Different diff strategies in add --interactive in GIT

Question

I've just been trying to use "add -p" to stage some changes which happen to be textually entangled with other changes that I do not want to stage.

It turns out that "git diff --patience" does a really good job splitting this into exactly the hunks I want, but "add --interactive" doesn't let me change the diff algorithm it uses. I tried setting "diff.algorithm" to "patience", but of course add--interactive uses plumbing diff commands that ignore configuration settings.

As a one off, I locally modified add--interactive to unconditionally use patience diff and it has worked perfectly in this case, but I don't want to have to apply a patch if I ever want this behaviour in the future.

I think the first thing to do is read the "diff.algorithm" setting in git-add--interactive and pass its value to the underlying diff-index and diff-files commands, but should we also have a command line parameter to git-add to specify the diff algorithm in interactive mode? And if so, can we simply add "--diff-algorithm" to git-add, or is that too confusing?

Answer 1

Making "git add--interactive" read from diff.algorithm is probably a good idea, because the command itself definitely is a Porcelain. We would probably need a way to defeat the configured default for completeness, either:

git add -p --diff-algorithm=default
git -c diff.algorithm=default add -p

but I suspect that a new option to "git add" that only takes effect together with "-p" is probably an overkill, only in order to support the former and not having to say the latter, but I can be persuaded either way.

As long as "git add --diff-algorithm=foo" without "-i" or "-p" option lets the user know it has no effect (error out, give warning and continue, etc. whose details I do not deeply care), that is.