Remove Mattermost team with GitLab group

When destroying a group, now an API call is made to the Mattermost
server to request the deletion of the project. Actual team deletion on
the Mattermost side happens async, so the runtime shouldn't increase by
more than a second.

app/models/chat_team.rb

@@ -3,4 +3,13 @@ class ChatTeam < ActiveRecord::Base
   validates :namespace, uniqueness: true
 
   belongs_to :namespace
+
+  def remove_mattermost_team(current_user)
+    Mattermost::Team.new(current_user).destroy(team_id: team_id)
+  rescue Mattermost::ClientError => e
+    # Either the group is not found, or the user doesn't have the proper
+    # access on the mattermost instance. In the first case, we're done either way
+    # in the latter case, we can't recover by retrying, so we just log what happened
+    Rails.logger.error("Mattermost team deletion failed: #{e}")
+  end
 end

app/services/groups/destroy_service.rb

@@ -21,6 +21,8 @@ module Groups
         DestroyService.new(group, current_user).execute
       end
 
+      group.chat_team&.remove_mattermost_team(current_user)
+
       group.really_destroy!
     end
   end

changelogs/unreleased/zj-delete-mm-team.yml

+---
+title: Remove Mattermost team when deleting a group
+merge_request: 11362
+author:

lib/mattermost/client.rb

@@ -24,6 +24,10 @@ module Mattermost
       json_response session.post(path, options)
     end
 
+    def delete(session, path, options)
+      json_response session.delete(path, options)
+    end
+
     def session_get(path, options = {})
       with_session do |session|
         get(session, path, options)
@@ -36,6 +40,12 @@ module Mattermost
       end
     end
 
+    def session_delete(path, options = {})
+      with_session do |session|
+        delete(session, path, options)
+      end
+    end
+
     def json_response(response)
       json_response = JSON.parse(response.body)
 

lib/mattermost/team.rb

@@ -14,5 +14,12 @@ module Mattermost
         type: type
       }.to_json)
     end
+
+    # The deletion is done async, so the response is fast.
+    # On the mattermost side, this triggers an soft deletion first, after which
+    # the actuall data is removed
+    def destroy(team_id:)
+      session_delete("/api/v4/teams/#{team_id}?permanent=true")
+    end
   end
 end

spec/services/groups/destroy_service_spec.rb

@@ -35,6 +35,16 @@ describe Groups::DestroyService, services: true do
       it { expect(NotificationSetting.unscoped.all).not_to include(notification_setting) }
     end
 
+    context 'mattermost team' do
+      let!(:chat_team) { create(:chat_team, namespace: group) }
+
+      it 'destroys the team too' do
+        expect_any_instance_of(Mattermost::Team).to receive(:destroy)
+
+        destroy_group(group, user, async)
+      end
+    end
+
     context 'file system' do
       context 'Sidekiq inline' do
         before do