Re: [PATCH 4/7] checkout: fix merge.conflictstyle handling

[Phillip Wood <phillip.wood123@gmail.com>]

On 10/06/2021 17:32, Felipe Contreras wrote:
> Phillip Wood wrote:
>> On 10/06/2021 15:11, Felipe Contreras wrote:
>>> Phillip Wood wrote:
>>>> On 09/06/2021 20:28, Felipe Contreras wrote:
>>>>> Currently both merge.conflictStyle and `git commit --merge
>>>>> --conflict=diff3` don't work together, since the former wrongly
>>>>> overrides the later.
>>>>>
>>>>> The way merge configurations are handled is not correct.
>>>>> It should be possible to do git_config(merge_recursive_config, ...) just
>>>>> like we can with git_diff_basic_config and others.
>>>>
>>>> It would be helpful to explain what the problem with
>>>> merge_recursive_config() actually is rather than just saying "it should
>>>> be possible ..."
>>>
>>> The problem is that you can't do this:
>>>
>>>     git_config(merge_recursive_config, NULL);
>>>
>>> As it was explained.
>>
>> You do not explain why you cannot do that
> 
>    % git grep merge_recursive_config
>    static void merge_recursive_config(struct merge_options *opt)
> 
> For starters it's a static function.
> 
> Second, clearly the type of functions git_config() receives are not
> `void (*)(struct merge_options *)`.
> 
> I mean, I do see value in explaning as much detail as needed in the
> commit message, but it shouldn't be a lesson on git's codebase:
> git_config() is a standard thing, and it's even mentioned in the user
> manual.

I'm not asking for a lesson on git's config system, I'm asking you to 
add a sentence to the commit message to explain what the problem is 
rather than just saying "you should be able to do this but you can't".

> https://git-scm.com/docs/user-manual#birdview-on-the-source-code
> 
>>> That is the problem. I don't know how that's not clear.
>>>
>>>>> Therefore builtins like `git merge` can't call this function at the
>>>>> right time.
>>>>    >
>>>>> We shuffle the functions a little bit so at least merge_recursive_config
>>>>> doesn't call git_xmerge_config directly and thus override previous
>>>>> configurations.
>>>>
>>>> Rather than papering of the problem, how difficult would it be to add a
>>>> field to ll_merge_options and pass the conflict style with that rather
>>>> than fiddling with the order that we set a global variable.
>>>
>>> Probably not that difficult, but then we also need a parser that
>>> converts from "diff3" to whatever values we decide in that new field. We
>>> would need a new parse_config_conflict_style() function.
>>> And that function will be only used by `git checkout` and nothing else.
>>> So I don't think there's much value in it.
>>
>> It would allow us to add a --conflict option to all the mergey commands
>> in the future and would be much easier to reason about than the approach
>> of juggling where we call git_xmerge_config().
> 
> Feel free to write a patch for that.
> 
>> This patch requires us to audit all the code paths that end up in
>> merge_recursive_config() to make sure they now call
>> git_xmerge_config() themselves. You don't seem to have done that as
>> you don't know if am/apply are affected or not.
> 
> That is a separate issue, that I already mentioned...

I know you are going to add some tests but the point is that when making 
a change like this you need to actively audit all the callers of 
init_merge_options() and ensure that they are now calling 
git_config(git_xmerge_config) and base you tests on what you find while 
doing that. Have you run 'grep init_merge_options()' to see where it is 
being called?

Best Wishes

Phillip

>>> That problem whoever, is orthogonal to this series.
>>>
>>>> Does this change affect 'am/apply -3'? - Do they still read the config
>>>> setting properly?
>>>
>>> Good question. I'll have to add more tests to make sure that works
>>> properly.
> 
> here.
>