Re: [PATCH v4] sparse-checkout.txt: new document with sparse-checkout directions

[ZheNing Hu <adlternative@gmail.com>]

ZheNing Hu <adlternative@gmail.com> 于2022年11月16日周三 18:10写道：
>
> ZheNing Hu <adlternative@gmail.com> 于2022年11月16日周三 18:04写道：
> >
> > Elijah Newren <newren@gmail.com> 于2022年11月16日周三 13:49写道：
> > >
> > > Perhaps it's worth noting why I think the sparse specification should
> > > be extended when dealing with the index:
> > >
> > >   * "mergy" commands (merge, rebase, cherry-pick, am, revert) can
> > > modify the index outside the sparsity patterns, without creating a
> > > commit.
> > >   * `git commit` (or `rebase --continue`, or whatever) will create a
> > > commit from whatever staged versions of files there are
> > >   => `git status` should show what is about to be committed
> > >   => `git diff --cached --name-only` ought to be usable to show what
> > > is to be committed
> > >   => `git grep --cached ...` ought to be usable to search through what
> > > is about to be committed
> > >
> > > See also https://lore.kernel.org/git/CABPp-BESkb=04vVnqTvZyeCa+7cymX7rosUW3rhtA02khMJKHA@mail.gmail.com/
> > > (starting with the paragraph with "leery" in it), and the thread
> > > starting there.  If the sparse specification is not expanded, users
> > > will get some nasty surprises, and the only other alternative I can
> > > think of to avoid such surprises would be making several commands
> > > always run full tree.  Running full-tree with a non-default option to
> > > run sparse forces behavior A folks into a "pick your poison"
> > > situation, which is not nice.  Extending the sparse specification to
> > > include files whose index entries do not match HEAD for index-related
> > > operations provides the nice middle ground that avoids such usability
> > > problems while also allowing users to avoid operating on a full tree.
> > >
> >
> > I can understand the reason why we need to extend sparse specification:
> > index often needs to handle files that are not in the sparse pattern.
> >
>
> I might have one more question: when we use "git diff -cached HEAD~",
> what is the best way to check if an index entry is the same as HEAD here?
> Do we need to run "git diff --cached HEAD <file>" again?

I found that git commit will execute index_differs_from() to determine
whether the index has changed, It defaults to comparing HEAD.
But if we use git commit --amend, index_differs_from() will compare
to HEAD~.

the docs say:

       * When modifying or showing results from the index, the sparse
         specification is the set of files with a clear SKIP_WORKTREE bit
         or that differ in the index from HEAD.

I wonder if there is some description error here? Not always "from HEAD"?