format-patch: add --reroll-count=$N option

The --reroll-count=$N option, when given a positive integer:

 - Adds " v$N" to the subject prefix specified.  As the default
   subject prefix string is "PATCH", --reroll-count=2 makes it
   "PATCH v2".

 - Prefixes "v$N-" to the names used for output files.  The cover
   letter, whose name is usually 0000-cover-letter.patch, becomes
   v2-0000-cover-letter.patch when given --reroll-count=2.

This allows users to use the same --output-directory for multiple
iterations of the same series, without letting the output for a
newer round overwrite output files from the earlier rounds.  The
user can incorporate materials from earlier rounds to update the
newly minted iteration, and use "send-email v2-*.patch" to send out
the patches belonging to the second iteration easily.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/log-tree.c b/log-tree.c
index 670beae..5dc126b 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -308,6 +308,8 @@ void fmt_output_subject(struct strbuf *filename,
 	int start_len = filename->len;
 	int max_len = start_len + FORMAT_PATCH_NAME_MAX - (strlen(suffix) + 1);
 
+	if (0 < info->reroll_count)
+		strbuf_addf(filename, "v%d-", info->reroll_count);
 	strbuf_addf(filename, "%04d-%s", nr, subject);
 
 	if (max_len < filename->len)