Save a fetchable ref per deployement

CHANGELOG

@@ -8,6 +8,7 @@ v 8.13.0 (unreleased)
   - Replaced the check sign to arrow in the show build view. !6501
   - Add a /wip slash command to toggle the Work In Progress status of a merge request. !6259 (tbalthazar)
   - Speed-up group milestones show page
+  - Keep refs for each deployment
   - Log LDAP lookup errors and don't swallow unrelated exceptions. !6103 (Markus Koller)
   - Add more tests for calendar contribution (ClemMakesApps)
   - Avoid database queries on Banzai::ReferenceParser::BaseParser for nodes without references

app/models/deployment.rb

@@ -11,7 +11,7 @@ class Deployment < ActiveRecord::Base
 
   delegate :name, to: :environment, prefix: true
 
-  after_save :keep_around_commit
+  after_save :create_ref
 
   def commit
     project.commit(sha)
@@ -30,7 +30,7 @@ class Deployment < ActiveRecord::Base
   end
 
   def keep_around_commit
-    project.repository.keep_around(self.sha)
+    project.repository.fetch_ref(project.repository.path_to_repo, ref, ref_path)
   end
 
   def manual_actions
@@ -76,4 +76,10 @@ class Deployment < ActiveRecord::Base
       where.not(id: self.id).
       take
   end
+
+  private
+
+  def ref_path
+    "#{environment.ref_path}#{id}"
+  end
 end

app/models/environment.rb

@@ -47,4 +47,8 @@ class Environment < ActiveRecord::Base
   def update_merge_request_metrics?
     self.name == "production"
   end
+
+  def ref_path
+    "refs/environments/#{Shellwords.shellescape(name)}/"
+  end
 end

doc/ci/environments.md

@@ -14,6 +14,19 @@ Defining environments in a project's `.gitlab-ci.yml` lets developers track
 
 Deployments are created when [jobs] deploy versions of code to [environments].
 
+### Checkout deployments locally
+
+Since 8.13, a reference in the git repository is saved for each deployment. So
+knowing what the state is of your current environments is only a `git fetch`
+away.
+
+In your git config, append the `[remote "<your-remote>"] block with an extra
+fetch line:
+
+```
+fetch = +refs/environments/*:refs/remotes/origin/environments/*
+```
+
 ## Defining environments
 
 You can create and delete environments manually in the web interface, but we