Allow non-hash values in config files

Fix: https://github.com/rails/rails/issues/37800

railties/lib/rails/application.rb

@@ -220,27 +220,25 @@ def message_verifier(verifier_name)
     #       config.middleware.use ExceptionNotifier, config_for(:exception_notification)
     #     end
     def config_for(name, env: Rails.env)
-      if name.is_a?(Pathname)
+      yaml = name.is_a?(Pathname) ? name : Pathname.new("#{paths["config"].existent.first}/#{name}.yml")
-        yaml = name
-      else
-        yaml = Pathname.new("#{paths["config"].existent.first}/#{name}.yml")
-      end
 
       if yaml.exist?
         require "erb"
-        config = YAML.load(ERB.new(yaml.read).result, symbolize_names: true) || {}
+        all_configs    = YAML.load(ERB.new(yaml.read).result, symbolize_names: true) || {}
-        config = (config[:shared] || {}).deep_merge(config[env.to_sym] || {})
+        config, shared = all_configs[env.to_sym], all_configs[:shared]
 
-        ActiveSupport::OrderedOptions.new.tap do |options|
+        if config.is_a?(Hash)
-          options.update(config)
+          ActiveSupport::OrderedOptions.new.update(shared&.deep_merge(config) || config)
+        else
+          config || shared
         end
       else
         raise "Could not load configuration. No such file - #{yaml}"
       end
-    rescue Psych::SyntaxError => e
+    rescue Psych::SyntaxError => error
       raise "YAML syntax error occurred while parsing #{yaml}. " \
         "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
-        "Error: #{e.message}"
+        "Error: #{error.message}"
     end
 
     # Stores some of the Rails initial environment parameters which

railties/test/application/configuration_test.rb

@@ -1958,6 +1958,22 @@ class D < C
       assert_equal({ baz: 1 }, actual[:bar])
     end
 
+    test "config_for does not assume config is a hash" do
+      app_file "config/custom.yml", <<~RUBY
+        development:
+          - foo
+          - bar
+      RUBY
+
+      add_to_config <<~RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+
+      app "development"
+
+      assert_equal %w( foo bar ), Rails.application.config.my_custom_config
+    end
+
     test "config_for uses the Pathname object if it is provided" do
       app_file "config/custom.yml", <<-RUBY
       development:
@@ -1985,19 +2001,19 @@ class D < C
       assert_equal "Could not load configuration. No such file - #{app_path}/config/custom.yml", exception.message
     end
 
-    test "config_for without the environment configured returns an empty hash" do
+    test "config_for without the environment configured returns nil" do
-      app_file "config/custom.yml", <<-RUBY
+      app_file "config/custom.yml", <<~RUBY
-      test:
+        test:
-        key: 'custom key'
+          key: 'custom key'
       RUBY
 
-      add_to_config <<-RUBY
+      add_to_config <<~RUBY
         config.my_custom_config = config_for('custom')
       RUBY
 
       app "development"
 
-      assert_equal({}, Rails.application.config.my_custom_config)
+      assert_nil Rails.application.config.my_custom_config
     end
 
     test "config_for implements shared configuration as secrets case found" do
@@ -2055,17 +2071,16 @@ class D < C
       assert_equal({ baz: 1, qux: 2 }, Rails.application.config.my_custom_config[:foo][:bar])
     end
 
-    test "config_for with empty file returns an empty hash" do
+    test "config_for with empty file returns nil" do
-      app_file "config/custom.yml", <<-RUBY
+      app_file "config/custom.yml", ""
-      RUBY
 
-      add_to_config <<-RUBY
+      add_to_config <<~RUBY
         config.my_custom_config = config_for('custom')
       RUBY
 
       app "development"
 
-      assert_equal({}, Rails.application.config.my_custom_config)
+      assert_nil Rails.application.config.my_custom_config
     end
 
     test "config_for containing ERB tags should evaluate" do