Merge branch 'ps/fetch-atomic' into ps/fetch-mirror-optim

* ps/fetch-atomic:
  fetch: make `--atomic` flag cover pruning of refs
  fetch: make `--atomic` flag cover backfilling of tags
  refs: add interface to iterate over queued transactional updates
  fetch: report errors when backfilling tags fails
  fetch: control lifecycle of FETCH_HEAD in a single place
  fetch: backfill tags before setting upstream
  fetch: increase test coverage of fetches

refs.h

@@ -776,6 +776,20 @@ int ref_transaction_abort(struct ref_transaction *transaction,
 int initial_ref_transaction_commit(struct ref_transaction *transaction,
 				   struct strbuf *err);
 
+/*
+ * Execute the given callback function for each of the reference updates which
+ * have been queued in the given transaction. `old_oid` and `new_oid` may be
+ * `NULL` pointers depending on whether the update has these object IDs set or
+ * not.
+ */
+typedef void ref_transaction_for_each_queued_update_fn(const char *refname,
+						       const struct object_id *old_oid,
+						       const struct object_id *new_oid,
+						       void *cb_data);
+void ref_transaction_for_each_queued_update(struct ref_transaction *transaction,
+					    ref_transaction_for_each_queued_update_fn cb,
+					    void *cb_data);
+
 /*
  * Free `*transaction` and all associated data.
  */