fix support for a string result from get-data' of clipboard-client%'

and properly report an error when the result from `get-data' is not
  allowed
 Closes PR 11821

original commit: d77c92d0878384024a3b00f6bfaa7fe3214493f6

collects/mred/private/wx/cocoa/clipboard.rkt

@@ -63,13 +63,17 @@
                             owner: #f))
         (set! client c)
         (for ([type (in-list types)])
-          (let* ([bstr (send c get-data type)]
-                 [data (tell NSData 
-                             dataWithBytes: #:type _bytes bstr
-                             length: #:type _NSUInteger (bytes-length bstr))])
-            (tellv (tell NSPasteboard generalPasteboard)
-                   setData: data
-                   forType: #:type _NSString (map-type type))))))))
+          (let ([bstr (send c get-data type)])
+            (when bstr
+              (let* ([bstr (if (string? bstr)
+                               (string->bytes/utf-8 bstr)
+                               bstr)]
+                     [data (tell NSData 
+                                 dataWithBytes: #:type _bytes bstr
+                                 length: #:type _NSUInteger (bytes-length bstr))])
+                (tellv (tell NSPasteboard generalPasteboard)
+                       setData: data
+                       forType: #:type _NSString (map-type type))))))))))
   
   (define/public (get-data-for-type type)
     (log-error "didn't expect clipboard data request"))

collects/mred/private/wx/common/clipboard.rkt

@@ -11,7 +11,21 @@
               get-the-clipboard
               get-the-x-selection))
 
-(defclass clipboard-client% object%
+(define pre-client%
+  (class object%
+    (super-new)
+
+    (def/pubment (get-data [string? format])
+      (let ([d (inner #f get-data format)])
+        (when d
+          (unless (or (string? d) (bytes? d))
+            (raise-mismatch-error 
+             '|get-data method of clipboard-client%|
+             "result is not #f, a string, or byte string: "
+             d)))
+        d))))
+
+(defclass clipboard-client% pre-client%
   (define types null)
   (define es (current-eventspace))
   (define/public (get-client-eventspace) es)
@@ -22,7 +36,7 @@
     types)
   (def/public (add-type [string? str])
     (set! types (cons (string->immutable-string str) types)))
-  (def/public (get-data [string? format])
+  (define/augride (get-data format)
     #f)
   (def/public (on-replaced)
     (void))

collects/mred/private/wx/gtk/clipboard.rkt

@@ -227,16 +227,19 @@
 			(list-ref client-data i)
 			(constrained-reply (send client get-client-eventspace)
 					   (lambda () 
-					     (send client get-data 
-						   (list-ref client-orig-types i)))
+                                             (send client get-data 
+                                                   (list-ref client-orig-types i)))
 					   #f))
                     #f)])
       (when bstr
-        (gtk_selection_data_set sel-data
-				(gdk_atom_intern (list-ref client-types i) #t)
-				8
-				bstr
-				(bytes-length bstr)))))
+        (let ([bstr (if (string? bstr)
+                        (string->bytes/utf-8 bstr)
+                        bstr)])
+          (gtk_selection_data_set sel-data
+                                  (gdk_atom_intern (list-ref client-types i) #t)
+                                  8
+                                  bstr
+                                  (bytes-length bstr))))))
 
   (define/public (get-data data-format)
     (let* ([data-format (if (equal? data-format "TEXT")

collects/mred/private/wx/win32/clipboard.rkt

@@ -126,7 +126,10 @@
                            (RegisterClipboardFormatW t)))]
            [all-data (for/list ([t (in-list types)]
                                 [t-id (in-list type-ids)])
-                       (let ([d (send c get-data t)])
+                       (let ([d (let ([d (send c get-data t)])
+                                  (if (string? d)
+                                      (string->bytes/utf-8 d)
+                                      d))])
                          (cond
                           [(equal? t-id CF_UNICODETEXT)
                            ;; convert UTF-8 to UTF-16: