/notification_service_spec.rb
but we'll leave it alone for now.