[PATCH 2/2] merge: allow fast-forwarding to an annotated but unsigned tag

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

Update the merging_signed_tag() helper to check if the tag object
actually has a signature-looking string, so that we do not forbid
fast-forwarding to an annotated but unsigned tag.  By definition,
there will be no signed payload in such a tag to be moved to the
mergetag header, so we are not losing anything by fast-forwarding.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/merge.c  | 14 +++++++++++++-
 t/t7600-merge.sh | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/builtin/merge.c b/builtin/merge.c
index 23389f2..82d343c 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -28,6 +28,7 @@
 #include "remote.h"
 #include "fmt-merge-msg.h"
 #include "gpg-interface.h"
+#include "tag.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)
@@ -1102,10 +1103,21 @@ static void write_merge_state(void)
 static int merging_signed_tag(struct commit *parent)
 {
 	struct merge_remote_desc *desc = merge_remote_util(parent);
+	unsigned long size;
+	enum object_type type;
+	char *buf;
+	size_t sig_offset;
 
 	if (!desc || !desc->obj || desc->obj->type != OBJ_TAG)
 		return 0;
-	return 1;
+
+	buf = read_sha1_file(desc->obj->sha1, &type, &size);
+	if (!buf || type != OBJ_TAG) {
+		free(buf);
+		return 0; /* error will be caught downstream */
+	}
+	sig_offset = parse_signature(buf, size);
+	return (sig_offset < size);
 }
 
 int cmd_merge(int argc, const char **argv, const char *prefix)
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 9e27bbf..3c48327 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -695,4 +695,42 @@ test_expect_success GPG 'merge --no-edit tag should skip editor' '
 	test_cmp actual expect
 '
 
+test_expect_success 'merge ff annotated tag should just ff' '
+	git reset --hard c0 &&
+	git commit --allow-empty -m "A newer commit" &&
+	git tag -a -m "An annotated tag" anno &&
+	git reset --hard c0 &&
+
+	# This should not even bother with an editor session; "false"
+	# will ensure that an attempt to run the editor is caught.
+	EDITOR=false git merge anno &&
+
+	git rev-parse anno^0 >expect &&
+	git rev-parse HEAD >actual &&
+	test_cmp actual expect &&
+
+	git rev-parse c0^0 >expect &&
+	git rev-parse HEAD^ >actual &&
+	test_cmp actual expect
+'
+
+test_expect_success 'merge --no-ff annotated tag' '
+	git reset --hard c0 &&
+	git commit --allow-empty -m "A newer commit" &&
+	git tag -f -a -m "An annotated tag" anno &&
+	git reset --hard c0 &&
+
+	EDITOR=./editor git merge --no-ff --edit anno &&
+	git rev-parse anno^0 >expect &&
+	git rev-parse HEAD^2 >actual &&
+	test_cmp actual expect &&
+
+	git rev-parse c0^0 >expect &&
+	git rev-parse HEAD^ >actual &&
+	test_cmp actual expect &&
+
+	git cat-file commit HEAD >raw &&
+	grep "An annotated tag" raw
+'
+
 test_done
-- 
1.7.11.rc1.37.g09843ac