Move the silently macro to helpers library

emacs/.emacs.d/site-lisp/oni-helpers.el

@@ -24,6 +24,29 @@
 
 ;;; Code:
 
+(defmacro silently (title &rest body)
+  "Only output something when an error occurs.
+Prefix with TITLE any output that occurs while executing BODY,
+but only when an error occurs, otherwise discard it."
+  (declare (indent 1))
+  (let ((buffer-var (cl-gensym))
+        (error-var (cl-gensym)))
+    `(with-temp-buffer
+       (let ((,buffer-var (current-buffer)))
+         (cl-letf (((symbol-function 'message)
+                    (lambda (msg &rest args)
+                      (with-current-buffer ,buffer-var
+                        (insert "  " (apply 'format msg args) "\n")))))
+           (condition-case ,error-var
+               (progn ,@body)
+             (error
+              (princ ,(concat title " output:\n"))
+              (princ (with-current-buffer ,buffer-var (buffer-string)))
+              (princ "Error:\n")
+              (princ "  ")
+              (princ (cadr ,error-var))
+              (princ "\n"))))))))
+
 (defun oni:data-location (file-name)
   "Return the location of FILE-NAME within my data directory.
 This is currently the data directory under the