schemify: ensure that deserialized constants are immutable

Closes #2394

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

@@ -2185,6 +2185,26 @@
   (test 'cons exn:fail:contract:variable-id e)
   (test #t regexp-match? #rx"^cons: " (exn-message e)))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check immutability after saving and restoring quoted constants
+
+(let ([m `(module defines-immutable-objects racket/base
+            (provide objs)
+            (define objs
+              '(#"x"
+                "x"
+                #()
+                #(1)
+                #(#:x)
+                #(#"x")
+                #&1
+                #&#:x
+                #&#"x"
+                #hasheq((a . b)))))])
+  (define c (compile m))
+  (eval c)
+  (test #t andmap immutable? (dynamic-require ''defines-immutable-objects 'objs)))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/schemify/serialize.rkt

@@ -181,16 +181,14 @@
                       `(cons ,a ,d))))]
            [(vector? q)
             (let ([args (map make-construct (vector->list q))])
-              (if (and (andmap quote? args)
+              `(vector->immutable-vector
+                ,(if (and (andmap quote? args)
                           (not (impersonator? q)))
                      `(quote ,q)
-                  `(vector ,@args)))]
+                     `(vector ,@args))))]
            [(box? q)
             (let ([arg (make-construct (unbox q))])
-              (if (and (quote? arg)
-                       (not (impersonator? q)))
-                  `(quote ,q)
-                  `(box ,arg)))]
+              `(box-immutable ,arg))]
            [(prefab-struct-key q)
             => (lambda (key)
                  `(make-prefab-struct ',key ,@(map make-construct