describe: fix --contains when a tag is given as input

"git describe" takes a commit and gives it a name based on tags in
its neighbourhood.  The command does take a commit-ish but when
given a tag that points at a commit, it should dereference the tag
before computing the name for the commit.

As the whole processing is internally delegated to name-rev, if we
unwrap tags down to the underlying commit when invoking name-rev, it
will make the name-rev issue an error message based on the unwrapped
object name (i.e. either 40-hex object name, or "$tag^0") that is
different from what the end-user gave to the command when the commit
cannot be described.  Introduce an internal option --peel-tag to the
name-rev to tell it to unwrap a tag in its input from the command
line.

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

1 files changed, 12 insertions, 0 deletions

diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
index 1d20854..c0e5b2a 100755
--- a/t/t6120-describe.sh
+++ b/t/t6120-describe.sh
@@ -186,4 +186,16 @@ test_expect_success 'name-rev with exact tags' '
 	test_cmp expect actual
 '
 
+test_expect_success 'describe --contains with the exact tags' '
+	echo "A^0" >expect &&
+	tag_object=$(git rev-parse refs/tags/A) &&
+	git describe --contains $tag_object >actual &&
+	test_cmp expect actual &&
+
+	echo "A^0" >expect &&
+	tagged_commit=$(git rev-parse "refs/tags/A^0") &&
+	git describe --contains $tagged_commit >actual &&
+	test_cmp expect actual
+'
+
 test_done