An alternate model for preparing partial commits

["Robert Anderson" <rwa000@gmail.com>]

Seems to me the concept of the "index" is a half-baked version of what
I really want, which is the ability to factor a working tree's changes
into its constituent parts in preparation for committing them.  The
index provides some very nice facilities to factor out changes in a
working tree into a "staging area", but the fundamental flaw of this
in my view is that this "staging area" is not instantiated as a tree,
so it cannot be compiled and/or tested before committing.

Consider a facility where the state you want to commit next is built
up in the current working directory, and the original set of changes
exists in some proto-space like the index currently inhabits, where
you can query and manipulate that state, but it isn't instantiated in
your working tree.

Imagine a session like this:

You've got a couple of conflated changes in your working tree, that
you think you can break up into two orthogonal changes, each of which
will compile and pass a set of tests you've got.  You think.  You'd
like to verify the build and test before you commit each piece.

git prep

where "prep" means "prepare commit".  Don't get hung up on command or
option names I'm using as placeholders, I just made that up without
much deep thought about what to call it.

Now my tree appears clean (and git diff returns nothing).  I can now
start adding the changes I had in my working tree that I want to
include in the next commit, using git add (which would know I am in
the "prep" mode).  I can examine those original working dir changes I
am choosing from with:

git diff --prep

which, at this point, shows the same output that "git diff" did before
I ran "git prep."  Now I want to add some subset of my original
changes:

git add newfile.c
git add -i
<add a couple of hunks of the changes from file modfile.c>

Now I have a working tree state that I think I want to commit.  I can
examine it with:

git diff

and I can compile and test it.  Yep, it works and passes my test suite
(an option I did not have if I had added these changes to the index).
So now I want to commit:

git commit -a -m "made change A"

I think the commit should probably "pop" the rest of the changes I did
not commit back into the working directory.  If I want to pull another
subset of changes again, I can repeat the process with another "git
prep".

Does this idea resonate with anyone else?

Thanks,
Bob Anderson