[rubygems/rubygems] Show exception cause in bug report template

https://github.com/rubygems/rubygems/commit/84b163e804

lib/bundler/friendly_errors.rb

@@ -65,8 +65,7 @@ module Bundler
         --- ERROR REPORT TEMPLATE -------------------------------------------------------
 
         ```
-        #{e.class}: #{e.message}
-          #{e.backtrace && e.backtrace.join("\n          ").chomp}
+        #{exception_message(e)}
         ```
 
         #{Bundler::Env.report}
@@ -85,6 +84,21 @@ module Bundler
       EOS
     end
 
+    def exception_message(error)
+      message = serialized_exception_for(error)
+      cause = error.cause
+      return message unless cause
+
+      message + serialized_exception_for(cause)
+    end
+
+    def serialized_exception_for(e)
+      <<-EOS.gsub(/^ {8}/, "")
+        #{e.class}: #{e.message}
+          #{e.backtrace && e.backtrace.join("\n          ").chomp}
+      EOS
+    end
+
     def issues_url(exception)
       message = exception.message.lines.first.tr(":", " ").chomp
       message = message.split("-").first if exception.is_a?(Errno)