refs: include committer info in `ref_update` struct

The reference backends obtain the committer information from
`git_committer_info(0)` when adding a reflog. The upcoming patches
introduce support for migrating reflogs between the reference backends.
This requires an interface to creating reflogs, including custom
committer information.

Add a new field `committer_info` to the `ref_update` struct, which is
then used by the reference backends. If there is no `committer_info`
provided, the reference backends default to using
`git_committer_info(0)`. The field itself cannot be set to
`git_committer_info(0)` since the values are dynamic and must be
obtained right when the reflog is being committed.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -1151,6 +1151,7 @@ void ref_transaction_free(struct ref_transaction *transaction)
 
 	for (i = 0; i < transaction->nr; i++) {
 		free(transaction->updates[i]->msg);
+		free(transaction->updates[i]->committer_info);
 		free((char *)transaction->updates[i]->new_target);
 		free((char *)transaction->updates[i]->old_target);
 		free(transaction->updates[i]);

refs/files-backend.c

@@ -1858,6 +1858,9 @@ static int log_ref_write_fd(int fd, const struct object_id *old_oid,
 	struct strbuf sb = STRBUF_INIT;
 	int ret = 0;
 
+	if (!committer)
+		committer = git_committer_info(0);
+
 	strbuf_addf(&sb, "%s %s %s", oid_to_hex(old_oid), oid_to_hex(new_oid), committer);
 	if (msg && *msg) {
 		strbuf_addch(&sb, '\t');
@@ -1871,8 +1874,10 @@ static int log_ref_write_fd(int fd, const struct object_id *old_oid,
 }
 
 static int files_log_ref_write(struct files_ref_store *refs,
-			       const char *refname, const struct object_id *old_oid,
+			       const char *refname,
-			       const struct object_id *new_oid, const char *msg,
+			       const struct object_id *old_oid,
+			       const struct object_id *new_oid,
+			       const char *committer_info, const char *msg,
 			       int flags, struct strbuf *err)
 {
 	int logfd, result;
@@ -1889,8 +1894,7 @@ static int files_log_ref_write(struct files_ref_store *refs,
 
 	if (logfd < 0)
 		return 0;
-	result = log_ref_write_fd(logfd, old_oid, new_oid,
+	result = log_ref_write_fd(logfd, old_oid, new_oid, committer_info, msg);
-				  git_committer_info(0), msg);
 	if (result) {
 		struct strbuf sb = STRBUF_INIT;
 		int save_errno = errno;
@@ -1974,8 +1978,7 @@ static int commit_ref_update(struct files_ref_store *refs,
 	files_assert_main_repository(refs, "commit_ref_update");
 
 	clear_loose_ref_cache(refs);
-	if (files_log_ref_write(refs, lock->ref_name,
+	if (files_log_ref_write(refs, lock->ref_name, &lock->old_oid, oid, NULL,
-				&lock->old_oid, oid,
 				logmsg, flags, err)) {
 		char *old_msg = strbuf_detach(err, NULL);
 		strbuf_addf(err, "cannot update the ref '%s': %s",
@@ -2007,9 +2010,9 @@ static int commit_ref_update(struct files_ref_store *refs,
 		if (head_ref && (head_flag & REF_ISSYMREF) &&
 		    !strcmp(head_ref, lock->ref_name)) {
 			struct strbuf log_err = STRBUF_INIT;
-			if (files_log_ref_write(refs, "HEAD",
+			if (files_log_ref_write(refs, "HEAD", &lock->old_oid,
-						&lock->old_oid, oid,
+						oid, NULL, logmsg, flags,
-						logmsg, flags, &log_err)) {
+						&log_err)) {
 				error("%s", log_err.buf);
 				strbuf_release(&log_err);
 			}
@@ -2969,7 +2972,8 @@ static int parse_and_write_reflog(struct files_ref_store *refs,
 	}
 
 	if (files_log_ref_write(refs, lock->ref_name, &lock->old_oid,
-				&update->new_oid, update->msg, update->flags, err)) {
+				&update->new_oid, update->committer_info,
+				update->msg, update->flags, err)) {
 		char *old_msg = strbuf_detach(err, NULL);
 
 		strbuf_addf(err, "cannot update the ref '%s': %s",

refs/refs-internal.h

@@ -113,6 +113,7 @@ struct ref_update {
 	void *backend_data;
 	unsigned int type;
 	char *msg;
+	char *committer_info;
 
 	/*
 	 * If this ref_update was split off of a symref update via

refs/reftable-backend.c

@@ -1379,11 +1379,21 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 			}
 
 			if (create_reflog) {
+				struct ident_split c;
+
 				ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 				log = &logs[logs_nr++];
 				memset(log, 0, sizeof(*log));
 
-				fill_reftable_log_record(log, &committer_ident);
+				if (u->committer_info) {
+					if (split_ident_line(&c, u->committer_info,
+							     strlen(u->committer_info)))
+						BUG("failed splitting committer info");
+				} else {
+					c = committer_ident;
+				}
+
+				fill_reftable_log_record(log, &c);
 				log->update_index = ts;
 				log->refname = xstrdup(u->refname);
 				memcpy(log->value.update.new_hash,