+bisect_checkout() {
+ _rev="$1"
+ _msg="$2"
+ echo "Bisecting: $_msg"
+ mark_expected_rev "$_rev"
+ git checkout -q "$_rev" || exit
+ git show-branch "$_rev"
+}
+
+is_among() {
+ _rev="$1"
+ _list="$2"
+ case "$_list" in *$_rev*) return 0 ;; esac
+ return 1
+}
+
+handle_bad_merge_base() {
+ _badmb="$1"
+ _good="$2"
+ if is_expected_rev "$_badmb"; then
+ cat >&2 <<EOF
+The merge base $_badmb is bad.
+This means the bug has been fixed between $_badmb and [$_good].
+EOF
+ exit 3
+ else
+ cat >&2 <<EOF
+Some good revs are not ancestor of the bad rev.
+git bisect cannot work properly in this case.
+Maybe you mistake good and bad revs?
+EOF
+ exit 1
+ fi
+}
+
+handle_skipped_merge_base() {
+ _mb="$1"
+ _bad="$2"
+ _good="$3"
+ cat >&2 <<EOF
+Warning: the merge base between $_bad and [$_good] must be skipped.
+So we cannot be sure the first bad commit is between $_mb and $_bad.
+We continue anyway.
+EOF
+}
+
+#
+# "check_merge_bases" checks that merge bases are not "bad".
+#
+# - If one is "good", that's good, we have nothing to do.
+# - If one is "bad", it means the user assumed something wrong
+# and we must exit.
+# - If one is "skipped", we can't know but we should warn.
+# - If we don't know, we should check it out and ask the user to test.
+#
+# In the last case we will return 1, and otherwise 0.
+#
+check_merge_bases() {
+ _bad="$1"
+ _good="$2"
+ _skip="$3"
+ for _mb in $(git merge-base --all $_bad $_good)
+ do
+ if is_among "$_mb" "$_good"; then
+ continue
+ elif test "$_mb" = "$_bad"; then
+ handle_bad_merge_base "$_bad" "$_good"
+ elif is_among "$_mb" "$_skip"; then
+ handle_skipped_merge_base "$_mb" "$_bad" "$_good"
+ else
+ bisect_checkout "$_mb" "a merge base must be tested"
+ return 1
+ fi
+ done
+ return 0
+}
+
+#
+# "check_good_are_ancestors_of_bad" checks that all "good" revs are
+# ancestor of the "bad" rev.
+#
+# If that's not the case, we need to check the merge bases.
+# If a merge base must be tested by the user we return 1 and
+# otherwise 0.
+#
+check_good_are_ancestors_of_bad() {
+ test -f "$GIT_DIR/BISECT_ANCESTORS_OK" &&
+ return
+
+ _bad="$1"
+ _good=$(echo $2 | sed -e 's/\^//g')
+ _skip="$3"
+
+ # Bisecting with no good rev is ok
+ test -z "$_good" && return
+
+ _side=$(git rev-list $_good ^$_bad)
+ if test -n "$_side"; then
+ # Return if a checkout was done
+ check_merge_bases "$_bad" "$_good" "$_skip" || return
+ fi
+
+ : > "$GIT_DIR/BISECT_ANCESTORS_OK"
+
+ return 0
+}
+