Merge branch 'api-delete-tag' into 'master'

Delete tag via API

### What does this MR do?

Implements deleting a tag via the API.

### Are there points in the code the reviewer needs to double check?

On success, it returns the name of the deleted tag. This is similar to the [delete branch API](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/api/branches.rb#L111).

###  What are the relevant issue numbers / Feature requests?

* This MR closes #1575 
* Closes http://feedback.gitlab.com/forums/176466-general/suggestions/6599203-delete-tags-through-the-api

@stanhu Could you do a review?

See merge request !1862

CHANGELOG

@@ -27,6 +27,7 @@ v 8.4.0 (unreleased)
   - Properly set task-list class on single item task lists
   - Add file finder feature in tree view (Kyungchul Shin)
   - Ajax filter by message for commits page
+  - API: Add support for deleting a tag via the API (Robert Schilling)
 
 v 8.3.3 (unreleased)
   - Get "Merge when build succeeds" to work when commits were pushed to MR target branch while builds were running

doc/api/tags.md

@@ -83,6 +83,26 @@ it will contain the annotation.
 It returns 200 if the operation succeed. In case of an error,
 405 with an explaining error message is returned.
 
+## Delete a tag
+
+Deletes a tag of a repository with given name. On success, this API method
+returns 200 with the name of the deleted tag. If the tag does not exist, the
+API returns 404.
+
+```
+DELETE /projects/:id/repository/tags/:tag_name
+```
+
+Parameters:
+
+- `id` (required) - The ID of a project
+- `tag_name` (required) - The name of a tag
+
+```json
+{
+  "tag_name": "v4.3.0"
+}
+```
 
 ## Create a new release
 

lib/api/tags.rb

@@ -40,6 +40,27 @@ module API
         end
       end
 
+      # Delete tag
+      #
+      # Parameters:
+      #   id (required) - The ID of a project
+      #   tag_name (required) - The name of the tag
+      # Example Request:
+      #   DELETE /projects/:id/repository/tags/:tag
+      delete ":id/repository/tags/:tag_name", requirements: { tag_name: /.*/ } do
+        authorize_push_project
+        result = DeleteTagService.new(user_project, current_user).
+          execute(params[:tag_name])
+
+        if result[:status] == :success
+          {
+            tag_name: params[:tag_name]
+          }
+        else
+          render_api_error!(result[:message], result[:return_code])
+        end
+      end
+
       # Add release notes to tag
       #
       # Parameters:

spec/requests/api/tags_spec.rb

@@ -65,6 +65,27 @@ describe API::API, api: true  do
       end
     end
 
+    describe 'DELETE /projects/:id/repository/tags/:tag_name' do
+      let(:tag_name) { project.repository.tag_names.sort.reverse.first }
+
+      before do
+        allow_any_instance_of(Repository).to receive(:rm_tag).and_return(true)
+      end
+
+      context 'delete tag' do
+        it 'should delete an existing tag' do
+          delete api("/projects/#{project.id}/repository/tags/#{tag_name}", user)
+          expect(response.status).to eq(200)
+          expect(json_response['tag_name']).to eq(tag_name)
+        end
+
+        it 'should raise 404 if the tag does not exist' do
+          delete api("/projects/#{project.id}/repository/tags/foobar", user)
+          expect(response.status).to eq(404)
+        end
+      end
+    end
+
     context 'annotated tag' do
       it 'should create a new annotated tag' do
         # Identity must be set in .gitconfig to create annotated tag.