[PATCH 3/9] bisect: implement support for --ignore-checkout-failure option

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

If the option is not specified, git bisect has the current behaviour
in case of checkout failure. Specifically, it will exit immediately
with a non-zero status code.

With this commit, we allow checkout failures of damaged trees
to be ignored. To allow the bisect to proceed, as expected we
fall back to updating the HEAD ref directly.

This will leave the working tree and index in an inconsistent state, but
the user of --ignore-checkout-failure should expect that.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
---
 bisect.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/bisect.c b/bisect.c
index ce04092..993c48b 100644
--- a/bisect.c
+++ b/bisect.c
@@ -24,6 +24,7 @@ struct argv_array {
 
 static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
 static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
+static const char *argv_update_ref[] = {"update-ref", "--no-deref", "HEAD", NULL, NULL};
 static int module_ignore_checkout_failure = 0;
 
 /* bits #0-15 in revision.h */
@@ -716,8 +717,18 @@ static int bisect_checkout(char *bisect_rev_hex)
 
 	argv_checkout[2] = bisect_rev_hex;
 	res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
-	if (res)
+	if (res) {
+	  if (!module_ignore_checkout_failure) {
 		exit(res);
+	  } else {
+	    fprintf(stderr, "warn: checkout failed. Updating HEAD directly. The working tree and index may be inconsistent.\n");
+	    argv_update_ref[3] = bisect_rev_hex;
+	    res = run_command_v_opt(argv_update_ref, RUN_GIT_CMD);
+	    if (res) {
+	      die("update-ref --no-deref HEAD failed on %s", bisect_rev_hex);
+	    }
+	  }
+	}
 
 	argv_show_branch[1] = bisect_rev_hex;
 	return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
-- 
1.7.6.347.g96e0b.dirty