[PATCH] bisect: print an error message when "git rev-list --bisect-vars" fails

[Christian Couder <chriscool@tuxfamily.org>]

Before this patch no error was printed when "git rev-list --bisect-vars"
failed. This can happen when bad and good revs are mistaken.

This patch prints an error message on stderr that describe the likely
failure cause.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 git-bisect.sh               |   19 +++++++++++++++++--
 t/t6030-bisect-porcelain.sh |    7 +++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/git-bisect.sh b/git-bisect.sh
index b5171c9..164e8ed 100755
--- a/git-bisect.sh
+++ b/git-bisect.sh
@@ -224,18 +224,33 @@ bisect_auto_next() {
 	bisect_next_check && bisect_next || :
 }
 
+eval_rev_list() {
+	_eval="$1"
+
+	eval $_eval
+	res=$?
+
+	if [ $res -ne 0 ]; then
+		echo >&2 "'git rev-list --bisect-vars' failed:"
+		echo >&2 "maybe you mistake good and bad revs?"
+		exit $res
+	fi
+
+	return $res
+}
+
 filter_skipped() {
 	_eval="$1"
 	_skip="$2"
 
 	if [ -z "$_skip" ]; then
-		eval $_eval
+		eval_rev_list "$_eval"
 		return
 	fi
 
 	# Let's parse the output of:
 	# "git rev-list --bisect-vars --bisect-all ..."
-	eval $_eval | while read hash line
+	eval_rev_list "$_eval" | while read hash line
 	do
 		case "$VARS,$FOUND,$TRIED,$hash" in
 			# We display some vars.
diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index ccd459b..b5102fb 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -302,6 +302,13 @@ test_expect_success 'bisect refuses to start if branch new-bisect exists' '
 	git branch -d new-bisect
 '
 
+test_expect_success 'bisect errors out if bad and good are mistaken' '
+	git bisect reset &&
+	test_must_fail git bisect start $HASH2 $HASH4 2> rev_list_error &&
+	grep "mistake good and bad" rev_list_error &&
+	git bisect reset
+'
+
 #
 #
 test_done
-- 
1.5.5.1.322.g312d.dirty