Subject: Re: git-mergetool reverse file ordering

From: David Aguilar <[email-masked]>
Date: Sat, 13 Aug 2016 20:42:21 -0700

On Wed, Jul 27, 2016 at 11:14:28AM +0100, Luis Gutierrez wrote:
> Hi,
> 
> Attached is a potential patch for reversing the order on which
> git-mergetool presents the files to merge.
> 
> Currently, when running git-mergetool, it performs a sort of the files
> to merge by alphabetical ordering. When working on C, this has the
> annoying effect of presenting the merge for a .c* files before the
> header files; which is always a bit harder to do. Reading the header
> first to figure out what the other dude changed is usually preferred.
> 
> The attach patch reverse the order (-r flag to sort) so *.h* are
> merged before  *.c* files
> 
> PS, given the simplicity of the patch, I have not tested it.
> 
> Regards
> 
> Luis

Thanks for the sug, this is an interesting idea and I definitely
see why we would want something like this...

> diff --git a/git-mergetool.sh b/git-mergetool.sh
> index bf86270..cce3b0d 100755
> --- a/git-mergetool.sh
> +++ b/git-mergetool.sh
> @@ -453,10 +453,10 @@ then
>  	then
>  		files=$(git rerere remaining)
>  	else
> -		files=$(git ls-files -u | sed -e 's/^[^	]*	//' | sort -u)
> +		files=$(git ls-files -u | sed -e 's/^[^	]*	//' | sort -u -r)
>  	fi
>  else
> -	files=$(git ls-files -u -- "$@" | sed -e 's/^[^	]*	//' | sort -u)
> +	files=$(git ls-files -u -- "$@" | sed -e 's/^[^	]*	//' | sort -u -r)
>  fi
>  
>  if test -z "$files"

While we won't take this patch as-is (please see
Documentation/SubmittingPatches for details about the patch
submission process), I am interested in the use case you've
described.

This use case makes me wonder whether the sorting we do here is
something that should be opened up a bit so that the it's not
quite so set in stone.

For example, an extension to the approach taken by this patch
would be to have `mergetool.reverseOrder` git config boolean
option that would tell us whether or not to use the "-r" flag
when calling sort.

But, IMO that is too rigid, and only addresses this narrow use
case.  What if users want a case-insensitive sort, or some other
preferred ordering?

We can address these concerns, and your use case, by opening it
up. Something like,

	sort=$(git config mergetool.sort || echo sort -u)

That preserves the existing behavior, and it opens it up so that
we can accomplish the same result as this patch by doing:

	git config mergetool.sort "sort -u -r"

Then, if someone later writes a nicer C/C++-specific sort that
sorts in the natural order but also keeps .h files before .c,
.cpp, etc. files with the same basename, then they could do:

	git config mergetool.sort crescent-fresh-sort

...and it'll be totally crescent.

Thoughts?  Would you be interested in helping work up a patch
for this idea?  At a minimum we should also write a test case in
t/t7610-mergetool.sh to verify that it works as advertised.

Let me know if you have any questions.

cheers,
-- 
David