Subject: Re: [PATCH v2 1/2] builtin/sparse-checkout: remove NEED_WORK_TREE flag

From: SZEDER Gábor <[email-masked]>
Date: Fri, 7 Apr 2023 18:16:55 +0200

On Mon, Mar 27, 2023 at 10:51:04AM -0700, Junio C Hamano wrote:
> "William Sprent via GitGitGadget" <[email-masked]> writes:
> 
> > diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
> > index c3738154918..5fdc3d9aab5 100644
> > --- a/builtin/sparse-checkout.c
> > +++ b/builtin/sparse-checkout.c
> > @@ -57,6 +57,7 @@ static int sparse_checkout_list(int argc, const char **argv, const char *prefix)
> >  	char *sparse_filename;
> >  	int res;
> >  
> > +	setup_work_tree();
> >  	if (!core_apply_sparse_checkout)
> >  		die(_("this worktree is not sparse"));
> > ...
> > @@ -898,6 +903,7 @@ static int sparse_checkout_disable(int argc, const char **argv,
> >  	 * forcibly return to a dense checkout regardless of initial state.
> >  	 */
> >  
> > +	setup_work_tree();
> >  	argc = parse_options(argc, argv, prefix,
> >  			     builtin_sparse_checkout_disable_options,
> >  			     builtin_sparse_checkout_disable_usage, 0);
> 
> I am throwing this out not as "we must tackle this ugliness before
> this patch can proceed" but as "this is ugly, I wish somebody can
> figure it out in a cleaner way", so do not take this as a blocking
> comment or objection, but more as something to think about improving
> if possible as a bonus point.
> 
> It really is a shame that we have a nice "dispatch" table at the
> beginning of the single caller:
> 
>         int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
>         {
>                 parse_opt_subcommand_fn *fn = NULL;
>                 struct option builtin_sparse_checkout_options[] = {
>                         OPT_SUBCOMMAND("list", &fn, sparse_checkout_list),
>                         OPT_SUBCOMMAND("init", &fn, sparse_checkout_init),
>                         OPT_SUBCOMMAND("set", &fn, sparse_checkout_set),
>                         OPT_SUBCOMMAND("add", &fn, sparse_checkout_add),
>                         OPT_SUBCOMMAND("reapply", &fn, sparse_checkout_reapply),
>                         OPT_SUBCOMMAND("disable", &fn, sparse_checkout_disable),
>                         OPT_END(),
>                 };
> 
> yet we have to sprinkle setup_work_tree() to all of these functions'
> implementation.  If we were able to describe which selected ones do
> not need the setup call, we could let the parse-options API to look
> up the function and then before calling "fn" we could make the setup
> call.  That would allow us to maintain the subcommands much nicely.

It's easy enough to do in this particular case: there is an
OPT_SUBCOMMAND_F() variant which takes an additional flags parameter,
so we could add a PARSE_OPT_SETUP_WORK_TREE flag, check it in e.g.
parse_subcommand(), and act accordingly if it's set.

However, this wouldn't work when the command has a default operation
mode and is invoked without any subcommands.  And I'm not sure about
doing this in parse-options, because it's about, well, parsing
options, not about doing fancy setup stuff.