Re: [PATCH v4 10/10] sparse-checkout: add config to disable deleting dirs

[Elijah Newren <newren@gmail.com>]

On Tue, Aug 24, 2021 at 2:51 PM Derrick Stolee via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Derrick Stolee <dstolee@microsoft.com>
>
> The clean_tracked_sparse_directories() method deletes the tracked
> directories that go out of scope when the sparse-checkout cone changes,
> at least in cone mode. This is new behavior, but is recommended based on
> our understanding of how users are interacting with the feature in most
> cases.
>
> It is possible that some users will object to the new behavior, so
> create a new configuration option 'index.deleteSparseDirectories' that
> can be set to 'false' to make clean_tracked_sparse_directories() do
> nothing. This will keep all untracked files in the working tree and
> cause performance problems with the sparse index, but those trade-offs
> are for the user to decide.

I'm not sold that we need anything here, and it sounds like this is
all being added based on a theoretical concern.  I might not object
too much normally to trying to address theoretical conerns with new
features, but:

* I'm a little concerned that we're adding a configuration option
(which live forever and are harder to work with
backward-compatibility-wise) rather than a command line flag.

* It's not clear to me that the option name is what we want.  For
example, git checkout has a --[no-]overwrite-ignored for overwriting
ignored files (or not) when switching to a different branch.  git
merge has the same flags (though only the fast-forwarding backend
heeds it currently).  This behavior is quite similar to that flag, and
has the same default of treating ignored files as expendable.  Should
the naming be more similar?

* It's not clear to me that the option has the right level of
implementation granularity.  If someone wants ignored files to be
treated as important, should they need to set a
merge.no_overwrite_ignored AND a checkout.no_overwrite_ignored AND a
index.deleteSparseDirectories AND other names, or have one high-level
option that sets all of these behaviors?

>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  Documentation/config/index.txt     | 6 ++++++
>  builtin/sparse-checkout.c          | 9 ++++++++-
>  t/t1091-sparse-checkout-builtin.sh | 4 ++++
>  3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
> index 75f3a2d1054..c65da20a931 100644
> --- a/Documentation/config/index.txt
> +++ b/Documentation/config/index.txt
> @@ -1,3 +1,9 @@
> +index.deleteSparseDirectories::
> +       When enabled, the cone mode sparse-checkout feature will delete
> +       directories that are outside of the sparse-checkout cone, unless
> +       such a directory contains an untracked, non-ignored file. Defaults
> +       to true.
> +
>  index.recordEndOfIndexEntries::
>         Specifies whether the index file should include an "End Of Index
>         Entry" section. This reduces index load time on multiprocessor
> diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
> index d0f5c4702be..33ec729d9de 100644
> --- a/builtin/sparse-checkout.c
> +++ b/builtin/sparse-checkout.c
> @@ -102,7 +102,7 @@ static int sparse_checkout_list(int argc, const char **argv)
>
>  static void clean_tracked_sparse_directories(struct repository *r)
>  {
> -       int i, was_full = 0;
> +       int i, value, was_full = 0;
>         struct strbuf path = STRBUF_INIT;
>         size_t pathlen;
>         struct string_list_item *item;
> @@ -118,6 +118,13 @@ static void clean_tracked_sparse_directories(struct repository *r)
>             !r->index->sparse_checkout_patterns->use_cone_patterns)
>                 return;
>
> +       /*
> +        * Users can disable this behavior.
> +        */
> +       if (!repo_config_get_bool(r, "index.deletesparsedirectories", &value) &&
> +           !value)
> +               return;
> +
>         /*
>          * Use the sparse index as a data structure to assist finding
>          * directories that are safe to delete. This conversion to a
> diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
> index 71236981e64..e0f31186d89 100755
> --- a/t/t1091-sparse-checkout-builtin.sh
> +++ b/t/t1091-sparse-checkout-builtin.sh
> @@ -666,6 +666,10 @@ test_expect_success 'cone mode clears ignored subdirectories' '
>         git -C repo status --porcelain=v2 >out &&
>         test_must_be_empty out &&
>
> +       git -C repo -c index.deleteSparseDirectories=false sparse-checkout reapply &&
> +       test_path_is_dir repo/folder1 &&
> +       test_path_is_dir repo/deep/deeper2 &&
> +
>         git -C repo sparse-checkout reapply &&
>         test_path_is_missing repo/folder1 &&
>         test_path_is_missing repo/deep/deeper2 &&
> --
> gitgitgadget