Add CI variable CI_MERGE_REQUEST_APPROVED

This variable indicates the approval status of the merge request.
It is set to `true` when the merge request approval feature is available
and the merge request has been approved.

Changelog: added
EE: true

doc/ci/variables/predefined_variables.md

@@ -130,6 +130,7 @@ These variables are available when:
 
 | Variable                               | GitLab | Runner | Description |
 |----------------------------------------|--------|--------|-------------|
+| `CI_MERGE_REQUEST_APPROVED`            | 14.1   | all    | Approval status of the merge request. `true` when [merge request approvals](../../user/project/merge_requests/approvals/index.md) is available and the merge request has been approved. |
 | `CI_MERGE_REQUEST_ASSIGNEES`           | 11.9   | all    | Comma-separated list of usernames of assignees for the merge request. |
 | `CI_MERGE_REQUEST_ID`                  | 11.6   | all    | The instance-level ID of the merge request. This is a unique ID across all projects on GitLab. |
 | `CI_MERGE_REQUEST_IID`                 | 11.6   | all    | The project-level IID (internal ID) of the merge request. This ID is unique for the current project. |

ee/app/models/ee/merge_request.rb

@@ -110,6 +110,11 @@ module EE
       end
     end
 
+    override :predefined_variables
+    def predefined_variables
+      super.concat(merge_request_approval_variables)
+    end
+
     override :mergeable?
     def mergeable?(skip_ci_check: false, skip_discussions_check: false)
       return false unless approved?
@@ -298,5 +303,15 @@ module EE
         ApprovalWrappedRule.wrap(self, rule).approved?
       end
     end
+
+    def merge_request_approval_variables
+      return unless approval_feature_available?
+
+      strong_memoize(:merge_request_approval_variables) do
+        ::Gitlab::Ci::Variables::Collection.new.tap do |variables|
+          variables.append(key: 'CI_MERGE_REQUEST_APPROVED', value: approved?.to_s) if approved?
+        end
+      end
+    end
   end
 end

ee/spec/models/merge_request_spec.rb

@@ -1062,6 +1062,49 @@ RSpec.describe MergeRequest do
     end
   end
 
+  describe '#predefined_variables' do
+    context 'when merge request has approver feature' do
+      before do
+        stub_licensed_features(merge_request_approvers: true)
+      end
+
+      context 'without any rules' do
+        it 'includes variable CI_MERGE_REQUEST_APPROVED=true' do
+          expect(merge_request.predefined_variables.to_hash).to include('CI_MERGE_REQUEST_APPROVED' => 'true')
+        end
+      end
+
+      context 'with a rule' do
+        let(:approver) { create(:user) }
+        let!(:rule) { create(:approval_merge_request_rule, merge_request: merge_request, approvals_required: 1, users: [approver]) }
+
+        context 'that has been approved' do
+          it 'includes variable CI_MERGE_REQUEST_APPROVED=true' do
+            create(:approval, merge_request: merge_request, user: approver)
+
+            expect(merge_request.predefined_variables.to_hash).to include('CI_MERGE_REQUEST_APPROVED' => 'true')
+          end
+        end
+
+        context 'that has not been approved' do
+          it 'does not include variable CI_MERGE_REQUEST_APPROVED' do
+            expect(merge_request.predefined_variables.to_hash.keys).not_to include('CI_MERGE_REQUEST_APPROVED')
+          end
+        end
+      end
+    end
+
+    context 'when merge request does not have approver feature' do
+      before do
+        stub_licensed_features(merge_request_approvers: false)
+      end
+
+      it 'does not include variable CI_MERGE_REQUEST_APPROVED' do
+        expect(merge_request.predefined_variables.to_hash.keys).not_to include('CI_MERGE_REQUEST_APPROVED')
+      end
+    end
+  end
+
   describe '#mergeable?' do
     subject { merge_request.mergeable? }