Add due_date text field to sidebar issue#show
Add ability sorting issues by due date ASC and DESC
Add ability to filtering issues by No Due Date, Any Due Date, Due to tomorrow, Due in this week options
Add handling issue due_date field for MergeRequest
Update CHANGELOG
Fix ambigous match for issues#show sidebar
Fix SCREAMING_SNAKE_CASE offenses for due date contants
Add specs for due date sorting and filtering on issues
Improve performance of getting issues on group level
For testing I used the URL http://localhost:3000/groups/gitlab-org/issues?milestone_title=8.1. Prior to these changes said URL would take about 10-12 seconds to load. By applying these changes the loading time has been reduced to roughly 2-3 seconds.
There's still some stuff going on in some views that I have to look at, resolving those changes might reduce the loading time a bit more. I also still have to check if I didn't break too many tests.
Fixes: gitlab-org/gitlab-ce#3707 gitlab-org/gitlab-ce#4071
See merge request !2318
Sorting by "id" has the same effect as sorting by created_at while
performing far better and without the need of an extra index (in case
one wanted to speed up sorting by "created_at").
Sorting by "Recently updated" still uses the physical "updated_at"
column as there's no way to use the "id" column for this instead.
