From: Antonin Delpeuch <antonin@delpeuch.eu>
Date: Thu, 30 Oct 2025 09:22:41 GMT
Subject: Re: [PATCH v3] blame: make diff algorithm configurable
Message-ID: <33d44dc6-36b3-4736-b3ed-96861a3c4003@delpeuch.eu>
In-Reply-To: <fde3dae1-bb11-45e8-9211-50ae003ca497@gmail.com>

Hi Phillip,

On 29/10/2025 11:16, Phillip Wood wrote:
> Unfortunately XDF_DIFF_ALGORITHM_MASK does not include 
> XDF_NEED_MINIMAL so if the user has a config file that looks like
>
>     [diff]
>         algorithm = minimal
>         algorithm = myers
>
> We'll parse it as "minimal" rather than "myers"
>
> As we need to reset the diff algorithm in a number of places I think 
> it would be best to define a macro
>
>         #define CLEAR_DIFF_ALGORITHM(flags) \
>         flags &= ~(XDF_DIFF_ALGORITHM_MASK | XDF_NEED_MINIMAL)

Ouch, good catch! This problem is affecting other places as well.

I'm wondering if we couldn't even add XDF_NEED_MINIMAL to 
XDF_DIFF_ALGORITHM_MASK. I've reviewed all the places where 
XDF_DIFF_ALGORITHM_MASK is used, and it seems that in all cases it would 
either preserve the existing behaviour (potentially allowing us to 
remove an accompanying "DIFF_XDL_CLR(opts, NEED_MINIMAL);" macro which 
becomes redundant), or in some other cases it would fix a similar issue 
(for instance, in merge-file.c).

Is your suggestion to introduce a new macro motivated by stability 
concerns? I'm aware that xdiff is used in other code bases as a library, 
so I guess changing XDF_DIFF_ALGORITHM_MASK can indeed be seen as a 
breaking change.

Antonin