Allow async command output buffer to be shown only on output

* lisp/simple.el (async-shell-command-display-buffer): Add
defcustom.
(shell-command): Use the new defcustom to determine whether to show
the buffer immediately, or add a process filter that shows it only
when there is some output.
* etc/NEWS: Document the new variable.
* doc/emacs/misc.texi: Likewise.

Thanks to Juri Linkov and Eli Zaretskii for advice and guidance.

1 files changed, 5 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index b47bf959bed..58b08348b10 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -206,6 +206,11 @@ the behavior of 'shell-command', 'shell-command-on-region' and
 'async-shell-command' is as usual.
 
 +++
+** The new user option 'async-shell-command-display-buffer' controls
+whether the output buffer of an asynchronous command is shown
+immediately, or only when there is output.
+
++++
 ** The new user option 'mouse-select-region-move-to-beginning'
 controls the position of point when double-clicking mouse-1 on the end
 of a parenthetical grouping or string-delimiter: the default value nil