Add latest changes from gitlab-org/gitlab@master

23 files changed, 842 insertions, 118 deletions

diff --git a/spec/factories/issue_links.rb b/spec/factories/issue_links.rb
new file mode 100644
index 00000000000..884e4dfac08
--- /dev/null
+++ b/spec/factories/issue_links.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :issue_link do
+    source factory: :issue
+    target factory: :issue
+  end
+end
diff --git a/spec/finders/fork_targets_finder_spec.rb b/spec/finders/fork_targets_finder_spec.rb
index 7208f46cfff..12f01227af8 100644
--- a/spec/finders/fork_targets_finder_spec.rb
+++ b/spec/finders/fork_targets_finder_spec.rb
@@ -35,5 +35,13 @@ RSpec.describe ForkTargetsFinder do
     it 'returns all user manageable namespaces' do
       expect(finder.execute).to match_array([user.namespace, maintained_group, owned_group, project.namespace])
     end
+
+    it 'returns only groups when only_groups option is passed' do
+      expect(finder.execute(only_groups: true)).to match_array([maintained_group, owned_group, project.namespace])
+    end
+
+    it 'returns groups relation when only_groups option is passed' do
+      expect(finder.execute(only_groups: true)).to include(a_kind_of(Group))
+    end
   end
 end
diff --git a/spec/frontend/add_context_commits_modal/components/__snapshots__/add_context_commits_modal_spec.js.snap b/spec/frontend/add_context_commits_modal/components/__snapshots__/add_context_commits_modal_spec.js.snap
index 5fad0d07f97..30dc58f0f28 100644
--- a/spec/frontend/add_context_commits_modal/components/__snapshots__/add_context_commits_modal_spec.js.snap
+++ b/spec/frontend/add_context_commits_modal/components/__snapshots__/add_context_commits_modal_spec.js.snap
@@ -47,4 +47,4 @@ exports[`AddContextCommitsModal renders modal with 2 tabs 1`] = `
     </gl-tab-stub>
   </gl-tabs-stub>
 </gl-modal-stub>
-`;
+`;
\ No newline at end of file
diff --git a/spec/graphql/mutations/discussions/toggle_resolve_spec.rb b/spec/graphql/mutations/discussions/toggle_resolve_spec.rb
index 9ac4d6ab165..d779a2227c1 100644
--- a/spec/graphql/mutations/discussions/toggle_resolve_spec.rb
+++ b/spec/graphql/mutations/discussions/toggle_resolve_spec.rb
@@ -51,7 +51,7 @@ RSpec.describe Mutations::Discussions::ToggleResolve do
           it 'raises an error' do
             expect { subject }.to raise_error(
               Gitlab::Graphql::Errors::ArgumentError,
-              "#{discussion.to_global_id} is not a valid id for Discussion."
+              "#{discussion.to_global_id} is not a valid ID for Discussion."
             )
           end
         end
diff --git a/spec/lib/gitlab/config_checker/external_database_checker_spec.rb b/spec/lib/gitlab/config_checker/external_database_checker_spec.rb
index 712903e020a..85bafc77553 100644
--- a/spec/lib/gitlab/config_checker/external_database_checker_spec.rb
+++ b/spec/lib/gitlab/config_checker/external_database_checker_spec.rb
@@ -6,84 +6,35 @@ RSpec.describe Gitlab::ConfigChecker::ExternalDatabaseChecker do
   describe '#check' do
     subject { described_class.check }
 
-    let_it_be(:deprecation_warning) { "Please upgrade" }
-    let_it_be(:upcoming_deprecation_warning) { "Please consider upgrading" }
-
-    context 'when database meets minimum version and there is no upcoming deprecation' do
+    context 'when database meets minimum supported version' do
       before do
         allow(Gitlab::Database).to receive(:postgresql_minimum_supported_version?).and_return(true)
-        allow(Gitlab::Database).to receive(:postgresql_upcoming_deprecation?).and_return(false)
       end
 
       it { is_expected.to be_empty }
     end
 
-    context 'when database does not meet minimum version and there is no upcoming deprecation' do
+    context 'when database does not meet minimum supported version' do
       before do
         allow(Gitlab::Database).to receive(:postgresql_minimum_supported_version?).and_return(false)
-        allow(Gitlab::Database).to receive(:postgresql_upcoming_deprecation?).and_return(false)
-      end
-
-      it 'only returns notice about deprecated database version' do
-        is_expected.to include(a_hash_including(message: include(deprecation_warning)))
-        is_expected.not_to include(a_hash_including(message: include(upcoming_deprecation_warning)))
       end
-    end
 
-    context 'when database meets minimum version and there is an upcoming deprecation' do
-      before do
-        allow(Gitlab::Database).to receive(:postgresql_minimum_supported_version?).and_return(true)
-        allow(Gitlab::Database).to receive(:postgresql_upcoming_deprecation?).and_return(true)
+      let(:notice_deprecated_database) do
+        {
+          type: 'warning',
+          message: _('You are using PostgreSQL %{pg_version_current}, but PostgreSQL ' \
+                     '%{pg_version_minimum} is required for this version of GitLab. ' \
+                     'Please upgrade your environment to a supported PostgreSQL version, ' \
+                     'see %{pg_requirements_url} for details.') % {
+                                                                    pg_version_current: Gitlab::Database.version,
+                                                                    pg_version_minimum: Gitlab::Database::MINIMUM_POSTGRES_VERSION,
+                                                                    pg_requirements_url: '<a href="https://docs.gitlab.com/ee/install/requirements.html#database">database requirements</a>'
+                                                                  }
+        }
       end
 
-      context 'inside the deprecation notice window' do
-        before do
-          allow(Gitlab::Database).to receive(:within_deprecation_notice_window?).and_return(true)
-        end
-
-        it 'only returns notice about an upcoming deprecation' do
-          is_expected.to include(a_hash_including(message: include(upcoming_deprecation_warning)))
-          is_expected.not_to include(a_hash_including(message: include(deprecation_warning)))
-        end
-      end
-
-      context 'outside the deprecation notice window' do
-        before do
-          allow(Gitlab::Database).to receive(:within_deprecation_notice_window?).and_return(false)
-        end
-
-        it { is_expected.to be_empty }
-      end
-    end
-
-    context 'when database does not meet minimum version and there is an upcoming deprecation' do
-      before do
-        allow(Gitlab::Database).to receive(:postgresql_minimum_supported_version?).and_return(false)
-        allow(Gitlab::Database).to receive(:postgresql_upcoming_deprecation?).and_return(true)
-      end
-
-      context 'inside the deprecation notice window' do
-        before do
-          allow(Gitlab::Database).to receive(:within_deprecation_notice_window?).and_return(true)
-        end
-
-        it 'returns notice about deprecated database version and an upcoming deprecation' do
-          is_expected.to include(
-            a_hash_including(message: include(deprecation_warning)),
-            a_hash_including(message: include(upcoming_deprecation_warning))
-          )
-        end
-      end
-
-      context 'outside the deprecation notice window' do
-        before do
-          allow(Gitlab::Database).to receive(:within_deprecation_notice_window?).and_return(false)
-        end
-
-        it 'only returns notice about deprecated database version' do
-          is_expected.to include(a_hash_including(message: include(deprecation_warning)))
-          is_expected.not_to include(a_hash_including(message: include(upcoming_deprecation_warning)))
-        end
+      it 'reports deprecated database notice' do
+        is_expected.to contain_exactly(notice_deprecated_database)
       end
     end
   end
diff --git a/spec/lib/gitlab/database_spec.rb b/spec/lib/gitlab/database_spec.rb
index 47d2cb05240..420aa0a8df6 100644
--- a/spec/lib/gitlab/database_spec.rb
+++ b/spec/lib/gitlab/database_spec.rb
@@ -109,46 +109,6 @@ RSpec.describe Gitlab::Database do
     end
   end
 
-  describe '.postgresql_upcoming_deprecation?' do
-    it 'returns true when database version is lower than the upcoming minimum' do
-      allow(described_class).to receive(:version).and_return('11')
-
-      expect(described_class.postgresql_upcoming_deprecation?).to eq(true)
-    end
-
-    it 'returns false when database version equals the upcoming minimum' do
-      allow(described_class).to receive(:version).and_return('12')
-
-      expect(described_class.postgresql_upcoming_deprecation?).to eq(false)
-    end
-
-    it 'returns false when database version is greater the upcoming minimum' do
-      allow(described_class).to receive(:version).and_return('13')
-
-      expect(described_class.postgresql_upcoming_deprecation?).to eq(false)
-    end
-  end
-
-  describe '.within_deprecation_notice_window?' do
-    using RSpec::Parameterized::TableSyntax
-
-    where(:case_name, :days, :result) do
-      'outside window'  | Gitlab::Database::DEPRECATION_WINDOW_DAYS + 1 | false
-      'equal to window' | Gitlab::Database::DEPRECATION_WINDOW_DAYS     | true
-      'within window'   | Gitlab::Database::DEPRECATION_WINDOW_DAYS - 1 | true
-    end
-
-    with_them do
-      it "returns #{params[:result]} when #{params[:case_name]}" do
-        allow(Date)
-          .to receive(:today)
-          .and_return Date.parse(Gitlab::Database::UPCOMING_POSTGRES_VERSION_DETAILS[:gl_version_date]) - days
-
-        expect(described_class.within_deprecation_notice_window?).to eq(result)
-      end
-    end
-  end
-
   describe '.check_postgres_version_and_print_warning' do
     subject { described_class.check_postgres_version_and_print_warning }
 
diff --git a/spec/models/issue_link_spec.rb b/spec/models/issue_link_spec.rb
new file mode 100644
index 00000000000..00791d4a48b
--- /dev/null
+++ b/spec/models/issue_link_spec.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssueLink do
+  describe 'Associations' do
+    it { is_expected.to belong_to(:source).class_name('Issue') }
+    it { is_expected.to belong_to(:target).class_name('Issue') }
+  end
+
+  describe 'link_type' do
+    it { is_expected.to define_enum_for(:link_type).with_values(relates_to: 0, blocks: 1, is_blocked_by: 2) }
+
+    it 'provides the "related" as default link_type' do
+      expect(create(:issue_link).link_type).to eq 'relates_to'
+    end
+  end
+
+  describe 'Validation' do
+    subject { create :issue_link }
+
+    it { is_expected.to validate_presence_of(:source) }
+    it { is_expected.to validate_presence_of(:target) }
+    it do
+      is_expected.to validate_uniqueness_of(:source)
+                       .scoped_to(:target_id)
+                       .with_message(/already related/)
+    end
+
+    context 'self relation' do
+      let(:issue) { create :issue }
+
+      context 'cannot be validated' do
+        it 'does not invalidate object with self relation error' do
+          issue_link = build :issue_link, source: issue, target: nil
+
+          issue_link.valid?
+
+          expect(issue_link.errors[:source]).to be_empty
+        end
+      end
+
+      context 'can be invalidated' do
+        it 'invalidates object' do
+          issue_link = build :issue_link, source: issue, target: issue
+
+          expect(issue_link).to be_invalid
+          expect(issue_link.errors[:source]).to include('cannot be related to itself')
+        end
+      end
+    end
+  end
+end
diff --git a/spec/models/issue_spec.rb b/spec/models/issue_spec.rb
index 59634524e74..af0348b972a 100644
--- a/spec/models/issue_spec.rb
+++ b/spec/models/issue_spec.rb
@@ -311,6 +311,50 @@ RSpec.describe Issue do
     end
   end
 
+  describe '#related_issues' do
+    let(:user) { create(:user) }
+    let(:authorized_project) { create(:project) }
+    let(:authorized_project2) { create(:project) }
+    let(:unauthorized_project) { create(:project) }
+
+    let(:authorized_issue_a) { create(:issue, project: authorized_project) }
+    let(:authorized_issue_b) { create(:issue, project: authorized_project) }
+    let(:authorized_issue_c) { create(:issue, project: authorized_project2) }
+
+    let(:unauthorized_issue) { create(:issue, project: unauthorized_project) }
+
+    let!(:issue_link_a) { create(:issue_link, source: authorized_issue_a, target: authorized_issue_b) }
+    let!(:issue_link_b) { create(:issue_link, source: authorized_issue_a, target: unauthorized_issue) }
+    let!(:issue_link_c) { create(:issue_link, source: authorized_issue_a, target: authorized_issue_c) }
+
+    before do
+      authorized_project.add_developer(user)
+      authorized_project2.add_developer(user)
+    end
+
+    it 'returns only authorized related issues for given user' do
+      expect(authorized_issue_a.related_issues(user))
+        .to contain_exactly(authorized_issue_b, authorized_issue_c)
+    end
+
+    it 'returns issues with valid issue_link_type' do
+      link_types = authorized_issue_a.related_issues(user).map(&:issue_link_type)
+
+      expect(link_types).not_to be_empty
+      expect(link_types).not_to include(nil)
+    end
+
+    describe 'when a user cannot read cross project' do
+      it 'only returns issues within the same project' do
+        expect(Ability).to receive(:allowed?).with(user, :read_all_resources, :global).at_least(:once).and_call_original
+        expect(Ability).to receive(:allowed?).with(user, :read_cross_project).and_return(false)
+
+        expect(authorized_issue_a.related_issues(user))
+          .to contain_exactly(authorized_issue_b)
+      end
+    end
+  end
+
   describe '#can_move?' do
     let(:issue) { create(:issue) }
 
diff --git a/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/create_spec.rb b/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/create_spec.rb
index 0e2da94f0f9..10ca2cf1cf8 100644
--- a/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/create_spec.rb
+++ b/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/create_spec.rb
@@ -101,7 +101,7 @@ RSpec.describe Mutations::Metrics::Dashboard::Annotations::Create do
           graphql_mutation(:create_annotation, variables)
         end
 
-        it_behaves_like 'a mutation that returns top-level errors', errors: ['invalid_id is not a valid GitLab id.']
+        it_behaves_like 'a mutation that returns top-level errors', errors: ['invalid_id is not a valid GitLab ID.']
       end
     end
   end
@@ -188,7 +188,7 @@ RSpec.describe Mutations::Metrics::Dashboard::Annotations::Create do
         graphql_mutation(:create_annotation, variables)
       end
 
-      it_behaves_like 'a mutation that returns top-level errors', errors: ['invalid_id is not a valid GitLab id.']
+      it_behaves_like 'a mutation that returns top-level errors', errors: ['invalid_id is not a valid GitLab ID.']
     end
   end
 
diff --git a/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/delete_spec.rb b/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/delete_spec.rb
index 2459a6f3828..7357f3e1e35 100644
--- a/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/delete_spec.rb
+++ b/spec/requests/api/graphql/mutations/metrics/dashboard/annotations/delete_spec.rb
@@ -45,7 +45,7 @@ RSpec.describe Mutations::Metrics::Dashboard::Annotations::Delete do
         graphql_mutation(:delete_annotation, variables)
       end
 
-      it_behaves_like 'a mutation that returns top-level errors', errors: ['invalid_id is not a valid GitLab id.']
+      it_behaves_like 'a mutation that returns top-level errors', errors: ['invalid_id is not a valid GitLab ID.']
     end
 
     context 'when the delete fails' do
diff --git a/spec/requests/api/graphql/mutations/todos/mark_done_spec.rb b/spec/requests/api/graphql/mutations/todos/mark_done_spec.rb
index 9c4733f6769..c1232500d79 100644
--- a/spec/requests/api/graphql/mutations/todos/mark_done_spec.rb
+++ b/spec/requests/api/graphql/mutations/todos/mark_done_spec.rb
@@ -80,7 +80,7 @@ RSpec.describe 'Marking todos done' do
 
   context 'when using an invalid gid' do
     let(:input) { { id: 'invalid_gid' } }
-    let(:invalid_gid_error) { 'invalid_gid is not a valid GitLab id.' }
+    let(:invalid_gid_error) { 'invalid_gid is not a valid GitLab ID.' }
 
     it 'contains the expected error' do
       post_graphql_mutation(mutation, current_user: current_user)
diff --git a/spec/requests/api/graphql/mutations/todos/restore_spec.rb b/spec/requests/api/graphql/mutations/todos/restore_spec.rb
index 6dedde56e13..0797961f65f 100644
--- a/spec/requests/api/graphql/mutations/todos/restore_spec.rb
+++ b/spec/requests/api/graphql/mutations/todos/restore_spec.rb
@@ -80,7 +80,7 @@ RSpec.describe 'Restoring Todos' do
 
   context 'when using an invalid gid' do
     let(:input) { { id: 'invalid_gid' } }
-    let(:invalid_gid_error) { 'invalid_gid is not a valid GitLab id.' }
+    let(:invalid_gid_error) { 'invalid_gid is not a valid GitLab ID.' }
 
     it 'contains the expected error' do
       post_graphql_mutation(mutation, current_user: current_user)
diff --git a/spec/serializers/fork_namespace_entity_spec.rb b/spec/serializers/fork_namespace_entity_spec.rb
index 7ce6b77da44..7740ed77540 100644
--- a/spec/serializers/fork_namespace_entity_spec.rb
+++ b/spec/serializers/fork_namespace_entity_spec.rb
@@ -8,13 +8,17 @@ RSpec.describe ForkNamespaceEntity do
 
   let_it_be(:user) { create(:user) }
   let_it_be(:project) { create(:project) }
+  let_it_be(:namespace) { create(:group, :with_avatar, description: 'test') }
+  let(:memberships) do
+    user.members.index_by(&:source_id)
+  end
 
-  let(:namespace) { create(:group, :with_avatar, description: 'test') }
-  let(:entity) { described_class.new(namespace, current_user: user, project: project) }
+  let(:entity) { described_class.new(namespace, current_user: user, project: project, memberships: memberships) }
 
   subject(:json) { entity.as_json }
 
   before do
+    namespace.add_developer(user)
     project.add_maintainer(user)
   end
 
@@ -52,7 +56,6 @@ RSpec.describe ForkNamespaceEntity do
   end
 
   it 'exposes human readable permission level' do
-    namespace.add_developer(user)
     expect(json[:permission]).to eql 'Developer'
   end
 
diff --git a/spec/serializers/linked_project_issue_entity_spec.rb b/spec/serializers/linked_project_issue_entity_spec.rb
new file mode 100644
index 00000000000..864b5c45599
--- /dev/null
+++ b/spec/serializers/linked_project_issue_entity_spec.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe LinkedProjectIssueEntity do
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project) }
+  let_it_be(:issue_link) { create(:issue_link) }
+
+  let(:request) { double('request') }
+  let(:related_issue) { issue_link.source.related_issues(user).first }
+  let(:entity) { described_class.new(related_issue, request: request, current_user: user) }
+
+  before do
+    allow(request).to receive(:current_user).and_return(user)
+    allow(request).to receive(:issuable).and_return(issue_link.source)
+    issue_link.target.project.add_developer(user)
+  end
+
+  describe 'issue_link_type' do
+    it { expect(entity.as_json).to include(link_type: 'relates_to') }
+  end
+end
diff --git a/spec/services/issue_links/create_service_spec.rb b/spec/services/issue_links/create_service_spec.rb
new file mode 100644
index 00000000000..a60950e64cb
--- /dev/null
+++ b/spec/services/issue_links/create_service_spec.rb
@@ -0,0 +1,176 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssueLinks::CreateService do
+  describe '#execute' do
+    let(:namespace) { create :namespace }
+    let(:project) { create :project, namespace: namespace }
+    let(:issue) { create :issue, project: project }
+    let(:user) { create :user }
+    let(:params) do
+      {}
+    end
+
+    before do
+      project.add_developer(user)
+    end
+
+    subject { described_class.new(issue, user, params).execute }
+
+    context 'when the reference list is empty' do
+      let(:params) do
+        { issuable_references: [] }
+      end
+
+      it 'returns error' do
+        is_expected.to eq(message: 'No Issue found for given params', status: :error, http_status: 404)
+      end
+    end
+
+    context 'when Issue not found' do
+      let(:params) do
+        { issuable_references: ["##{non_existing_record_iid}"] }
+      end
+
+      it 'returns error' do
+        is_expected.to eq(message: 'No Issue found for given params', status: :error, http_status: 404)
+      end
+
+      it 'no relationship is created' do
+        expect { subject }.not_to change(IssueLink, :count)
+      end
+    end
+
+    context 'when user has no permission to target project Issue' do
+      let(:target_issuable) { create :issue }
+
+      let(:params) do
+        { issuable_references: [target_issuable.to_reference(project)] }
+      end
+
+      it 'returns error' do
+        target_issuable.project.add_guest(user)
+
+        is_expected.to eq(message: 'No Issue found for given params', status: :error, http_status: 404)
+      end
+
+      it 'no relationship is created' do
+        expect { subject }.not_to change(IssueLink, :count)
+      end
+    end
+
+    context 'source and target are the same issue' do
+      let(:params) do
+        { issuable_references: [issue.to_reference] }
+      end
+
+      it 'does not create notes' do
+        expect(SystemNoteService).not_to receive(:relate_issue)
+
+        subject
+      end
+
+      it 'no relationship is created' do
+        expect { subject }.not_to change(IssueLink, :count)
+      end
+    end
+
+    context 'when there is an issue to relate' do
+      let(:issue_a) { create :issue, project: project }
+      let(:another_project) { create :project, namespace: project.namespace }
+      let(:another_project_issue) { create :issue, project: another_project }
+
+      let(:issue_a_ref) { issue_a.to_reference }
+      let(:another_project_issue_ref) { another_project_issue.to_reference(project) }
+
+      let(:params) do
+        { issuable_references: [issue_a_ref, another_project_issue_ref] }
+      end
+
+      before do
+        another_project.add_developer(user)
+      end
+
+      it 'creates relationships' do
+        expect { subject }.to change(IssueLink, :count).from(0).to(2)
+
+        expect(IssueLink.find_by!(target: issue_a)).to have_attributes(source: issue, link_type: 'relates_to')
+        expect(IssueLink.find_by!(target: another_project_issue)).to have_attributes(source: issue, link_type: 'relates_to')
+      end
+
+      it 'returns success status' do
+        is_expected.to eq(status: :success)
+      end
+
+      it 'creates notes' do
+        # First two-way relation notes
+        expect(SystemNoteService).to receive(:relate_issue)
+          .with(issue, issue_a, user)
+        expect(SystemNoteService).to receive(:relate_issue)
+          .with(issue_a, issue, user)
+
+        # Second two-way relation notes
+        expect(SystemNoteService).to receive(:relate_issue)
+          .with(issue, another_project_issue, user)
+        expect(SystemNoteService).to receive(:relate_issue)
+          .with(another_project_issue, issue, user)
+
+        subject
+      end
+    end
+
+    context 'when reference of any already related issue is present' do
+      let(:issue_a) { create :issue, project: project }
+      let(:issue_b) { create :issue, project: project }
+      let(:issue_c) { create :issue, project: project }
+
+      before do
+        create :issue_link, source: issue, target: issue_b, link_type: IssueLink::TYPE_RELATES_TO
+        create :issue_link, source: issue, target: issue_c, link_type: IssueLink::TYPE_RELATES_TO
+      end
+
+      let(:params) do
+        {
+          issuable_references: [
+            issue_a.to_reference,
+            issue_b.to_reference,
+            issue_c.to_reference
+          ],
+          link_type: IssueLink::TYPE_RELATES_TO
+        }
+      end
+
+      it 'creates notes only for new relations' do
+        expect(SystemNoteService).to receive(:relate_issue).with(issue, issue_a, anything)
+        expect(SystemNoteService).to receive(:relate_issue).with(issue_a, issue, anything)
+        expect(SystemNoteService).not_to receive(:relate_issue).with(issue, issue_b, anything)
+        expect(SystemNoteService).not_to receive(:relate_issue).with(issue_b, issue, anything)
+        expect(SystemNoteService).not_to receive(:relate_issue).with(issue, issue_c, anything)
+        expect(SystemNoteService).not_to receive(:relate_issue).with(issue_c, issue, anything)
+
+        subject
+      end
+    end
+
+    context 'when there are invalid references' do
+      let(:issue_a) { create :issue, project: project }
+
+      let(:params) do
+        { issuable_references: [issue.to_reference, issue_a.to_reference] }
+      end
+
+      it 'creates links only for valid references' do
+        expect { subject }.to change { IssueLink.count }.by(1)
+      end
+
+      it 'returns error status' do
+        expect(subject).to eq(
+          status: :error,
+          http_status: 422,
+          message: "#{issue.to_reference} cannot be added: cannot be related to itself"
+        )
+      end
+    end
+  end
+end
diff --git a/spec/services/issue_links/destroy_service_spec.rb b/spec/services/issue_links/destroy_service_spec.rb
new file mode 100644
index 00000000000..3f5b7ccf9ba
--- /dev/null
+++ b/spec/services/issue_links/destroy_service_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssueLinks::DestroyService do
+  describe '#execute' do
+    let(:project) { create(:project_empty_repo) }
+    let(:user) { create(:user) }
+
+    subject { described_class.new(issue_link, user).execute }
+
+    context 'when successfully removes an issue link' do
+      let(:issue_a) { create(:issue, project: project) }
+      let(:issue_b) { create(:issue, project: project) }
+
+      let!(:issue_link) { create(:issue_link, source: issue_a, target: issue_b) }
+
+      before do
+        project.add_reporter(user)
+      end
+
+      it 'removes related issue' do
+        expect { subject }.to change(IssueLink, :count).from(1).to(0)
+      end
+
+      it 'creates notes' do
+        # Two-way notes creation
+        expect(SystemNoteService).to receive(:unrelate_issue)
+                                       .with(issue_link.source, issue_link.target, user)
+        expect(SystemNoteService).to receive(:unrelate_issue)
+                                       .with(issue_link.target, issue_link.source, user)
+
+        subject
+      end
+
+      it 'returns success message' do
+        is_expected.to eq(message: 'Relation was removed', status: :success)
+      end
+    end
+
+    context 'when failing to remove an issue link' do
+      let(:unauthorized_project) { create(:project) }
+      let(:issue_a) { create(:issue, project: project) }
+      let(:issue_b) { create(:issue, project: unauthorized_project) }
+
+      let!(:issue_link) { create(:issue_link, source: issue_a, target: issue_b) }
+
+      it 'does not remove relation' do
+        expect { subject }.not_to change(IssueLink, :count).from(1)
+      end
+
+      it 'does not create notes' do
+        expect(SystemNoteService).not_to receive(:unrelate_issue)
+      end
+
+      it 'returns error message' do
+        is_expected.to eq(message: 'No Issue Link found', status: :error, http_status: 404)
+      end
+    end
+  end
+end
diff --git a/spec/services/issue_links/list_service_spec.rb b/spec/services/issue_links/list_service_spec.rb
new file mode 100644
index 00000000000..7a3ba845c7c
--- /dev/null
+++ b/spec/services/issue_links/list_service_spec.rb
@@ -0,0 +1,194 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssueLinks::ListService do
+  let(:user) { create :user }
+  let(:project) { create(:project_empty_repo, :private) }
+  let(:issue) { create :issue, project: project }
+  let(:user_role) { :developer }
+
+  before do
+    project.add_role(user, user_role)
+  end
+
+  describe '#execute' do
+    subject { described_class.new(issue, user).execute }
+
+    context 'user can see all issues' do
+      let(:issue_b) { create :issue, project: project }
+      let(:issue_c) { create :issue, project: project }
+      let(:issue_d) { create :issue, project: project }
+
+      let!(:issue_link_c) do
+        create(:issue_link, source: issue_d,
+                            target: issue)
+      end
+
+      let!(:issue_link_b) do
+        create(:issue_link, source: issue,
+                            target: issue_c)
+      end
+
+      let!(:issue_link_a) do
+        create(:issue_link, source: issue,
+                            target: issue_b)
+      end
+
+      it 'ensures no N+1 queries are made' do
+        control_count = ActiveRecord::QueryRecorder.new { subject }.count
+
+        project = create :project, :public
+        milestone = create :milestone, project: project
+        issue_x = create :issue, project: project, milestone: milestone
+        issue_y = create :issue, project: project, assignees: [user]
+        issue_z = create :issue, project: project
+        create :issue_link, source: issue_x, target: issue_y
+        create :issue_link, source: issue_x, target: issue_z
+        create :issue_link, source: issue_y, target: issue_z
+
+        expect { subject }.not_to exceed_query_limit(control_count)
+      end
+
+      it 'returns related issues JSON' do
+        expect(subject.size).to eq(3)
+
+        expect(subject).to include(include(id: issue_b.id,
+                                           title: issue_b.title,
+                                           state: issue_b.state,
+                                           reference: issue_b.to_reference(project),
+                                           path: "/#{project.full_path}/-/issues/#{issue_b.iid}",
+                                           relation_path: "/#{project.full_path}/-/issues/#{issue.iid}/links/#{issue_link_a.id}"))
+
+        expect(subject).to include(include(id: issue_c.id,
+                                           title: issue_c.title,
+                                           state: issue_c.state,
+                                           reference: issue_c.to_reference(project),
+                                           path: "/#{project.full_path}/-/issues/#{issue_c.iid}",
+                                           relation_path: "/#{project.full_path}/-/issues/#{issue.iid}/links/#{issue_link_b.id}"))
+
+        expect(subject).to include(include(id: issue_d.id,
+                                           title: issue_d.title,
+                                           state: issue_d.state,
+                                           reference: issue_d.to_reference(project),
+                                           path: "/#{project.full_path}/-/issues/#{issue_d.iid}",
+                                           relation_path: "/#{project.full_path}/-/issues/#{issue.iid}/links/#{issue_link_c.id}"))
+      end
+    end
+
+    context 'referencing a public project issue' do
+      let(:public_project) { create :project, :public }
+      let(:issue_b) { create :issue, project: public_project }
+
+      let!(:issue_link) do
+        create(:issue_link, source: issue, target: issue_b)
+      end
+
+      it 'presents issue' do
+        expect(subject.size).to eq(1)
+      end
+    end
+
+    context 'referencing issue with removed relationships' do
+      context 'when referenced a deleted issue' do
+        let(:issue_b) { create :issue, project: project }
+        let!(:issue_link) do
+          create(:issue_link, source: issue, target: issue_b)
+        end
+
+        it 'ignores issue' do
+          issue_b.destroy!
+
+          is_expected.to eq([])
+        end
+      end
+
+      context 'when referenced an issue with deleted project' do
+        let(:issue_b) { create :issue, project: project }
+        let!(:issue_link) do
+          create(:issue_link, source: issue, target: issue_b)
+        end
+
+        it 'ignores issue' do
+          project.destroy!
+
+          is_expected.to eq([])
+        end
+      end
+
+      context 'when referenced an issue with deleted namespace' do
+        let(:issue_b) { create :issue, project: project }
+        let!(:issue_link) do
+          create(:issue_link, source: issue, target: issue_b)
+        end
+
+        it 'ignores issue' do
+          project.namespace.destroy!
+
+          is_expected.to eq([])
+        end
+      end
+    end
+
+    context 'user cannot see relations' do
+      context 'when user cannot see the referenced issue' do
+        let!(:issue_link) do
+          create(:issue_link, source: issue)
+        end
+
+        it 'returns an empty list' do
+          is_expected.to eq([])
+        end
+      end
+
+      context 'when user cannot see the issue that referenced' do
+        let!(:issue_link) do
+          create(:issue_link, target: issue)
+        end
+
+        it 'returns an empty list' do
+          is_expected.to eq([])
+        end
+      end
+    end
+
+    context 'remove relations' do
+      let!(:issue_link) do
+        create(:issue_link, source: issue, target: referenced_issue)
+      end
+
+      context 'user can admin related issues just on target project' do
+        let(:user_role) { :guest }
+        let(:target_project) { create :project }
+        let(:referenced_issue) { create :issue, project: target_project }
+
+        it 'returns no destroy relation path' do
+          target_project.add_developer(user)
+
+          expect(subject.first[:relation_path]).to be_nil
+        end
+      end
+
+      context 'user can admin related issues just on source project' do
+        let(:user_role) { :developer }
+        let(:target_project) { create :project }
+        let(:referenced_issue) { create :issue, project: target_project }
+
+        it 'returns no destroy relation path' do
+          target_project.add_guest(user)
+
+          expect(subject.first[:relation_path]).to be_nil
+        end
+      end
+
+      context 'when user can admin related issues on both projects' do
+        let(:referenced_issue) { create :issue, project: project }
+
+        it 'returns related issue destroy relation path' do
+          expect(subject.first[:relation_path])
+            .to eq("/#{project.full_path}/-/issues/#{issue.iid}/links/#{issue_link.id}")
+        end
+      end
+    end
+  end
+end
diff --git a/spec/services/issues/duplicate_service_spec.rb b/spec/services/issues/duplicate_service_spec.rb
index 78e030e6ac7..0b5bc3f32ef 100644
--- a/spec/services/issues/duplicate_service_spec.rb
+++ b/spec/services/issues/duplicate_service_spec.rb
@@ -83,6 +83,17 @@ RSpec.describe Issues::DuplicateService do
 
         expect(duplicate_issue.reload.duplicated_to).to eq(canonical_issue)
       end
+
+      it 'relates the duplicate issues' do
+        canonical_project.add_reporter(user)
+        duplicate_project.add_reporter(user)
+
+        subject.execute(duplicate_issue, canonical_issue)
+
+        issue_link = IssueLink.last
+        expect(issue_link.source).to eq(duplicate_issue)
+        expect(issue_link.target).to eq(canonical_issue)
+      end
     end
   end
 end
diff --git a/spec/services/issues/move_service_spec.rb b/spec/services/issues/move_service_spec.rb
index 5f944d1213b..5d032b28399 100644
--- a/spec/services/issues/move_service_spec.rb
+++ b/spec/services/issues/move_service_spec.rb
@@ -223,6 +223,45 @@ RSpec.describe Issues::MoveService do
     end
   end
 
+  describe '#rewrite_related_issues' do
+    include_context 'user can move issue'
+
+    let(:admin) { create(:admin) }
+    let(:authorized_project) { create(:project) }
+    let(:authorized_project2) { create(:project) }
+    let(:unauthorized_project) { create(:project) }
+
+    let(:authorized_issue_b) { create(:issue, project: authorized_project) }
+    let(:authorized_issue_c) { create(:issue, project: authorized_project2) }
+    let(:authorized_issue_d) { create(:issue, project: authorized_project2) }
+    let(:unauthorized_issue) { create(:issue, project: unauthorized_project) }
+
+    let!(:issue_link_a) { create(:issue_link, source: old_issue, target: authorized_issue_b) }
+    let!(:issue_link_b) { create(:issue_link, source: old_issue, target: unauthorized_issue) }
+    let!(:issue_link_c) { create(:issue_link, source: old_issue, target: authorized_issue_c) }
+    let!(:issue_link_d) { create(:issue_link, source: authorized_issue_d, target: old_issue) }
+
+    before do
+      authorized_project.add_developer(user)
+      authorized_project2.add_developer(user)
+    end
+
+    context 'multiple related issues' do
+      it 'moves all related issues and retains permissions' do
+        new_issue = move_service.execute(old_issue, new_project)
+
+        expect(new_issue.related_issues(admin))
+          .to match_array([authorized_issue_b, authorized_issue_c, authorized_issue_d, unauthorized_issue])
+
+        expect(new_issue.related_issues(user))
+          .to match_array([authorized_issue_b, authorized_issue_c, authorized_issue_d])
+
+        expect(authorized_issue_d.related_issues(user))
+          .to match_array([new_issue])
+      end
+    end
+  end
+
   context 'updating sent notifications' do
     let!(:old_issue_notification_1) { create(:sent_notification, project: old_issue.project, noteable: old_issue) }
     let!(:old_issue_notification_2) { create(:sent_notification, project: old_issue.project, noteable: old_issue) }
diff --git a/spec/services/notes/quick_actions_service_spec.rb b/spec/services/notes/quick_actions_service_spec.rb
index e9decd44730..794491fc50d 100644
--- a/spec/services/notes/quick_actions_service_spec.rb
+++ b/spec/services/notes/quick_actions_service_spec.rb
@@ -4,9 +4,9 @@ require 'spec_helper'
 
 RSpec.describe Notes::QuickActionsService do
   shared_context 'note on noteable' do
-    let(:project) { create(:project, :repository) }
-    let(:maintainer) { create(:user).tap { |u| project.add_maintainer(u) } }
-    let(:assignee) { create(:user) }
+    let_it_be(:project) { create(:project, :repository) }
+    let_it_be(:maintainer) { create(:user).tap { |u| project.add_maintainer(u) } }
+    let_it_be(:assignee) { create(:user) }
 
     before do
       project.add_maintainer(assignee)
@@ -41,6 +41,36 @@ RSpec.describe Notes::QuickActionsService do
         end
       end
 
+      context '/relate' do
+        let_it_be(:issue) { create(:issue, project: project) }
+        let_it_be(:other_issue) { create(:issue, project: project) }
+        let(:note_text) { "/relate #{other_issue.to_reference}" }
+        let(:note) { create(:note_on_issue, noteable: issue, project: project, note: note_text) }
+
+        context 'user cannot relate issues' do
+          before do
+            project.team.find_member(maintainer.id).destroy!
+            project.update!(visibility: Gitlab::VisibilityLevel::PUBLIC)
+          end
+
+          it 'does not create issue relation' do
+            expect do
+              _, update_params = service.execute(note)
+              service.apply_updates(update_params, note)
+            end.not_to change { IssueLink.count }
+          end
+        end
+
+        context 'user is allowed to relate issues' do
+          it 'creates issue relation' do
+            expect do
+              _, update_params = service.execute(note)
+              service.apply_updates(update_params, note)
+            end.to change { IssueLink.count }.by(1)
+          end
+        end
+      end
+
       describe '/reopen' do
         before do
           note.noteable.close!
diff --git a/spec/services/quick_actions/interpret_service_spec.rb b/spec/services/quick_actions/interpret_service_spec.rb
index 57e32b1aea9..b970a48051f 100644
--- a/spec/services/quick_actions/interpret_service_spec.rb
+++ b/spec/services/quick_actions/interpret_service_spec.rb
@@ -1644,6 +1644,103 @@ RSpec.describe QuickActions::InterpretService do
         end
       end
     end
+
+    context 'relate command' do
+      let_it_be_with_refind(:group) { create(:group) }
+
+      shared_examples 'relate command' do
+        it 'relates issues' do
+          service.execute(content, issue)
+
+          expect(IssueLink.where(source: issue).map(&:target)).to match_array(issues_related)
+        end
+      end
+
+      context 'user is member of group' do
+        before do
+          group.add_developer(developer)
+        end
+
+        context 'relate a single issue' do
+          let(:other_issue) { create(:issue, project: project) }
+          let(:issues_related) { [other_issue] }
+          let(:content) { "/relate #{other_issue.to_reference}" }
+
+          it_behaves_like 'relate command'
+        end
+
+        context 'relate multiple issues at once' do
+          let(:second_issue) { create(:issue, project: project) }
+          let(:third_issue) { create(:issue, project: project) }
+          let(:issues_related) { [second_issue, third_issue] }
+          let(:content) { "/relate #{second_issue.to_reference} #{third_issue.to_reference}" }
+
+          it_behaves_like 'relate command'
+        end
+
+        context 'empty relate command' do
+          let(:issues_related) { [] }
+          let(:content) { '/relate' }
+
+          it_behaves_like 'relate command'
+        end
+
+        context 'already having related issues' do
+          let(:second_issue) { create(:issue, project: project) }
+          let(:third_issue) { create(:issue, project: project) }
+          let(:issues_related) { [second_issue, third_issue] }
+          let(:content) { "/relate #{third_issue.to_reference(project)}" }
+
+          before do
+            create(:issue_link, source: issue, target: second_issue)
+          end
+
+          it_behaves_like 'relate command'
+        end
+
+        context 'cross project' do
+          let(:another_group) { create(:group, :public) }
+          let(:other_project) { create(:project, group: another_group) }
+
+          before do
+            another_group.add_developer(developer)
+          end
+
+          context 'relate a cross project issue' do
+            let(:other_issue) { create(:issue, project: other_project) }
+            let(:issues_related) { [other_issue] }
+            let(:content) { "/relate #{other_issue.to_reference(project)}" }
+
+            it_behaves_like 'relate command'
+          end
+
+          context 'relate multiple cross projects issues at once' do
+            let(:second_issue) { create(:issue, project: other_project) }
+            let(:third_issue) { create(:issue, project: other_project) }
+            let(:issues_related) { [second_issue, third_issue] }
+            let(:content) { "/relate #{second_issue.to_reference(project)} #{third_issue.to_reference(project)}" }
+
+            it_behaves_like 'relate command'
+          end
+
+          context 'relate a non-existing issue' do
+            let(:issues_related) { [] }
+            let(:content) { "/relate imaginary##{non_existing_record_iid}" }
+
+            it_behaves_like 'relate command'
+          end
+
+          context 'relate a private issue' do
+            let(:private_project) { create(:project, :private) }
+            let(:other_issue) { create(:issue, project: private_project) }
+            let(:issues_related) { [] }
+            let(:content) { "/relate #{other_issue.to_reference(project)}" }
+
+            it_behaves_like 'relate command'
+          end
+        end
+      end
+    end
   end
 
   describe '#explain' do
diff --git a/spec/services/system_note_service_spec.rb b/spec/services/system_note_service_spec.rb
index 969e5955609..0f5558738ac 100644
--- a/spec/services/system_note_service_spec.rb
+++ b/spec/services/system_note_service_spec.rb
@@ -86,6 +86,40 @@ RSpec.describe SystemNoteService do
     end
   end
 
+  describe '.relate_issue' do
+    let(:noteable_ref) { double }
+    let(:noteable) { double }
+
+    before do
+      allow(noteable).to receive(:project).and_return(double)
+    end
+
+    it 'calls IssuableService' do
+      expect_next_instance_of(::SystemNotes::IssuablesService) do |service|
+        expect(service).to receive(:relate_issue).with(noteable_ref)
+      end
+
+      described_class.relate_issue(noteable, noteable_ref, double)
+    end
+  end
+
+  describe '.unrelate_issue' do
+    let(:noteable_ref) { double }
+    let(:noteable) { double }
+
+    before do
+      allow(noteable).to receive(:project).and_return(double)
+    end
+
+    it 'calls IssuableService' do
+      expect_next_instance_of(::SystemNotes::IssuablesService) do |service|
+        expect(service).to receive(:unrelate_issue).with(noteable_ref)
+      end
+
+      described_class.unrelate_issue(noteable, noteable_ref, double)
+    end
+  end
+
   describe '.change_due_date' do
     let(:due_date) { double }
 
diff --git a/spec/services/system_notes/issuables_service_spec.rb b/spec/services/system_notes/issuables_service_spec.rb
index 1b5b26d90da..536e9792534 100644
--- a/spec/services/system_notes/issuables_service_spec.rb
+++ b/spec/services/system_notes/issuables_service_spec.rb
@@ -13,6 +13,38 @@ RSpec.describe ::SystemNotes::IssuablesService do
 
   let(:service) { described_class.new(noteable: noteable, project: project, author: author) }
 
+  describe '#relate_issue' do
+    let(:noteable_ref) { create(:issue) }
+
+    subject { service.relate_issue(noteable_ref) }
+
+    it_behaves_like 'a system note' do
+      let(:action) { 'relate' }
+    end
+
+    context 'when issue marks another as related' do
+      it 'sets the note text' do
+        expect(subject.note).to eq "marked this issue as related to #{noteable_ref.to_reference(project)}"
+      end
+    end
+  end
+
+  describe '#unrelate_issue' do
+    let(:noteable_ref) { create(:issue) }
+
+    subject { service.unrelate_issue(noteable_ref) }
+
+    it_behaves_like 'a system note' do
+      let(:action) { 'unrelate' }
+    end
+
+    context 'when issue relation is removed' do
+      it 'sets the note text' do
+        expect(subject.note).to eq "removed the relation with #{noteable_ref.to_reference(project)}"
+      end
+    end
+  end
+
   describe '#change_assignee' do
     subject { service.change_assignee(assignee) }