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

This allows to enable/disable a feature flag for a given user, or a
given Flipper group (must be declared statically in the `flipper.rb`
initializer beforehand).
Signed-off-by: NRémy Coutable <remy@rymai.me>

In CE only the admin has access to all private groups & projects. In EE also an
auditor can have full private access.

To overcome merge conflicts, or accidental incorrect access rights, abstract
this out in `User#full_private_access?`.

`User#admin?` now only should be used for admin-only features. For private
access-related features `User#full_private_access?` should be used.

Backported from gitlab-org/gitlab-ee!2199

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

To avoid the use of slow queries, remove some deprecated methods and encourage
the use of ProjectFinder to find projects.

we do this on attribute read since migrating all existing users is not a
feasible solution.

Older namespace records may be both `type == ‘Group` AND `owner_id` is not null.

This commit introduces the usage of Common Table Expressions (CTEs) to
efficiently retrieve nested group hierarchies, without having to rely on
the "routes" table (which is an _incredibly_ inefficient way of getting
the data). This requires a patch to ActiveRecord (found in the added
initializer) to work properly as ActiveRecord doesn't support WITH
statements properly out of the box.

Unfortunately MySQL provides no efficient way of getting nested groups.
For example, the old routes setup could easily take 5-10 seconds
depending on the amount of "routes" in a database. Providing vastly
different logic for both MySQL and PostgreSQL will negatively impact the
development process. Because of this the various nested groups related
methods return empty relations when used in combination with MySQL.

For project authorizations the logic is split up into two classes:

* Gitlab::ProjectAuthorizations::WithNestedGroups
* Gitlab::ProjectAuthorizations::WithoutNestedGroups

Both classes get the fresh project authorizations (= as they should be
in the "project_authorizations" table), including nested groups if
PostgreSQL is used. The logic of these two classes is quite different
apart from their public interface. This complicates development a bit,
but unfortunately there is no way around this.

This commit also introduces Gitlab::GroupHierarchy. This class can be
used to get the ancestors and descendants of a base relation, or both by
using a UNION. This in turn is used by methods such as:

* Namespace#ancestors
* Namespace#descendants
* User#all_expanded_groups

Again this class relies on CTEs and thus only works on PostgreSQL. The
Namespace methods will return an empty relation when MySQL is used,
while User#all_expanded_groups will return only the groups a user is a
direct member of.

Performance wise the impact is quite large. For example, on GitLab.com
Namespace#descendants used to take around 580 ms to retrieve data for a
particular user. Using CTEs we are able to reduce this down to roughly 1
millisecond, returning the exact same data.

== On The Fly Refreshing

Refreshing of authorizations on the fly (= when
users.authorized_projects_populated was not set) is removed with this
commit. This simplifies the code, and ensures any queries used for
authorizations are not mutated because they are executed in a Rails
scope (e.g. Project.visible_to_user).

This commit includes a migration to schedule refreshing authorizations
for all users, ensuring all of them have their authorizations in place.
Said migration schedules users in batches of 5000, with 5 minutes
between every batch to smear the load around a bit.

== Spec Changes

This commit also introduces some changes to various specs. For example,
some specs for ProjectTeam assumed that creating a personal project
would _not_ lead to the owner having access, which is incorrect. Because
we also no longer refresh authorizations on the fly for new users some
code had to be added to the "empty_project" factory. This chunk of code
ensures that the owner's permissions are refreshed after creating the
project, something that is normally done in Projects::CreateService.

Use the EnforcedStyleForMultiline: no_comma option.
Signed-off-by: NRémy Coutable <remy@rymai.me>

Not assigning the trackable fields seems to cause strange side-effects.

Every time a user logs in or out, the Trackable attributes are written to the
database. This is causing a lot of load on the database, for data that isn't
really critical.

So to avoid the database being hammered, add a Gitlab::ExclusiveLease before
writing trackable attributes to the database. This lease expires after an hour,
so only when the attributes were written more than an hour ago, they can be
written again. Otherwise they are ignored.

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

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

1. Have `MigrateToGhostUser` be a service rather than a mixed-in module, to keep
   things explicit. Specs testing the behavior of this class are moved into a
   separate service spec file.

2. Add a `user.reported_abuse_reports` association to make the
   `migrate_abuse_reports` method more consistent with the other `migrate_`
   methods.

Introduction
------------

1. The foreign key was not explicitly specified on the association.
2. The `AbuseReport` model contains two references to user - `reporter_id` and
   `user_id`
3. `user.abuse_report` is supposed to return the single abuse report where
   `user_id` refers to the given user.

Bug Description
---------------

1. `user.abuse_report` would return an abuse report where `reporter_id` referred
   to the current user, if such an abuse report was present.

2. This implies a slightly more serious bug as well:

   - Assume User A filed an abuse report against User B
   - We have an abuse report where `reporter_id` is User A and `user_id` is User B
   - If User A is updated (`user_a.block`, for example), the abuse report would
     also be updated, such that both `reporter_id` _and_ `user_id` point to User A.

Fix
---

Explicitly declare the foreign key `user_id` in the `has_one` declaration