Test tracking of non-commit upstreams

git-checkout and git-branch allow setting up an arbitrary committish as
the upstream reference for --track. In particular, tags are allowed. But
they and git-status barf on non-commit upstreams as soon as they are
asked for trackings stats.

Expose this shortcoming by adding two tests: annotated tags are affected
but lightweight tags are OK.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6040-tracking-info.sh

@@ -66,5 +66,19 @@ test_expect_success 'status' '
 	grep "have 1 and 1 different" actual
 '
 
+test_expect_success 'status when tracking lightweight tags' '
+	git checkout master &&
+	git tag light &&
+	git branch --track lighttrack light >actual &&
+	grep "set up to track" actual &&
+	git checkout lighttrack
+'
 
+test_expect_failure 'status when tracking annotated tags' '
+	git checkout master &&
+	git tag -m heavy heavy &&
+	git branch --track heavytrack heavy >actual &&
+	grep "set up to track" actual &&
+	git checkout heavytrack
+'
 test_done