Added checks for migration downtime

These new checks can be used to check if migrations require downtime or
not (as tagged by their authors). In CI this compares the current branch
with master so migrations added by merge requests are automatically
verified.

To check the migrations added since a Git reference simply run:

    bundle exec rake gitlab:db:downtime_check[GIT_REF]

1 files changed, 28 insertions, 0 deletions

diff --git a/lib/gitlab/downtime_check/message.rb b/lib/gitlab/downtime_check/message.rb
new file mode 100644
index 00000000000..4446e921e0d
--- /dev/null
+++ b/lib/gitlab/downtime_check/message.rb
@@ -0,0 +1,28 @@
+module Gitlab
+  class DowntimeCheck
+    class Message
+      attr_reader :path, :offline, :reason
+
+      OFFLINE = "\e[32moffline\e[0m"
+      ONLINE = "\e[31monline\e[0m"
+
+      # path - The file path of the migration.
+      # offline - When set to `true` the migration will require downtime.
+      # reason - The reason as to why the migration requires downtime.
+      def initialize(path, offline = false, reason = nil)
+        @path = path
+        @offline = offline
+        @reason = reason
+      end
+
+      def to_s
+        label = offline ? OFFLINE : ONLINE
+
+        message = "[#{label}]: #{path}"
+        message += ": #{reason}" if reason
+
+        message
+      end
+    end
+  end
+end