Subject: Re: How to split a patch

From: Junio C Hamano <[email-masked]>
Date: Mon, 28 Jan 2008 02:27:23 -0800

Matthieu Moy <[email-masked]> writes:

> "Paolo Ciarrocchi" <[email-masked]> writes:
>
>> Yes it helps but I still wonder whether thereis a "simpler" way to achive that.
>> Is it possible to split a patch selecting the hunk in git gui or any
>> other graphical
>> tool?
>
> You can apply the patch without commiting it, and them make several
> partial commits, by right-click "stage hunk for commit" in git-gui.

Yes, and you can do the same with "git add -i".  These tools are
not quite nice, as they encourage a wrong workflow of committing
what you haven't had as a whole in the work tree.  By
definition, you are making untested commits between your base
commit (that presumably was tested well) and your final commit
(that would also be tested well).

Ideally, once you have a perfect state (i.e. the shape of the
tree recorded by the last commit in your "split" series), you
should be able to make a commit, and walk backwards, removing
the fanciest "finishing touches" changes from the work tree
files, test it, and record it as a new commit between where you
are and one commit before it.  A possible workflow could be:

	$ work work work, now it is perfect.
	$ git commit -a -m 'Now it is perfect'
        $ edit away the fanciest bits
        $ test test, the basics still work.
        $ git commit --splice -a -m 'Almost there'

And the last "git commit --splice" would record the tree object
as a commit, whose parent is the parent of the current HEAD, and
record the tree of the current HEAD as a (rewritten) commit that
is a child of that commit.

Graphically, you would start from (X is "the perfect commit"):

	---o-------X

then "--splice" would create a new commit "W" and record the
same tree as X as a new commit X' that is a child of W:

             .--W---X'
            /
	---o-------X

There is no such tool yet, though.

The splitting you can do with "rebase -i" instead walks
forwards.  That also lets you test before you make commits in
each step.