[PATCH] mailinfo: remove [PATCH...] prefix from Subject regardless of length

[Jim Meyering <meyering@redhat.com>]

Before this change, a [...] prefix would be removed only as long as
its length did not exceed 2/3 of the subject length.  Now, when the
bracketed quantity starts with PATCH, it is removed unconditionally.
Otherwise, the existing behavior remains unchanged.

While with a bare "PATCH M/N" prefix, this inconsistency shows up only
on a subject of length 2 or 1 (assuming one-digit M and N), if you set
format.subjectprefix to the name of a project or sub-project, the
minimum affected length may be substantially larger.

Contrast the behavior before:

  for i in 1234 123 12 1 ''; do echo 'Subject: [PATCH 1/1] '$i \
    | git mailinfo m p | head -1; done
  Subject: 1234
  Subject: 123
  Subject: [PATCH 1/1] 12
  Subject: [PATCH 1/1] 1
  Subject: [PATCH 1/1]

and after this change:

  for i in 1234 123 12 1 ''; do echo 'Subject: [PATCH 1/1] '$i \
    | ./git mailinfo m p | head -1; done
  Subject: 1234
  Subject: 123
  Subject: 12
  Subject: 1
  Subject:

Along the way, I added a "const" to indicate that the "header"
array itself is constant.

Signed-off-by: Jim Meyering <meyering@redhat.com>
---
 builtin-mailinfo.c  |   10 ++++++++--
 t/t5100-mailinfo.sh |    9 +++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/builtin-mailinfo.c b/builtin-mailinfo.c
index 3c4f075..f07bca6 100644
--- a/builtin-mailinfo.c
+++ b/builtin-mailinfo.c
@@ -237,9 +237,15 @@ static void cleanup_subject(struct strbuf *subject)
 			strbuf_remove(subject, 0, 1);
 			continue;
 		case '[':
+			/* If there's a [...] enclosed prefix, always remove
+			   it when it starts with "PATCH".  If it does not
+			   start with PATCH, remove the bracketed quantity
+			   only as long as that removes no more than 2/3 of
+			   the length.  */
 			if ((pos = strchr(subject->buf, ']'))) {
 				remove = pos - subject->buf;
-				if (remove <= (subject->len - remove) * 2) {
+				if (remove <= (subject->len - remove) * 2
+				    || !prefixcmp (subject->buf + 1, "PATCH")) {
 					strbuf_remove(subject, 0, remove + 1);
 					continue;
 				}
@@ -265,7 +271,7 @@ static void cleanup_space(struct strbuf *sb)
 }

 static void decode_header(struct strbuf *line);
-static const char *header[MAX_HDR_PARSED] = {
+static const char *const header[MAX_HDR_PARSED] = {
 	"From","Subject","Date",
 };

diff --git a/t/t5100-mailinfo.sh b/t/t5100-mailinfo.sh
index ebc36c1..86fb116 100755
--- a/t/t5100-mailinfo.sh
+++ b/t/t5100-mailinfo.sh
@@ -89,4 +89,13 @@ test_expect_success 'mailinfo on from header without name works' '

 '

+test_expect_success 'mailinfo strips [PATCH... even on very short Subject' '
+
+	printf "Subject: [PATCH 1/1] ..\n" > in &&
+	printf "Subject: ..\n\n" > expect &&
+	git mailinfo /dev/null /dev/null < in > out &&
+	test_cmp expect out
+
+'
+
 test_done
--
1.6.6.rc0.236.ge0b94