refs: move duplicate refname update check to generic layer

Move the tracking of refnames in `affected_refnames` from individual
backends into the generic layer in 'refs.c'. This centralizes the
duplicate refname detection that was previously handled separately by
each backend.

Make some changes to accommodate this move:

  - Add a `string_list` field `refnames` to `ref_transaction` to contain
    all the references in a transaction. This field is updated whenever
    a new update is added via `ref_transaction_add_update`, so manual
    additions in reference backends are dropped.

  - Modify the backends to use this field internally as needed. The
    backends need to check if an update for refname already exists when
    splitting symrefs or adding an update for 'HEAD'.

  - In the reftable backend, within `reftable_be_transaction_prepare()`,
    move the `string_list_has_string()` check above
    `ref_transaction_add_update()`. Since `ref_transaction_add_update()`
    automatically adds the refname to `transaction->refnames`,
    performing the check after will always return true, so we perform
    the check before adding the update.

This helps reduce duplication of functionality between the backends and
makes it easier to make changes in a more centralized manner.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/refs.c b/refs.c
index 79d5a8b8d4..22000798c7 100644
--- a/refs.c
+++ b/refs.c
@@ -1175,6 +1175,7 @@ struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
 	CALLOC_ARRAY(tr, 1);
 	tr->ref_store = refs;
 	tr->flags = flags;
+	string_list_init_dup(&tr->refnames);
 	return tr;
 }
 
@@ -1205,6 +1206,7 @@ void ref_transaction_free(struct ref_transaction *transaction)
 		free((char *)transaction->updates[i]->old_target);
 		free(transaction->updates[i]);
 	}
+	string_list_clear(&transaction->refnames, 0);
 	free(transaction->updates);
 	free(transaction);
 }
@@ -1218,6 +1220,7 @@ struct ref_update *ref_transaction_add_update(
 		const char *committer_info,
 		const char *msg)
 {
+	struct string_list_item *item;
 	struct ref_update *update;
 
 	if (transaction->state != REF_TRANSACTION_OPEN)
@@ -1245,6 +1248,16 @@ struct ref_update *ref_transaction_add_update(
 		update->msg = normalize_reflog_message(msg);
 	}
 
+	/*
+	 * This list is generally used by the backends to avoid duplicates.
+	 * But we do support multiple log updates for a given refname within
+	 * a single transaction.
+	 */
+	if (!(update->flags & REF_LOG_ONLY)) {
+		item = string_list_append(&transaction->refnames, refname);
+		item->util = update;
+	}
+
 	return update;
 }
 
@@ -2405,6 +2418,10 @@ int ref_transaction_prepare(struct ref_transaction *transaction,
 		return -1;
 	}
 
+	string_list_sort(&transaction->refnames);
+	if (ref_update_reject_duplicates(&transaction->refnames, err))
+		return TRANSACTION_GENERIC_ERROR;
+
 	ret = refs->be->transaction_prepare(refs, transaction, err);
 	if (ret)
 		return ret;