Use CTEs for nested groups and authorizations

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.

1 files changed, 86 insertions, 45 deletions

diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index f2c059010f4..e880651b091 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -611,16 +611,6 @@ describe User, models: true do
     it { expect(User.without_projects).to include user_without_project2 }
   end
 
-  describe '.not_in_project' do
-    before do
-      User.delete_all
-      @user = create :user
-      @project = create(:empty_project)
-    end
-
-    it { expect(User.not_in_project(@project)).to include(@user, @project.owner) }
-  end
-
   describe 'user creation' do
     describe 'normal user' do
       let(:user) { create(:user, name: 'John Smith') }
@@ -1535,48 +1525,103 @@ describe User, models: true do
     end
   end
 
-  describe '#nested_groups' do
+  describe '#all_expanded_groups' do
+    # foo/bar would also match foo/barbaz instead of just foo/bar and foo/bar/baz
     let!(:user) { create(:user) }
-    let!(:group) { create(:group) }
-    let!(:nested_group) { create(:group, parent: group) }
 
-    before do
-      group.add_owner(user)
+    #                group
+    #        _______ (foo) _______
+    #       |                     |
+    #       |                     |
+    # nested_group_1        nested_group_2
+    # (bar)                 (barbaz)
+    #       |                     |
+    #       |                     |
+    # nested_group_1_1      nested_group_2_1
+    # (baz)                 (baz)
+    #
+    let!(:group) { create :group }
+    let!(:nested_group_1) { create :group, parent: group, name: 'bar' }
+    let!(:nested_group_1_1) { create :group, parent: nested_group_1, name: 'baz' }
+    let!(:nested_group_2) { create :group, parent: group, name: 'barbaz' }
+    let!(:nested_group_2_1) { create :group, parent: nested_group_2, name: 'baz' }
 
-      # Add more data to ensure method does not include wrong groups
-      create(:group).add_owner(create(:user))
+    subject { user.all_expanded_groups }
+
+    context 'user is not a member of any group' do
+      it 'returns an empty array' do
+        is_expected.to eq([])
+      end
     end
 
-    it { expect(user.nested_groups).to eq([nested_group]) }
-  end
+    context 'user is member of all groups' do
+      before do
+        group.add_owner(user)
+        nested_group_1.add_owner(user)
+        nested_group_1_1.add_owner(user)
+        nested_group_2.add_owner(user)
+        nested_group_2_1.add_owner(user)
+      end
 
-  describe '#all_expanded_groups' do
-    let!(:user) { create(:user) }
-    let!(:group) { create(:group) }
-    let!(:nested_group_1) { create(:group, parent: group) }
-    let!(:nested_group_2) { create(:group, parent: group) }
+      it 'returns all groups' do
+        is_expected.to match_array [
+          group,
+          nested_group_1, nested_group_1_1,
+          nested_group_2, nested_group_2_1
+        ]
+      end
+    end
 
-    before { nested_group_1.add_owner(user) }
+    context 'user is member of the top group' do
+      before { group.add_owner(user) }
 
-    it { expect(user.all_expanded_groups).to match_array [group, nested_group_1] }
-  end
+      if Group.supports_nested_groups?
+        it 'returns all groups' do
+          is_expected.to match_array [
+            group,
+            nested_group_1, nested_group_1_1,
+            nested_group_2, nested_group_2_1
+          ]
+        end
+      else
+        it 'returns the top-level groups' do
+          is_expected.to match_array [group]
+        end
+      end
+    end
 
-  describe '#nested_groups_projects' do
-    let!(:user) { create(:user) }
-    let!(:group) { create(:group) }
-    let!(:nested_group) { create(:group, parent: group) }
-    let!(:project) { create(:empty_project, namespace: group) }
-    let!(:nested_project) { create(:empty_project, namespace: nested_group) }
+    context 'user is member of the first child (internal node), branch 1', :nested_groups do
+      before { nested_group_1.add_owner(user) }
 
-    before do
-      group.add_owner(user)
+      it 'returns the groups in the hierarchy' do
+        is_expected.to match_array [
+          group,
+          nested_group_1, nested_group_1_1
+        ]
+      end
+    end
+
+    context 'user is member of the first child (internal node), branch 2', :nested_groups do
+      before { nested_group_2.add_owner(user) }
 
-      # Add more data to ensure method does not include wrong projects
-      other_project = create(:empty_project, namespace: create(:group, :nested))
-      other_project.add_developer(create(:user))
+      it 'returns the groups in the hierarchy' do
+        is_expected.to match_array [
+          group,
+          nested_group_2, nested_group_2_1
+        ]
+      end
     end
 
-    it { expect(user.nested_groups_projects).to eq([nested_project]) }
+    context 'user is member of the last child (leaf node)', :nested_groups do
+      before { nested_group_1_1.add_owner(user) }
+
+      it 'returns the groups in the hierarchy' do
+        is_expected.to match_array [
+          group,
+          nested_group_1, nested_group_1_1
+        ]
+      end
+    end
   end
 
   describe '#refresh_authorized_projects', redis: true do
@@ -1596,10 +1641,6 @@ describe User, models: true do
       expect(user.project_authorizations.count).to eq(2)
     end
 
-    it 'sets the authorized_projects_populated column' do
-      expect(user.authorized_projects_populated).to eq(true)
-    end
-
     it 'stores the correct access levels' do
       expect(user.project_authorizations.where(access_level: Gitlab::Access::GUEST).exists?).to eq(true)
       expect(user.project_authorizations.where(access_level: Gitlab::Access::REPORTER).exists?).to eq(true)
@@ -1709,7 +1750,7 @@ describe User, models: true do
       end
     end
 
-    context 'with 2FA requirement on nested parent group' do
+    context 'with 2FA requirement on nested parent group', :nested_groups do
       let!(:group1) { create :group, require_two_factor_authentication: true }
       let!(:group1a) { create :group, require_two_factor_authentication: false, parent: group1 }
 
@@ -1724,7 +1765,7 @@ describe User, models: true do
       end
     end
 
-    context 'with 2FA requirement on nested child group' do
+    context 'with 2FA requirement on nested child group', :nested_groups do
       let!(:group1) { create :group, require_two_factor_authentication: false }
       let!(:group1a) { create :group, require_two_factor_authentication: true, parent: group1 }