sequencer.c: check for lock failure and bail early in fast_forward_to

Change fast_forward_to() to check if locking the ref failed, print a
nice error message and bail out early.

The old code did not check if ref_lock was NULL and relied on the
fact that the write_ref_sha1() would safely detect this condition
and set the return variable ret to indicate an error.

While that is safe, it makes the code harder to read for two reasons:

* Inconsistency.  Almost all other places we do check the lock for
NULL explicitly, so the naive reader is confused "why don't we
check here?"

* And relying on write_ref_sha1() to detect and return an error for
when a previous lock_any_ref_for_update() failed feels obfuscated.

This change should not change any functionality or logic aside from
adding an extra error message when this condition is triggered
(write_ref_sha1() returns an error silently for this condition).

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/sequencer.c b/sequencer.c
index bde5f047b01376e05255a55516d3bdd261f497ea..0a80c58d1194c3476dfd2861a98fbd08610597a3 100644 (file)
--- a/sequencer.c
+++ b/sequencer.c
@@ -281,8 +281,12 @@ static int fast_forward_to(const unsigned char *to, const unsigned char *from,
                exit(1); /* the callee should have complained already */
        ref_lock = lock_any_ref_for_update("HEAD", unborn ? null_sha1 : from,
                                           0, NULL);
                exit(1); /* the callee should have complained already */
        ref_lock = lock_any_ref_for_update("HEAD", unborn ? null_sha1 : from,
                                           0, NULL);

+       if (!ref_lock)
+               return error(_("Failed to lock HEAD during fast_forward_to"));
+

        strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
        ret = write_ref_sha1(ref_lock, to, sb.buf);
        strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
        ret = write_ref_sha1(ref_lock, to, sb.buf);

+

        strbuf_release(&sb);
        return ret;
 }
        strbuf_release(&sb);
        return ret;
 }