Re: [RFC PATCH v3 8/8] --sparse for porcelains

[Nguyen Thai Ngoc Duy <pclouds@gmail.com>]

On Mon, Aug 17, 2009 at 4:08 PM, Johannes
Schindelin<Johannes.Schindelin@gmx.de> wrote:
> Turns out that somebody on IRC had a problem that requires to have
> sparse'd out files which _do_ have working directory copies.
>
> So just having the assume-changed bit may not be enough.
>
> The scenario is this: the repository contains a file that users are
> supposed to change, but not commit to (only the super-intelligent inventor
> of this scenario is allowed to).  As this repository is originally a
> subversion one, there is no problem: people just do not switch branches.
>
> But this guy uses git-svn, so he does switch branches, and to avoid
> committing the file by mistake, he marked it assume-unchanged.

Hmm.. never thought of this use before. If he does not want to commit
by mistake, should he add to-be-committed changes to index and do "git
commit" without "-a" (even better, do "git diff --cached" first)?

> Only that a branch switch overwrites the local changes.

I don't think branch switch overwrites changes in this case. Whenever
Git is to touch worktree files, it ignores assumed-unchanged bit and
does lstat() to make sure worktree files are up to date.

> I suggested the use of the sparse feature, and mark this file (and this
> file alone) as sparse'd-out.

Sparse checkout only removes a file if its assume-unchanged bit
changes from 0 to 1. If it's already 1, it does not care whether there
is a corresponding file in worktree. So something like this should
work:

git checkout my-branch
git update-index --assume-unchanged that-special-file
echo that-special-file > .git/info/sparse
# edit that-special-file
git commit -a
# do whatever you want, git pull/checkout/read-tree... won't touch
that-special-file because it's assume-unchanged already

Too subtle?

Anyway I would not recommend this. the versions of that-special-file
in worktree and and in index will diverse. When you unmark
assume-unchanged (be it sparse checkout or plain assume-unchanged),
you may have already forgot what changes you made to this file and
"git diff" would not help.

> Is this an intended usage scenario?  Then we cannot reuse the
> assume-changed bit [*1*].

It'd be great if people tell us all the scenarios they have. My use
could be too limited.
-- 
Duy