fix chaperone-of? and property-only impersonators

Closes #1263

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

@@ -2495,6 +2495,38 @@
                           'neg)])
         (f 6)))))
 
+;; ----------------------------------------
+;; Check that property-only impersonator does not
+;; interfere with `chaperone-of?`
+;; (Test provided by Vincent)
+
+(let ()
+  (define-values (prop has-prop? get-prop)
+    (make-impersonator-property 'prop))
+  
+  (define add1* (impersonate-procedure add1 #f
+                                       prop #f))
+  
+  (test #t chaperone-of? (chaperone-procedure add1* #f)
+        add1*)
+  (test #t chaperone-of? (chaperone-procedure add1* (lambda (x) x))
+        add1*)
+  
+  (test #f chaperone-of? (chaperone-procedure add1* #f)
+        add1)
+  (test #f chaperone-of? (chaperone-procedure add1* (lambda (x) x))
+        add1)
+
+  (test #t impersonator-of? (chaperone-procedure add1* #f)
+        add1*)
+  (test #t impersonator-of? (chaperone-procedure add1* (lambda (x) x))
+        add1*)
+
+  (test #t impersonator-of? (chaperone-procedure add1* #f)
+        add1)
+  (test #t impersonator-of? (chaperone-procedure add1* (lambda (x) x))
+        add1))
+
 ;; ----------------------------------------
 
 (report-errs)

racket/src/racket/src/bool.c

@@ -575,6 +575,8 @@ int is_equal (Scheme_Object *obj1, Scheme_Object *obj2, Equal_Info *eql)
 
   if (eql->for_chaperone 
       && SCHEME_CHAPERONEP(obj2)
+      && (!(SCHEME_CHAPERONE_FLAGS((Scheme_Chaperone *)obj2) & SCHEME_CHAPERONE_IS_IMPERSONATOR)
+          || (eql->for_chaperone > 1))
       && scheme_is_noninterposing_chaperone(obj2)) {
     obj2 = ((Scheme_Chaperone *)obj2)->prev;
     goto top_after_next;