refs: add TRANSACTION_CREATE_EXISTS error

Currently there is only one special error for transaction, for when
there is a naming conflict, all other errors are dumped under a generic
error. Add a new special error case for when the caller requests the
reference to be updated only when it does not yet exist and the
reference actually does exist.

Signed-off-by: Bence Ferdinandy <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>

Author: ferdinandyb

refs.h

@@ -762,8 +762,10 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 
 /* Naming conflict (for example, the ref names A and A/B conflict). */
 #define TRANSACTION_NAME_CONFLICT -1
+/* When only creation was requested, but the ref already exists. */
+#define TRANSACTION_CREATE_EXISTS -2
 /* All other errors. */
-#define TRANSACTION_GENERIC_ERROR -2
+#define TRANSACTION_GENERIC_ERROR -3
 
 /*
  * Perform the preparatory stages of committing `transaction`. Acquire

refs/files-backend.c

@@ -2502,14 +2502,18 @@ static int split_symref_update(struct ref_update *update,
 static int check_old_oid(struct ref_update *update, struct object_id *oid,
 			 struct strbuf *err)
 {
+	int ret = TRANSACTION_GENERIC_ERROR;
+
 	if (!(update->flags & REF_HAVE_OLD) ||
 		   oideq(oid, &update->old_oid))
 		return 0;
 
-	if (is_null_oid(&update->old_oid))
+	if (is_null_oid(&update->old_oid)) {
 		strbuf_addf(err, "cannot lock ref '%s': "
 			    "reference already exists",
 			    ref_update_original_update_refname(update));
+		ret = TRANSACTION_CREATE_EXISTS;
+	}
 	else if (is_null_oid(oid))
 		strbuf_addf(err, "cannot lock ref '%s': "
 			    "reference is missing but expected %s",
@@ -2522,7 +2526,7 @@ static int check_old_oid(struct ref_update *update, struct object_id *oid,
 			    oid_to_hex(oid),
 			    oid_to_hex(&update->old_oid));
 
-	return -1;
+	return ret;
 }
 
 /*
@@ -2602,9 +2606,11 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 					ret = TRANSACTION_GENERIC_ERROR;
 					goto out;
 				}
-			} else if  (check_old_oid(update, &lock->old_oid, err)) {
-				ret = TRANSACTION_GENERIC_ERROR;
-				goto out;
+			} else {
+				ret = check_old_oid(update, &lock->old_oid, err);
+				if  (ret) {
+					goto out;
+				}
 			}
 		} else {
 			/*
@@ -2635,9 +2641,11 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 				    update->old_target);
 			ret = TRANSACTION_GENERIC_ERROR;
 			goto out;
-		} else if  (check_old_oid(update, &lock->old_oid, err)) {
-			ret = TRANSACTION_GENERIC_ERROR;
-			goto out;
+		} else {
+			ret = check_old_oid(update, &lock->old_oid, err);
+			if  (ret) {
+				goto out;
+			}
 		}
 
 		/*

refs/reftable-backend.c

@@ -1206,10 +1206,13 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 				goto done;
 			}
 		} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
-			if (is_null_oid(&u->old_oid))
+			ret = TRANSACTION_NAME_CONFLICT;
+			if (is_null_oid(&u->old_oid)) {
 				strbuf_addf(err, _("cannot lock ref '%s': "
 						   "reference already exists"),
 					    ref_update_original_update_refname(u));
+				ret = TRANSACTION_CREATE_EXISTS;
+			}
 			else if (is_null_oid(&current_oid))
 				strbuf_addf(err, _("cannot lock ref '%s': "
 						   "reference is missing but expected %s"),
@@ -1221,7 +1224,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 					    ref_update_original_update_refname(u),
 					    oid_to_hex(&current_oid),
 					    oid_to_hex(&u->old_oid));
-			ret = -1;
 			goto done;
 		}