From: Alexandre Julliard <julliard@winehq.org>
Date: Sat, 8 Nov 2008 12:03:59 +0000 (+0100)
Subject: checkout: Don't crash when switching away from an invalid branch.
X-Git-Tag: v1.6.1-rc1~7^2~18
X-Git-Url: https://git.tokkee.org/?a=commitdiff_plain;h=323e00fd46afb9293b25ee85f061ce11a2f95ca6;p=git.git

checkout: Don't crash when switching away from an invalid branch.

When using alternates, it is possible for HEAD to end up pointing to
an invalid commit. git checkout should be able to recover from that
situation without crashing.

Signed-off-by: Alexandre Julliard <julliard@winehq.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

diff --git a/builtin-checkout.c b/builtin-checkout.c
index 1deda927c..05eee4ecc 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -32,7 +32,7 @@ static int post_checkout_hook(struct commit *old, struct commit *new,
 
 	memset(&proc, 0, sizeof(proc));
 	argv[0] = name;
-	argv[1] = xstrdup(sha1_to_hex(old->object.sha1));
+	argv[1] = xstrdup(sha1_to_hex(old ? old->object.sha1 : null_sha1));
 	argv[2] = xstrdup(sha1_to_hex(new->object.sha1));
 	argv[3] = changed ? "1" : "0";
 	argv[4] = NULL;
@@ -360,10 +360,10 @@ static void update_refs_for_switch(struct checkout_opts *opts,
 
 	strbuf_init(&msg, 0);
 	old_desc = old->name;
-	if (!old_desc)
+	if (!old_desc && old->commit)
 		old_desc = sha1_to_hex(old->commit->object.sha1);
 	strbuf_addf(&msg, "checkout: moving from %s to %s",
-		    old_desc, new->name);
+		    old_desc ? old_desc : "(invalid)", new->name);
 
 	if (new->path) {
 		create_symref("HEAD", new->path, msg.buf);
@@ -419,7 +419,7 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 	 * a new commit, we want to mention the old commit once more
 	 * to remind the user that it might be lost.
 	 */
-	if (!opts->quiet && !old.path && new->commit != old.commit)
+	if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
 		describe_detached_head("Previous HEAD position was", old.commit);
 
 	if (!old.commit) {
diff --git a/t/t2011-checkout-invalid-head.sh b/t/t2011-checkout-invalid-head.sh
new file mode 100755
index 000000000..764bb0a6b
--- /dev/null
+++ b/t/t2011-checkout-invalid-head.sh
@@ -0,0 +1,18 @@
+#!/bin/sh
+
+test_description='checkout switching away from an invalid branch'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo hello >world &&
+	git add world &&
+	git commit -m initial
+'
+
+test_expect_success 'checkout master from invalid HEAD' '
+	echo 0000000000000000000000000000000000000000 >.git/HEAD &&
+	git checkout master --
+'
+
+test_done