Add error dialogue for failed contact-saving

contact.scm

@@ -168,11 +168,7 @@
          menu-file-save "triggered()"
          (qt:receiver
           (lambda ()
-            (call-with-output-file *vcard-pathname*
-              (lambda (in-port)
-               (vcard:write-vcard
-                 (populate-vcard-with-window window *vcard-alist*)
-                 in-port)))))))
+            (save-vcard-file window)))))
     ;; If they want a new contact, create a new, blank, window.
     ;; That is, a new process.
     (if menu-file-new
@@ -246,6 +242,26 @@
             title: "File error" type: 'critical)]))))
 
 
+;; Save the window contents to the currently-selected file-path in vCard format.
+(define (save-vcard-file window)
+  (thread-start!
+   (lambda ()
+     (condition-case
+         (begin
+           (set! *vcard-alist* (populate-vcard-with-window window *vcard-alist*))
+           (call-with-output-file *vcard-pathname*
+             (lambda (in-port)
+               (vcard:write-vcard *vcard-alist*
+                                  in-port))))
+       [exn ()
+            (qt:message
+             (string-join (list "Failed to save the file:"
+                                ((condition-property-accessor 'exn 'message) exn)
+                                "Try saving to a another location with “File→Save as…”.")
+                          "\n")
+             title: "Saving error")]))))
+
+
 ;; Simply map vCard property-names to their corresponding name in the window’s
 ;; fields.
 (define property->formname-alist