fix redundant-require checking

When a module defines and exports an identifier at two phases,
and when another module imports both of them at the same phase,
an error was not reported as it should have been.

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

@@ -1795,6 +1795,27 @@ case of module-leve bindings; it doesn't cover local bindings.
 
 (test 333 dynamic-require ''module-that-uses-eval-to-define-a-macro-in-its-own-namespace 'result)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check that multiple imports of a name are disallowed
+;; when they're from the from the same module but different
+;; phases of that module
+
+(module defines-a-at-two-phase-levels racket/base
+  (require (for-syntax racket/base))
+  
+  (provide a (for-syntax a))
+  
+  (define a 0)
+  (begin-for-syntax
+    (define a 1)))
+
+(err/rt-test (eval #'(module b racket/base
+                       (require 'defines-a-at-two-phase-levels
+                                (for-syntax racket/base
+                                            'defines-a-at-two-phase-levels))))
+             (lambda (exn)
+               (regexp-match? #rx" already" (exn-message exn))))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/racket/src/module.c

@@ -7956,7 +7956,8 @@ static void check_require_name(Scheme_Object *id, Scheme_Object *self_modidx,
     intptr_t fromsrclen = 0;
 
     if (same_resolved_modidx(SCHEME_VEC_ELS(vec)[1], modidx)
-	&& SAME_OBJ(SCHEME_VEC_ELS(vec)[2], exname)) {
+	&& SAME_OBJ(SCHEME_VEC_ELS(vec)[2], exname)
+        && SAME_OBJ(SCHEME_VEC_ELS(vec)[8], scheme_make_integer(exet))) {
       /* already required, same source; add redundant nominal (for re-provides),
          and also add source phase for re-provides. */
       nml = scheme_make_pair(nominal_modidx, SCHEME_VEC_ELS(vec)[0]);