Before, this would:

1. Not use the correct reference for non-JIRA external trackers.
2. Append 'Closes ' if an external tracker was enabled, but no issue matched the
   branch name.

When JIRA or Redmine were enabled and the branch name did not match the
matching regular expression, the `issue_iid` would be `nil`, preventing
users from creating merge requests.

Closes #43193

Fixes #37439
Fixes gitaly#1000

check project access on MR create

See merge request gitlab/gitlabhq!2273

(cherry picked from commit 1fe2325d6ef2bced4c5e97b57691c894f38b2834)

43e85f49 check project access on MR create

Instead of storing detailed rebase error, only a generic message is
stored with MR. The reason is that this message is exposed and displayed
to end user and there is no reason to expose detailed backend
information. Error message is still logged so detailed information
can be found in logfile by admin if needed.

Related #41820

When a project uses fast-forward merging strategy user has
to rebase MRs to target branch before it can be merged.
Now user can do rebase in UI by clicking 'Rebase' button
instead of doing rebase locally.

This feature was already present in EE, this is only backport
of the feature to CE. Couple of changes:
* removed rebase license check
* renamed migration (changed timestamp)

Closes #40301

add a spec for commit merge request diff notes

* new merge request can be created by sending an email to the specific
email address (similar to creating issues by email)
* for the first iteration, source branch must be specified in the mail
subject, other merge request parameters can not be set yet
* user should enable "Receive notifications about your own activity" in
user settings to receive a notification about created merge request

Part of #32878

If a merge request was created with a branch name that also matched a tag name,
we'd generate a comparison to or from the tag respectively, rather than the
branch. Merging would still use the branch, of course.

To avoid this, ensure that when we get the branch heads, we prepend the
reference prefix for branches, which will ensure that we generate the correct
comparison.

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

Compared to the merge_request_diff association:

1. It's simpler to query. The query uses a foreign key to the
   merge_request_diffs table, so no ordering is necessary.
2. It's faster for preloading. The merge_request_diff association has to load
   every diff for the MRs in the set, then discard all but the most recent for
   each. This association means that Rails can just query for N diffs from N
   MRs.
3. It's more complicated to update. This is a bidirectional foreign key, so we
   need to update two tables when adding a diff record. This also means we need
   to handle this as a special case when importing a GitLab project.

There is some juggling with this association in the merge request model:

* `MergeRequest#latest_merge_request_diff` is _always_ the latest diff.
* `MergeRequest#merge_request_diff` reuses
  `MergeRequest#latest_merge_request_diff` unless:
    * Arguments are passed. These are typically to force-reload the association.
    * It doesn't exist. That means we might be trying to implicitly create a
      diff. This only seems to happen in specs.
    * The association is already loaded. This is important for the reasons
      explained in the comment, which I'll reiterate here: if we a) load a
      non-latest diff, then b) get its `merge_request`, then c) get that MR's
      `merge_request_diff`, we should get the diff we loaded in c), even though
      that's not the latest diff.

Basically, `MergeRequest#merge_request_diff` is the latest diff in most cases,
but not quite all.

Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.

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

When a build is retried automatically, we close any open todos. However, we do
that _before_ creating a new build failed todo.

To solve this, we check if the build is retried before creating the todo. We
also ensure that the build _instance_ has the correct attribute set, without
needing to reload it from the database.

Rename classes to (hopefully) clearer names while we're doing that.

This prepares the codebase for a Gitaly migration. See
https://gitlab.com/gitlab-org/gitaly/issues/553

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

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

Before this change, the MR counter in the sidebar would be wrong if an MR had
been merged since the last update, but not opened or closed, as merging did not
trigger a counter cache update.