Hide the output of refreshing packages

emacs/.emacs.d/init.org

@@ -38,12 +38,45 @@ To start off, first I need to enable lexical binding.
     (eval-and-compile (package-initialize))
   #+END_SRC
 
+  Some actions produce a lot of output that is usually uninteresting
+  during compilation. However, this information may be crucial when an
+  error occurs. So for these actions I can use this macro, which
+  stores all sent messages in a temporary buffer and prints them when
+  an error occurs, and hides them when it doesn't.
+
+  #+BEGIN_SRC emacs-lisp
+    (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"))))))))
+  #+END_SRC
+
   Refresh the package contents so packages can be installed from all
   configured archives. Don't do this at run-time because it slows down
   the process too much.
 
   #+BEGIN_SRC emacs-lisp
-    (eval-when-compile (package-refresh-contents))
+    (eval-when-compile
+      (silently "Refresh packages"
+        (package-refresh-contents)))
   #+END_SRC
 
   This macro is inspired by use-package, but I want to maintain some