Ticket #12089: plugin-activation.patch

wp-admin/includes/plugin.php

@@ -359 +359 @@
                         wp_redirect(add_query_arg('_error_nonce', wp_create_nonce('plugin-activation-error_' . $plugin), $redirect)); // we'll override this later if the plugin can be included without fatal error
                 ob_start();
                 @include(WP_PLUGIN_DIR . '/' . $plugin);
+                if ( ob_get_length() > 0 ) {
+                        $output = ob_get_clean();
+                        return new WP_Error('unexpected_output', __('The plugin generated unexpected output.') . '<br />' . htmlspecialchars($output));
+                }
                 do_action( 'activate_plugin', trim( $plugin) );
                 if ( $network_wide ) {
                         $current[$plugin] = time();