Re: [PATCH] merge-file: add --diff-algorithm option

[Antonin Delpeuch <antonin@xxxxxxxxxxx>]

Hi all,

Here a few more thoughts about this patch, to explain what brought me to 
needing that. If this need is misguided, perhaps you could redirect me 
to a better solution.

I am writing a custom merge driver for Java files. This merge driver 
internally calls git-merge-file and then solves the merge conflicts 
which only consist of import statements (there might be cases where it 
gets it wrong, but I can then use other tools to cleanup those import 
statements). When testing this, I noticed that the merge driver 
performed more poorly on other sorts of conflicts, compared to the 
standard "ort" merge strategy. This is because "ort" uses the 
"histogram" diff algorithm, which gives better results than the "myers" 
diff algorithm that merge-file uses.

Intuitively, if "histogram" is the default diff algorithm used by "git 
merge", then it would also make sense to have the same default for "git 
merge-file", but I assume that changing this default could be considered 
a bad breaking change. So I thought that making this diff algorithm 
configurable would be an acceptable move, hence my patch.

Of course, the diffing could be configured in other ways, for instance 
with its handling of whitespace or EOL (similarly to what the "git-diff" 
command offers). I think those options would definitely be worth 
exposing in merge-file as well. If you think this makes sense, then I 
would be happy to work on a new version of this patch which would 
attempt to include all the relevant options. I could also try to add the 
corresponding tests.

But perhaps my need is misguided? Could it be that I should not be 
writing a custom merge driver, but instead use another extension point 
to only process the conflicting hunks after execution of the existing 
merge driver? I couldn't find such an extension point, but it can well 
be that I missed it.

Thank you,

Antonin