Re: [RFC PATCH] mergetools: support difftool.tabbed setting

On Tue, Jan 12, 2021 at 10:07 PM Nicholas Guriev [off-list ref] wrote:

I was asked how to configure "git difftool" to open files using several
tabs and stop spawning diff application on every modified file. I looked
into Git source and found no possibility to run diff tool at one step.

The patch allows a user to view diffs in single window at one go. The
current implementation is still poor and it can be used solely for
demonstration purposes. To see it in action, tweak the local gitconfig:

    git config difftool.prompt false
    git config difftool.tabbed true

Then run:

    git difftool -t vimdiff

Or:

    git difftool -t meld

The solution has some restrictions, diffing up to ten files works now (I
did not bother with dynamic memory allocation), and it does not handle spaces
in file names (I do not know how to pass them correctly to underlying tools
without "xargs -0").

I think the git-difftool--helper should be changed so that it could
process many files in single invocation and it would not use a temporary
file by itself. A similar behaviour can be done in git-mergetool, too.

Do you have ideas how to better implement such a feature? Any comments
are welcome.

P.S.: I'm attaching screenshots for a clear demo what I mean.
---
 diff.c                |  4 ++--
 git-mergetool--lib.sh | 36 +++++++++++++++++++++++++++++++++++-
 mergetools/meld       |  4 ++++
 mergetools/vimdiff    | 17 +++++++++++++++++
 4 files changed, 58 insertions(+), 3 deletions(-)

I'm not really sure if "tabbed" is the best name for what's going on,
though.  It's really more of a "diff everything in one shot" mode, and
it just so happens that the tools in question use tabs.

General note -- similar to the convention followed by
mergetool.hideResolved and other difftool things I think it would make
sense for tools to be able to override this on a per-tool basis.

That said, I wonder whether we need this new feature, or whether we
should instead improve an existing one.  I'm leaning towards improving
the existing dir-diff feature as a better alternative.

It's unfortunate that the "git difftool --dir-diff" feature doesn't
seem to mesh well with vimdiff.  It does work well with other tools
that support diffing arbitrary directories, notably meld, xxdiff, etc.

Regarding vimdiff + git difftool -d, there is this advice:
https://stackoverflow.com/questions/8156493/git-vimdiff-and-dirdiff

meld works just fine with "git difftool -d" (arguably nicer, since it
gives you a directory view and a diff view in separate tabs), so if
the only improvement is for vimdiff, then maybe the advice with the
DirDiff plugin might be a better way to go.

Having something like a "difftool.vimdiff.useDirDiff" configuration
variable could be a way for us to adopt the advice that they offer
there.  We could have the dir-diff difftool mode set a variable that
the vimdiff scriptlet could use to detect that we're in dir-diff mode.
Then, when that variable is set, vimdiff could use,

    vim -f '+next' '+execute \"DirDiff\" argv(0) argv(1)' $LOCAL $REMOTE

(as mentioned in the SO page) to invoke dir-diff mode in vim.

That way the user only needs to set:

git config difftool.vimdiff.useDirDiff

... and then "git diffftool -d" will integrate with the DirDiff plugin.

What do you think about improving the vimdiff scriptlet to better
integrate with "git difftool -d" instead?
-- 
David