New user option vc-display-failed-async-commands

* lisp/vc/vc-dispatcher.el (vc-display-failed-async-commands):
New user option.
(vc-do-async-command): Use it.
* doc/emacs/vc1-xtra.texi (General VC Options):
* etc/NEWS: Document it.
* lisp/vc/vc-dispatcher.el (vc-do-command): Adjust message to
begin "Failed" not "Done" when command exits non-zero.
* lisp/vc/vc.el (vc-checkin): Adjust message to end in
"...failed" not "...done" when async command exits non-zero.

doc/emacs/vc1-xtra.texi

@@ -896,6 +896,18 @@ to indicate which shell commands it runs, and logs additional messages
 when the commands finish.  If the variable has any other non-@code{nil}
 value, Emacs both logs and displays these messages.
 
+@vindex vc-display-failed-async-commands
+  VC mode runs certain shall commands asynchronously, allow you to
+continue to use Emacs for other purposes while the command completes.
+This is mostly used for commands which access the network, such as
+pulling and pushing for distributed VCS (@pxref{Pulling / Pushing}).
+When the command starts, VC displays a buffer into which the commands
+output will be written.  If @code{vc-display-failed-async-commands} is
+non-@code{nil}, VC will additionally ensure that this buffer is
+displayed when the command finishes running but failed.  This means you
+can freely close the window displaying the command's buffer and know
+that it'll pop up again in the case that running the command failed.
+
 @vindex vc-async-checkin
   Normally checkin operations are done synchronously; that is, Emacs
 waits until the checkin has completed before doing anything else.  This

etc/NEWS

@@ -2932,6 +2932,11 @@ You can disable this by customizing 'vc-dir-show-outgoing-count' to nil.
 *** New user option 'vc-async-checkin' to enable async checkin operations.
 Currently only supported by the Git and Mercurial backends.
 
++++
+*** New user option 'vc-display-failed-async-commands'.
+If non-nil, displays the buffer with the output of the failed command
+when an asynchronous VC command (e.g. pulls and pushes) fails.
+
 ---
 *** New 'log-edit-hook' option to display diff of changes to commit.
 You can customize 'log-edit-hook' to include its new

lisp/vc/vc-dispatcher.el

@@ -150,6 +150,13 @@ logged in the *Messages* buffer, but not displayed."
   :type 'boolean
   :group 'vc)
 
+(defcustom vc-display-failed-async-commands nil
+  "If non-nil, display VC async command buffers when the command fails.
+Considers VC async commands to have failed whenever they die to a signal
+or exit non-zero."
+  :type 'boolean
+  :group 'vc)
+
 ;; Variables the user doesn't need to know about.
 
 (defvar vc-log-operation nil)
@@ -527,7 +534,9 @@ that is inserted into the command line before the filename."
                   (vc-run-delayed
                     (let ((message-truncate-lines t)
                           (inhibit-message vc--inhibit-message))
-                      (message "Done in background: %s"
+                      (message "%s in background: %s"
+                               (if (zerop (process-exit-status proc))
+                                   "Done" "Failed")
                                full-command)))))
             ;; Run synchronously
             (vc--command-message "Running in foreground: %s"
@@ -596,7 +605,10 @@ Display the buffer in some window, but don't select it."
                                     (time-to-seconds
                                      (time-since start-time))))
                            (set-marker (process-mark proc)
-                                       (point))))))))))
+                                       (point)))))
+                     (when (and vc-display-failed-async-commands
+                                (not (zerop (process-exit-status proc))))
+                       (vc--display-async-command-buffer buffer)))))))
     (setq buffer (get-buffer-create buffer))
     (if (get-buffer-process buffer)
 	(error "Another VC action on %s is running" root))

lisp/vc/vc.el

@@ -2192,7 +2192,7 @@ have changed; continue with old fileset?" (current-buffer))))
         ;; NOQUERY parameter non-nil.
         (vc-buffer-sync-fileset (list backend files)))
       (when register (vc-register (list backend register)))
-      (let (to-remove-props)
+      (let (to-remove-props proc)
         (cl-flet ((do-it ()
                     ;; We used to change buffers to get local value of
                     ;; `vc-checkin-switches', but the (singular) local
@@ -2206,18 +2206,23 @@ have changed; continue with old fileset?" (current-buffer))))
                   (remove-props-done-msg ()
                     (dolist (file to-remove-props)
                       (vc-file-setprop file 'display-state nil))
-                    (message "Checking in %s...done" (vc-delistify files))))
+                    (message "Checking in %s...%s"
+                             (vc-delistify files)
+                             (if (or (not proc)
+                                     (zerop (process-exit-status proc)))
+                                 "done" "failed"))))
           (if do-async
               ;; Rely on `vc-set-async-update' to update properties
               ;; other than the display-only `display-state' property.
               (let ((ret (do-it)))
                 (when (eq (car-safe ret) 'async)
+                  (setq proc (cadr ret))
                   (dolist (file files)
                     (let ((file (expand-file-name file)))
                       (vc-file-setprop file 'display-state "committing")
                       (vc-dir-resynch-file file)
                       (push file to-remove-props)))
-                  (vc-exec-after #'remove-props-done-msg nil (cadr ret)))
+                  (vc-exec-after #'remove-props-done-msg nil proc))
                 ret)
             (prog2 (message "Checking in %s..." (vc-delistify files))
                 (with-vc-properties files (do-it)