get_sha1: warn about full or short object names that look like refs

When we get 40 hex digits, we immediately assume it's an SHA-1. This
is the right thing to do because we have no way else to specify an
object. If there is a ref with the same object name, it will be
ignored. Warn the user about this case because the ref with full
object name is likely a mistake, for example

    git checkout -b $empty_var $(git rev-parse something)

advice.object_name_warning is not documented because frankly people
should not be aware about it until they encounter this situation.

While at there, warn about ambiguation with abbreviated SHA-1 too.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/t/t1512-rev-parse-disambiguation.sh b/t/t1512-rev-parse-disambiguation.sh
index 6b3d797cea..db228086d3 100755
--- a/t/t1512-rev-parse-disambiguation.sh
+++ b/t/t1512-rev-parse-disambiguation.sh
@@ -261,4 +261,22 @@ test_expect_success 'rev-parse --disambiguate' '
 	test "$(sed -e "s/^\(.........\).*/\1/" actual | sort -u)" = 000000000
 '
 
+test_expect_success 'ambiguous 40-hex ref' '
+	TREE=$(git mktree </dev/null) &&
+	REF=`git rev-parse HEAD` &&
+	VAL=$(git commit-tree $TREE </dev/null) &&
+	git update-ref refs/heads/$REF $VAL &&
+	test `git rev-parse $REF 2>err` = $REF &&
+	grep "refname.*${REF}.*ambiguous" err
+'
+
+test_expect_success 'ambiguous short sha1 ref' '
+	TREE=$(git mktree </dev/null) &&
+	REF=`git rev-parse --short HEAD` &&
+	VAL=$(git commit-tree $TREE </dev/null) &&
+	git update-ref refs/heads/$REF $VAL &&
+	test `git rev-parse $REF 2>err` = $VAL &&
+	grep "refname.*${REF}.*ambiguous" err
+'
+
 test_done