[PATCH] rebase: fix garbled progress display with '-x'

["SZEDER Gábor" <szeder.dev@gmail.com>]

When running a command with the 'exec' instruction during an
interactive rebase session, or for a range of commits using 'git
rebase -x', the output can be a bit garbled when the name of the
command is short enough:

  $ git rebase -x true HEAD~5
  Executing: true
  Executing: true
  Executing: true
  Executing: true
  Executing: true)
  Successfully rebased and updated refs/heads/master.

Note the ')' at the end of the last line.  It gets more garbled as the
range of commits increases:

  $ git rebase -x true HEAD~50
  Executing: true)
  [ repeated 3 more times ]
  Executing: true0)
  [ repeated 44 more times ]
  Executing: true00)
  Successfully rebased and updated refs/heads/master.

Those extra numbers and ')' are remnants of the previously displayed
"Rebasing (N/M)" progress lines that are usually completely
overwritten by the "Executing: <cmd>" lines, unless 'cmd' is short and
the "N/M" part is long.

Make sure that the previously displayed "Rebasing (N/M)" line is
completely covered up by printing a terminal width worth of space
characters.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---

This issue has already been present in the scripted rebase as well.

As far as I could tell, if any other rebase instruction prints a
message, then that tends to be so long (including abbreviated commit
OIDs and whatnot) that they practically always overwrite that
"Rebasing (N/M)" progress line (well, except, perhaps, when rebasing
billions of commits at a time?).

 sequencer.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index 546f281898..c2e4baa90e 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3631,6 +3631,12 @@ static int pick_commits(struct repository *r,
 			int saved = *end_of_arg;
 			struct stat st;
 
+			if (!opts->verbose)
+				/*
+				 * Fully cover the previous "Rebasing (n/m)"
+				 * progress line.
+				 */
+				fprintf(stderr, "%*s\r", term_columns(), "");
 			*end_of_arg = '\0';
 			res = do_exec(r, arg);
 			*end_of_arg = saved;
-- 
2.21.0.1181.g24122a4251