improves the reloading disabled error message

The original message from Zeitwerk is "can't reload, please call
loader.enable_reloading before setup (Zeitwerk::Error)", which is not
very informative for Rails programmers.

Rails should err with a message worded in terms of its interface.

1 files changed, 5 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb b/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
index b0f7a3f9cc..f16a9f7e57 100644
--- a/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
+++ b/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
@@ -9,7 +9,11 @@ module ActiveSupport
       module Decorations
         def clear
           Dependencies.unload_interlock do
-            Rails.autoloaders.main.reload
+            begin
+              Rails.autoloaders.main.reload
+            rescue Zeitwerk::ReloadingDisabledError
+              raise "reloading is disabled because config.cache_classes is true"
+            end
           end
         end