Marcin Zalewski, 29.04.2009:
> Hi,
>
> When git-difftool calls a diff tool, it uses file names given to it by
> git-diff. This is a problem because often one of the files to be
> compared is the same as the file to be merged into. What I mean is
> that, in the following fragment of the git-difftool--helper file, $1
> and $2 (I think) may end up being the same:
>
> launch_merge_tool () {
> # Merged is the filename as it appears in the work tree
> # Local is the contents of a/filename
> # Remote is the contents of b/filename
> # Custom merge tool commands might use $BASE so we provide it
> MERGED="$1"
> LOCAL="$2"
> REMOTE="$3"
> BASE="$1"
>
> Git-mergetool creates a temporary file for merging, but git-difftool
> does not. Since git-diff tools is not meant for merging anything, it
> may seem that there is no problem. However, some merge tools (such as
> ediff) do not like when the merge target is the same as one of the
> files to be compared. I use the following emacs snippet by Theodore
> Tso:
>
> http://kerneltrap.org/mailarchive/git/2007/7/2/250505
>
> With that emacs code, ediff refuses to do a diff with the way that
> difftool is done now. I do not have a patch, but it seems that a
> simple fix would be to copy the code that creates temporary files from
> mergetool.
The real fix would be to adjust the ediff snippet for difftool support.
As you said yourself, git-difftool is not meant for merging files, so
there is no reason to open more than 2 files at all.
The built-in difftools 'emerge' and 'ecmerge' still seem to open LOCAL,
REMOTE and MERGED. This should be fixed, so that they don't open MERGED
any more, but I don't have emacs installed, so I shouldn't try it
myself.
Oh, and LOCAL shouldn't be copied to a temporary file in the first
place, because people don't use git-difftool in read-only mode only.
Markus
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