fix expand on a module containing a #%declare form

pkgs/racket-pkgs/racket-test/tests/racket/cross-phase.rkt

@@ -116,5 +116,21 @@
             '(module m '#%kernel
                (#%declare #:cross-phase-persistent))))))
 
+;; Check that `expand` produces valies syntax
+(let ()
+  (define e
+    (syntax->datum
+     (parameterize ([current-namespace (make-base-namespace)])
+       (expand '(module m '#%kernel
+                  (#%declare #:cross-phase-persistent))))))
+  (let loop ([e e])
+    (cond
+     [(syntax? e) (loop (syntax-e e))]
+     [(pair? e) (loop (car e)) (loop (cdr e))]
+     [(null? e) (void)]
+     [(symbol? e) (void)]
+     [(keyword? e) (void)]
+     [else (error 'expand-test "unexpected value: ~e" e)])))
+
 (displayln "All tests passed.")
 

racket/src/racket/src/module.c

@@ -9312,9 +9312,7 @@ static Scheme_Object *do_module_begin_at_phase(Scheme_Object *form, Scheme_Comp_
     SCHEME_EXPAND_OBSERVE_NEXT(observer);
 
     if (kind == SAVED_MODFORM_KIND) {
-      expanded_l = scheme_make_pair(SCHEME_CDR(e), expanded_l);
+      expanded_l = scheme_make_pair(e, expanded_l);
-      SCHEME_CAR(p) = SCHEME_CAR(e);
-      prev_p = p;
       p = SCHEME_CDR(p);      
     } else if ((kind == PROVIDE_MODFORM_KIND)
                || (kind == MODULE_MODFORM_KIND)) {