[PATCH] describe: output tag's ref instead of embedded name

[Matheus Tavares <matheus.bernardino@usp.br>]

If a tag describes a commit, we currently output not the tag's ref but
its embedded name. This means that when the tag is locally stored under
a different name, the output given cannot be used to access the tag in
any way. A warning is also emitted in this case, but the message is not
very enlightening:

$ git tag -am "testing tag body" testing-tag
$ mv .git/refs/tags/testing-tag .git/refs/tags/testing-tag-with-new-name
$ git describe --tags --abbrev=0
warning: tag 'testing-tag' is really 'testing-tag-with-new-name' here
testing-tag

Let's make git-describe output the tag's local name instead and
rephrase the warning to reflect the situation a little better.

Since the embedded name will no longer be needed for correct output, we
can convert the die() call in append_name() when a tag doesn't have the
embedded name to a warning(). Also, this function will now have two
disconnected responsibilities: verifying if the tag's embedded name
matches the ref and actually appending the ref to a given buffer (which
does not depend on the parsed tag object itself). Thus, to increase
intelligibility, let's make the function specialize in the former and do
the latter outside it.

Suggested-by: Jeff King <peff@peff.net>
Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
---
 builtin/describe.c  | 23 ++++++++---------------
 t/t6120-describe.sh |  4 ++--
 2 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/builtin/describe.c b/builtin/describe.c
index b6df81d8d0..6a11604d2e 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -267,7 +267,7 @@ static unsigned long finish_depth_computation(
 	return seen_commits;
 }
 
-static void append_name(struct commit_name *n, struct strbuf *dst)
+static void verify_tag_embedded_name(struct commit_name *n)
 {
 	if (n->prio == 2 && !n->tag) {
 		n->tag = lookup_tag(the_repository, &n->oid);
@@ -276,19 +276,11 @@ static void append_name(struct commit_name *n, struct strbuf *dst)
 	}
 	if (n->tag && !n->name_checked) {
 		if (!n->tag->tag)
-			die(_("annotated tag %s has no embedded name"), n->path);
-		if (strcmp(n->tag->tag, all ? n->path + 5 : n->path))
-			warning(_("tag '%s' is really '%s' here"), n->tag->tag, n->path);
+			warning(_("annotated tag %s has no embedded name"), n->path);
+		else if (strcmp(n->tag->tag, all ? n->path + 5 : n->path))
+			warning(_("tag '%s' is externally known as '%s'"), n->path, n->tag->tag);
 		n->name_checked = 1;
 	}
-
-	if (n->tag) {
-		if (all)
-			strbuf_addstr(dst, "tags/");
-		strbuf_addstr(dst, n->tag->tag);
-	} else {
-		strbuf_addstr(dst, n->path);
-	}
 }
 
 static void append_suffix(int depth, const struct object_id *oid, struct strbuf *dst)
@@ -313,7 +305,8 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
 		/*
 		 * Exact match to an existing ref.
 		 */
-		append_name(n, dst);
+		verify_tag_embedded_name(n);
+		strbuf_addstr(dst, n->path);
 		if (longformat)
 			append_suffix(0, n->tag ? get_tagged_oid(n->tag) : oid, dst);
 		if (suffix)
@@ -447,8 +440,8 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
 				oid_to_hex(&gave_up_on->object.oid));
 		}
 	}
-
-	append_name(all_matches[0].name, dst);
+	verify_tag_embedded_name(all_matches[0].name);
+	strbuf_addstr(dst, all_matches[0].name->path);
 	if (abbrev)
 		append_suffix(all_matches[0].depth, &cmit->object.oid, dst);
 	if (suffix)
diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
index 09c50f3f04..d34c091e0b 100755
--- a/t/t6120-describe.sh
+++ b/t/t6120-describe.sh
@@ -129,9 +129,9 @@ test_expect_success 'rename tag A to Q locally' '
 	mv .git/refs/tags/A .git/refs/tags/Q
 '
 cat - >err.expect <<EOF
-warning: tag 'A' is really 'Q' here
+warning: tag 'Q' is externally known as 'A'
 EOF
-check_describe A-* HEAD
+check_describe Q-* HEAD
 test_expect_success 'warning was displayed for Q' '
 	test_i18ncmp err.expect err.actual
 '
-- 
2.25.0