Re: [PATCH v2 00/14] Sparse-checkout: modify 'git add', 'git rm', and 'git add' behavior

On Sun, Sep 12, 2021 at 6:23 AM Derrick Stolee via GitGitGadget
[off-list ref] wrote:

This series is based on ds/mergies-with-sparse-index.

As requested, this series looks to update the behavior of git add, git rm,
and git mv when they attempt to modify paths outside of the sparse-checkout
cone. In particular, this care is expanded to not just cache entries with
the SKIP_WORKTREE bit, but also paths that do not match the sparse-checkout
definition.

This means that commands that worked before this series can now fail. In
particular, if 'git merge' results in a conflict outside of the
sparse-checkout cone, then 'git add ' will now fail.

In order to allow users to circumvent these protections, a new '--sparse'
option is added that ignores the sparse-checkout patterns and the
SKIP_WORKTREE bit. The message for advice.updateSparsePath is adjusted to
assist with discovery of this option.

There is a subtle issue with git mv in that it does not check the index
until it discovers a directory and then uses the index to find the contained
entries. This means that in non-cone-mode patterns, a pattern such as
"sub/dir" will not match the path "sub" and this can cause an issue.

In order to allow for checking arbitrary paths against the sparse-checkout
patterns, some changes to the underlying pattern matching code is required.
It turns out that there are some bugs in the methods as advertised, but
these bugs were never discovered because of the way methods like
unpack_trees() will check a directory for a pattern match before checking
its contained paths. Our new "check patterns on-demand" approach pokes holes
in that approach, specifically with patterns that match entire directories.


Updates in v2
=============

 * I got no complaints about these restrictions, so this is now a full
   series, not RFC.

 * Thanks to Matheus, several holes are filled with extra testing and
   bugfixes.

 * New patches add --chmod and --renormalize improvements. These are added
   after the --sparse option to make them be one change each.

Sorry for taking so long, but I finally read through the series.  Only
had a few small comments here and there; the high level direction
looks good.