[PATCH 4/9] bisect: introduce a helper function to tolerate checkout failures.

[Jon Seymour <jon.seymour@gmail.com>]

In the case that git bisect is being used on a repo with damaged trees,
git checkout may not succeed.

This function allows checkout to succeed even if the current commit
references a damaged tree. This will be useful for git bisect reset, for example.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
---
 git-bisect.sh |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/git-bisect.sh b/git-bisect.sh
index b2186a8..486a860 100755
--- a/git-bisect.sh
+++ b/git-bisect.sh
@@ -34,6 +34,8 @@ require_work_tree
 _x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
 _x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
 
+IGNORE_CHECKOUT_FAILURE=$(test -f "${GIT_DIR}/BISECT_IGNORE_CHECKOUT_FAILURE" && cat "${GIT_DIR}/BISECT_IGNORE_CHECKOUT_FAILURE")
+
 bisect_autostart() {
 	test -s "$GIT_DIR/BISECT_START" || {
 		(
@@ -325,6 +327,23 @@ bisect_visualize() {
 	eval '"$@"' --bisect -- $(cat "$GIT_DIR/BISECT_NAMES")
 }
 
+bisect_checkout_with_ignore()
+{
+    ref=$1
+    if test -z "$IGNORE_CHECKOUT_FAILURE"; then
+	git checkout "$ref" -- || exit
+    else
+	if git checkout "$ref" -- 2>/dev/null; then
+	# If the current tree contains missing objects
+	# git checkout will fail. It might be
+	# possible to recover from this if we update
+	# the HEAD first.
+	    git update-ref --no-deref HEAD "$ref" &&
+	    git checkout "$ref" -- || exit
+	fi
+    fi
+}
+
 bisect_reset() {
 	test -s "$GIT_DIR/BISECT_START" || {
 		gettext "We are not bisecting."; echo
-- 
1.7.6.347.g96e0b.dirty