Re: [PATCH v2 5/7] refs: introduce enum-based transaction error types

> On Tue, Feb 25, 2025 at 10:29:08AM +0100, Karthik Nayak wrote:
>> diff --git a/refs.h b/refs.h
>> index b14ba1f9ff..8e9ead174c 100644
>> --- a/refs.h
>> +++ b/refs.h
>> @@ -16,6 +16,31 @@ struct worktree;
>>  enum ref_storage_format ref_storage_format_by_name(const char *name);
>>  const char *ref_storage_format_to_name(enum ref_storage_format ref_storage_format);
>>
>> +/*
>> + * enum transaction_error represents the following return codes:
>> + * TRANSACTION_OK: success code.
>> + * TRANSACTION_GENERIC_ERROR error_code: default error code.
>> + * TRANSACTION_NAME_CONFLICT error_code: ref name conflict like A vs A/B.
>> + * TRANSACTION_CREATE_EXISTS error_code: ref to be created already exists.
>> + * TRANSACTION_NONEXISTENT_REF error_code: ref expected but doesn't exist.
>> + * TRANSACTION_INCORRECT_OLD_VALUE error_code: provided old_oid or old_target of
>> + * reference doesn't match actual.
>> + * TRANSACTION_INVALID_NEW_VALUE error_code: provided new_oid or new_target is
>> + * invalid.
>> + * TRANSACTION_EXPECTED_SYMREF error_code: expected ref to be symref, but is a
>> + * regular ref.
>> + */
>> +enum transaction_error {
>> +	TRANSACTION_OK = 0,
>> +	TRANSACTION_GENERIC_ERROR = -1,
>> +	TRANSACTION_NAME_CONFLICT = -2,
>> +	TRANSACTION_CREATE_EXISTS = -3,
>> +	TRANSACTION_NONEXISTENT_REF = -4,
>> +	TRANSACTION_INCORRECT_OLD_VALUE = -5,
>> +	TRANSACTION_INVALID_NEW_VALUE = -6,
>> +	TRANSACTION_EXPECTED_SYMREF = -7,
>> +};
>
> Nit: how about we name this `ref_transaction_error` and adapt the the
> enum values accordingly? We may eventually also introduce similar errors
> for the object database, so it may make sense to have the errors be
> specific. Doing both the enum and changing the name might be a bit hard
> to review, so we could also rename in a preparatory commit. Or we just
> punt on it for now and do it once it becomes necessary, that would also
> be fine with me.
>

> I also wonder whether we really want to introduce `TRANSACTION_OK`. It's
> always a bit of a mouthful, and in many cases one ends up with a mixture
> of `ret < 0`, `ret != TRANSACTION_OK` and `ret != 0`, which may lead to
> confusion. Continuing to use `0` for the successful case should be fine.
>

>> diff --git a/refs/packed-backend.c b/refs/packed-backend.c
>> index 3247871574..75e1ebf67d 100644
>> --- a/refs/packed-backend.c
>> +++ b/refs/packed-backend.c
>> @@ -1672,7 +1676,8 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
>>  		data->own_lock = 1;
>>  	}
>>
>> -	if (write_with_updates(refs, &transaction->refnames, err))
>> +	ret = write_with_updates(refs, &transaction->refnames, err);
>> +	if (ret)
>>  		goto failure;
>>
>>  	transaction->state = REF_TRANSACTION_PREPARED;
>
> Do we also want to change the local variable declaration of `int ret` to
> use the new type?
>

>> diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
>> index 2c1e2995de..e1fd9c2de2 100644
>> --- a/refs/reftable-backend.c
>> +++ b/refs/reftable-backend.c
>> @@ -1255,11 +1255,12 @@ static int prepare_single_update(struct reftable_ref_store *refs,
>>  					   "but is a regular ref"),
>>  				    ref_update_original_update_refname(u),
>>  				    u->old_target);
>> -			return -1;
>> +			return TRANSACTION_EXPECTED_SYMREF;
>>  		}
>>
>> -		if (ref_update_check_old_target(referent->buf, u, err)) {
>> -			return -1;
>> +		ret = ref_update_check_old_target(referent->buf, u, err);
>> +		if (ret) {
>> +			return ret;
>>  		}
>>  	} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
>>  		if (is_null_oid(&u->old_oid)) {
>
> Nit: superfluous braces that we could remove while at it.
>