[PATCH v4 2/2] format-patch: "--rfc=-(WIP)" appends to produce [PATCH (WIP)]

[Junio C Hamano <gitster@pobox.com>]

In the previous step, the "--rfc" option of "format-patch" learned
to take an optional string value to prepend to the subject prefix,
so that --rfc=WIP can give "[WIP PATCH]".

There may be cases in which the extra string wants to come after the
subject prefix.  Extend the mechanism to allow "--rfc=-(WIP)" [*] to
signal that the extra string is to be appended instead of getting
prepended, resulting in "[PATCH (WIP)]".

In the documentation, discourage (ab)using "--rfc=-RFC" to say
"[PATCH RFC]" just to be different, when "[RFC PATCH]" is the norm.

[Footnote]

 * The syntax takes inspiration from Perl's open syntax that opens
   pipes "open fh, '|-', 'cmd'", where the dash signals "the other
   stuff comes here".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-format-patch.txt | 6 ++++++
 builtin/log.c                      | 8 ++++++--
 t/t4014-format-patch.sh            | 9 +++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-format-patch.txt b/Documentation/git-format-patch.txt
index e553810b1e..369af2c4a7 100644
--- a/Documentation/git-format-patch.txt
+++ b/Documentation/git-format-patch.txt
@@ -247,6 +247,12 @@ RFC means "Request For Comments"; use this when sending
 an experimental patch for discussion rather than application.
 "--rfc=WIP" may also be a useful way to indicate that a patch
 is not complete yet ("WIP" stands for "Work In Progress").
++
+If the convention of the receiving community for a particular extra
+string is to have it _after_ the subject prefix, the string _<rfc>_
+can be prefixed with a dash ("`-`") to signal that the the rest of
+the _<rfc>_ string should be appended to the subject prefix instead,
+e.g., `--rfc='-(WIP)'` results in "PATCH (WIP)".
 
 -v <n>::
 --reroll-count=<n>::
diff --git a/builtin/log.c b/builtin/log.c
index 97ca885b33..4750e480e6 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -2065,8 +2065,12 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	if (cover_from_description_arg)
 		cover_from_description_mode = parse_cover_from_description(cover_from_description_arg);
 
-	if (rfc && rfc[0])
-		strbuf_insertf(&sprefix, 0, "%s ", rfc);
+	if (rfc && rfc[0]) {
+		if (rfc[0] == '-')
+			strbuf_addf(&sprefix, " %s", rfc + 1);
+		else
+			strbuf_insertf(&sprefix, 0, "%s ", rfc);
+	}
 
 	if (reroll_count) {
 		strbuf_addf(&sprefix, " v%s", reroll_count);
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 645c4189f9..fcbde15b16 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -1394,6 +1394,15 @@ test_expect_success '--rfc=WIP and --rfc=' '
 	test_cmp expect-raw actual
 '
 
+test_expect_success '--rfc=-(WIP) appends' '
+	cat >expect <<-\EOF &&
+	Subject: [PATCH (WIP) 1/1] header with . in it
+	EOF
+	git format-patch -n -1 --stdout --rfc="-(WIP)" >patch &&
+	grep "^Subject:" patch >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success '--rfc does not overwrite prefix' '
 	cat >expect <<-\EOF &&
 	Subject: [RFC PATCH foobar 1/1] header with . in it
-- 
2.45.0-rc0-3-g00e10ef10e