bisect: test merge base if good rev is not an ancestor of bad rev

Before this patch, "git bisect", when it was given some good revs that
are not ancestor of the bad rev, didn't check if the merge bases were
good. "git bisect" just supposed that the user knew what he was doing,
and that, when he said the revs were good, he knew that it meant that
all the revs in the history leading to the good revs were also
considered good.

But in pratice, the user may not know that a good rev is not an
ancestor of the bad rev, or he may not know/remember that all revs
leading to the good rev will be considered good. So he may give a good
rev that is a sibling, instead of an ancestor, of the bad rev, when in
fact there can be one rev becoming good in the branch of the good rev
(because the bug was already fixed there, for example) instead of one
rev becoming bad in the branch of the bad rev.

For example, if there is the following history:

    A--B--C--D
	\
	 E--F

and we launch "git bisect start D F" then only C and D would have been
considered as possible first bad commit before this patch. This could
invite user errors; F could be the commit that fixes the bug that exists
everywhere else.

The purpose of this patch is to detect when "git bisect" is passed
some good revs that are not ancestors of the bad rev, and then to first
ask the user to test the merge bases between the good and bad revs.

If the merge bases are good then all is fine, we can continue
bisecting. Otherwise, if one merge base is bad, it means that the
assumption that all revs leading to the good one are good too is
wrong and we error out. In the case where one merge base is skipped we
issue a warning and then continue bisecting anyway.

These checks will also catch the case where good and bad have been
mistaken. This means that we can remove the check that was done latter
on the output of "git rev-list --bisect-vars".

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 90 insertions, 0 deletions

diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index 244fda62a..a1ce95c5a 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -350,6 +350,96 @@ test_expect_success 'bisect does not create a "bisect" branch' '
 	git branch -D bisect
 '
 
+# This creates a "side" branch to test "siblings" cases.
+#
+# H1-H2-H3-H4-H5-H6-H7  <--other
+#            \
+#             S5-S6-S7  <--side
+#
+test_expect_success 'side branch creation' '
+	git bisect reset &&
+	git checkout -b side $HASH4 &&
+	add_line_into_file "5(side): first line on a side branch" hello2 &&
+	SIDE_HASH5=$(git rev-parse --verify HEAD) &&
+	add_line_into_file "6(side): second line on a side branch" hello2 &&
+	SIDE_HASH6=$(git rev-parse --verify HEAD) &&
+	add_line_into_file "7(side): third line on a side branch" hello2 &&
+	SIDE_HASH7=$(git rev-parse --verify HEAD)
+'
+
+test_expect_success 'good merge base when good and bad are siblings' '
+	git bisect start "$HASH7" "$SIDE_HASH7" > my_bisect_log.txt &&
+	grep "merge base must be tested" my_bisect_log.txt &&
+	grep $HASH4 my_bisect_log.txt &&
+	git bisect good > my_bisect_log.txt &&
+	test_must_fail grep "merge base must be tested" my_bisect_log.txt &&
+	grep $HASH6 my_bisect_log.txt &&
+	git bisect reset
+'
+test_expect_success 'skipped merge base when good and bad are siblings' '
+	git bisect start "$SIDE_HASH7" "$HASH7" > my_bisect_log.txt &&
+	grep "merge base must be tested" my_bisect_log.txt &&
+	grep $HASH4 my_bisect_log.txt &&
+	git bisect skip > my_bisect_log.txt 2>&1 &&
+	grep "Warning" my_bisect_log.txt &&
+	grep $SIDE_HASH6 my_bisect_log.txt &&
+	git bisect reset
+'
+
+test_expect_success 'bad merge base when good and bad are siblings' '
+	git bisect start "$HASH7" HEAD > my_bisect_log.txt &&
+	grep "merge base must be tested" my_bisect_log.txt &&
+	grep $HASH4 my_bisect_log.txt &&
+	test_must_fail git bisect bad > my_bisect_log.txt 2>&1 &&
+	grep "merge base $HASH4 is bad" my_bisect_log.txt &&
+	grep "fixed between $HASH4 and \[$SIDE_HASH7\]" my_bisect_log.txt &&
+	git bisect reset
+'
+
+# This creates a few more commits (A and B) to test "siblings" cases
+# when a good and a bad rev have many merge bases.
+#
+# We should have the following:
+#
+# H1-H2-H3-H4-H5-H6-H7
+#            \  \     \
+#             S5-A     \
+#              \        \
+#               S6-S7----B
+#
+# And there A and B have 2 merge bases (S5 and H5) that should be
+# reported by "git merge-base --all A B".
+#
+test_expect_success 'many merge bases creation' '
+	git checkout "$SIDE_HASH5" &&
+	git merge -m "merge HASH5 and SIDE_HASH5" "$HASH5" &&
+	A_HASH=$(git rev-parse --verify HEAD) &&
+	git checkout side &&
+	git merge -m "merge HASH7 and SIDE_HASH7" "$HASH7" &&
+	B_HASH=$(git rev-parse --verify HEAD) &&
+	git merge-base --all "$A_HASH" "$B_HASH" > merge_bases.txt &&
+	test $(wc -l < merge_bases.txt) = "2" &&
+	grep "$HASH5" merge_bases.txt &&
+	grep "$SIDE_HASH5" merge_bases.txt
+'
+
+test_expect_success 'good merge bases when good and bad are siblings' '
+	git bisect start "$B_HASH" "$A_HASH" > my_bisect_log.txt &&
+	grep "merge base must be tested" my_bisect_log.txt &&
+	git bisect good > my_bisect_log2.txt &&
+	grep "merge base must be tested" my_bisect_log2.txt &&
+	{
+		{
+			grep "$SIDE_HASH5" my_bisect_log.txt &&
+			grep "$HASH5" my_bisect_log2.txt
+		} || {
+			grep "$SIDE_HASH5" my_bisect_log2.txt &&
+			grep "$HASH5" my_bisect_log.txt
+		}
+	} &&
+	git bisect reset
+'
+
 #
 #
 test_done