lock_ref_sha1_basic(): report errors via a "struct strbuf *err"

For now, change the callers to spew the error to stderr like before.
But soon we will change them to incorporate the reason for the failure
into their own error messages.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>

refs.c

@@ -2333,7 +2333,8 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 					    const unsigned char *old_sha1,
 					    const struct string_list *extras,
 					    const struct string_list *skip,
-					    unsigned int flags, int *type_p)
+					    unsigned int flags, int *type_p,
+					    struct strbuf *err)
 {
 	char *ref_file;
 	const char *orig_refname = refname;
@@ -2343,7 +2344,8 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 	int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
 	int resolve_flags = 0;
 	int attempts_remaining = 3;
-	struct strbuf err = STRBUF_INIT;
+
+	assert(err);
 
 	lock = xcalloc(1, sizeof(struct ref_lock));
 	lock->lock_fd = -1;
@@ -2367,7 +2369,8 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 		ref_file = git_path("%s", orig_refname);
 		if (remove_empty_directories(ref_file)) {
 			last_errno = errno;
-			error("there are still refs under '%s'", orig_refname);
+			strbuf_addf(err, "there are still refs under '%s'",
+				    orig_refname);
 			goto error_return;
 		}
 		refname = resolve_ref_unsafe(orig_refname, resolve_flags,
@@ -2377,8 +2380,8 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 	    *type_p = type;
 	if (!refname) {
 		last_errno = errno;
-		error("unable to resolve reference %s: %s",
-			orig_refname, strerror(errno));
+		strbuf_addf(err, "unable to resolve reference %s: %s",
+			    orig_refname, strerror(errno));
 		goto error_return;
 	}
 	/*
@@ -2389,8 +2392,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 	 */
 	if (is_null_sha1(lock->old_sha1) &&
 	    verify_refname_available(refname, extras, skip,
-				     get_packed_refs(&ref_cache), &err)) {
-		error("%s", err.buf);
+				     get_packed_refs(&ref_cache), err)) {
 		last_errno = ENOTDIR;
 		goto error_return;
 	}
@@ -2416,7 +2418,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 		/* fall through */
 	default:
 		last_errno = errno;
-		error("unable to create directory for %s", ref_file);
+		strbuf_addf(err, "unable to create directory for %s", ref_file);
 		goto error_return;
 	}
 
@@ -2431,16 +2433,14 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 			 */
 			goto retry;
 		else {
-			unable_to_lock_message(ref_file, errno, &err);
-			error("%s", err.buf);
+			unable_to_lock_message(ref_file, errno, err);
 			goto error_return;
 		}
 	}
 	return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
 
  error_return:
 	unlock_ref(lock);
-	strbuf_release(&err);
 	errno = last_errno;
 	return NULL;
 }
@@ -2854,6 +2854,7 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 	struct stat loginfo;
 	int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
 	const char *symref = NULL;
+	struct strbuf err = STRBUF_INIT;
 
 	if (log && S_ISLNK(loginfo.st_mode))
 		return error("reflog for %s is a symlink", oldrefname);
@@ -2896,8 +2897,10 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 
 	logmoved = log;
 
-	lock = lock_ref_sha1_basic(newrefname, NULL, NULL, NULL, 0, NULL);
+	lock = lock_ref_sha1_basic(newrefname, NULL, NULL, NULL, 0, NULL, &err);
 	if (!lock) {
+		error("%s", err.buf);
+		strbuf_release(&err);
 		error("unable to lock %s for update", newrefname);
 		goto rollback;
 	}
@@ -2910,8 +2913,10 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 	return 0;
 
  rollback:
-	lock = lock_ref_sha1_basic(oldrefname, NULL, NULL, NULL, 0, NULL);
+	lock = lock_ref_sha1_basic(oldrefname, NULL, NULL, NULL, 0, NULL, &err);
 	if (!lock) {
+		error("%s", err.buf);
+		strbuf_release(&err);
 		error("unable to lock %s for rollback", oldrefname);
 		goto rollbacklog;
 	}
@@ -3824,11 +3829,14 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 				 update->old_sha1 : NULL),
 				&affected_refnames, NULL,
 				flags,
-				&update->type);
+				&update->type,
+				err);
 		if (!update->lock) {
 			ret = (errno == ENOTDIR)
 				? TRANSACTION_NAME_CONFLICT
 				: TRANSACTION_GENERIC_ERROR;
+			error("%s", err->buf);
+			strbuf_reset(err);
 			strbuf_addf(err, "Cannot lock the ref '%s'.",
 				    update->refname);
 			goto cleanup;
@@ -4088,6 +4096,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	char *log_file;
 	int status = 0;
 	int type;
+	struct strbuf err = STRBUF_INIT;
 
 	memset(&cb, 0, sizeof(cb));
 	cb.flags = flags;
@@ -4099,9 +4108,12 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	 * reference itself, plus we might need to update the
 	 * reference if --updateref was specified:
 	 */
-	lock = lock_ref_sha1_basic(refname, sha1, NULL, NULL, 0, &type);
-	if (!lock)
+	lock = lock_ref_sha1_basic(refname, sha1, NULL, NULL, 0, &type, &err);
+	if (!lock) {
+		error("%s", err.buf);
+		strbuf_release(&err);
 		return error("cannot lock ref '%s'", refname);
+	}
 	if (!reflog_exists(refname)) {
 		unlock_ref(lock);
 		return 0;