Add script to upgrade HAML syntax

[skip-ci]

script/haml-up.rb

@@ -0,0 +1,22 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# Upgrade HAML attribute syntax to prepare for HAML 6.
+#
+# HAML 6 stopped supporting nested hash attributes other than `data` and `aria`.
+# We used to be able to write:
+#
+#     %div{ ng: { class: "upper", bind: "model" } }
+#
+# This needs to be written in a flat structure now:
+#
+#     %div{ "ng-class" => "upper", "ng-bind" => "model" }
+#
+# This script rewrites HAML files automatically. It may be used like:
+#
+#     git ls-files '*.haml' | while read f; do ./haml-up.rb "$f"; done
+#
+require "haml_up"
+
+puts ARGV[0]
+HamlUp.new.upgrade_file(ARGV[0])