refs: introduce enum-based transaction error types

Replace preprocessor-defined transaction errors with a strongly-typed
enum `ref_transaction_error`. This change:

  - Improves type safety and function signature clarity.
  - Makes error handling more explicit and discoverable.
  - Maintains existing error cases, while adding new error cases for
    common scenarios.

This refactoring paves the way for more comprehensive error handling
which we will utilize in the upcoming commits to add batch reference
update support.

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, 26 insertions, 23 deletions

diff --git a/refs.c b/refs.c
index b34969c792..ca0a6b61b8 100644
--- a/refs.c
+++ b/refs.c
@@ -2271,7 +2271,7 @@ int refs_update_symref_extended(struct ref_store *refs, const char *ref,
 					   REF_NO_DEREF, logmsg, &err))
 			goto error_return;
 		prepret = ref_transaction_prepare(transaction, &err);
-		if (prepret && prepret != TRANSACTION_CREATE_EXISTS)
+		if (prepret && prepret != REF_TRANSACTION_ERROR_CREATE_EXISTS)
 			goto error_return;
 	} else {
 		if (ref_transaction_update(transaction, ref, NULL, NULL,
@@ -2289,7 +2289,7 @@ int refs_update_symref_extended(struct ref_store *refs, const char *ref,
 		}
 	}
 
-	if (prepret == TRANSACTION_CREATE_EXISTS)
+	if (prepret == REF_TRANSACTION_ERROR_CREATE_EXISTS)
 		goto cleanup;
 
 	if (ref_transaction_commit(transaction, &err))
@@ -2425,7 +2425,7 @@ int ref_transaction_prepare(struct ref_transaction *transaction,
 
 	string_list_sort(&transaction->refnames);
 	if (ref_update_reject_duplicates(&transaction->refnames, err))
-		return TRANSACTION_GENERIC_ERROR;
+		return REF_TRANSACTION_ERROR_GENERIC;
 
 	ret = refs->be->transaction_prepare(refs, transaction, err);
 	if (ret)
@@ -2497,19 +2497,19 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	return ret;
 }
 
-int refs_verify_refnames_available(struct ref_store *refs,
-				   const struct string_list *refnames,
-				   const struct string_list *extras,
-				   const struct string_list *skip,
-				   unsigned int initial_transaction,
-				   struct strbuf *err)
+enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs,
+					  const struct string_list *refnames,
+					  const struct string_list *extras,
+					  const struct string_list *skip,
+					  unsigned int initial_transaction,
+					  struct strbuf *err)
 {
 	struct strbuf dirname = STRBUF_INIT;
 	struct strbuf referent = STRBUF_INIT;
 	struct string_list_item *item;
 	struct ref_iterator *iter = NULL;
 	struct strset dirnames;
-	int ret = -1;
+	int ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 
 	/*
 	 * For the sake of comments in this function, suppose that
@@ -2625,12 +2625,13 @@ cleanup:
 	return ret;
 }
 
-int refs_verify_refname_available(struct ref_store *refs,
-				  const char *refname,
-				  const struct string_list *extras,
-				  const struct string_list *skip,
-				  unsigned int initial_transaction,
-				  struct strbuf *err)
+enum ref_transaction_error refs_verify_refname_available(
+	struct ref_store *refs,
+	const char *refname,
+	const struct string_list *extras,
+	const struct string_list *skip,
+	unsigned int initial_transaction,
+	struct strbuf *err)
 {
 	struct string_list_item item = { .string = (char *) refname };
 	struct string_list refnames = {
@@ -2818,8 +2819,9 @@ int ref_update_has_null_new_value(struct ref_update *update)
 	return !update->new_target && is_null_oid(&update->new_oid);
 }
 
-int ref_update_check_old_target(const char *referent, struct ref_update *update,
-				struct strbuf *err)
+enum ref_transaction_error ref_update_check_old_target(const char *referent,
+						       struct ref_update *update,
+						       struct strbuf *err)
 {
 	if (!update->old_target)
 		BUG("called without old_target set");
@@ -2827,17 +2829,18 @@ int ref_update_check_old_target(const char *referent, struct ref_update *update,
 	if (!strcmp(referent, update->old_target))
 		return 0;
 
-	if (!strcmp(referent, ""))
+	if (!strcmp(referent, "")) {
 		strbuf_addf(err, "verifying symref target: '%s': "
 			    "reference is missing but expected %s",
 			    ref_update_original_update_refname(update),
 			    update->old_target);
-	else
-		strbuf_addf(err, "verifying symref target: '%s': "
-			    "is at %s but expected %s",
+		return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
+	}
+
+	strbuf_addf(err, "verifying symref target: '%s': is at %s but expected %s",
 			    ref_update_original_update_refname(update),
 			    referent, update->old_target);
-	return -1;
+	return REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
 }
 
 struct migration_data {