fix expand[-syntax[-to-top-form]] to add namespace's scope

Make `expand` more consistent with `eval` and with the old expander.

pkgs/racket-test-core/tests/racket/macro.rktl

@@ -1335,6 +1335,26 @@
                 #'#t)])
   (void (m)))
 
+;; ----------------------------------------
+;; Check that `expand-syntax` attaches the namespace's 
+
+(test 573
+      'expand
+      (parameterize ([current-namespace (make-base-namespace)])
+        (eval '(require (for-syntax racket/base)))
+        (eval '(define-syntax (m stx)
+                (with-syntax ([id (datum->syntax #f 'gen-id)])
+                  #`(begin
+                      (define id 573)
+                      id))))
+        (define stx (namespace-syntax-introduce (datum->syntax #f '(m))))
+        (syntax-case (expand-syntax-to-top-form stx) (begin)
+          [(begin a b)
+           (begin
+             (eval-syntax #'a)
+             (eval-syntax (expand-syntax #'b)))])))
+
+
 ;; ----------------------------------------
 
 (report-errs)

racket/src/racket/src/eval.c

@@ -4620,6 +4620,12 @@ static void *expand_k(void)
     obj = scheme_top_introduce(obj, env->genv);
   }
 
+  if (rename && env->genv->stx_context) {
+    obj = scheme_stx_push_introduce_module_context(obj, env->genv->stx_context);
+    env->expand_result_adjust = scheme_stx_push_introduce_module_context;
+    env->expand_result_adjust_arg = env->genv->stx_context;
+  }
+  
   observer = scheme_get_expand_observe();
   SCHEME_EXPAND_OBSERVE_START_EXPAND(observer);
 
@@ -4694,10 +4700,6 @@ static void *expand_k(void)
       break;
   }
 
-  if (rename && !just_to_top) {
-    /* scheme_simplify_stx(obj, scheme_new_stx_simplify_cache()); */ /* too expensive */
-  }
-
   return obj;
 }