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

From: René Scharfe <l.s.r@web.de>
Date: Feb 27, 2017, 22:18 UTC
Message-ID: <f191e3a8-a55b-7030-ebbb-3f46c74fdc94@web.de>
In-Reply-To: <xmqqmvd7wgc7.fsf@gitster.mtv.corp.google.com>

Am 27.02.2017 um 21:04 schrieb Junio C Hamano:

Show 28 quoted lines

> 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.

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.

René