fix an identifier binding bug

Merge to 5.2

collects/tests/racket/macro.rktl

@@ -566,6 +566,42 @@
      (q))))
 (require 'm-check-varref-expand)
 
+;; ----------------------------------------
+;; Check that a modul-level binding with 0 marks
+;;  but lexical context is found correctly with
+;;  1 and 2 marks (test case by Carl):
+
+(module check-macro-introduced-via-defctx racket/base
+  (require (for-syntax racket/base racket/syntax))
+
+  (begin-for-syntax
+   (define env (box #false)))
+  
+  (define-syntax (one stx)
+    (define ctx (syntax-local-make-definition-context #false))
+    (define id
+      (internal-definition-context-apply 
+       ctx
+       (syntax-local-introduce (datum->syntax #false 'private))))
+    (syntax-local-bind-syntaxes (list id) #false ctx)
+    (internal-definition-context-seal ctx)
+    #`(begin
+        (begin-for-syntax (set-box! env #'#,id))
+        (define #,id #false)))
+  (one)
+  
+  (define-syntax (two stx)
+    (define id ((make-syntax-introducer) (unbox env)))
+    (unless (free-identifier=? id (syntax-local-introduce id))
+      (raise-syntax-error 
+       #false
+       (format "mark changes identifier's binding: ~v / ~v"
+               (identifier-binding id)
+               (identifier-binding (syntax-local-introduce id)))
+       id))
+    #'#f)
+  (two))
+
 ;; ----------------------------------------
 
 (report-errs)

src/racket/src/compenv.c

@@ -1086,10 +1086,13 @@ Scheme_Object *scheme_tl_id_sym(Scheme_Env *env, Scheme_Object *id, Scheme_Objec
 	  break;
 	}
       } else {
-        if (!SCHEME_PAIRP(marks)) {
+        if (SCHEME_NULLP(amarks)) {
+          /* can always match empty marks */
+          best_match = SCHEME_CDR(a);
+          best_match_skipped = 0;
+        } else if (!SCHEME_PAIRP(marks)) {
 	  /* To be better than nothing, could only match exactly: */
-	  if (scheme_equal(amarks, marks)
-              || SCHEME_NULLP(amarks)) {
+	  if (scheme_equal(amarks, marks)) {
 	    best_match = SCHEME_CDR(a);
 	    best_match_skipped = 0;
 	  }