checkout: don't crash on file checkout before running post-checkout hook

In the case of

	git init
	echo exit >.git/hooks/post-checkout
	chmod +x .git/hooks/post-checkout
	touch foo
	git add foo
	rm foo
	git checkout -- foo

git-checkout resulted in a Segmentation fault, because there is no new
branch set for the post-checkout hook.

This patch makes use of the null SHA as it is set for the old branch.

While at it, I removed the xstrdup() around the sha1_to_hex(...) calls
in builtin-checkout.c/post_checkout_hook() because sha1_to_hex()
uses four buffers for the hex-dumped SHA and we only need two.
(Duplicating one buffer is only needed if we need more than four.)

Signed-off-by: Stephan Beyer <s-beyer@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-checkout.c b/builtin-checkout.c
index b5dd9c07b42e0130384259715730f52bc8c4e6c3..149343e3a939611dd9862cbbd6c92c40124dc348 100644 (file)
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -47,8 +47,10 @@ 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 ? old->object.sha1 : null_sha1));
-       argv[2] = xstrdup(sha1_to_hex(new->object.sha1));
+       argv[1] = sha1_to_hex(old ? old->object.sha1 : null_sha1);
+       argv[2] = sha1_to_hex(new ? new->object.sha1 : null_sha1);
+       /* "new" can be NULL when checking out from the index before
+          a commit exists. */
        argv[3] = changed ? "1" : "0";
        argv[4] = NULL;
        proc.argv = argv;