Add `r'/`l' grep command history commands

* doc/emacs/building.texi (Grep Searching): Mention the
`r'/`l' commands.

* lisp/progmodes/grep.el (grep-forward-history): New command.
(grep-backward-history): Ditto.
(grep--save-buffers): New function.
(grep): Use it to record the history.
(grep--command-history, grep--history-inhibit)
(grep--history-place): New internal variables for the grep
history (bug#22627).

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/emacs/building.texi b/doc/emacs/building.texi
index 03fa0ed83b2..059c7cae89c 100644
--- a/doc/emacs/building.texi
+++ b/doc/emacs/building.texi
@@ -390,6 +390,13 @@ is called with the file name as the parameter and should return
 non-nil if the buffer is to be saved), and any other non-@code{nil}
 value means that all buffers should be saved without asking.
 
+  In addition to the normal compilation mode commands (for
+next/previous match and so on), two additional commands are available
+for accessing the @command{grep} command history.  @kbd{l}
+(@code{grep-backward-history}) will re-run successively the previous
+@command{grep} commands, and @kbd{r} (@code{grep-forward-history}
+will go ``forward'' in the command history.
+
 @findex grep-find
 @findex find-grep
   The command @kbd{M-x grep-find} (also available as @kbd{M-x