add forgotten piece to the opt/c -> fix

collects/racket/contract/private/opters.rkt

@@ -633,7 +633,17 @@
   (chaperone-procedure
    val
    (make-keyword-procedure
-    (λ (kwds kwd-args . regular-args) (raise-blame-error '...))
+    (λ (kwds kwd-args . regular-args) 
+      (raise-blame-error (blame-swap blame)
+                         val
+                         '(expected: "no keyword arguments" given: "~a")
+                         (apply string-append
+                                (let loop ([kwds kwds])
+                                  (cons
+                                   (format "~a" (car kwds))
+                                   (cond
+                                     [(null? (cdr kwds)) '()]
+                                     [else (cons " " (loop (cdr kwds)))]))))))
     exact-proc)))
 
 (define (raise-flat-arrow-err blame val n)

collects/tests/racket/contract-test.rktl

@@ -1120,6 +1120,30 @@
                'pos
                'neg)
      1))
+  
+  (test/neg-blame
+   'contract-arrow-keyword17
+   '((contract (-> integer? integer?)
+               (λ (x #:y [y #f]) x)
+               'pos
+               'neg)
+     #f))
+  
+  (test/pos-blame
+   'contract-arrow-keyword18
+   '((contract (-> integer? integer?)
+               (λ (x #:y [y #f]) y)
+               'pos
+               'neg)
+     1))
+  
+  (test/neg-blame
+   'contract-arrow-keyword19
+   '((contract (-> boolean?)
+               (λ (#:x [x #f]) x)
+               'pos
+               'neg)
+     #:x 1))
 
   (test/spec-passed
    'contract-arrow1