Monkey-patch Sprockets to prevent cache ballooning

Signed-off-by: Rémy Coutable <remy@rymai.me>

config/initializers/sprockets_base_file_digest_key.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+Sprockets::Base.prepend(Gitlab::Patch::SprocketsBaseFileDigestKey)

lib/gitlab/patch/sprockets_base_file_digest_key.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+# This monkey patch prevent cache ballooning when caching tmp/cache/assets/sprockets
+# on the CI. See https://github.com/rails/sprockets/issues/563 and
+# https://github.com/rails/sprockets/compare/3.x...jmreid:no-mtime-for-digest-key.
+module Gitlab
+  module Patch
+    module SprocketsBaseFileDigestKey
+      def file_digest(path)
+        if stat = self.stat(path)
+          digest = self.stat_digest(path, stat)
+          integrity_uri = self.hexdigest_integrity_uri(digest)
+
+          key = Sprockets::UnloadedAsset.new(path, self).file_digest_key(integrity_uri)
+          cache.fetch(key) do
+            digest
+          end
+        end
+      end
+    end
+  end
+end