Re: [PATCH v4 1/4] sparse index: enable only for git repos

[Elijah Newren <newren@gmail.com>]

On Mon, Nov 22, 2021 at 2:42 PM Lessley Dennington via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Lessley Dennington <lessleydennington@gmail.com>
>
> Check whether git dir exists before adding any repo settings. If it
> does not exist, BUG with the message that one cannot add settings for an
> uninitialized repository. If it does exist, proceed with adding repo
> settings.
>
> Additionally, ensure the above BUG is not triggered when users pass the -h
> flag by adding a check for the repository to the checkout and pack-objects
> builtins.

Why only checkout and pack-objects?  Why don't the -h flags to all of
the following need it as well?:

$ git grep -l prepare_repo_settings | grep builtin/
builtin/add.c
builtin/blame.c
builtin/checkout.c
builtin/commit.c
builtin/diff.c
builtin/fetch.c
builtin/gc.c
builtin/merge.c
builtin/pack-objects.c
builtin/rebase.c
builtin/reset.c
builtin/revert.c
builtin/sparse-checkout.c
builtin/update-index.c

If none of these need it, was it because they put
prepare_repo_settings() calls after some other basic checks had been
done so more do not have to be added?  If so, is there a similar place
in checkout and pack-objects where their calls to
prepare_repo_settings() can be moved?  (Looking ahead, it appears you
moved some code in patch 2 to do something like this.  Are the similar
moves that could be done here?)

> Finally, ensure the above BUG is not triggered for commit-graph by
> returning early if the git directory does not exist.

If commit-graph needs a special case to avoid triggering the BUG,
wouldn't several of these need it too?:

$ git grep -l prepare_repo_settings | grep -v builtin/
commit-graph.c
fetch-negotiator.c
merge-recursive.c
midx.c
read-cache.c
repo-settings.c
repository.c
repository.h
sparse-index.c
t/helper/test-read-cache.c
t/helper/test-read-graph.c
unpack-trees.c

or are their calls to prepare_repo_settings() only done after gitdir
setup?  If the latter, perhaps the commit-graph function calls could
be moved after gitdir setup too to avoid the need to do extra checks
in it?

> Signed-off-by: Lessley Dennington <lessleydennington@gmail.com>
> ---
>  builtin/checkout.c     | 6 ++++--
>  builtin/pack-objects.c | 9 ++++++---
>  commit-graph.c         | 5 ++++-
>  repo-settings.c        | 3 +++
>  4 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index 8c69dcdf72a..31632b07888 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -1588,8 +1588,10 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
>
>         git_config(git_checkout_config, opts);
>
> -       prepare_repo_settings(the_repository);
> -       the_repository->settings.command_requires_full_index = 0;
> +       if (startup_info->have_repository) {
> +               prepare_repo_settings(the_repository);
> +               the_repository->settings.command_requires_full_index = 0;
> +       }
>
>         opts->track = BRANCH_TRACK_UNSPECIFIED;
>
> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
> index 1a3dd445f83..45dc2258dc7 100644
> --- a/builtin/pack-objects.c
> +++ b/builtin/pack-objects.c
> @@ -3976,9 +3976,12 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
>         read_replace_refs = 0;
>
>         sparse = git_env_bool("GIT_TEST_PACK_SPARSE", -1);
> -       prepare_repo_settings(the_repository);
> -       if (sparse < 0)
> -               sparse = the_repository->settings.pack_use_sparse;
> +
> +       if (startup_info->have_repository) {
> +               prepare_repo_settings(the_repository);
> +               if (sparse < 0)
> +                       sparse = the_repository->settings.pack_use_sparse;
> +       }
>
>         reset_pack_idx_option(&pack_idx_opts);
>         git_config(git_pack_config, NULL);
> diff --git a/commit-graph.c b/commit-graph.c
> index 2706683acfe..265c010122e 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -632,10 +632,13 @@ static int prepare_commit_graph(struct repository *r)
>         struct object_directory *odb;
>
>         /*
> +        * Early return if there is no git dir or if the commit graph is
> +        * disabled.
> +        *
>          * This must come before the "already attempted?" check below, because
>          * we want to disable even an already-loaded graph file.
>          */
> -       if (r->commit_graph_disabled)
> +       if (!r->gitdir || r->commit_graph_disabled)
>                 return 0;
>
>         if (r->objects->commit_graph_attempted)
> diff --git a/repo-settings.c b/repo-settings.c
> index b93e91a212e..00ca5571a1a 100644
> --- a/repo-settings.c
> +++ b/repo-settings.c
> @@ -17,6 +17,9 @@ void prepare_repo_settings(struct repository *r)
>         char *strval;
>         int manyfiles;
>
> +       if (!r->gitdir)
> +               BUG("Cannot add settings for uninitialized repository");
> +
>         if (r->settings.initialized++)
>                 return;

I'm not what the BUG() is trying to help us catch, but I'm worried
that there are many additional places that now need workarounds to
avoid triggering bugs.