refs: use 'uint64_t' for 'ref_update.index'

The 'ref_update.index' variable is used to store an index for a given
reference update. This index is used to order the updates in a
predetermined order, while the default ordering is alphabetical as per
the refname.

For large repositories with millions of references, it should be safer
to use 'uint64_t'. Let's do that. This also is applied for all other
code sections where we store 'index' and pass it around.

Reported-by: brian m. carlson <[email protected]>
Signed-off-by: Karthik Nayak <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: KarthikNayak

refs.c

@@ -1331,7 +1331,7 @@ static int ref_transaction_update_reflog(struct ref_transaction *transaction,
 					 const char *committer_info,
 					 unsigned int flags,
 					 const char *msg,
-					 unsigned int index,
+					 uint64_t index,
 					 struct strbuf *err)
 {
 	struct ref_update *update;
@@ -2813,7 +2813,7 @@ static int migrate_one_ref(const char *refname, const char *referent UNUSED, con
 }
 
 struct reflog_migration_data {
-	unsigned int index;
+	uint64_t index;
 	const char *refname;
 	struct ref_store *old_refs;
 	struct ref_transaction *transaction;

refs/refs-internal.h

@@ -120,7 +120,7 @@ struct ref_update {
 	 * when migrating reflogs and we want to ensure we carry over the
 	 * same order.
 	 */
-	unsigned int index;
+	uint64_t index;
 
 	/*
 	 * If this ref_update was split off of a symref update via
@@ -203,7 +203,7 @@ struct ref_transaction {
 	enum ref_transaction_state state;
 	void *backend_data;
 	unsigned int flags;
-	unsigned int max_index;
+	uint64_t max_index;
 };
 
 /*

refs/reftable-backend.c

@@ -942,7 +942,7 @@ struct write_transaction_table_arg {
 	size_t updates_nr;
 	size_t updates_alloc;
 	size_t updates_expected;
-	unsigned int max_index;
+	uint64_t max_index;
 };
 
 struct reftable_transaction_data {