fix an inconsistency in free-identifier=?

Closes PR 13982

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

@@ -970,6 +970,33 @@
 
     (lam x x)))
 
+;; ----------------------------------------
+;; Check consistency of `free-identifier=?' and binding
+
+(module consistency-free-id-A racket
+  (provide g (rename-out [*a a]))
+  (define *a 10)
+  (define a 10)
+  (define-syntax g #'a))
+
+(module consistency-free-id-B racket
+  (require 'consistency-free-id-A)
+  (provide consistency-free-id)
+  (define-syntax (n stx)
+    (syntax-case stx ()
+      [(_ ref)
+       (with-syntax ([in (syntax-local-introduce
+                          (syntax-local-value #'g))])
+         #'(let ([in 10]) ; BINDING
+             (list (free-identifier=? #'in #'ref)
+                   in
+                   ref)))])) ; REFERENCE
+  (define (consistency-free-id) (n a)))
+
+(require 'consistency-free-id-B)
+
+(test (list #t 10 10) consistency-free-id)
+
 ;; ----------------------------------------
 
 (report-errs)

racket/src/racket/src/syntax.c

@@ -4707,6 +4707,7 @@ int scheme_stx_module_eq3(Scheme_Object *a, Scheme_Object *b,
 {
   Scheme_Object *bsym;
   Scheme_Hash_Table *free_id_recur;
+  int must_be_lex;
 
   if (!a || !b)
     return (a == b);
@@ -4730,9 +4731,18 @@ int scheme_stx_module_eq3(Scheme_Object *a, Scheme_Object *b,
       asym = a;
   }
 
+  must_be_lex = 0;
+
   /* Same name? */
-  if (!SAME_OBJ(asym, bsym))
+  if (!SAME_OBJ(asym, bsym)) {
-    return 0;
+    /* It's ok to have different names if they have
+       the same symbolic name and the same lexical binding,
+       so double-check that our shortcut worked... */
+    if (SAME_OBJ(SCHEME_STX_VAL(a), SCHEME_STX_VAL(b)))
+      must_be_lex = 1;
+    else
+      return 0;
+  }
 
   if ((a == asym) || (b == bsym))
     return 1;
@@ -4741,6 +4751,9 @@ int scheme_stx_module_eq3(Scheme_Object *a, Scheme_Object *b,
   a = resolve_env(a, a_phase, 1, NULL, NULL, NULL, NULL, 0, free_id_recur);
   release_recur_table(free_id_recur);
 
+  if (must_be_lex && !SCHEME_SYMBOLP(a))
+    return 0;
+
   free_id_recur = make_recur_table();
   b = resolve_env(b, b_phase, 1, NULL, NULL, NULL, NULL, 0, free_id_recur);
   release_recur_table(free_id_recur);