Re: [PATCH v4 1/3] config: rename `git_etc_config()`

From: Patrick Steinhardt <ps@pks.im>
To: Jeff King <peff@peff.net>
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	git@vger.kernel.org, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Eric Sunshine" <sunshine@sunshineco.com>
Subject: Re: [PATCH v4 1/3] config: rename `git_etc_config()`
Date: Mon, 19 Apr 2021 13:03:56 +0200	[thread overview]
Message-ID: <YH1jnIhuF4UjXVNW@tanuki> (raw)
In-Reply-To: <YHvGE5/LRPN9obZi@coredump.intra.peff.net>

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On Sun, Apr 18, 2021 at 01:39:31AM -0400, Jeff King wrote:
> On Sat, Apr 17, 2021 at 02:37:39PM -0700, Junio C Hamano wrote:
> 
> > Jeff King <peff@peff.net> writes:
> > 
> > > On Fri, Apr 16, 2021 at 11:14:51PM +0200, SZEDER Gábor wrote:
> > >
> > >> > @@ -1883,6 +1880,7 @@ static int do_git_config_sequence(const struct config_options *opts,
> > >> >  				  config_fn_t fn, void *data)
> > >> >  {
> > >> >  	int ret = 0;
> > >> > +	char *system_config = git_system_config();
> > >> >  	char *xdg_config = xdg_config_home("config");
> > >> >  	char *user_config = expand_user_path("~/.gitconfig", 0);
> > >> >  	char *repo_config;
> > >> > @@ -1896,11 +1894,10 @@ static int do_git_config_sequence(const struct config_options *opts,
> > >> >  		repo_config = NULL;
> > >> >  
> > >> >  	current_parsing_scope = CONFIG_SCOPE_SYSTEM;
> > >> > -	if (git_config_system() && !access_or_die(git_etc_gitconfig(), R_OK,
> > >> 
> > >> Removing git_config_system() from the condition breaks
> > >> GIT_CONFIG_NOSYSTEM:
> > >
> > > Good catch. My gut feeling is that the new git_system_config() should
> > > check NOSYSTEM and return NULL if it's set, and then we can get rid of
> > > git_config_system() entirely.
> > 
> > NULL -> /dev/null I guess?
> 
> I was thinking NULL to catch this line from the post-image of Patrick's
> series:
> 
>           if (system_config && !access_or_die(system_config, R_OK,
>                                               opts->system_gently ?
>                                               ACCESS_EACCES_OK : 0))
>                   ret += git_config_from_file(fn, system_config, data);
> 
> which would see that we have no file at all. But that may be unexpected
> for other callers (right now git_etc_gitconfig() can never return NULL,
> and I'm not sure what would happen with "git config --system"; I suspect
> it would do the regular config sequence instead, which is wrong).
> 
> So yeah, probably returning /dev/null is more sensible (and makes it a
> true alias for GIT_CONFIG_SYSTEM=/dev/null).
> 
> -Peff

It's only by accident that I dropped the call to `git_config_system()`,
must've happened when resolving conflicts somewhere. The issue with just
returning `/dev/null` from `git_system_config()` is that git-config(1)
would be broken, as you hint at. We do not honor GIT_CONFIG_NOSYSTEM
there if the "--system" flag was given.

So yes, we could change it to return `/dev/null`, but that would change
semantics of GIT_CONFIG_NOSYSTEM. I'm not sure doing this in the same
series is a good idea. Even more so because with returning `/dev/null`,
the conversion would be silent: whereas previous versions simply wrote
to or read from the system-level config, we now pretend to have read or
written something even though we didn't.

Patrick

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