Re: [PATCH 2/2] apply: handle assertion failure gracefully

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 27, 2017, 22:33 UTC
Message-ID: <xmqq1sujnu1g.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <f191e3a8-a55b-7030-ebbb-3f46c74fdc94@web.de>

René Scharfe <l.s.r@web.de> writes:

Show 32 quoted lines

> Am 27.02.2017 um 21:04 schrieb Junio C Hamano:
>> René Scharfe <l.s.r@web.de> writes:
>>
>>>> diff --git a/apply.c b/apply.c
>>>> index cbf7cc7f2..9219d2737 100644
>>>> --- a/apply.c
>>>> +++ b/apply.c
>>>> @@ -3652,7 +3652,6 @@ static int check_preimage(struct apply_state *state,
>>>>  	if (!old_name)
>>>>  		return 0;
>>>>
>>>> -	assert(patch->is_new <= 0);
>>>
>>> 5c47f4c6 (builtin-apply: accept patch to an empty file) added that
>>> line. Its intent was to handle diffs that contain an old name even for
>>> a file that's created.  Citing from its commit message: "When we
>>> cannot be sure by parsing the patch that it is not a creation patch,
>>> we shouldn't complain when if there is no such a file."  Why not stop
>>> complaining also in case we happen to know for sure that it's a
>>> creation patch? I.e., why not replace the assert() with:
>>>
>>> 	if (patch->is_new == 1)
>>> 		goto is_new;
>>>
>>>>  	previous = previous_patch(state, patch, &status);
>>
>> When the caller does know is_new is true, old_name must be made/left
>> NULL.  That is the invariant this assert is checking to catch an
>> error in the calling code.
>
> There are some places in apply.c that set ->is_new to 1, but none of
> them set ->old_name to NULL at the same time.

I thought all of these are flipping ->is_new that used to be -1 (unknown) to (now we know it is new), and sets only new_name without doing anything to old_name, because they know originally both names are set to NULL.

> Having to keep these two members in sync sounds iffy anyway.  Perhaps
> accessors can help, e.g. a setter which frees old_name when is_new is
> set to 1, or a getter which returns NULL for old_name if is_new is 1.

Definitely, the setter would make it harder to make the mistake.