[PATCH 2/2] bisect: only check merge bases when needed

[Christian Couder <chriscool@tuxfamily.org>]

When one good revision is not an ancestor of the bad revision, the
merge bases between the good and the bad revision should be checked
to make sure that they are also good revisions.

Some previous patches take care of that, but they may check the
merge bases more often than really needed. In fact the previous
patches did not try to optimize this as much as possible because
it is not so simple. So this is the purpose of this patch.

One may think that when all the merge bases have been checked then
we can save a flag, so that we don't need to check the merge bases
again during the bisect process.

The problem is that the user may choose to checkout and test
something completely different from what the bisect process
suggested. In this case we have to check the merge bases again,
because there may be new merge bases relevant to the bisect
process.

That's why, in this patch, when we detect that the user tested
something else than what the bisect process suggested, we remove
the flag that says that we don't need to check the merge bases
again.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 git-bisect.sh               |   47 +++++++++++++++++++++++++++++++-----------
 t/t6030-bisect-porcelain.sh |   23 +++++++++++++++++++++
 2 files changed, 57 insertions(+), 13 deletions(-)

diff --git a/git-bisect.sh b/git-bisect.sh
index f6cb110..a7f5347 100755
--- a/git-bisect.sh
+++ b/git-bisect.sh
@@ -172,6 +172,25 @@ bisect_write() {
 	test -n "$nolog" || echo "git bisect $state $rev" >>"$GIT_DIR/BISECT_LOG"
 }
 
+is_expected_rev() {
+	test -f "$GIT_DIR/BISECT_EXPECTED_REV" &&
+	test "$1" = $(cat "$GIT_DIR/BISECT_EXPECTED_REV")
+}
+
+mark_expected_rev() {
+	echo "$1" > "$GIT_DIR/BISECT_EXPECTED_REV"
+}
+
+check_expected_revs() {
+	for _rev in "$@"; do
+		if ! is_expected_rev "$_rev"; then
+			rm -f "$GIT_DIR/BISECT_ANCESTORS_OK"
+			rm -f "$GIT_DIR/BISECT_EXPECTED_REV"
+			return
+		fi
+	done
+}
+
 bisect_state() {
 	bisect_autostart
 	state=$1
@@ -181,7 +200,8 @@ bisect_state() {
 	1,bad|1,good|1,skip)
 		rev=$(git rev-parse --verify HEAD) ||
 			die "Bad rev input: HEAD"
-		bisect_write "$state" "$rev" ;;
+		bisect_write "$state" "$rev"
+		check_expected_revs "$rev" ;;
 	2,bad|*,good|*,skip)
 		shift
 		eval=''
@@ -191,7 +211,8 @@ bisect_state() {
 				die "Bad rev input: $rev"
 			eval="$eval bisect_write '$state' '$sha'; "
 		done
-		eval "$eval" ;;
+		eval "$eval"
+		check_expected_revs "$@" ;;
 	*,bad)
 		die "'git bisect bad' can take only one argument." ;;
 	*)
@@ -320,6 +341,7 @@ checkout() {
 	_rev="$1"
 	_msg="$2"
 	echo "Bisecting: $_msg"
+	mark_expected_rev "$_rev"
 	git checkout -q "$_rev" || exit
 	git show-branch "$_rev"
 }
@@ -339,18 +361,10 @@ mark_merge_base_ok() {
 	echo "$1 $2 ok" >> "$GIT_DIR/BISECT_MERGE_BASES"
 }
 
-is_testing_merge_base() {
-	grep "^testing $1$" "$GIT_DIR/BISECT_MERGE_BASES" >/dev/null 2>&1
-}
-
-mark_testing_merge_base() {
-	echo "testing $1" >> "$GIT_DIR/BISECT_MERGE_BASES"
-}
-
 handle_bad_merge_base() {
 	_badmb="$1"
 	_g="$2"
-	if is_testing_merge_base "$_badmb"; then
+	if is_expected_rev "$_badmb"; then
 		cat >&2 <<EOF
 The merge base $_badmb is bad.
 This means the bug has been fixed between $_badmb and $_g.
@@ -391,7 +405,6 @@ check_merge_bases() {
 			elif is_among "$_mb" "$_skip"; then
 				handle_skipped_merge_base "$_bad" "$_g" "_mb"
 			else
-				mark_testing_merge_base "$_mb"
 				checkout "$_mb" "a merge base must be tested"
 				checkout_done=1
 				return
@@ -402,11 +415,17 @@ check_merge_bases() {
 }
 
 check_good_are_ancestors_of_bad() {
+	test -f "$GIT_DIR/BISECT_ANCESTORS_OK" &&
+		return
 	_bad="$1"
 	_good=$(echo $2 | sed -e 's/\^//g')
 	_skip="$3"
 	_side=$(git rev-list $_good ^$_bad)
-	test -n "$_side" && check_merge_bases "$_bad" "$_good" "$_skip"
+	if test -n "$_side"; then
+		check_merge_bases "$_bad" "$_good" "$_skip" || return
+		test "$checkout_done" -eq "1" && return
+	fi
+	: > "$GIT_DIR/BISECT_ANCESTORS_OK"
 }
 
 bisect_next() {
@@ -496,6 +515,8 @@ bisect_clean_state() {
 		git update-ref -d $ref $hash || exit
 	done
 	rm -f "$GIT_DIR/BISECT_MERGE_BASES" &&
+	rm -f "$GIT_DIR/BISECT_EXPECTED_REV" &&
+	rm -f "$GIT_DIR/BISECT_ANCESTORS_OK" &&
 	rm -f "$GIT_DIR/BISECT_LOG" &&
 	rm -f "$GIT_DIR/BISECT_NAMES" &&
 	rm -f "$GIT_DIR/BISECT_RUN" &&
diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index 503229b..17f264b 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -440,6 +440,29 @@ test_expect_success 'good merge bases when good and bad are siblings' '
 	git bisect reset
 '
 
+check_trace() {
+	grep "$1" "$GIT_TRACE" | grep "\^$2" | grep "$3" >/dev/null
+}
+
+test_expect_success 'optimized merge base checks' '
+	GIT_TRACE="$(pwd)/trace.log" &&
+	export GIT_TRACE &&
+	git bisect start "$HASH7" "$SIDE_HASH7" > my_bisect_log.txt &&
+	grep "merge base must be tested" my_bisect_log.txt &&
+	grep "$HASH4" my_bisect_log.txt &&
+	check_trace "rev-list" "$HASH7" "$SIDE_HASH7" &&
+	git bisect good > my_bisect_log2.txt &&
+	test -f ".git/BISECT_ANCESTORS_OK" &&
+	test "$HASH6" = $(git rev-parse --verify HEAD) &&
+	: > "$GIT_TRACE" &&
+	git bisect bad > my_bisect_log3.txt &&
+	test_must_fail check_trace "rev-list" "$HASH6" "$SIDE_HASH7" &&
+	git bisect good "$A_HASH" > my_bisect_log4.txt &&
+	grep "merge base must be tested" my_bisect_log4.txt &&
+	test_must_fail test -f ".git/BISECT_ANCESTORS_OK" &&
+	check_trace "rev-list" "$HASH6" "$A_HASH"
+'
+
 #
 #
 test_done
-- 
1.5.6.2.300.gbed4