[PATCH v3] commit: check result of resolve_ref_unsafe

[Andrey Okoshkin <a.okoshkin@samsung.com>]

Add check of the resolved HEAD reference while printing of a commit summary.
resolve_ref_unsafe() may return NULL pointer if underlying calls of lstat() or
open() fail in files_read_raw_ref().
Such situation can be caused by race: file becomes inaccessible to this moment.

Signed-off-by: Andrey Okoshkin <a.okoshkin@samsung.com>
---
die_errno fits better here as resolve_ref_unsafe preserves errno value.

Changes since the previous patch:
* die is replaced with die_errno.
 builtin/commit.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/builtin/commit.c b/builtin/commit.c
index 1a0da71a4..b52829090 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1483,6 +1483,8 @@ static void print_summary(const char *prefix, const struct object_id *oid,
 	diff_setup_done(&rev.diffopt);
 
 	head = resolve_ref_unsafe("HEAD", 0, junk_oid.hash, NULL);
+	if (!head)
+		die_errno(_("unable to resolve HEAD after creating commit"));
 	if (!strcmp(head, "HEAD"))
 		head = _("detached HEAD");
 	else
-- 
2.14.2