1. These changes bring down page load time for 100 issues from more than
   a minute to about 1.5 seconds.

2. This entire commit is composed of these types of performance
   enhancements:

     - Cache relevant data in `IssueMetrics` wherever possible.
     - Cache relevant data in `MergeRequestMetrics` wherever possible.
     - Preload metrics

3. Given these improvements, we now only need to make 4 SQL calls:

    - Load all issues
    - Load all merge requests
    - Load all metrics for the issues
    - Load all metrics for the merge requests

4. A list of all the data points that are now being pre-calculated:

    a. The first time an issue is mentioned in a commit

      - In `GitPushService`, find all issues mentioned by the given commit
        using `ReferenceExtractor`. Set the `first_mentioned_in_commit_at`
        flag for each of them.

      - There seems to be a (pre-existing) bug here - files (and
        therefore commits) created using the Web CI don't have
        cross-references created, and issues are not closed even when
        the commit title is "Fixes #xx".

    b. The first time a merge request is deployed to production

      When a `Deployment` is created, find all merge requests that
      were merged in before the deployment, and set the
      `first_deployed_to_production_at` flag for each of them.

    c. The start / end time for a merge request pipeline

      Hook into the `Pipeline` state machine. When the `status` moves to
      `running`, find the merge requests whose tip commit matches the
      pipeline, and record the `latest_build_started_at` time for each
      of them. When the `status` moves to `success`, record the
      `latest_build_finished_at` time.

    d. The merge requests that close an issue

      - This was a big cause of the performance problems we were having
        with Cycle Analytics. We need to use `ReferenceExtractor` to make
        this calculation, which is slow when we have to run it on a large
        number of merge requests.

      - When a merge request is created, updated, or refreshed, find the
        issues it closes, and create an instance of
        `MergeRequestsClosingIssues`, which acts as a join model between
        merge requests and issues.

      - If a `MergeRequestsClosingIssues` instance links a merge request
        and an issue, that issue closes that merge request.

5. The `Queries` module was changed into a class, so we can cache the
   results of `issues` and `merge_requests_closing_issues` across
   various cycle analytics stages.

6. The code added in this commit is untested. Tests will be added in the
   next commit.

- Added an extra new line to the prepend of the Close message

Fixes #21710

Add test for closed MR without fork

Add view test visibility of Reopen and Close buttons

Fix controller tests and validation method

Fix missing space

Remove unused variables from test

closed_without_fork? method refactoring

Add information about missing fork

When closed MR without fork can't edit target branch

Tests for closed MR edit view

Fix indentation and rebase, refactoring

Forks may not be up-to-date with the target project, and so might not
contain one of the parent refs in their repo. Fetch this if it isn't
present.

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

Some important things to note:

- commands are removed from noteable.description / note.note
- commands are translated to params so that they are treated as normal
  params in noteable Creation services
- the logic is not in the models but in the Creation services, which is
  the right place for advanced logic that has nothing to do with what
  models should be responsible of!
- UI/JS needs to be updated to handle notes which consist of commands
  only
- the `/merge` command is not handled yet

Other improvements:

- Don't process commands in commit notes and display a flash is note is only commands
- Add autocomplete for slash commands
- Add description and params to slash command DSL methods
- Ensure replying by email with a commands-only note works
- Use :subscription_event instead of calling noteable.subscribe
- Support :todo_event in IssuableBaseService
Signed-off-by: NRémy Coutable <remy@rymai.me>

DRY code + fix rubocop

Add more test cases

Append to changelog

DRY changes list

find_url service for merge_requests

use GET for getting merge request links

remove files

rename to get_url_service

reduce loop

add test case for cross project

refactor tiny thing

update changelog

So we have raw_diffs too

This object will manage Gitlab::Git::Compare instances

Instead calling diff_collection.count use diff_collection.size which is cache on the diff_collection

Introducing the concept of SafeDiffs which relates 
diffs with UI highlighting.

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

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

If somehow a user attempted to accept a merge request that had
conflicts (e.g. the "Accept Merge Request" button or the MR itself was
not updated), `MergeService` did not properly detect that a conflict
occurred. It would assume that the MR went through without any issues
and close the MR as though everything was fine. This could cause
data loss if the source branch were removed.

Closes #20425

This reverts commit 530f5158.

See !4892.
Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit 9ca633eb, reversing
changes made to fb229bbf.

- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4892#note_12892160
- This is more consistent.

1. When a merge request is being merged, save the merge commit SHA in
   the `in_progress_merge_commit_sha` database column.

2. The `pre-receive` hook looks for any locked (in progress) merge
   request with `in_progress_merge_commit_sha` matching the `newrev` it
   is passed.

3. If it finds a matching MR, the merge is legitimate.

4. Update `git_access_spec` to test the behaviour we added here. Also
   refactored this spec a bit to make it easier to add more contexts / conditions.

Rails's form helpers use the `$attr_before_type_cast` method where
available, and this value only appears to be updated on assignment, not
when the object is mutated in some other way:

    [1] pry(main)> mr = MergeRequest.new
    => #<MergeRequest:0x007fcf28395d88 ...>
    [2] pry(main)> mr.description = 'foo'
    => "foo"
    [3] pry(main)> mr.description << ' bar'
    => "foo bar"
    [4] pry(main)> mr.description
    => "foo bar"
    [5] pry(main)> mr.description_before_type_cast
    => "foo"
    [6] pry(main)> mr.description += ' bar'
    => "foo bar bar"
    [7] pry(main)> mr.description_before_type_cast
    => "foo bar bar"

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb