Subject: Re: [PATCH 1/2] checkout/fetch/pull/pack-objects: allow `-h` outside a repository

From: Junio C Hamano <[email-masked]>
Date: Mon, 07 Feb 2022 22:50:02 -0800

"Johannes Schindelin via GitGitGadget" <[email-masked]>
writes:

> From: Johannes Schindelin <[email-masked]>
>
> When we taught these commands about the sparse index, we did not account
> for the fact that the `cmd_*()` functions _can_ be called without a
> gitdir, namely when `-h` is passed to show the usage.
>
> A plausible approach to address this is to move the
> `prepare_repo_settings()` calls right after the `parse_options()` calls:
> The latter will never return when it handles `-h`, and therefore it is
> safe to assume that we have a `gitdir` at that point, as long as the
> built-in is marked with the `RUN_SETUP` flag.
>
> However, it is unfortunately not that simple. In `cmd_pack_objects()`,
> for example, the repo settings need to be fully populated so that the
> command-line options `--sparse`/`--no-sparse` can override them, not the
> other way round.
>
> Therefore, we choose to imitate the strategy taken in `cmd_diff()`,
> where we simply do not bother to prepare and initialize the repo
> settings unless we have a `gitdir`.
>
> This fixes https://github.com/git-for-windows/git/issues/3688
>
> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---

These "prepare" calls are always tricky.  This somehow reminds me of
44c7e62e (repo-settings: prepare_repo_settings only in git repos,
2021-12-06) and e5b17bda (git: ensure correct git directory setup
with -h, 2021-12-06), which were part of the ld/sparse-diff-blame
topic that was merged at 8d2c3732 during the last cycle.

> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index cc804ba8e1e..1c13d7fedb3 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -1602,9 +1602,10 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
>  	opts->show_progress = -1;
>  
>  	git_config(git_checkout_config, opts);
> -
> -	prepare_repo_settings(the_repository);
> -	the_repository->settings.command_requires_full_index = 0;
> +	if (the_repository->gitdir) {
> +		prepare_repo_settings(the_repository);
> +		the_repository->settings.command_requires_full_index = 0;
> +	}

Looks quite straight-forward and sensible.  Of course, the checkout
command will go berserk and do nonsense if it is allowed to proceed
much further from here without .gitdir, but we know that 

 (1) the only case where .gitdir is NULL at this point is when
     running "-h" from outside a repository (we would have done a
     full RUN_SETUP without demoting it to RUN_SETUP_GENTLY if we
     weren't doing "-h"), and that

 (2) this is soon followed by parse_options() where it notices "-h"
     and stops.

so skipping "prepare" outside a repository is totally safe.

> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index 5f06b21f8e9..e0a05de10ee 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -2014,11 +2014,14 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
>  	}
>  
>  	git_config(git_fetch_config, NULL);
> -	prepare_repo_settings(the_repository);
> -	the_repository->settings.command_requires_full_index = 0;
> +	if (the_repository->gitdir) {
> +		prepare_repo_settings(the_repository);
> +		the_repository->settings.command_requires_full_index = 0;
> +	}

Ditto.

>  	argc = parse_options(argc, argv, prefix,
>  			     builtin_fetch_options, builtin_fetch_usage, 0);
> +
>  	if (recurse_submodules != RECURSE_SUBMODULES_OFF) {

Unrelated blank line?

>  		int *sfjc = submodule_fetch_jobs_config == -1
>  			    ? &submodule_fetch_jobs_config : NULL;
> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
> index ba2006f2212..87cb7b45c37 100644
> --- a/builtin/pack-objects.c
> +++ b/builtin/pack-objects.c
> @@ -3976,9 +3976,11 @@ 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 (the_repository->gitdir) {
> +		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);

This has a bit more sequence of calls until it reaches parse_options(),
but their side effect, when run outside a repository, are all benign
in-core effects, so this is safe, too.

> diff --git a/builtin/pull.c b/builtin/pull.c
> index 100cbf9fb85..d15007d93f3 100644
> --- a/builtin/pull.c
> +++ b/builtin/pull.c
> @@ -994,8 +994,10 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
>  		set_reflog_message(argc, argv);
>  
>  	git_config(git_pull_config, NULL);
> -	prepare_repo_settings(the_repository);
> -	the_repository->settings.command_requires_full_index = 0;
> +	if (the_repository->gitdir) {
> +		prepare_repo_settings(the_repository);
> +		the_repository->settings.command_requires_full_index = 0;
> +	}
>  
>  	argc = parse_options(argc, argv, prefix, pull_options, pull_usage, 0);