Add show route to project_approval_rules

Updated api to include project_approval_rules show
Updated associated tests

doc/api/merge_request_approvals.md

@@ -173,6 +173,104 @@ GET /projects/:id/approval_rules
 ]
 ```
 
+### Get a single project-level rule
+
+> - Introduced 13.7.
+
+You can request information about a single project approval rules using the following endpoint:
+
+```plaintext
+GET /projects/:id/approval_rules/:approval_rule_id
+```
+
+**Parameters:**
+
+| Attribute            | Type    | Required | Description                                               |
+|----------------------|---------|----------|-----------------------------------------------------------|
+| `id`                 | integer | yes      | The ID of a project                                       |
+| `approval_rule_id`   | integer | yes      | The ID of a approval rule                                 |
+
+```json
+{
+  "id": 1,
+  "name": "security",
+  "rule_type": "regular",
+  "eligible_approvers": [
+    {
+      "id": 5,
+      "name": "John Doe",
+      "username": "jdoe",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/0?s=80&d=identicon",
+      "web_url": "http://localhost/jdoe"
+    },
+    {
+      "id": 50,
+      "name": "Group Member 1",
+      "username": "group_member_1",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/0?s=80&d=identicon",
+      "web_url": "http://localhost/group_member_1"
+    }
+  ],
+  "approvals_required": 3,
+  "users": [
+    {
+      "id": 5,
+      "name": "John Doe",
+      "username": "jdoe",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/0?s=80&d=identicon",
+      "web_url": "http://localhost/jdoe"
+    }
+  ],
+  "groups": [
+    {
+      "id": 5,
+      "name": "group1",
+      "path": "group1",
+      "description": "",
+      "visibility": "public",
+      "lfs_enabled": false,
+      "avatar_url": null,
+      "web_url": "http://localhost/groups/group1",
+      "request_access_enabled": false,
+      "full_name": "group1",
+      "full_path": "group1",
+      "parent_id": null,
+      "ldap_cn": null,
+      "ldap_access": null
+    }
+  ],
+  "protected_branches": [
+    {
+      "id": 1,
+      "name": "master",
+      "push_access_levels": [
+        {
+          "access_level": 30,
+          "access_level_description": "Developers + Maintainers"
+        }
+      ],
+      "merge_access_levels": [
+        {
+          "access_level": 30,
+          "access_level_description": "Developers + Maintainers"
+        }
+      ],
+      "unprotect_access_levels": [
+        {
+          "access_level": 40,
+          "access_level_description": "Maintainers"
+        }
+      ],
+      "code_owner_approval_required": "false"
+    }
+  ],
+  "contains_hidden_groups": false
+}
+```
+
 ### Create project-level rule
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/11877) in [GitLab Starter](https://about.gitlab.com/pricing/) 12.3.

ee/changelogs/unreleased/emilyring-approval-show.yml

+---
+title: Add get api endpoint for a single project approval rule
+merge_request: 47823
+author:
+type: added

ee/lib/api/project_approval_rules.rb

@@ -33,6 +33,17 @@ module API
         end
 
         segment ':approval_rule_id' do
+          desc 'Get a single approval rule' do
+            success EE::API::Entities::ProjectApprovalRule
+          end
+          get do
+            authorize_create_merge_request_in_project
+
+            approval_rule = user_project.approval_rules.find(params[:approval_rule_id])
+
+            present approval_rule, with: EE::API::Entities::ProjectApprovalRule, current_user: current_user
+          end
+
           desc 'Update project approval rule' do
             success EE::API::Entities::ProjectApprovalRule
           end

ee/spec/requests/api/project_approval_rules_spec.rb

@@ -11,6 +11,35 @@ RSpec.describe API::ProjectApprovalRules do
   let_it_be(:approver) { create(:user) }
   let_it_be(:other_approver) { create(:user) }
 
+  describe 'GET /projects/:id/approval_rules/:approval_rule_id' do
+    let_it_be(:private_project) { create(:project, :private, creator: user, namespace: user.namespace) }
+    let!(:approval_rule) { create(:approval_project_rule, project: private_project) }
+    let(:url) { "/projects/#{private_project.id}/approval_rules/#{approval_rule.id}" }
+
+    context 'when the request is correct' do
+      it 'matches the response schema', :aggregate_failures do
+        get api(url, user)
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(response).to match_response_schema('public_api/v4/project_approval_rule', dir: 'ee')
+
+        rule = json_response
+
+        expect(rule['approvals_required']).to eq(approval_rule.approvals_required)
+        expect(rule['id']).to eq(approval_rule.id)
+        expect(rule['name']).to eq(approval_rule.name)
+      end
+    end
+
+    context 'when the user is not authorized' do
+      it 'does not display rule information' do
+        get api(url, user2)
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+  end
+
   describe 'GET /projects/:id/approval_rules' do
     let(:url) { "/projects/#{project.id}/approval_rules" }