Allow deprecated non-symbol access to nested `config_for` hashes

A change to `Rails::Application.config_for` in
https://github.com/rails/rails/pull/33815 and
https://github.com/rails/rails/pull/33882 has altered the behaviour of
the returned object in a breaking manner. Before that change, nested
hashes returned from `config_for` could be accessed using non-symbol keys.
After the change, all keys are recursively symbolized so non-symbol access
fails to read the expected values.

This is a breaking change for any app that might be relying on the
nested hashes returned from `config_for` calls, and thus should be
deprecated before being removed from the codebase.

This commit introduces a temporary `NonSymbolAccessDeprecatedHash` class
that recursively wraps any nested hashes inside the `OrderedOptions`
object returned from `config_for` and issues a deprecation notice when a
non-symbol based access is performed.

This way, apps that are still relying on the ability to access these
nested hashes using non-symbol keys will be able to observe the
deprecation notices and have time to implement changes before non-symbol
access is removed for good.

A CHANGELOG entry is also added to note that non-symbol access to nested
`config_for` hashes is deprecated.

1 files changed, 102 insertions, 1 deletions

diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 37fba72ee3..1cafdedcdc 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -1714,7 +1714,7 @@ module ApplicationTests
       assert_equal true, Rails.application.config.action_mailer.show_previews
     end
 
-    test "config_for loads custom configuration from yaml accessible as symbol" do
+    test "config_for loads custom configuration from yaml accessible as symbol or string" do
       app_file "config/custom.yml", <<-RUBY
       development:
         foo: 'bar'
@@ -1727,6 +1727,7 @@ module ApplicationTests
       app "development"
 
       assert_equal "bar", Rails.application.config.my_custom_config[:foo]
+      assert_equal "bar", Rails.application.config.my_custom_config["foo"]
     end
 
     test "config_for loads nested custom configuration from yaml as symbol keys" do
@@ -1746,6 +1747,25 @@ module ApplicationTests
       assert_equal 1, Rails.application.config.my_custom_config[:foo][:bar][:baz]
     end
 
+    test "config_for loads nested custom configuration from yaml with deprecated non-symbol access" do
+      app_file "config/custom.yml", <<-RUBY
+      development:
+        foo:
+          bar:
+            baz: 1
+      RUBY
+
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+
+      app "development"
+
+      assert_deprecated do
+        assert_equal 1, Rails.application.config.my_custom_config["foo"]["bar"]["baz"]
+      end
+    end
+
     test "config_for makes all hash methods available" do
       app_file "config/custom.yml", <<-RUBY
       development:
@@ -1770,6 +1790,87 @@ module ApplicationTests
       assert_equal actual[:bar], baz: 1
     end
 
+    test "config_for generates deprecation notice when nested hash methods are called with non-symbols" do
+      app_file "config/custom.yml", <<-RUBY
+      development:
+        foo:
+          bar: 1
+          baz: 2
+          qux:
+            boo: 3
+      RUBY
+
+      app "development"
+
+      actual = Rails.application.config_for("custom")[:foo]
+
+      # slice
+      assert_deprecated do
+        assert_equal({ bar: 1, baz: 2 }, actual.slice("bar", "baz"))
+      end
+
+      # except
+      assert_deprecated do
+        assert_equal({ qux: { boo: 3 } }, actual.except("bar", "baz"))
+      end
+
+      # dig
+      assert_deprecated do
+        assert_equal(3, actual.dig("qux", "boo"))
+      end
+
+      # fetch - hit
+      assert_deprecated do
+        assert_equal(1, actual.fetch("bar", 0))
+      end
+
+      # fetch - miss
+      assert_deprecated do
+        assert_equal(0, actual.fetch("does-not-exist", 0))
+      end
+
+      # fetch_values
+      assert_deprecated do
+        assert_equal([1, 2], actual.fetch_values("bar", "baz"))
+      end
+
+      # key? - hit
+      assert_deprecated do
+        assert(actual.key?("bar"))
+      end
+
+      # key? - miss
+      assert_deprecated do
+        assert_not(actual.key?("does-not-exist"))
+      end
+
+      # slice!
+      actual = Rails.application.config_for("custom")[:foo]
+
+      assert_deprecated do
+        slice = actual.slice!("bar", "baz")
+        assert_equal({ bar: 1, baz: 2 }, actual)
+        assert_equal({ qux: { boo: 3 } }, slice)
+      end
+
+      # extract!
+      actual = Rails.application.config_for("custom")[:foo]
+
+      assert_deprecated do
+        extracted = actual.extract!("bar", "baz")
+        assert_equal({ bar: 1, baz: 2 }, extracted)
+        assert_equal({ qux: { boo: 3 } }, actual)
+      end
+
+      # except!
+      actual = Rails.application.config_for("custom")[:foo]
+
+      assert_deprecated do
+        actual.except!("bar", "baz")
+        assert_equal({ qux: { boo: 3 } }, actual)
+      end
+    end
+
     test "config_for uses the Pathname object if it is provided" do
       app_file "config/custom.yml", <<-RUBY
       development: