Re: tools for easily "uncommitting" parts of a patch I just commited?

> On Sun, Oct 23, 2016 at 08:23:01AM +0700, Duy Nguyen wrote:
>
>> I hit the same problem sometimes, but in my case sometimes I
>> accidentally do "git add" after "git add -p" and a configuration in
>> "git commit -a" won't help me. I'd prefer we could undo changes in
>> index instead. Something like reflog but for index.
>
> An index write always writes the whole file from scratch, so you really
> just need to save a copy of the old file. Perhaps something like:
>
>   rm -f $GIT_DIR/index.old
>   ln $GIT_DIR/index.old $GIT_DIR/index
>   ... and then open $GIT_DIR/index.tmp ...
>   ... and then rename(index.tmp, index) ...
>
> could do it cheaply. It's a little more complicated if you want to save
> a sequence of versions, and eventually would take a lot of space, but
> presumably a handful of saved indexes would be sufficient.

> Another option would be an index format that journals, and you could
> potentially walk back the journal to a point. That seems like a much
> bigger change (and has weird layering, because deciding when to fold in
> the journal is usually a performance thing, but obviously this would
> have user-visible impact about how far back you could undo).