verify_lock(): return 0/-1 rather than struct ref_lock *

Its return value wasn't conveying any extra information, but it made
the reader wonder whether the ref_lock that it returned might be
different than the one that was passed to it. So change the function
to the traditional "return 0 on success or a negative value on error".

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: mhagger

refs.c

@@ -2218,9 +2218,14 @@ static void unlock_ref(struct ref_lock *lock)
 	free(lock);
 }
 
-/* This function should make sure errno is meaningful on error */
-static struct ref_lock *verify_lock(struct ref_lock *lock,
-	const unsigned char *old_sha1, int mustexist)
+/*
+ * Verify that the reference locked by lock has the value old_sha1.
+ * Fail if the reference doesn't exist and mustexist is set. Return 0
+ * on success or a negative value on error. This function should make
+ * sure errno is meaningful on error.
+ */
+static int verify_lock(struct ref_lock *lock,
+		       const unsigned char *old_sha1, int mustexist)
 {
 	if (read_ref_full(lock->ref_name,
 			  mustexist ? RESOLVE_REF_READING : 0,
@@ -2229,16 +2234,16 @@ static struct ref_lock *verify_lock(struct ref_lock *lock,
 		error("Can't verify ref %s", lock->ref_name);
 		unlock_ref(lock);
 		errno = save_errno;
-		return NULL;
+		return -1;
 	}
 	if (hashcmp(lock->old_sha1, old_sha1)) {
 		error("Ref %s is at %s but expected %s", lock->ref_name,
 			sha1_to_hex(lock->old_sha1), sha1_to_hex(old_sha1));
 		unlock_ref(lock);
 		errno = EBUSY;
-		return NULL;
+		return -1;
 	}
-	return lock;
+	return 0;
 }
 
 static int remove_empty_directories(const char *file)
@@ -2466,7 +2471,9 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 			goto error_return;
 		}
 	}
-	return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
+	if (old_sha1 && verify_lock(lock, old_sha1, mustexist))
+		return NULL;
+	return lock;
 
  error_return:
 	unlock_ref(lock);