Re: git-mergetool: wrap tools with 3 files only to use the BASE file instead of MERGED

[Jonathan Nieder <jrnieder@gmail.com>]

(+cc: some relevant people)
Hi,

Tanguy Ortolo wrote[1]:

> git-mergetool ideally uses tools that work with 4 files: BASE, LOCAL,
> REMOTE, which are the usual original and two new version of the file,
> and MERGED, which is where the tool is supposed to write the result of
> the merge.
>
> The problem is that most tools, at least graphical ones, specifically
> meld, can only work with three files, as they save the result to the
> original file.
>
> git-mergetool currently handles this situation by passing MERGED LOCAL
> REMOTE to the tool. This could be fine, but unfortunately MERGE contains
> the conflicts, formatted for manual resolution, so it is not really
> appropriate as an original file.
>
> I think it would be better to wrap such merge tools by:
> 1. passing them BASE LOCAL REMOTE;
> 2. checking whether or not BASE hase been modified:
>    * if it has, then copying it to MERGED,
>    * if it has not, exiting with return code 1 (merge failed).
> This check can be by either saving and comparing the mdate, or perhaps
> the SHA-1 hash of the BASE file.
>
> If this sounds good enough, I can dive into git-mergetoo--lib and
> implement it. In the meantime, here is an example of a custom merge tool
> that wraps meld for that purpose.

I think you forgot to include the example.  Anyway, at first glance it
sounds like a sensible idea.  David et al: thoughts?

Regards,
Jonathan

[1] http://bugs.debian.org/637355