Remove Mattermost team with GitLab group

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