refs: simplify logic when migrating reflog entries

When migrating reflog entries between two storage formats we have to do
so via two callback-driven functions:

  - `migrate_one_reflog()` gets invoked via `refs_for_each_reflog()` to
    first list all available reflogs.

  - `migrate_one_reflog_entry()` gets invoked via
    `refs_for_each_reflog_ent()` in `migrate_one_reflog()`.

Before the preceding commit we didn't have the refname available in
`migrate_one_reflog_entry()`, which made it necessary to have a separate
structure that we pass to the second callback so that we can propagate
the refname. Now that `refs_for_each_reflog_ent()` knows to pass the
refname to the callback though that indirection isn't necessary anymore.

There's one catch though: we do have an update index that is also stored
in the entry-specific callback data. This update index is required so
that we can tell the ref backend in which order it should persist the
reflog entries to disk.

But that purpose can be trivially achieved by just converting it into a
global counter that is used for all reflog entries, regardless of which
reference they are for. The ordering will remain the same as both the
update index and the refname is considered when sorting the entries.

Move the index into `struct migration_data` and drop the now-unused
`struct reflog_migration_data` to simplify the code a bit.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

refs.c

@@ -2941,6 +2941,7 @@ struct migration_data {
 	struct ref_transaction *transaction;
 	struct strbuf *errbuf;
 	struct strbuf sb, name, mail;
+	uint64_t index;
 };
 
 static int migrate_one_ref(const char *refname, const char *referent UNUSED, const struct object_id *oid,
@@ -2973,58 +2974,41 @@ static int migrate_one_ref(const char *refname, const char *referent UNUSED, con
 	return ret;
 }
 
-struct reflog_migration_data {
-	uint64_t index;
-	struct ref_store *old_refs;
-	struct ref_transaction *transaction;
-	struct strbuf *errbuf;
-	struct strbuf *sb, *name, *mail;
-};
-
 static int migrate_one_reflog_entry(const char *refname,
 				    struct object_id *old_oid,
 				    struct object_id *new_oid,
 				    const char *committer,
 				    timestamp_t timestamp, int tz,
 				    const char *msg, void *cb_data)
 {
-	struct reflog_migration_data *data = cb_data;
+	struct migration_data *data = cb_data;
 	struct ident_split ident;
 	const char *date;
 	int ret;
 
 	if (split_ident_line(&ident, committer, strlen(committer)) < 0)
 		return -1;
 
-	strbuf_reset(data->name);
-	strbuf_add(data->name, ident.name_begin, ident.name_end - ident.name_begin);
-	strbuf_reset(data->mail);
-	strbuf_add(data->mail, ident.mail_begin, ident.mail_end - ident.mail_begin);
+	strbuf_reset(&data->name);
+	strbuf_add(&data->name, ident.name_begin, ident.name_end - ident.name_begin);
+	strbuf_reset(&data->mail);
+	strbuf_add(&data->mail, ident.mail_begin, ident.mail_end - ident.mail_begin);
 
 	date = show_date(timestamp, tz, DATE_MODE(NORMAL));
-	strbuf_reset(data->sb);
-	strbuf_addstr(data->sb, fmt_ident(data->name->buf, data->mail->buf, WANT_BLANK_IDENT, date, 0));
+	strbuf_reset(&data->sb);
+	strbuf_addstr(&data->sb, fmt_ident(data->name.buf, data->mail.buf, WANT_BLANK_IDENT, date, 0));
 
 	ret = ref_transaction_update_reflog(data->transaction, refname,
-					    new_oid, old_oid, data->sb->buf,
+					    new_oid, old_oid, data->sb.buf,
 					    msg, data->index++, data->errbuf);
 	return ret;
 }
 
 static int migrate_one_reflog(const char *refname, void *cb_data)
 {
 	struct migration_data *migration_data = cb_data;
-	struct reflog_migration_data data = {
-		.old_refs = migration_data->old_refs,
-		.transaction = migration_data->transaction,
-		.errbuf = migration_data->errbuf,
-		.sb = &migration_data->sb,
-		.name = &migration_data->name,
-		.mail = &migration_data->mail,
-	};
-
 	return refs_for_each_reflog_ent(migration_data->old_refs, refname,
-					migrate_one_reflog_entry, &data);
+					migrate_one_reflog_entry, migration_data);
 }
 
 static int move_files(const char *from_path, const char *to_path, struct strbuf *errbuf)