fix argument check for instantiate-linklet

Closes #2962

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

@@ -11,6 +11,7 @@
 (load-relative "letrec.rktl")
 (load-relative "procs.rktl")
 (load-relative "stx.rktl")
+(load-relative "linklet.rktl")
 (load-relative "module.rktl")
 (load-relative "submodule.rktl")
 (load-relative "stxparam.rktl")

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

@@ -0,0 +1,26 @@
+
+(load-relative "loadtest.rktl")
+
+(Section 'linklet)
+
+(require racket/linklet)
+
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(let ()
+  (define l (compile-linklet '(linklet
+                                  ()
+                                  ()
+                                4)))
+  (test #t linklet? l)
+  (test #t instance? (instantiate-linklet l '()))
+  (test 4 instantiate-linklet l '() (make-instance 'l))
+
+  (err/rt-test (instantiate-linklet l) exn:fail:contract:arity?)
+  (err/rt-test (instantiate-linklet l '#()))
+  (err/rt-test (instantiate-linklet l (list 5)))
+  (err/rt-test (instantiate-linklet l '() 5)))
+
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(report-errs)

racket/src/cs/linklet.sls

@@ -697,8 +697,18 @@
      [(linklet import-instances target-instance)
       (instantiate-linklet linklet import-instances target-instance #f)]
      [(linklet import-instances target-instance use-prompt?)
+      (unless (linklet? linklet)
+        (raise-argument-error 'instantiate-linklet "linklet?" linklet))
+      (let loop ([l import-instances])
+        (unless (null? l)
+          (if (and (pair? l)
+                   (instance? (car l)))
+              (loop (cdr l))
+              (raise-argument-error 'instantiate-linklet "(listof instance?)" import-instances))))
       (cond
        [target-instance
+        (unless (instance? target-instance)
+          (raise-argument-error 'instantiate-linklet "(or/c instance? #f)" target-instance))
         ;; Instantiate into the given instance and return the
         ;; result of the linklet body:
         (with-continuation-mark

racket/src/racket/src/linklet.c

@@ -593,7 +593,7 @@ static Scheme_Object *instantiate_linklet(int argc, Scheme_Object **argv)
     scheme_wrong_contract("instantiate-linklet", "linklet?", 0, argc, argv);
 
   l = argv[1];
-  while (!SCHEME_NULLP(l)) {
+  while (SCHEME_PAIRP(l)) {
     if (!SAME_TYPE(SCHEME_TYPE(SCHEME_CAR(l)), scheme_instance_type))
       break;
     l = SCHEME_CDR(l);