Re: [PATCH v2 0/7] Sparse index: integrate with 'read-tree'

[Elijah Newren <newren@gmail.com>]

On Thu, Feb 24, 2022 at 2:34 PM Victoria Dye via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> Like previous integrations [1] [2], this series allows 'git read-tree' to
> operate using a sparse index.
>
> The first two patches are bugfixes for issues found while implementing the
> 'read-tree' integration:
>
>  * The first (patch 1/7) fixes an edge case in which a repo with no in-cone
>    files or directories would have its root collapsed into a sparse
>    directory; the fix ensures the root directory is never collapsed into a
>    sparse directory.
>  * The second (patch 2/7) corrects the 'git status' reporting of changes
>    nested inside the subdirectory of a sparse directory, ensuring that the
>    modified file (not the subdirectory) is correctly reported as having
>    changes.
>
> The remainder of the series focuses on utilizing the sparse index in 'git
> read-tree'. After some baseline behavior-establishing tests (patch 3/7),
> sparse index usage is trivially enabled (patch 4/7) for 'read-tree' except:
>
>  * usage with '--prefix'
>  * two- and three-way merge
>
> These cases require additional changes in order to work as expected (i.e.,
> outwardly matching non-sparse index sparse-checkout). For the former, the
> sparse index can be enabled as long as the index is expanded when the prefix
> is a directory outside the sparse cone (patch 5/7). For the latter, sparse
> directories that cannot be trivially merged must have their contents merged
> file-by-file, done by recursively traversing the trees represented by the
> sparse directories (patches 6/7 & 7/7).
>
>
> Changes since V1
> ================
>
>  * switched an empty string check from '!strlen(path)' to the
>    slightly-less-expensive '!*path'

I've read over the series.  It was a nice read, well motivated, and
split up rather nicely.  I only had a few small commetns.

I think it'd be nice to insert another patch into the series that
throws an error if the argument to --prefix starts with a '/'.  That
would also allow you to simplify patch 5/7 a little.

Patch 6/7 has the right idea, but I'm worried about one part of it; a
test would go a long way towards verifying whether that aspect is
handled correctly or whether my concern is warranted.

I had a couple smaller comments on some of the other patches.

Overall, nicely done.


> Thanks!
>
>  * Victoria
>
> [1]
> https://lore.kernel.org/git/pull.1109.v2.git.1641924306.gitgitgadget@gmail.com/
> [2]
> https://lore.kernel.org/git/pull.1048.v6.git.1638201164.gitgitgadget@gmail.com/
>
> Victoria Dye (7):
>   sparse-index: prevent repo root from becoming sparse
>   status: fix nested sparse directory diff in sparse index
>   read-tree: expand sparse checkout test coverage
>   read-tree: integrate with sparse index
>   read-tree: narrow scope of index expansion for '--prefix'
>   read-tree: make two-way merge sparse-aware
>   read-tree: make three-way merge sparse-aware
>
>  builtin/read-tree.c                      |  10 +-
>  dir.c                                    |   7 +-
>  t/perf/p2000-sparse-operations.sh        |   1 +
>  t/t1092-sparse-checkout-compatibility.sh | 129 +++++++++++++++++++++++
>  unpack-trees.c                           | 121 ++++++++++++++++++++-
>  wt-status.c                              |   9 ++
>  6 files changed, 268 insertions(+), 9 deletions(-)
>
>
> base-commit: e6ebfd0e8cbbd10878070c8a356b5ad1b3ca464e
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1157%2Fvdye%2Fsparse%2Fread-tree-v2
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1157/vdye/sparse/read-tree-v2
> Pull-Request: https://github.com/gitgitgadget/git/pull/1157
>
> Range-diff vs v1:
>
>  1:  90da1f9f33a ! 1:  744668eeece sparse-index: prevent repo root from becoming sparse
>      @@ Commit message
>           non-cone sparse-checkouts), the new check does not cause additional changes
>           to how sparse patterns are applied.
>
>      +    Helped-by: Derrick Stolee <derrickstolee@github.com>
>           Signed-off-by: Victoria Dye <vdye@github.com>
>
>        ## dir.c ##
>      @@ dir.c: static int path_in_sparse_checkout_1(const char *path,
>       +  * patterns, or the patterns are of the wrong type.
>          */
>       - if (init_sparse_checkout_patterns(istate) ||
>      -+ if (!strlen(path) ||
>      ++ if (!*path ||
>       +     init_sparse_checkout_patterns(istate) ||
>             (require_cone_mode &&
>              !istate->sparse_checkout_patterns->use_cone_patterns))
>  2:  c21c9b9be34 = 2:  f0cff03b95d status: fix nested sparse directory diff in sparse index
>  3:  ac42ae21d4a = 3:  ffe0b6aff2b read-tree: expand sparse checkout test coverage
>  4:  5ee193bfa87 = 4:  cb7e0cf419c read-tree: integrate with sparse index
>  5:  bea482b6b28 = 5:  4f05fa70209 read-tree: narrow scope of index expansion for '--prefix'
>  6:  9fdcab038b2 = 6:  94c2aad2f93 read-tree: make two-way merge sparse-aware
>  7:  1502e9acb32 = 7:  c4080e99d6e read-tree: make three-way merge sparse-aware
>
> --
> gitgitgadget