Add docs and first specs

doc/api/labels.md

@@ -186,6 +186,40 @@ Example response:
 }
 ```
 
+## Promote a project label to a group label
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25218) in GitLab 11.9.
+
+Promotes a project label to a group label.
+
+```
+POST /projects/:id/labels/promote
+```
+
+| Attribute       | Type    | Required                          | Description                      |
+| --------------- | ------- | --------------------------------- | -------------------------------  |
+| `id`      | integer/string    | yes      | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user |
+| `name`          | string  | yes                               | The name of the existing label   |
+
+```bash
+curl --request POST --data "name=documentation" --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/1/labels/promote"
+```
+
+Example response:
+
+```json
+{
+  "id" : 8,
+  "name" : "documentation",
+  "color" : "#8E44AD",
+  "description": "Documentation",
+  "open_issues_count": 1,
+  "closed_issues_count": 0,
+  "open_merge_requests_count": 2,
+  "subscribed": false
+}
+```
+
 ## Subscribe to a label
 
 Subscribes the authenticated user to a label to receive notifications.

lib/api/labels.rb

@@ -71,12 +71,12 @@ module API
         requires :name, type: String, desc: 'The name of the label to be promoted'
       end
       post ':id/labels/promote' do
-        authorize! :admin_label, parent
+        authorize! :admin_label, user_project
 
-        label = find_label(parent, params[:name], include_ancestor_groups: false)
+        label = find_label(user_project, params[:name], include_ancestor_groups: false)
 
         begin
-          group_label = Labels::PromoteService.new(user_project, current_user).execute(label)
+          group_label = ::Labels::PromoteService.new(user_project, current_user).execute(label)
 
           if group_label
             present group_label, with: Entities::GroupLabel, current_user: current_user, parent: user_project.group

spec/requests/api/labels_spec.rb

@@ -473,6 +473,29 @@ describe API::Labels do
     end
   end
 
+  describe 'POST /projects/:id/labels/promote' do
+    it 'returns 200 if label is promoted' do
+      post api("/projects/#{project.id}/labels/promote", user), params: { name: 'label1' }
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(json_response['name']).to eq(label1.name)
+      expect(json_response['color']).to eq('#FFFFFF')
+    end
+
+    it 'returns 404 if label does not exist' do
+      post api("/projects/#{project.id}/labels/promote", user), params: { name: 'unknown' }
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it 'returns 400 if no label name given' do
+      post api("/projects/#{project.id}/labels/promote", user)
+
+      expect(response).to have_gitlab_http_status(400)
+      expect(json_response['error']).to eq('name is missing')
+    end
+  end
+
   describe "POST /projects/:id/labels/:label_id/subscribe" do
     context "when label_id is a label title" do
       it "subscribes to the label" do