* upstream/master: (206 commits)
  Implement fourth round of comments from @DouweM.
  Fix `CreateDeploymentService` spec.
  Reload issues in spec to ensure label<->issue mapping properly loaded
  Fix build.
  Remove unnecessary #{} in cycle analytics template.
  Update cycle analytics icon and fix color of the dismiss button.
  Use triple dashes for the empty value in cycle analytics.
  Fix typo on cycle analytics copy.
  Add page title and fix sub menu width in Cycle Analytics page.
  Update Cycle Analytics Read more link URL.
  Display the cycle analytics navbar based on the `:read_cycle_analytics` ability.
  Improve indentation in `Gitlab::Database::Median`
  Add a spec for merge request metric caching while refreshing a merge request from a forked project.
  Use the `IssuableBaseService` lifecycle hooks to cache `MergeRequestsClosingIssues`
  Implement a second round of review comments from @DouweM.
  Add docs on Cycle Analytics
  Test if issue authors can access private projects
  Update .pkgr.yml with Ubuntu 16.04 dependencies
  fix issues mr counter
  Move JSON generation (cycle analytics) into a controller method.
  ...

Upgrade Sidekiq to 4.2.1, remove dependency on Sinatra

This updates Sidekiq to 4.2.1, which adds full support for Rails 5 by removing a dependency on Sinatra which was one of the remaining Rails 5 blockers.

Major things to check: Sidekiq still works, obviously. Also that the Web UI/Admin dashboard works and doesn't lose any functionality (based on my testing it works fine).

Working toward #14286.

Changelog: https://github.com/mperham/sidekiq/blob/921e939f995fbb5238975d4121d728b95be99ab5/Changes.md#421

See merge request !6349

So that we could read last few lines rather than read
the entire file which could be huge.

Cycle Analytics: first iteration

## What does this MR do?

- Implement the first iteration of the "Cycle Analytics" feature.

## What are the relevant issue numbers?

- Closes #21170 

## Screenshots

![cycle_analytics_screencast.gif](/uploads/d23c3c912caa6935fd47b53ca3a56b97/cycle_analytics.gif)

## Backend Tasks

- [x]  Implementation
    - [x]  Phases
        - [x]  Issue (Tracker)
        - [x]  Plan (Board)
        - [x]  Code (IDE)
        - [x]  Test (CI)
        - [x]  Review (MR)
        - [x]  Staging (CD)
        - [x]  Production (Total)
    - [x]  Make heuristics more modular
    - [x]  Scope to project
    - [x]  Date range (30 days, 90 days)
    - [x]  Access restriction
- [x]  Test
    - [x]  Find a better way to test these phases
    - [x]  Phases
        - [x]  Issue (Tracker)
        - [x]  Plan (Board)
        - [x]  Code (IDE)
        - [x]  Test (CI)
        - [x]  Review (MR)
        - [x]  Staging (CD)
        - [x]  Production (Total)
    - [x]  Test for "end case happens before start case"
    - [x]  Consolidate helper
- [x]  Miniboss review
- [x]  Performance testing with mock data
- [x]  Improve performance
    - [x]  Pre-calculate "merge requests closing issues
    - [x]  Pre-calculate everything else
- [x]  Test performance against 10k issues
- [x]  Test all pre-calculation code
    - [x]  Ci::Pipeline -> build start/finish
    - [x]  Ci::Pipeline#merge_requests
    - [x]  Issue -> record default metrics after save
    - [x]  MergeRequest -> record default metrics after save
    - [x]  Deployment -> Update "first_deployed_to_production_at" for MR metrics
    - [x]  Git Push -> Update "first commit mention" for issue metrics
    - [x]  Merge request create/update/refresh -> Update "merge requests closing issues"
- [x]  Remove `MergeRequestsClosingIssues` when necessary
- [x]  Changes to unblock Fatih
    - [x]  Add summary data
    - [x]  `stats` should be array
    - [x]  Let `stats` be `null` if all `stats` are null
- [x]  Indexes for "merge requests closing issues"
- [x]  Test summary data
- [x]  Scope everything to project
    - [x]  Find out why tests were passing
- [x]  Filter should include issues/MRs which have made it to production within the range
- [x]  Don't create duplicate `MergeRequestsClosingIssues`
- [x]  Fix tests
- [x]  MySQL median
- [x]  Assign to Douwe for review
- [x]  Fix conflicts
- [x]  Implement suggestions from Yorick's review
    - [x]  Test on PG
    - [x]  Test on MySQL
- [x]  Refactor
    - [x]  Cleanup
        - [x]  What happens if we have no data at all?
        - [x]  Extract common queries to methods / scopes
    - [x]  Remove unused queries
    - [x]  Downtime for foreign key migrations
    - [x]  Find a way around "if issue.metrics.present?" all over the place
    - [x]  Find a way around "if merge_request.metrics.present?" all over the place
    - [x]  Test migrations on a fresh database
        - [x]  MySQL
        - [x]  Pg
- [x]  Access issues
    - While the project is public and the visibility is set to "Everyone with access", you cannot visit the cycle analytics page when signed out.
- [x]  CHANGELOG
- [x]  Implement suggestions from Douwe's review
    - [x]  First set of comments
    - [x]  Second set of comments
    - [x]  Third set of comments
    - [x]  Fourth set of comments
- [x]  Make sure build is green
- [ ]  Make issue for "polish"
- [ ]  EE MR


See merge request !5986

- Pluralize summary titles
- Remove the `run_query` method - always return sql strings from the
  `date_time_sql` methods

1. The spec tests that if:

  - The merge request is merged
  - The target branch is deployed to production
  - The `first_deployed_to_production_at` metric is `nil` (for some reason)
  - The target branch is deployed to production again
  - The `first_deployed_to_production_at` metric stays as `nil` (and is
    not overwritten).

2. Failure only on MySQL due to some datetime weirdness.

- Instead of overriding `create` and `update` in `MergeRequests::BaseService`
- Get all merge request service specs passing

Test if issue authors can access private projects

See merge request !6419

- Don't use `TableReferences` - using `.arel_table` is shorter!
- Move some database-related code to `Gitlab::Database`
- Remove the `MergeRequest#issues_closed` and
  `Issue#closed_by_merge_requests`  associations. They were either
  shadowing or were too similar to existing methods. They are not being
  used anywhere, so it's better to remove them to reduce confusion.
- Use Rails 3-style validations
- Index for `MergeRequest::Metrics#first_deployed_to_production_at`
- Only include `CycleAnalyticsHelpers::TestGeneration` for specs that
  need it.
- Other minor refactorings.

Add docs on Cycle Analytics

Document Cycle Analytics first iteration https://gitlab.com/gitlab-org/gitlab-ce/issues/21170

See merge request !6437

Fixed slash commands not loading

## What does this MR do?

Fixes an issue with slash commands not working when the autocomplete source is loading & then the new issue button is clicked. This also fixes an issue where the autocomplete source is loaded on pages where it isn't actually needed.

## What are the relevant issue numbers?

Closes #21774, #21807

See merge request !6207

[ci skip]

Fix issues with wrong issues/merge request counts when filters are selected

Closes #15356 plus counter for issues and MR are now displayed for the these paths `https://gitlab.com/groups/group-name/issues`  `https://gitlab.com/groups/group-name/merge_requests`  `https://gitlab.com/dashboard/issues` and  `https://gitlab.com/dashboard/merge_requests`

See merge request !4960

See gitlab-org/gitlab-ce!6247.