Re: [PATCH 3/5] config: add BUG() statement instead of possible segfault

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Tue, Sep 27 2022, Derrick Stolee via GitGitGadget wrote:

> From: Derrick Stolee <derrickstolee@github.com>
>
> The git_die_config() method calls git_config_get_value_multi() but
> immediately navigates to its first value without checking if the result
> is NULL or empty. Callers should only call git_die_config() if there is
> at least one value for the given 'key', but such a mistaken use might
> slip through. It would be better to show a BUG() statement than a
> possible segfault.
>
> Signed-off-by: Derrick Stolee <derrickstolee@github.com>
> ---
>  config.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/config.c b/config.c
> index bf89afbdab0..0c41606c7d4 100644
> --- a/config.c
> +++ b/config.c
> @@ -2833,8 +2833,13 @@ void git_die_config(const char *key, const char *err, ...)
>  		va_end(params);
>  	}
>  	values = git_config_get_value_multi(key);
> -	kv_info = values->items[values->nr - 1].util;
> -	git_die_config_linenr(key, kv_info->filename, kv_info->linenr);
> +
> +	if (values && values->nr) {
> +		kv_info = values->items[values->nr - 1].util;
> +		git_die_config_linenr(key, kv_info->filename, kv_info->linenr);
> +	} else {
> +		BUG("expected a non-empty list of values");
> +	}
>  }
>  
>  /*

AFAIKT the intent of the current code on "master" is that this will only
get called if the likes of git_configset_get_string() returns < 0, not
if it returns > 0.

So isn't the combination of your 1/5 and this 3/5 now conflating these
two conditions? See e.g. repo_config_get_string_tmp() and when it would
call git_die_config().

I.e. isn't the whole point of git_die_config() to print an error message
about a configuration *value* that we've parsed out of the config?

If e.g. the key itself is bad we'll get a -1, but in this case it seems
we would have a BUG(), but it's not that we "expected a non-empty list
of values", but that the state of the world changed between our previous
configset invocation, no?