Add note about #26929 in the upgrade guide

This is a small breaking change that we chose to make in 5.1 since the
fix can be done with a search and replace tool.

1 files changed, 17 insertions, 0 deletions

diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 3afc0e5309..ebfdc78dfc 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -84,6 +84,23 @@ Also, if you have pretty old YAML documents containing dumps of such objects,
 you may need to load and dump them again to make sure that they reference
 the right constant and that loading them won't break in the future.
 
+### `config.secrets` now load with all keys as symbols
+
+If you application stores nested configuration in `secrets.yml` now all keys are being
+laded as symbols so access using strings should be changed.
+
+From:
+
+```ruby
+Rails.appplication.config.secrets[:smtp_settings]["address"]
+```
+
+To:
+
+```ruby
+Rails.application.config.secrets[:smtp_settings][:address]
+```
+
 Upgrading from Rails 4.2 to Rails 5.0
 -------------------------------------