Clear error page state before each request

lib/better_errors/middleware.rb

@@ -81,11 +81,24 @@ def better_errors_call(env)
     end
 
     def protected_app_call(env)
+      # Hold any existing error outside the instance that it's not going to pollute the `#inspect` of this instance
+      # while the app is being called. Once the app returns, restore the original error so that it is still available
+      # to Better Errors. If a new error is raised during the call, it be stored replacing the old one.
+      #
+      # FIXME: wrap this (and therefore all application requests) in a mutex.
+      # This will have strange results in a multithreaded environment. Either the second thread will clear
+      # the error state, or another thread request that rescues an exception will be overwritten by a slower
+      # request finishing after it.
+      Thread.current[:better_errors_previous_error_page] = @error_page
+      @error_page = nil
       @app.call env
+      @error_page = Thread.current[:better_errors_previous_error_page]
     rescue Exception => ex
       @error_page = @handler.new ex, env
       log_exception
       show_error_page(env, ex)
+    ensure
+      Thread.current[:better_errors_previous_error_page] = nil
     end
 
     def show_error_page(env, exception=nil)