Re: GNU diff and git diff - difference on myers algorithm?

[Jacob Keller <jacob.keller-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Thu, Jul 16, 2015 at 9:22 PM, Jacob Keller <jacob.keller-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On Thu, Jul 16, 2015 at 12:07 PM, Luis R. Rodriguez
> <mcgrof-3uybbJdB1yH774rrrx3eTA@public.gmane.org> wrote:
>> On Fri, Jun 12, 2015 at 11:52 AM, Luis R. Rodriguez
>> <mcgrof-3uybbJdB1yH774rrrx3eTA@public.gmane.org> wrote:
>>> OK wells I'm curious about more research / effort when trying to
>>> evaluate a diff with two seprate but adjoining preprocessor directives
>>> and if anyone has implemented an optimizaiton option to let the diff
>>> generator join them.
>>>
>>> For example, to let it infer that:
>>>
>>> --- a/test.c
>>> +++ b/test.c
>>> @@ -10,8 +10,6 @@ int main(int argc, char *argv[])
>>>
>>>  #ifdef FOO
>>>         a = 4;
>>> -#endif /* FOO */
>>> -#ifdef FOO
>>>         a = 5;
>>>  #endif /* FOO */
>>>
>>> is possible.
>>
>> Anyone familiar if any tool exists today that would optimize this? Is
>> anyone working on it? Would git be a good place for such a thing? I'd
>> consider it as an option to optimize a diff. This for example is
>> extremely useful for us working with Coccinelle where we have a tool
>> writing code for us, while such an optimization might be useful to
>> Coccinelle it would seem like a rather generic feature, its just not
>> clear to me where to give such a tool a proper home.
>>
>>  Luis
>
> I do not understand exactly what would be optimized in this case?
>
> In any regards, that's not a diff transformation, that is a code
> transformation, and I would suggest starting with Coccinelle and
> seeing if you can get that to do what you want.
> http://coccinelle.lip6.fr/
>
> Regards,
> Jake

I misread your comment. Coccinelle is a tool that could probably be
coerced into doing this, but this is not a diff optimization unless I
am completely understanding it. This is a code transformation concept,
and doesn't have much to do with finding differences or code changes.
My above comment is correct, but I don't think this belongs in diff
parsing, but rather as part of something like Coccinelle

Regards,
Jake