Re: [FFmpeg-devel] [PATCH] all: Don't set AVClass.item_name to its default value

[Zhao Zhili <quinkblack@foxmail.com>]

> On Dec 25, 2023, at 18:21, Anton Khirnov <anton@khirnov.net> wrote:
> 
> Quoting Zhao Zhili (2023-12-25 10:27:59)
>> 
>> 
>>> On Dec 25, 2023, at 16:38, Anton Khirnov <anton@khirnov.net> wrote:
>>> 
>>> Quoting Kacper Michajlow (2023-12-24 11:41:52)
>>>> On Fri, 22 Dec 2023 at 14:57, Anton Khirnov <anton@khirnov.net> wrote:
>>>>> 
>>>>> Quoting Andreas Rheinhardt (2023-12-22 14:48:45)
>>>>>> Avoids relocations.
>>>>>> 
>>>>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>>>>>> ---
>>>>> 
>>>>> Maybe mention that it's not needed after
>>>>> acf63d5350adeae551d412db699f8ca03f7e76b9.
>>>> 
>>>> This is not the only user of this API, no?
>>>> 
>>>> I have a question for my own curiosity. This is ABI (and API) breaking
>>>> change,
>>> 
>>> It is not. This item was not guaranteed to be set, which was actually
>>> the reason I wrote the patch that this one refers to.
>> 
>> There is no problem to relax a restriction inside libavutil. However, since there is
>> no explicit documentation on whether item_name can be null or not, user may make
>> incorrect assumptions and depend on item_name not being null. I don’t think break
>> user’s code suddenly is a good idea, although we can say it’s break since the beginning.
> 
> My point is that the restriction never existed.

I’m not argue against this.

> There were always
> AVClass instances that did not set that pointer. There were fewer of
> them, but they did exist.

acf63d5350adeae551d412db699f8ca03f7e76b9 just shows that even libavutil can make
that incorrect assumption, we cannot expect more from users. If user’s code don’t trigger
those instances with null pointer, it works from user’s viewpoint. It’s hard to believe that
the bug found in MPV doesn’t exist in other  projects. We need another method to make
such change smoothly.

> 
> -- 
> Anton Khirnov
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